Tinbergen says that there are four biological explanations for behaviour: the ontogenetic explanation (how behaviour or a brain structure develop within an organism), the physiological explanation (the relation between the physiological condition of the brain and the behaviour), the functional explanation (why a certain brain structure has developed in a certain way) and the evolutionary explanation (relates behaviour to evolutionary history).
Neurons receive information and pass this information to other neurons, trough electrochemical signals. The three most important parts of most neurons are the soma or cell body, the axon (the part that passes impulses to other cells) and the dendrite (the part that receives the information). Many axons (an exception are those of invertebrates) are surrounded by an isolating shell, which is called the myelin sheath.
The membrane of a neuron maintains an electrical gradient. This is a difference in electrical charge within and outside the membrane. In rest, the neuron slightly has a negative charge, the so-called resting potential (polarisation). Action potentials are messages that are passed by axons. The firing of neurons takes place under an all-or-nothing principle: when the threshold is exceeded, an action potential of always the same size and shape comes into existence.
Sometimes, psychologists or other scientists use animals for testing. They look at the behaviour these animals show and how they react to certain signals/manipulations. Psychologists study animals to know more about the animal, the human evolution, to study mechanisms that look like human mechanisms or they study animals because certain restrictions don’t let them do the research on a human being. The abolitionists think that animals shouldn’t be used for testing, while the minimalists think that animal research is needed sometimes, but that it has to occur as little as possible. Some research think that animal research should be allowed, because it contributes to the greater good. The legal standard looks at the three Rs: reduction (using less animals), replacement (replacing animals with computer models) and refinement (avoiding uncomfortable and painful situations).
A synapse is a place where the information exchange between neurons takes place. This happens in a sequence of chemical events in the synapse. Neurotransmitters are chemicals that have been released by a neuron to influence another neuron. The chain of chemical events in a synapse goes as follows: (1) The neuron synthesizes chemicals that serve as neurotransmitters. Smaller neurotransmitters are synthesized in the ends of axons and neuropeptides are synthesized in the cell body. (2) The neuron transports the neuropeptides to the dendrites. Action potential make it possible for calcium to enter cell. Calcium helps release neurotransmitters from the ends of axons in the synaptic gap. (3) Neurotransmitters connect to the receptors and change the activity of the postsynaptic neuron. (4) The neurotransmitter molecules dispatch from the receptors. (5) Neurotransmitters are retaken in the presynaptic neuron for recycling or they spread far away. (6) Postsynaptic cells release retrograde transmitters to control the further release of neurotransmitters.
Repeating stimuli within a short timespan has a cumulative effect. Sherrington called this temporal summation. Synapses also have the characteristic of spatial summation, which means that the combined effect of synaptic input from different locations is combined and has an effect on the neuron.
Hormones are chemicals that are secreted from glands or cells from one part of the body and they are transported through blood to influence other cells. Hormones are synthesized by the adenohypophysis and the neurohypophysis. The hypothalamus is responsible for the release of certain hormones.
The brain has different types of receptors. Receptors differ in their chemical characteristics, their reactions to drugs and the role they play in behaviour. Because of this, medicine can be developed that has a specialised effect on different people, because there are differences between the hundred proteins associated with the synapse. People can differ genetically in many ways, when it comes to influence on the behaviour.
The nervous system can be divided into the central nervous system (the brains and the spinal cord) and the peripheral nervous system (all the other nerves), consisting of the autonomous nervous system (neurons that bring information from and to organs) and the somatic nervous system (neurons that bring information from the senses to the central nervous system).
The brain can be divided in the fore- mid- and hindbrain. The hindbrain consists out of the medulla. This part of the brain connects the brain stem with the spinal cord. It controls some vital reflexes, like breathing and sneezing. The forebrain is the most prominent part of mammals’ brains. The brain hemispheres are organised to receive sensory information and to control muscles. The outer part of the brain is called the cerebral cortex. Underneath this there are different structures with different functions. The thalamus is the most important source of input for the cerebral cortex. The basal ganglia plays a role in certain aspects of movement. The limbic system forms a border around the brain stem. This system is important for emotion and motivation.
The cerebral cortex exists of layers of cells at the outer side of the cerebral hemispheres. Within this cortex, four different lobes can be distinguished: the occipital lobe (vision), the parietal lobe (body sensations), the temporal lobe (hearing) and the frontal lobe (planning, emotions).
The most important categories of methods to study brain functions are: studying the effects of brain damage, noting the effects of brain stimulation, noting the brain activity during behaviour and correlating the anatomy of the brains with the behaviour. Different instruments can be used to scan brains and brain activity. With an elektro-encefalogram (EEG) electric activity of the brain can be measured with help of electrodes attached to a scalp. This method can note spontaneous brain activity or the activity that results from a reaction on a stimulus. A magnetoencephalogram (MEG) looks like the EEG, but magnetic fields are used (which are generated by brain activity). MEG has an excellent temporal resolution. Positronemissiontomography (PET) provides an image with a high resolution, by measuring the emission of radioactive chemicals that have been injected into the body. In brain areas with the most radioactivity, the most blood flows. That’s why these areas will show the most brain activity. Unfortunately, the brain is exposed to radioactivity by PET-scans. PET-scans are replaced by fMRIs( functional magnetic resonance imaging). This is less expensive and has less risk to it than PETs. The changes in haemoglobin molecules are measured when they release oxygen. This method has been of great value, and still is, but the interpretation of the fMRI data is rather complex.
A gene is a biological unit of heredity, which keeps its structure and identity from one generation to another generation. Genes consist of pairs and they are aligned on chromosomes (a structure in the cell nucleus and it carries hereditary traits), which also consist of pairs. A gene is part of a chromosome which consists of DNA, a molecule with two strings. RNA is one string of DNA. Every molecule DNA or RNA contains a few genes. A certain RNA molecule serves as a pattern for the synthesis of proteins. DNA has four fundaments: adenine, guanine, cytosine and thymine. De sequence of these fundaments determines the sequence of the corresponding fundaments on the RNA molecule. The DNA in the chromosomes contains the code for the hereditary traits. Genes transform through mutation. Mutation causes permanent changes.
Evolution is the gradual change in an amount of different genes within a population. Evolution means every change in the frequency of genes, good or bad in the long run for the species. A gene that keeps getting associated with successful reproduction will be more present in future generations. Some misconceptions about evolution are that the evolution of mankind has stopped, that certain body parts that aren’t used much or certain functions that are not used much, will be passed less to future generations and that evolution is enhancement. All these misconceptions aren’t true. Evolutionary psychology is concerned with the evolution of certain behaviour and in particular social behaviour.
The anatomy of the brains is plastic. That means that the organisation of the brain changes as part of normal development, a learning process or after brain damage. In the development of neurons, different processes can be distinguished: proliferation (the production of new cells), migration (transportation of cells), differentiation (forming of axons and dendrites), myelinisation (glia produce the greasy, isolating sheaths that enable the transmission of axons) and synaptogenesis (the forming of synapses). A big part of our brain is formed before birth or during the early years. Neurons can change their shape, but in some parts of our body new neurons can be formed. Stem cells in the nose stay undeveloped your whole life. Stem cells in the hippocampus of adult mammals differentiate to new neurons.
The most common cause of brain damage in older people is a cerebrovascular accident, CVA). That means that the bloodstream to a certain part of the brain stops temporarily. The most common form of a stroke is an ischaemia, which means that a brain area receives an inadequate amount of blood. To threat an ischaemia, one can use a tissue plasminogen activator, tPA. That is a medicine that cleans up blood clots. This can only be effective, if it’s given to a patient within three hours after the ischaemia. The most effective way to prevent brain damage after a stroke is to cool the brain. Later mechanisms of recovery are anatomical changes. The recovery of behaviour partly depends on slowly returning activity in neurons that have not been affected. Damaged axons can grow again.
