Ancient Egyptian physicians knew the importance of the brain in behaviour as was shown by the Edwin Smith Papyrus. Plato believed the soul consisted of three parts and the brain was the most important part.

Aristotle, on the other hand, believed that thought was located in the heart because of the heart’s central location (1), its importance for emotion (2) and because all living organisms have a heart (3). According to Aristotle, the function of the brain was to cool the heat of the heart.

Galenus discovered a function of the nerve pathways and established the role of the brain as the hub of behaviour. He believed the brain communicated with the body through ventricles (1), animal spirits (2) and nerves (3). Vesalius created a functional division for the ventricles; common sense and fantasy (1), thoughts (2) and memory (3).

Descartes introduced mechanical ideas and viewed other organisms as automatons. His mechanical theory of reflex states that a sensory sensation travels through the nerves (1), this is bounced back like a mirror (2) and this leads to involuntary behaviour (3). According to Descartes, the soul remained spiritual in nature and the body and the soul interact in the pineal gland.

Gall founded two different subdisciplines:

1. Organology
   This is the view that differences in predisposition can be seen in cortical development.
2. Cranioscopy
   This is the view that differences in cortical development can be seen in nodules of the skull.

Spurzheim formulated phrenology. Willis proposed that higher brain structures existed for more complex organisms and allowed for more complex functions and that the lower structures allowed for elementary functions. This means that a more complex animal has more brain structures and a less complex animal only has the lower brain structures.

In the 19^th century, there are five breakthroughs which altered the model of brain functioning:

1. Discovery of the cerebrospinal axis
   This is the finding that the body remains functioning when the cerebral hemispheres are disconnected and thus that many bodily functions do not require the cerebral hemispheres.
2. Growing impact of the reflex
   This is the finding of the reflex arc (Hall). Procháska proposes that reflexes were controlled by the spinal cord and Sechenov proposes that thinking is a reflex of the brain.
3. