Neurons are the basic signalling units that transmit information throughout the nervous system. Neurons vary in form, location and interconnectivity and this is related to their functions. Glial cells provide structural support and electrical insulation to neurons. Dendrites are branching extensions of the neuron that receive inputs from other neurons. Spines are little knobs attached by small necks to the surface of the dendrites and are specialized processes. The axon is a single process that extends from the cell body. Transmission occurs at the synapse. Axon collaterals are combined axons. Along the length of the axons, there are evenly spaced gaps in the myelin. These gaps are called the nodes of Ranvier.
Neuronal signalling is receiving, evaluating and transmitting information of neurons. Neurons are presynaptic when their axon makes a connection onto other neurons and postsynaptic when other neurons make a connection onto their dendrites. Energy is needed to generate signals, energy is in the form of an electrical potential, voltages depend on the concentrations of potassium, sodium and chloride ions and when a neuron is not signalling, the inside of the neuron is more negative than the outside.
Ion channels are proteins with a pore through their centres. They allow certain ions to flow down their concentration gradients. These channels selectively permit one type of ion to pass through the membrane. Permeability refers to the extent to which a particular ion can cross the membrane through a given ion channel. Neurons can change the permeability for a particular ion. This is also called gated ion channels. Ion pumps use energy to actively transport ions across the membrane against their concentration gradients.
The process of neurons transmitting information starts when excitatory postsynaptic potentials (EPSPs) at synapses on the neuron’s dendrites cause ionic currents to flow in the volume of the cell body. Neuronal signalling can be completed if these EPSPs reach the axon terminals. This usually does not happen because decremental conduction occurs. The electrical charge diminishes with distance.
An action potential is a rapid depolarization and repolarization of a small region of the membrane caused by the opening and closing of ion channels. Action potentials can travel infinitely far because the signal keeps being regenerated. The axon hillock is the place where the axon leaves the neuron. The action potential can regenerate itself because of the presence of voltage-gated ion channels. These are ion channels that open at a certain voltage, leading to depolarization. These channels open at around -55mV, which occurs when the neuron depolarizes. The depolarization of the neuron as a result of the voltage-gated ion channels leads to more depolarization as more channels open. This is the Hodgkin-Huxley cycle. The depolarization of the neuron leads to the opening of the slower voltage-gated K+ channels, which repolarizes the neuron leading to a decrease even below the equilibrium potential. In the hyperpolarization state, the voltage-gated Na+ channels are unable to open and another action potential cannot be generated. This is called the absolute refractory period. In the relative refractory period, action potentials can be generated but required more voltage than usual. Accelerated transmission of the action potential is accomplished in myelinated axons. In myelinated axons, action potentials only need to be generated at the nodes of Ranvier. Saltatory conduction refers to the jumping of action potentials down myelinated axons.
The synaptic cleft is the gap between neurons at the synapse. The transfer of a signal from the axon terminal to the next cell is called synaptic transmission. There are chemical and electrical synapses.
Most neurons send a signal to the cell across the synapse by releasing neurotransmitters into the synaptic cleft. The arrival of the action potential leads to depolarization of the terminal membrane, causing voltage-gated Ca2+ channels to open. The opening triggers small vesicles containing neurotransmitters to fuse with the membrane at the synapse and release the transmitter into the synaptic cleft. The transmitter reaches the postsynaptic membrane and binds with specific receptors embedded in the postsynaptic membrane. The binding results in either depolarization (excitation) or hyperpolarization (inhibition) of the postsynaptic cell. Hyperpolarization of the postsynaptic neuron produces an inhibitory postsynaptic potential (IPSP). The effect of a neurotransmitter is not determined by the substance but by the postsynaptic receptor. Conditional neurotransmitters only have an effect in combination with other neurotransmitters.
Neurons can also communicate via electrical synapses. These synapses do not include a synaptic cleft, but the neuronal membranes are touching at specialized channels called gap junctions. These gap junctions create pores connection the cytoplasm of the two neurons.
The central nervous system has three main types of glial cells. Astrocytes are large glial cells with round or symmetrical forms. They surround neurons and are in close contact with the brain’s vasculature. It makes contact with blood vessels. They might also modulate neuronal activity and modulate synaptic strength. It also helps form the blood-brain barrier. Microglial cells are small and irregularly shaped devour and remove damaged cells. Oligodendrocytes form myelin. In the peripheral nervous system, Schwann cells perform this task.
Neural circuits are groups of interconnected neurons that process specific kinds of information. Neural circuits can be combined to form neural systems.
The nervous system is composed of the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves and ganglia outside the CNS). The autonomic nervous system is involved in controlling the involuntary action of smooth muscles (e.g: heart). It consists of sympathetic and parasympathetic branches. The sympathetic system uses norepinephrine as its transmitter and the parasympathetic system uses acetylcholine.
The brain and the spinal cord are covered with three protective membranes. The outer membrane is the thick dura mater. The middle is the arachnoid mater and the inner is the pia mater. The outer layer of the brain is the cerebral cortex. Tracts are bundles of axons. Tracts that run from one region to another are called commissures.