Every object sends out rays, but we are only able to see the rays that fall normally on our retina. You can only perceive something when your brain activity changes. The brain codes information in a way which doesn’t agree with what you see, but in the way the neurons react, the velocity of the reaction and the timing. Light enters the eye through an opening in the middle of the iris, the pupil. This is then focused through the lens and the cornea and projected on the retina (at the backside of the eye, on which visual receptors are present). Messages run from receptors from the backside of the eye to bipolar cells, which are close to the centre of the eye. These will in turn send their messages to the ganglion cells. The axons of the ganglion cells come together and run back to the brain.
The retina of vertebrates contains rods and cones. Rods are at the outer part of the retina and they react to weak light. Cones are close to and in the fovea, they react to bright light and they are essential for seeing colour. You can see colour well in the fovea, but not in the surrounding parts. The fovea is a small area specialised in detailed sight. In that part, the receptors are close to each other and there are no (or a few) blood vessels and ganglion cells. Because of this, the sight is unobstructed.
Most ganglion cells go to a part of the thalamus: the lateral geniculate nucleus. Most information at the lateral geniculate nucleus goes to the primary motor cortex, which is in the occipital cortex. This is also called the V1 area. Cells with the same characteristics are grouped together in columns in the visual cortex. Trait detectors are neurons in the V1 area and their reactions show that a certain trait is present. The brain needs visual experience in order to keep and refine the connections. Most neurons in the visual cortex receive binocular input: stimulation from both eyes. Experiences is also needed to adjust and refine the mechanisms between the eyes.
Every part of the brain sees a different trait of an object we perceive. At least 80 brain areas contribute in different ways to vision. The primary visual cortex sends information to the secondary visual cortex, V2, which processes it further and sends it to other areas. The connections are reciprocal. A distinction is made between the ventral pathway and the dorsal pathway. The ventral pathway is called the ‘what-pathway’ and it’s specialised in the recognition of objects and goes through the temporal cortex. The dorsal pathway is called the ‘how-pathway’ and is specialised in the visual guidance of movement and goes through the parietal cortex. Damage to the dorsal pathway doesn’t result in impaired sight, but people who have damage in that area can’t localize an object. Damage to the ventral pathway means that a person can see where an object is, but a person doesn’t know what the object is.
Sounds is processed by different structures. Sound is localised in the pinna (the visible part of the ear). After the sound has passed through the auditory channel, it goes to the eardrum, in the middle ear. The ear drum has three small bones (ossicles): the hammer, the anvil and the stirrup. These three pass the vibrations to the oval window, which is a membrane in the inner ear. In the inner ear is the cochlea. In this, there are three tunnels filled with fluid. The stirrup makes the oval window vibrate at the entrance of one of these channels and this results in the movement of fluid in the cochlea. Between the basal membrane of the cochlea and the tectorial membrane are hair cells. These are auditory receptors. The hair cells move because of the vibrations in the fluid of the cochlea. This will open ion channels in the membrane.
Each brain hemisphere receives the most input from the ear of the opposite side of the head. That information comes in the primary auditory cortex, A1. This is located in the superior temporal cortex. The auditory system needs experience to develop fully. Damage to A1 doesn’t lead to deafness, but it does lead to not being able to recognize combinations or sequences of sounds.
Mechanical senses react to pressure, bending or other turns of the receptors. The somatosensory system is the sensation of the body and its movements, and it has a lot of sources of information. There are many somatosensory receptors on the skin. Stimulation of touch receptor opens up sodium channels in the axon, which triggers an action potential. A pain perception begins at a nerve ending. The axons that bring the information, don’t have much myelin and that’s why the transmission is relatively slow. Thicker axons transfer sharp pain, while thinner axons transfer less forceful pain. Motoric reactions to pain come about quicker than motoric reactions to touch stimuli.
Olfactory is especially important for the selection of food, but also for social behaviour. Evolutionary speaking, a human being prefers someone how smells similar to him/her, but not too similar (otherwise, it could be a blood relative and you do not want to have offspring with your relative). Olfactory cells are the neurons that are responsible for smell. The receptors are located on the cilia, which are dendrites that reach the surface of the nasal tubes. The vomeronasal organ (VNO) is a group receptors that is located near the olfactory receptors. These receptors are only specialised to react on pheromones. Pheromones are chemicals that are released by an animal and that have an influence on the behaviour of other members of the species. For example, the smell of sweat of a woman during her ovulation increases the testosterone content of man.
Movement of animals depends on muscles. There are three different categories of muscles: smooth muscles (controls the digestion system and other organs), skeletal muscles (control movement of the body in relation to the environment) and cardiac muscles (these have traits that fall between the traits of the other two muscle categories). A muscle consists of multiple fibres. Every fibre receives information from just one axon. It is possible for an axon to nerve together with multiple muscle fibres. To move an arm or leg to the front, one needs an opposite set of muscles, called the antagonistic muscles.
Direct stimulation of the primary motor cortex enables movement. The motor cortex doesn’t send direct signals to the muscles, but its axons run to the brain stem and the spinal cord, which make impulses that control muscles. The cerebral cortex is particularly important for complex actions. The primary cortex is important for making a movement, but not for planning a movement. The parts of the brain that are important for planning a movement are the posterior parietal cortex (this keeps track of the position and the stance of the body in relation to the environment), the prefrontal cortex and supplementary motor cortex (this stops a habit when you need to do something else) and the premotor cortex. The latter is most active directly before a movement. It receives information about the target the body wants to move to and the position and posture of the body.
Two well-known movement diseases are Parkinson’s disease and Huntington’s disease. The symptoms of Parkinson’s disease are stiffness, slow movements, muscle tremors and having trouble getting physical and mental activity started. Patients are slow on both motoric and cognitive tasks. They often get depressed during the early stages of the disease and they also show impairments in memory and reasoning. The immediate cause of Parkinson’s disease is the gradual, progressive death of neurons (substantia nigra) that send dopamine releasing axons to the caudate nucleus and the putamen. The loss of dopamine activity results in less stimulation on the motor cortex and a slower beginning of movements. One treatment is to restore the level of dopamine. L-dopa is a precursor of dopamine and it can cross the blood-brain barrier. L-dopa reaches the brain and it is converted into dopamine. L-dopa does have a few side effects. Huntington’s disease is a neurological condition, which often starts with twitches in the face and arms and is followed by tremors in other parts of the body. This will eventually turn into convulsions. The disease is controlled by an autosomal, dominant gene. Nowadays we know on which chromosome the gene for Huntington’s disease is located. The gene consists of a series of C-A-G fundaments, which is repeated. The more repetitions of this sequence, the sooner the onset of the disease will be. There are different medicine that seem promising. Some medicine try to block the formation of clusters of glutamine chains. Other medicine tries to interfere with the RNA part that enables the expression of the disease.
People and animals show certain behaviour regularly. Sometimes, a biological rhythm is present. The biological clock regulates the daily rhythm (circadian rhythm), but it can also regulate the annual rhythm (circa-annual rhythm). This latter is the case for birds that go to another country when it starts getting colder. Humans and animals have a 24-hour rhythm. Circadian rhythms can differ between people. Some people are more productive during the morning, while others are more active in the late afternoon or evening. The biological clock depends on the suprachiasmatic nucleus (SCN). This is a part of the hypothalamus, above the optic chiasm. The SCN controls the circadian rhythms of sleep and temperature. The SCN controls the sleep and wake rhythms by controlling the activation levels of other brain areas, like the pineal gland. The pineal gland releases melatonin, a hormone that influences the circadian rhythm and the circa-annual rhythm. Melatonin is usually released during the evening and that’s why we become sleepy during that time.