The front of the brain is the rostral (anterior) part. The top side of the brain is the dorsal (superior) part. The lower part of the brain is the ventral (inferior) part and the backside is the caudal (posterior) part. Chambers in the brain are called ventricles. This is filled with fluid that helps the brain float and offset pressure.
The spinal cord takes in sensory information from the body’s peripheral sensory receptors, relays it to the brain and conducts the final motor signals from the brain to muscles. Each spinal nerve has both sensory and motor axons. The spinal cord consists of a white butterfly and it consists of the dorsal horn and the ventral horn. The ventral horn contains the large motor neurons that project to muscles and the dorsal horn contains sensory neurons and interneurons.
The brainstem consists of several parts:
The diencephalon consists of two parts:
The telencephalon consists of several parts:
The infoldings of the cortex are called sulci (crevices) and gyri. The folding of the cortex enables more cortical surface to be packed in the skull (1), brings neurons closer to each other (2) and brings regions closer to each other (3).
The cerebral hemispheres have four main division: the parietal, temporal, frontal and occipital lobe. The central sulcus divides the frontal lobe from the parietal lobe. The Sylvian fissure divides temporal lobe from the frontal and parietal lobes. Cytoarchitectonics uses the microanatomy of cells and their organization to subdivide the cortex. This can be seen in Brodmann’s brain areas. The neocortex includes 90% of the cortex and consists of 6 layers. The mesocortex includes the paralimbic region.
The frontal lobe plays a major role in the planning and execution of movements. It consists of the prefrontal cortex and the motor cortex. The prefrontal cortex is involved in more complex aspects of planning, organizing and executing behaviour. It is the centre of executive function.
The parietal lobe receives sensory information from the outside world, from within the body and information from memory and integrates it. It is involved in spatial orientation. Neurons that involve body parts that are close to each other are also close to each other in the brain. This is called topography.
The temporal lobe is involved in auditory, visual and multimodal processing areas.
The occipital lobe is involved in vision. Visual information travels from the cells in the retina to the primary visual cortex through the primary visual pathway. The auditory cortex lies in the superior part of the temporal lobe. It has a tonotopic organization.
The portion of the neocortex that is neither sensory nor motor cortex is the association cortex and can be activated by more than one sensory modality.
Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 2
Neurons are the basic signalling units that transmit information throughout the nervous system. Neurons vary in form, location and interconnectivity and this is related to their functions. Glial cells provide structural support and electrical insulation to neurons. Dendrites are branching extensions of the neuron that receive inputs from other neurons. Spines are little knobs attached by small necks to the surface of the dendrites and are specialized processes. The axon is a single process that extends from the cell body. Transmission occurs at the synapse. Axon collaterals are combined axons. Along the length of the axons, there are evenly spaced gaps in the myelin. These gaps are called the nodes of Ranvier.
Neuronal signalling is receiving, evaluating and transmitting information of neurons. Neurons are presynaptic when their axon makes a connection onto other neurons and postsynaptic when other neurons make a connection onto their dendrites. Energy is needed to generate signals, energy is in the form of an electrical potential, voltages depend on the concentrations of potassium, sodium and chloride ions and when a neuron is not signalling, the inside of the neuron is more negative than the outside.
Ion channels are proteins with a pore through their centres. They allow certain ions to flow down their concentration gradients. These channels selectively permit one type of ion to pass through the membrane. Permeability refers to the extent to which a particular ion can cross the membrane through a given ion channel. Neurons can change the permeability for a particular ion. This is also called gated ion channels. Ion pumps use energy to actively transport ions across the membrane against their concentration gradients.
The process of neurons transmitting information starts when excitatory postsynaptic potentials (EPSPs) at synapses on the neuron’s dendrites cause ionic currents to flow in the volume of the cell body. Neuronal signalling can be completed if these EPSPs reach the axon terminals. This usually does not happen because decremental conduction occurs. The electrical charge diminishes with distance.
An action potential is a rapid depolarization and repolarization of a small region of the membrane caused by the opening and closing of ion channels. Action potentials can travel infinitely far because the signal keeps being regenerated. The axon hillock is the place where the axon leaves the neuron. The action potential can regenerate itself because of the presence of voltage-gated ion channels. These are ion channels that open at a certain voltage, leading to depolarization. These channels open at around -55mV, which occurs when the neuron depolarizes. The depolarization of the neuron as a result of the voltage-gated ion channels leads to more depolarization as more channels open. This is the Hodgkin-Huxley cycle. The depolarization of the neuron leads to the opening of the slower voltage-gated K+ channels, which repolarizes the neuron leading to a decrease even below the equilibrium potential. In the hyperpolarization state, the voltage-gated Na+ channels are unable to open and another action potential cannot be generated. This is
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 3Optogenetics refers to using light to control cell activation (e.g: neurons) in living tissue. The cognitive approach to psychology uses two key concepts: information processing depends on internal representations (1) and these mental representations undergo transformations (2). People derive multiple representations from stimuli. Physical representations are activated first, phonetic representations next and category representations last.
The chronometric method refers to measuring reaction time. Information perception is biased by memory and attention. People engage in four primary mental operations: encode (1), compare (2), decide (3) and respond (4). The word superiority effect refers to the fact that participants are most accurate in identifying the target letter when the stimuli are words. Letter and word representation are activated in parallel.
There are four broad groups of study populations. Neurologically intact animals and humans and neurologically abnormal animals and humans. There are several types of brain disorders:
Angiography is a clinical imaging method used to evaluate the circulatory system in the brain and diagnose disruptions in circulation. In a single dissociation, a between-group difference is apparent in only one task. A double dissociation identifies whether two cognitive functions are independent of each other. Researchers can choose people with similar anatomical lesions or people with similar behavioural deficits. Many diseases of the nervous system are not usually related to problems with neurons, but rather with how the flow of information is altered by the disease process.
Perturbing neural function refers to disturb interactions between neurons. There are several methods to perturb neural function:
Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 4There is lateralization of sensory processing and motor output. The contralateral control of movement for the motor cortex is not absolute. Proximal muscle control is largely bilateral and distal muscle control is largely contralateral. The lateralization of language can be tested by using the WADA-test (temporarily anaesthetize left hemisphere). Lateralization of language can be left, right or bilateral.
The following anatomical differences between the two hemispheres can be observed: a flatter Sylvian fissure on the left (1), difference in size in Heschl’s gyrus (2), difference in size in Planum Temporale (3), larger pyramidal cell bodies in the left Heschl’s gyrus (4) and more distance between patches in Wernicke’s area (5).
Connections between cells are organized in patches. Anatomical differences do not correlate with language lateralization. Macroscopic and microscopic anatomical differences and functional differences exist between the two hemispheres, but are not absolute.
The two hemispheres cooperate because the corpus callosum connects the two hemispheres, together with the anterior commissure and the posterior commissure.
There is interhemispheric synchrony between neurons that respond to the same stimulus that activates cells with receptive fields in both hemifields.
For split-brain patients, stimuli that are only presented to the right hemisphere cannot be verbally reported if there is a full split of the corpus callosum. When the posterior part of the callosum is sectioned, higher order, abstract information about the stimulus can be reported, but not the stimulus itself.
Two hemispheres can search for a visual target independently if the corpus callosum is cut. Search time increases with half the slope of regular subjects when items are presented to two hemispheres simultaneously.
There are differences between the left- and the right hemisphere. The right-hemisphere: is better at spatial and geometrical tasks (1), is better at recognizing faces (2), is better at perceptual organization (3), is better at processing global information (4), has a more prominent fusiform face area (5), uses the maximizing strategy (6). The left-hemisphere: is better at processing details (1), can recognize faces if verbal descriptions can be made (3), is biased towards recognizing the self (4), seeks patterns and sequences in events (5), uses the matching strategy (6).
The difference in spatial and geometrical tasks occurs because of a difference in sensory to motor mapping. Post-hoc rationalization refers to the left hemisphere trying to explain actions performed by the right hemisphere.
Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 5Each sense collects, filers and amplifies information. Each system has specialized receptor cells that transduce the environmental stimulus into neural signals. The sensory nerves of the body travel up the spinal cord and enter the brain through the medulla and then go to the thalamus. After going through the thalamus, they travel to the primary sensory cortex and the secondary sensory cortex.
Receptor cells share a few general properties:
Each level of processing (e.g: attention, memory, emotion) contributes to the end product of sensory stimulus. This leads to a subjective experience of sensory information. All senses pass through the thalamus before going to the appropriate sensory cortex. The nuclei in the thalamus are interconnected, which provides an opportunity for multisensory integration.
Sound waves arriving at the ear enter the auditory canal. Here, the signals are amplified. It makes the eardrum vibrate and these vibrations travel through air-filled middle ear and rattle tiny bones which causes another membrane (oval window) to vibrate. The oval window is the door to the fluid-filled cochlea. There are tiny hair cells in the cochlea and these are the sensory receptors of the auditory system. The location of a hair cell determines its frequency tuning.
The hair cells act as mechanoreceptors when deflected by the membrane, mechanically gated ion channels open in the cells allowing positively charged ions to flow into the cell. This will lead to depolarization and a release of a transmitter into a synapse between the hair cell and the nerve fibre.
Axons from the cochlear and the olivary nuclei projects to the inferior colliculus where it can access motor structures. Neurons throughout the auditory pathway continue to have frequency tuning and maintain their tonotopic arrangement as they travel up to the cortex. A neuron does not only respond to a specific frequency, but a range of frequency, but is fine-tuned to one specific frequency. The range differs across species.
The interaural time is the difference in the time it takes for sound to reach the two ears. Sound localization makes use of interaural time and the difference in sound intensity between the two ears.
There are different somatosensory receptors for touch, including corpuscles. Pain is signalled by nociceptors. There are three types of nociceptors: thermal, mechanical and polymodal (wide range of stimuli). Myelinated nociceptors are responsible for immediate pain and unmyelinated nociceptors are responsible for longer-lasting pain. Proprioception refers to information about the body’s position.
The initial receiving area is called the primary somatosensory cortex. It contains a somatotopic representation of the body. This is called sensory homunculus. The relative amount of cortical
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 6Agnosias refer to failures of perception while the processes itself (e.g: the eye itself) is functioning normally. Visual agnosia refers to agnosia limited to the visual modality. There are four major concepts of object recognition: there is a difference between perceiving and recognizing (1), perception is of unified objects (2), perceptual abilities are flexible and robust (3) and the product of perception is interwoven with memory (4).