Sleep is a state that the brain produces actively and it is characterised by a decrease of brain activity and reactions to stimuli. Coma is a state of unconsciousness, in which a person cannot be awakened and fails to respond normally to any stimuli. It is caused by stroke, disease or damage in the head. A person in a vegetative state shows partial arousal instead of true awareness, without purposeful activities. A person in a minimally conscious state can have moderate purposeful activities. Both states can last for months or even years. Brain death is a condition in which all the brain activity ends and there is no reaction to stimuli.
There are different sleep stages. In stage 1, the sleep has just started and the brain activity is less than during relaxed wakefulness, but more than in the other phases. In stage 2, shaking interactions between the cells of the thalamus and the cortex are present. During the later stages of sleep, the heart rate, velocity of breathing and brain activity decrease and slow waves with high amplitudes are more present (on the EEG). Stage 3 and 4 together are called slow-wave sleep. The REM-sleep (rapid eye movement) combines deep and light sleep and an irregular and fast pattern is present on the EEG. When you sleep, you will first enter stage 1, 2, 3 and 4. Then, you will go back from 4 to 3 to 2 and then REM-sleep. This sequence will repeat itself and will last approximately 90 minutes. REM-sleep and dreams often occur together, but they are not the same. The function of sleep is to enhance memory and to reorganise memories. Sleep enforces memories by cutting out less successful connections. One hypothesis states that the original function of sleep was to safe energy and that more functions were added during the course of evolution.
There are different sleeping disorders. Someone who doesn’t get enough sleep, suffers from insomnia. Sleep apnoea is a kind of insomnia, which is characterised by interruptions of breathing during sleep. Narcolepsy is characterised by frequent periods of sleepiness during the day. A person can suddenly fall asleep during the day. Many children also suffer from night terrors. These are experiences that cause intense fear and they are different from nightmares.
Homeostasis refers to temperature regulation and other biological processes that help the body to regulate a constant state. The body wants to hold onto one value: the set point. Processes that reduce the deviation from the set point are called negative feedback. Much motivated behaviour can be seen as negative feedback.
Allostasis is the adaptive mechanism the body uses to change its set points. Most energy of the body is used for basal metabolism: the energy to hold a consistent body temperature in resting. If an animal is poikilothermic, its internal temperature varies considerably. These animals don’t have physiological mechanisms (like sweating) to regulate their temperature and they are dependent on their own behavior to change. It is the opposite of a homeothermic animal, which maintains thermal homeostasis.
There are two types of thirst: osmotic thirst and hypovolemic thirst. Osmotic thirst is caused by eating sweet things. Losing fluid by bleeding or sweating causes hypovolemic thirst. Osmotic pressure means that water flows through a semi-permeable membrane from an area with little dissolvable concentrations to an area with higher concentrations. Brain areas that notice osmotic pressure are the organum vascolosum laminae terminalis (OVLT) and the subfornical organ (SFO). These areas are dependent on the different areas of the hypothalamus. When you lose a great amount of bodily fluids by sweating, bleeding or diarrhoea, your body reacts with producing hormones that contract blood vessels (vasopressine and angiotensine II).
Certain substances in our body let us know when we need to stop with eating and they also regulate the supply of certain chemicals. Normally, the prime signal to stop eating is the dilation of the stomach. Messages are sent from the stomach to the brain, via the vagus nerve (information about the dilation of the stomach) and the splanchnic nerve (information about the containment of nutrients). Meals can also end after the dilation of the duodenum. Fat in the duodenum releases a hormone, oleoylethanolamide (OEA), which stimulates the vagus nerve and which sends a message to the hypothalamus and delays the next meal. Brain areas which are involved with appetite, are two cells in the arcuate nucleus of the hypothalamus: one set of neurons sensitive to hunger signals and one set of neurons sensitive for saturation signals. The cells that are sensitive to hunger receive input from the taste path: good tasting food stimulates hunger.