The parahippocampal area and posterior parietal cortex process information about places and scenes.
Output from the visual cortex is contained primarily in two major fibre bundles: fasciculi. The ventral (occipitotemporal) stream is the “what pathway” and the dorsal (occipitoparietal) stream is the “where pathway”. The what pathway is responsible for object perception and recognition and the where the pathway is responsible for spatial perception. There is also a what and where pathway for auditory stimuli. The pathways may carry similar information but they each support different aspects of cognition.
Patients with optic ataxia can recognize objects but cannot use visual information to guide their actions. Saccades are quick eye movements. In patients with optic ataxia, saccades may be directed inappropriately. The two pathways are not isolated from each other but communicate extensively.
Neurons in the parietal lobe have large, nonselective receptive fields that include cells representing both the fovea and the periphery. Neurons in the temporal lobe have large receptive fields that are more selective and always represent foveal information.
There are three major subtypes of agnosia:
People with right-sided lesions cannot recognize objects. People with left-sided lesions cannot make the functional connection between two visual perceptions.
Facial stimuli activate the superior temporal sulcus and the inferotemporal gyrus. The FFA, the fusiform face area includes the fusiform gyrus and is the brain’s area for facial recognition. There are more face regions than this one. It is possible that different areas have different specialization for facial information. It is likely that the FFA is important for processing invariant facial properties and the superior temporal sulcus is important for processing more dynamic features. It is also possible that the FFA is used in fine perceptual discriminations among highly familiar
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 7The thalamus is the switchboard of the brain. The reticular formation regulates excitability and forms a sheet around the thalamus and can gate all information (high arousal) or block all information (coma). Arousal is a prerequisite for attention. Selective attention is a covert, cognitive brain mechanism which enables us to process relevant information, thoughts and actions and ignore or suppress irrelevant or distracting input, thoughts and actions. Selective attention can be voluntary or involuntary. Overt attention is attention located at the same location as the eyes. Covert attention is attention located at another location than the eyes.
Voluntary attention (top-down) is regulated by the dorsal frontoparietal network. It includes the superior parietal lobe (SPL), frontal eye fields (FEF) and the middle frontal gyrus (MFG). Involuntary attention (bottom-up) is regulated by the ventral frontoparietal network. It includes the temporoparietal junction (TPJ), inferior frontal gyrus (IFG) and the middle frontal gyrus (MFG). This network is strongly lateralized to the right hemisphere.
Subcortical structures are important for different aspects of attention. The superior colliculus is involved in moving attention. The temporoparietal junction is involved in disengaging attention and the pulvinar is involved in engaging attention.
Neglect involves the inability to disengage attention and occurs because of right-hemisphere lesions to the temporoparietal junction or the inferior frontal gyrus (involuntary attention) and is often temporary. Extinction, focussing on the contralateral side of the lesion when both visual fields are stimulated often remains.
Balint’s syndrome involves simultagnosia, only seeing one object at a time, optic ataxia, trouble with visual guidance for reaching objects and oculomotor apraxia, problems in making voluntary eye movements to objects and occurs because of bilateral lesions to the dorsal posterior parietal lobe and the lateral occipital complex (LOC).
The capacity of selective attention is 3-4 items and selective attention is relatively slow. It leads to processing at the expense of something else. This limited capacity is caused by the voluntary attention network. The attentional blink refers to missing a second target if it is presented about ±300ms after the first target because attention is still processing the first target.
In the Posner cueing task, participants have to react to a cue. The central cue triggers voluntary attention and the peripheral cue triggers involuntary attention.
A neutral cue is used to measure the baseline reaction time. Reaction time increases with a valid cue and reaction time decreases with an invalid cue and the time between the cue and the target needs to be at least ±200ms in the central cue condition. The cue validity is important. If the cue validity is too low, people stop using the cue.
In the peripheral cue condition, attention is reflexive and fast. If the cue-target interval is below ±200ms, there is facilitation of attention. If the cue-target interval is above ±200ms, there is inhibition of attention.
The feature integration theory of attention states
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 8The final common pathway of all motor output is the ventral horn in the spinal cord. The dorsolateral part of the ventral horn is involved in distal muscles and fine movements. The ventromedial part of the ventral horn is involved in proximal muscles and posture. Muscles make use of alpha neurons. It involves alpha neurons.
There are different reflexes of the human body:
The central pattern generator is the mechanism in the spinal cord that enables patterns (e.g., walking, breathing, swallowing) to be generated and is activated by a higher brain command or by proprioceptive feedback. Reflexes are processed and generated in the spinal cord. Reciprocal inhibition of antagonistic muscles refers to the relaxation of the flexor as the extensor contracts.
Pyramidal tracts are axons that travel directly from the cortex to the spinal cord. The extrapyramidal tracts are axons that travel through another cortical structure to the spinal cord. There are several extrapyramidal tracts:
The pyramidal system is involved in voluntary control of skeletal muscles. It begins at the upper motor neurons of the primary motor cortex and other cortical areas to the spinal cord.
Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 9Learning refers to whenever experience or interaction with the environment results in changes in behaviour. Memory refers to the complete collection of experiences that have been stored in the brain. Learning occurs in three steps: encoding (1), consolidation (2), retrieval (3).
Iconic memory is the memory storage for visual information. It can store information for ±500ms and can be assessed using Sperling’s whole-report/partial-report task. People’s performance is better for partial-report. Echoic memory is the memory storage for auditory information. It can store information for ±10s. A deviant tone evokes a ‘mismatch negativity’ when there is little time between the tones. In both types of memory, there is a passive decay of information.
The modal model states that information is first stored in sensory memory, then it can move, using attentional processes, to short-term storage. If the item is rehearsed, it can be moved into long-term memory. At each stage, memory can be lost by decay, interference or a combination of the two.
The working memory is the interface of memory. It is used to manipulate information, focus attention and operates over a few seconds. The storage of working memory is ±3/4 items and can be assessed using the change detection paradigm. It contains three parts:
Long-term memory consists of declarative memory (explicit memory), memory of events and facts and non-declarative memory (implicit memory), memory of skills. Episodic memory refers to memory about life-events. Semantic memory refers to memory of facts.
The hippocampus is important for encoding and retrieval of information. The function of the hippocampus may be to bind contextual information together to form a complex contextual memory. The perirhinal cortex supports recognition based on familiarity. The left frontal cortex is involved in encoding episodic information and the right frontal cortex is involved in the retrieval of episodic information. Retrieval of information from long-term memory reactivates brain areas active during encoding.
The working memory maintenance hypothesis states that activation of the parietal cortex is related to the maintenance of information in working memory. The binding of items and context model states that the perirhinal cortex represents information about specific items, the para-hippocampal cortex represents information about the context and processing in the hippocampus binds the representation of items with their context. Every time something is retrieved from memory, there is a new memory trace in the hippocampus. The more often something is retrieved, the more
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 10Emotions consist of a physiological response to the stimulus (1), a behavioural response (2) and a feeling (3). The function of emotions is activating the fight/flight response (1), making quick decisions based on emotional value (2) and anticipating the consequences of a decision (3)
Basic emotions (anger, sadness, happiness, disgust, surprise, fear) are innate and universal emotions that correspond to facial expressions. Complex emotions are learned emotions, shaped by the culture and the environment. Emotions can differ on arousal (subjective intensity of emotion) and valence (positive/negative experience). Emotions are not traceable to specific brain regions.
The James-Lange theory states that emotion has three components: cognition (1), readiness for action (2) and feeling (3). Emotion is a label to our responses. This theory is a flawed, as the autonomous nervous system is not differentiated enough to account for all emotions (1), hormonal feedback from the body is too slow to induce emotions (2) and hormone injections can cause different emotions (3).
The hypothalamus is responsible for the readiness for action component of emotion. The sympathetic nervous system is involved in action. Cortical processing is involved in experiencing feelings. The anterior insula is involved in the awareness of bodily responses. The ventromedial prefrontal cortex is involved in using emotions for decision making. If the ventromedial prefrontal cortex is damaged, there is emotional perseverance (e.g., no fear extinction).
The somatic marker theory states that the ventromedial prefrontal cortex starts an internal simulation to evaluate the emotional outcomes of decisions and these emotional outcomes (somatic markers) are used to guide decision making.
The amygdala receives information from the entire brain and can influence the entire brain. It responds to emotional stimuli and neutral stimuli predicting motivating stimuli. It judges the emotional value of the stimulus and is imperative for fear conditioning. The fear-stimulus can reach the amygdala through two routes:
In the Klüver-Bucy syndrome, there is reduced fear and aggression. The syndrome occurs if the amygdala is either removed or non-functional.
There is hemispherical asymmetry in emotions. The right-hemisphere is involved in feeling emotions and: is better at responding to strong emotional stimuli, is better at discriminating between emotions, includes predominantly negative emotions. The left-hemisphere is involved in cognitive control of emotions and: is better at focussing on context, includes predominantly positive emotions.
Lesions to the right hemisphere lead to indifference. Lesions to the left hemisphere lead to more extreme emotions. Bodily reactions are not necessary for experiencing emotions but contribute to the intensity
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 11Language production and language comprehension require a mental lexicon, a mental store of information that includes semantic information, syntactic information and details of word form. The mental lexicon is organised by morphemes (1), frequency of use (2), lexical neighbours (3) and semantic relationships between words (4). Lexical selection refers to integrating words into the full sentence.
A morpheme is the smallest meaningful unit in language. A phoneme is the smallest unit of sound that can make a difference in meaning. Each language has different phonemes. An infant can distinguish between all phonemes. People lose this ability later in life.
Speech production occurs in several steps:
Language perception can be either auditory (spoken language) or visually (written language). It occurs in several steps:
Orthographic input code can be changed into phonological input code, as most people use their inner voice to read.
Language is lateralized to the left-hemisphere surrounding areas of the Sylvian fissure in most people. Wernicke’s area is involved in assigning meaning to words, assigning words to concepts and lexical activation. Broca’s area is involved in production of speech, syntactic integration and lexical selection. The arcuate fasciculus connects Broca’s area and Wernicke’s area and is involved in repetition. The right-hemisphere is involved in the prosody of language and metaphorical meanings.