Other input to the hunger sensitive cells comes from axons that release the neurotransmitter gherlin. Gherlin is the hunger hormone and it is released during a period of food abstention, which triggers the contraction of the stomach. Most of the input from the arcuate nucleus goes to the PVN (paraventricular nucleus of hypothalamus) and the hypothalamus. The PVN inhibits the lateral hypothalamus, an area that is important for eating. The PVN is important for saturation.
Sexual differentiation begins with the chromosomes. During the early stages of prenatal development, both man and women have a set of channels of Müller (the precursors of the female internal structures) and of the channels of Wolff (precursors of the male internal structures), as well as primitive reproductive glands that will develop in testes or ovaries. The Y-chromosome of the man has the SRY-gene (sex defining region on the Y-chromosome). This gene is responsible for the primitive reproductive glands developing into testes, the sperm-producing organs. The developing testes produce androgens, which will cause the testes to grow more, which will result in the production of more androgens. Androgens are responsible for the development of seminal vesicle and the vas deferens. The peptide-hormone MIH (Müllerian inhibiting hormone) is responsible for the degeneration of the channels of Müller. The result of these changes is the development of the penis and the scrotum. Women don’t possess the SRY-gene and their reproductive glands develop into ovaries. The channels of Wolff degenerate and the channels of Müller develop into fallopian tubes, the uterus and the vagina. Estradiol and other oestrogens cause many changes in the development of the brains and other internal sex organs.
Androgens contain testosterone and they are referred to as male hormones, because males have more androgens. Oestrogens, a group of reproductive hormones that contain estradiol, are called female hormones, because women have more of them than men do. Androgens and oestrogens are common in both sexes. Progesterone is another common female reproductive hormone and it prepares the uterus for fertilization and it helps to maintain the pregnancy. A distinction is made between the activating and organising effects of sex hormones.
The organising effects are common during a sensitive period of development and decide whether the brain and the body will develop male or female characteristics. Activating effects can always occur when a hormone temporarily activates a certain response. The distinction between these effects isn’t absolute.
We call the biological differences between males and females sex differences. Men with lower testosterone levels can develop more feminine and women with higher testosterone levels can develop more masculine. The most common cause of this condition is the adrenogential syndrome (CAH): over-development in the adrenal glands since birth. Individuals that seem to be a mix between a man and a woman are called hermaphrodites. People that appear to have a sexual development between that of a woman and a man are called intersexual.
Psychologists define emotion in terms of three components: cognitions, feelings and actions. Emotional situations cause arousal in the autonomic nervous system. The autonomic nervous system exists of a sympathetic part and a parasympathetic part. Usually, both are active at the same time, but one is sometimes more active than the other.
The sympathetic part prepares the body for fight or flight reactions: it serves quick actions. The sympathetic part stimulates organs that are important for fight or flight reactions, like the heart, and it inhibits activities that can wait, like the intestines and the stomach. The parasympathetic part is for maintenance and relaxation. This part takes care (among other) of digestion. For some emotions, it’s quit self-evident that we need them. Fear makes us to be alert or it makes us attack or flee on certain moments. Furthermore, emotions play an important role in taking decisions quickly. Sometimes you just have a certain feelings that you trust. Also, emotions play a role in moral dilemmas.
There are different theories about emotions. One of the most popular is the James-Lange theory. According to this theory, the autonomous excitement and reactions of the skeleton come first. What we experience as emotion, is the label we give to our responses: I am afraid because I’m running away. According to James, emotions have three components: cognitions, behaviour and feelings. The cognitive part comes first: the assessment of the situation. This will then lead to certain actions, the behavioural aspect, which also brings physical reactions. Excitements and actions lead to the feeling aspect of emotions.
Multiple disorders are related to emotions. A panic disorder is characterised by frequent periods of fear and periods of increased breathing speed, increased sweating, shivering and heart rate. Stress is the non-specific response of the body on everything that is being asked of the body.