Broca’s aphasia occurs with damage to Broca’s area and surrounding regions and leads to deficits in speech-production, syntax and grammar. Wernicke’s aphasia occurs with damage to Wernicke’s area and surrounding regions and leads to deficits in assigning meaning to words and language comprehension. Apraxia refers to deficits in motor planning of articulation. Semantic paraphasia refers to problems in speech-production with picking out the right word and occurs in Wernicke’s aphasia.
Lesions in the anterior parts of the inferior and medial temporal cortex lead to deficits involving naming living things. The dissociation between naming non-living and living things may be due to the complexity of the features that help distinguish a living thing from another living thing and a non-living thing from another non-living thing.
The superior temporal gyrus is involved in general auditory processing of phonemes. There is no distinction between phonemes and non-phoneme sounds. The superior temporal sulcus is involved in linguistic processing of phonemes. Areas that are more sensitive to speech are located more ventrolateral in or to the superior temporal sulcus. Occipitotemporal regions in the brain are involved in letter perception. The inferior frontal gyrus is involved in lexical
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 12Cognitive control (executive function) allows us to use our perceptions, knowledge and goals to bias the selection of action and thoughts from a multitude of possibilities. It allows us to override automatic thoughts and behaviour and step out of the realm of habitual responses. It also allows us to plan for the future and troubleshoot problems. Cognitive control is essential for goal-oriented behaviour.
The border between the frontal lobe and the parietal lobe is marked by the central sulcus. The most posterior part of the frontal lobe is the primary motor cortex. The unique cognitive abilities of humans may arise because of the prefrontal cortex and more because of how our brains are connected rather than due to an increase in the number of neurons. The prefrontal cortex is connected with other parts of the brain. The largest input comes from the thalamus. Almost all cortical and subcortical areas influence the prefrontal cortex. The prefrontal cortex consists of the lateral prefrontal cortex, frontal pole, medial frontal cortex and ventromedial prefrontal cortex.
Dysfunction of the prefrontal cortex may result in perseveration, persisting in a response even after being told that it is incorrect. The patient may also be unable to understand the consequences of their actions. The deficits seem to be mild when the lesion is unilateral but severe when the lesion is bilateral. Dysfunction in the frontal cortex leads to a loss of goal-oriented behaviour. Patients show utilization behaviour, behaviour which an extreme dependency on prototypical responses for guiding behaviour.
Goal-oriented actions are based on the assessment of an expected reward or value and the knowledge that there is a causal relationship between the action and the reward. A habit is an action that is no longer under the control of a reward but is stimulus-driven and automatic. Working memory is the transient representation of task-relevant information. It is the temporary maintenance of information, providing an interface between perception, long-term memory and action.
The lateral prefrontal cortex is a major component of working memory. Recency memory refers to the ability to organize and segregate the timing or order of events in memory. There is a breakdown of temporal structure of working memory with frontal lobe lesions. The prefrontal cortex is necessary for working memory but not for associative memory. Cells remain firing while being held in working memory. Prefrontal activation reflects a representation of the task goal and serves as an interface with task-relevant long-term representations in other neural regions.
A key component of fluid intelligence is the ability to maintain focus on task-relevant information in working memory. As dopamine levels increase, learning performance improves, but only to a point. At some level, increasing dopamine levels results in a reduction in performance.
In Petrides’ model of working memory, information held in the posterior cortex is activated, retrieved and maintained by the ventrolateral prefrontal cortex and manipulated in more dorsal regions of the lateral prefrontal cortex.
The frontal pole
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 5/6/14 (combination)Sleepwalking involves typically automated behaviour and occurs most often in young children. It occurs more frequently after sleep deprivation and the prevalence is 1%-5%. It typically occurs during the deepest stages of sleep and the frontal cortex is deactivated during sleepwalking.
In normal sleep, there are successive sleep stages. Cycles last ±90 minutes. Deep sleep stages occur in the early part of the night. It includes high amplitude, low-frequency EEG. REM-sleep stages occur towards the end of the night.
Sleep paralysis refers to the muscle tone remaining flat because of muscle paralysis, but the person is awake. This is also shown on EEG. Sleep violence refers to REM-sleep without muscle paralysis. Narcolepsy is the sudden onset of REM-sleep. There are several disorders of consciousness:
The reticular activation system (RAS) is critical for maintaining consciousness. It either projects directly to the cortex or via the thalamus. Easy problems of consciousness include problems of consciousness that are very difficult to understand and explain, but it is possible to envision a solution. Hard problems of consciousness refer to explaining qualia. There is an explanatory gap, explaining the function of consciousness does not explain the experience of that part of consciousness.
Blindsight refers to not being able to consciously report stimuli in the visual field, but act appropriately as if one was still able to see. It is mediated via projections of the optic tract to the superior colliculus, which projects to the dorsal stream areas. Super blindsight refers to the ability of monkeys and humans with bilateral primary visual cortex lesions to behave normally.
The dorsal stream includes vision for action. The ventral stream includes vision for perception. Looking for the neural correlate of consciousness (NCC) through elimination may leave no area of the brain as belonging to the neural correlate of consciousness.
It is also possible to study the neural correlate of consciousness by studying which regions contribute to the conscious percept. This can be studied by using bi-stable stimuli (stimuli that remains constant but the constant percept switches spontaneously), electrical stimulation and illusions.
In a binocular rivalry task, there are two percepts and
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 2Neurons are the basic signalling units that transmit information throughout the nervous system. Neurons vary in form, location and interconnectivity and this is related to their functions. Glial cells provide structural support and electrical insulation to neurons. Dendrites are branching extensions of the neuron that receive inputs from other neurons. Spines are little knobs attached by small necks to the surface of the dendrites and are specialized processes. The axon is a single process that extends from the cell body. Transmission occurs at the synapse. Axon collaterals are combined axons. Along the length of the axons, there are evenly spaced gaps in the myelin. These gaps are called the nodes of Ranvier.
Neuronal signalling is receiving, evaluating and transmitting information of neurons. Neurons are presynaptic when their axon makes a connection onto other neurons and postsynaptic when other neurons make a connection onto their dendrites. Energy is needed to generate signals, energy is in the form of an electrical potential, voltages depend on the concentrations of potassium, sodium and chloride ions and when a neuron is not signalling, the inside of the neuron is more negative than the outside.
Ion channels are proteins with a pore through their centres. They allow certain ions to flow down their concentration gradients. These channels selectively permit one type of ion to pass through the membrane. Permeability refers to the extent to which a particular ion can cross the membrane through a given ion channel. Neurons can change the permeability for a particular ion. This is also called gated ion channels. Ion pumps use energy to actively transport ions across the membrane against their concentration gradients.
The process of neurons transmitting information starts when excitatory postsynaptic potentials (EPSPs) at synapses on the neuron’s dendrites cause ionic currents to flow in the volume of the cell body. Neuronal signalling can be completed if these EPSPs reach the axon terminals. This usually does not happen because decremental conduction occurs. The electrical charge diminishes with distance.
An action potential is a rapid depolarization and repolarization of a small region of the membrane caused by the opening and closing of ion channels. Action potentials can travel infinitely far because the signal keeps being regenerated. The axon hillock is the place where the axon leaves the neuron. The action potential can regenerate itself because of the presence of voltage-gated ion channels. These are ion channels that open at a certain voltage, leading to depolarization. These channels open at around -55mV, which occurs when the neuron depolarizes. The depolarization of the neuron as a result of the voltage-gated ion channels leads to more depolarization as more channels open. This is the Hodgkin-Huxley cycle. The depolarization of the neuron leads to the opening of the slower voltage-gated K+ channels, which repolarizes the neuron leading to a decrease even below the equilibrium potential. In the hyperpolarization state, the voltage-gated Na+ channels are unable to open and another action potential cannot be generated. This is
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 3Optogenetics refers to using light to control cell activation (e.g: neurons) in living tissue. The cognitive approach to psychology uses two key concepts: information processing depends on internal representations (1) and these mental representations undergo transformations (2). People derive multiple representations from stimuli. Physical representations are activated first, phonetic representations next and category representations last.
The chronometric method refers to measuring reaction time. Information perception is biased by memory and attention. People engage in four primary mental operations: encode (1), compare (2), decide (3) and respond (4). The word superiority effect refers to the fact that participants are most accurate in identifying the target letter when the stimuli are words. Letter and word representation are activated in parallel.
There are four broad groups of study populations. Neurologically intact animals and humans and neurologically abnormal animals and humans. There are several types of brain disorders:
Angiography is a clinical imaging method used to evaluate the circulatory system in the brain and diagnose disruptions in circulation. In a single dissociation, a between-group difference is apparent in only one task. A double dissociation identifies whether two cognitive functions are independent of each other. Researchers can choose people with similar anatomical lesions or people with similar behavioural deficits. Many diseases of the nervous system are not usually related to problems with neurons, but rather with how the flow of information is altered by the disease process.
Perturbing neural function refers to disturb interactions between neurons. There are several methods to perturb neural function:
Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 5Each sense collects, filers and amplifies information. Each system has specialized receptor cells that transduce the environmental stimulus into neural signals. The sensory nerves of the body travel up the spinal cord and enter the brain through the medulla and then go to the thalamus. After going through the thalamus, they travel to the primary sensory cortex and the secondary sensory cortex.
Receptor cells share a few general properties:
Each level of processing (e.g: attention, memory, emotion) contributes to the end product of sensory stimulus. This leads to a subjective experience of sensory information. All senses pass through the thalamus before going to the appropriate sensory cortex. The nuclei in the thalamus are interconnected, which provides an opportunity for multisensory integration.
Sound waves arriving at the ear enter the auditory canal. Here, the signals are amplified. It makes the eardrum vibrate and these vibrations travel through air-filled middle ear and rattle tiny bones which causes another membrane (oval window) to vibrate. The oval window is the door to the fluid-filled cochlea. There are tiny hair cells in the cochlea and these are the sensory receptors of the auditory system. The location of a hair cell determines its frequency tuning.
The hair cells act as mechanoreceptors when deflected by the membrane, mechanically gated ion channels open in the cells allowing positively charged ions to flow into the cell. This will lead to depolarization and a release of a transmitter into a synapse between the hair cell and the nerve fibre.