Every threat to the body activates a generalised reaction on stress: the general adaptation syndrome. The first phase, the alarm phase, is characterised by an increased activity of the sympathetic nervous system. During the second phase, the resistance phase, the activity of the sympathetic nervous system decreases, but the adrenal gland cortex excretes cortisol and other hormones that promote the extended alertness and fight against infections and heal wounds. The third phase is the exhaustion phase: the person is tired and vulnerable, because the nervous system and the immune system don’t have enough energy to react properly. Another definition of stressful events is: events that are interpreted as threatening for an individual and that evoke physical and behavioural reactions. Long-term stress will result in the weakening of the immune system.
There are many theories about learning. An early theory stated that a connection grew between two brain areas. Classical conditioning states that the connection between two stimuli will result in a change in one of the responses. The experimenter first presents a conditioned stimulus (CS), which doesn’t evoke a reaction. Then, he will present the unconditioned stimulus (OS), that automatically evokes an unconditioned response (UCR). After a few connections are made between the CS and UCR, the individual will start making a new, learned response to the CS, which is called a conditioned response (CR). In operant conditioning, a response of the individual will lead to punishment or enforcement. An enforcement is something that will enhance the chances of the same response being shown again in the future, while a punishment is something that lowers the chances of the response being shown again in the future.
There are different types of memory. The working memory used to be called the short-term memory. The working memory only saves information when someone is using this information. This is done in the prefrontal cortex. The long-term memory saves things for a longer period of time (memories). Implicit memory is the influence from a recent event on behaviour and the person doesn’t always recognize that the event has an influence on his/her behaviour. Explicit memory is declaring information a person has from his/her memory. There are also different types of memory loss. Anterograde amnesia is the inability to form new memories for events that take place after the brain damage. Retrograde amnesia is the memory loss of events that have taken place before the brain damage. Most people with amnesia have a normal functioning of the working memory. Saving thins in long-term memory isn’t really possible anymore (or not well enough) and the functioning of the episodic memory is deteriorated.
People with damage to the hippocampus have a deteriorated declarative memory, which is the ability to verbalize memories, but they have an intact procedural memory, which is the development of skills and habits. According to Squire, the hippocampus is essential for the declarative memory, and especially the episodic memory. Another hypothesis states that the hippocampus is important for spatial memory. A third hypothesis states that the hippocampus is important for remembering details and the context of an event. These three hypotheses don’t contradict each other. The episodic memory is depend on the hippocampus and it develops after just one experience. We need another mechanism to learn probabilistic things. This mechanism is the basal ganglia. Learning things gradually and updating information from learned things is important to the basal ganglia. There is a distinction between the tasks of the basal ganglia and other brain areas (like the hippocampus and cerebral cortex). However, it’s not possible to make a complete distinction between the functions of the areas.
The left hemisphere of the cerebral cortex is connected to the skin receptors and muscles, and especially to those on the right side of the body. The right hemisphere is especially connected to the skin receptors and muscles on the left side of the body. Both hemispheres control the facial muscles and torso muscles. The right part of the brain only sees things on the left side of the world, while the left side of the brain only sees things on the right side of the world. Auditory information comes from both ears, but just slightly more from the contralateral (opposite) ear. Smell and taste are not processed contralateral. Nobody knows why our brain control the contralateral part of the body. The corpus callosum is a bundle of axons that connects to two hemispheres with each other. The two hemispheres are not each other’s reflections. In most people, the left hemisphere is specialised in language. Lateralisation is the distinction in function between the two hemispheres. It basically the difference in specialisation between the two hemispheres.
Most theories that explain why people have developed language can be placed into one of the following categories: (1) we have developed language as a side-product of general brain development and (2) we have developed language as a brain specialisation. Different language disorders can be found. Aphasia means a language disorder. The Broca areas is localised in the left frontal cortex. People with Broca aphasia can’t really express themselves well or only slowly. This is the case for speaking, writing and gesturing. The aphasia of Broca is related to language, not to vocal muscles. People with this type of language disorder avoid certain word, like pronouns, prepositions and conjunctions. These people have trouble understanding words and they therefore just don’t use these words when they speak. However, they have not lost their complete grammatical knowledge. Damage to the left temporal cortex results in Wernicke’s aphasia. This is characterised by a bad understanding of language and a bad ability of remembering the names of objects. This is also called fluent aphasia, because the patient can still speak fluently.
With the mind-body problem we ask ourselves what the relationship between body and mind is. Two different ways of thinking have resulted from this: the dualism and the monism. Dualists think that the mind and body are two different substances that exist independently of each other. Monism thinks that the universe exists out of one substance. Attention is adjusted to consciousness. Inattentional blindness or change blindness is a phenomenon that suggests you are only aware of the things you pay attention to. You can be conscious without paying attention to anything, but you can’t pay attention to something if you are not conscious. Psychologists make a distinction between top-down and bottom-up attention. A bottom-up process depends on the stimulus. When you walk on the street and a barking dog runs around the corner, it will draw your attention. Top-down processes are intentional (you specifically look for something) and they depend on the prefrontal cortex and the parietal cortex.
A drug that blocks the effect of a neurotransmitter is called an antagonist, a drug that copies or enhances the effects of a neurotransmitter is called an agonist. A mixed agonist-antagonist is an agonist for one neurotransmitter and an antagonist for another neurotransmitter. Drugs influence synapses in many ways. A craving is common in every addiction. This means that a person is constantly longing and looking for the product or activity (gambling, gaming). Even after a long period of abstinence, cues that are related to the product will induce cravings. Someone who has a craving, really wants the product. It’s not just about liking the product, but it’s really longing and needing the product (because most addicts don’t like the product or the addiction, but they just have a strong need to take it). When an addiction develops, the effects (especially the fun effects) will decrease. This is called tolerance. Because of tolerance, heroin addicts take larger quantities of heroin and/or they take heroin more often.
A major depression is a state in which someone feels desperate and helpless and it is also characterised by a lack of pleasure and energy, which can take up to weeks or months. It seems there is more lack of happiness than an increase in desperation. People feel useless, can’t sleep, contemplate suicide, can’t concentrate or imagine ever being happy again. Antidepressant are used against depression. Antidepressant fall into one of the following categories: tricyclic antidepressant, selective serotonin reuptake inhibitors (SSRIs), serotonin norepinephrine reuptake inhibitors (SNRIs) and Monoamine oxidase inhibitors (MAOIs).
Schizophrenia is a disorder that is characterised by a deteriorated ability to function normally in everyday life and it is sometimes also characterised by hallucinations, movement disorders, delusions and inappropriate facial expressions. Schizophrenia can be acute or chronic. An acute condition arises acutely, and there is a chance for recovery. A chronic condition starts gradually and last long. The disorder is characterised by positive and negative symptoms. Negative symptoms are not present, but should be present. This means these people have weak social interactions, weak emotional expressions and not much speech and no good working memory. Positive symptoms are present, but shouldn’t be present. These exist of two clusters: psychotic positive symptoms and disorganised positive symptoms. Hallucinations (abnormal sensory experiences) and delusions (ungrounded convictions) are psychotic positive symptoms and inappropriate emotional expressions, bizarre behaviour and uncoherent speech are disorganised positive symptoms.
The autism spectrum disorder is used to indicate the disorder autism and what used to be called Asperger syndrome (high functioning autism). The autism spectrum disorder is used for different disorders, that vary in their severity (mild to really severe). The most important characteristics of this disorder are: shortcomings in social and emotional exchange, stereotyped behaviour (e.g. always placing the bike in a 45 degree angle with the wall), resistance to change of routine, shortcomings in non-verbal communication and facial expressions (they can’t understand emoji’s, unless you learn them what it means and they often can’t interpret facial expressions, unless they are smart enough to learn it) and extreme responses to stimuli.
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