Axons from the cochlear and the olivary nuclei projects to the inferior colliculus where it can access motor structures. Neurons throughout the auditory pathway continue to have frequency tuning and maintain their tonotopic arrangement as they travel up to the cortex. A neuron does not only respond to a specific frequency, but a range of frequency, but is fine-tuned to one specific frequency. The range differs across species.
The interaural time is the difference in the time it takes for sound to reach the two ears. Sound localization makes use of interaural time and the difference in sound intensity between the two ears.
There are different somatosensory receptors for touch, including corpuscles. Pain is signalled by nociceptors. There are three types of nociceptors: thermal, mechanical and polymodal (wide range of stimuli). Myelinated nociceptors are responsible for immediate pain and unmyelinated nociceptors are responsible for longer-lasting pain. Proprioception refers to information about the body’s position.
The initial receiving area is called the primary somatosensory cortex. It contains a somatotopic representation of the body. This is called sensory homunculus. The relative amount of cortical
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 6Agnosias refer to failures of perception while the processes itself (e.g: the eye itself) is functioning normally. Visual agnosia refers to agnosia limited to the visual modality. There are four major concepts of object recognition: there is a difference between perceiving and recognizing (1), perception is of unified objects (2), perceptual abilities are flexible and robust (3) and the product of perception is interwoven with memory (4).
The parahippocampal area and posterior parietal cortex process information about places and scenes.
Output from the visual cortex is contained primarily in two major fibre bundles: fasciculi. The ventral (occipitotemporal) stream is the “what pathway” and the dorsal (occipitoparietal) stream is the “where pathway”. The what pathway is responsible for object perception and recognition and the where the pathway is responsible for spatial perception. There is also a what and where pathway for auditory stimuli. The pathways may carry similar information but they each support different aspects of cognition.
Patients with optic ataxia can recognize objects but cannot use visual information to guide their actions. Saccades are quick eye movements. In patients with optic ataxia, saccades may be directed inappropriately. The two pathways are not isolated from each other but communicate extensively.
Neurons in the parietal lobe have large, nonselective receptive fields that include cells representing both the fovea and the periphery. Neurons in the temporal lobe have large receptive fields that are more selective and always represent foveal information.
There are three major subtypes of agnosia:
People with right-sided lesions cannot recognize objects. People with left-sided lesions cannot make the functional connection between two visual perceptions.
Facial stimuli activate the superior temporal sulcus and the inferotemporal gyrus. The FFA, the fusiform face area includes the fusiform gyrus and is the brain’s area for facial recognition. There are more face regions than this one. It is possible that different areas have different specialization for facial information. It is likely that the FFA is important for processing invariant facial properties and the superior temporal sulcus is important for processing more dynamic features. It is also possible that the FFA is used in fine perceptual discriminations among highly familiar
.....read more Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 12Cognitive control (executive function) allows us to use our perceptions, knowledge and goals to bias the selection of action and thoughts from a multitude of possibilities. It allows us to override automatic thoughts and behaviour and step out of the realm of habitual responses. It also allows us to plan for the future and troubleshoot problems. Cognitive control is essential for goal-oriented behaviour.
The border between the frontal lobe and the parietal lobe is marked by the central sulcus. The most posterior part of the frontal lobe is the primary motor cortex. The unique cognitive abilities of humans may arise because of the prefrontal cortex and more because of how our brains are connected rather than due to an increase in the number of neurons. The prefrontal cortex is connected with other parts of the brain. The largest input comes from the thalamus. Almost all cortical and subcortical areas influence the prefrontal cortex. The prefrontal cortex consists of the lateral prefrontal cortex, frontal pole, medial frontal cortex and ventromedial prefrontal cortex.
Dysfunction of the prefrontal cortex may result in perseveration, persisting in a response even after being told that it is incorrect. The patient may also be unable to understand the consequences of their actions. The deficits seem to be mild when the lesion is unilateral but severe when the lesion is bilateral. Dysfunction in the frontal cortex leads to a loss of goal-oriented behaviour. Patients show utilization behaviour, behaviour which an extreme dependency on prototypical responses for guiding behaviour.
Goal-oriented actions are based on the assessment of an expected reward or value and the knowledge that there is a causal relationship between the action and the reward. A habit is an action that is no longer under the control of a reward but is stimulus-driven and automatic. Working memory is the transient representation of task-relevant information. It is the temporary maintenance of information, providing an interface between perception, long-term memory and action.
The lateral prefrontal cortex is a major component of working memory. Recency memory refers to the ability to organize and segregate the timing or order of events in memory. There is a breakdown of temporal structure of working memory with frontal lobe lesions. The prefrontal cortex is necessary for working memory but not for associative memory. Cells remain firing while being held in working memory. Prefrontal activation reflects a representation of the task goal and serves as an interface with task-relevant long-term representations in other neural regions.
A key component of fluid intelligence is the ability to maintain focus on task-relevant information in working memory. As dopamine levels increase, learning performance improves, but only to a point. At some level, increasing dopamine levels results in a reduction in performance.
In Petrides’ model of working memory, information held in the posterior cortex is activated, retrieved and maintained by the ventrolateral prefrontal cortex and manipulated in more dorsal regions of the lateral prefrontal cortex.
The frontal pole
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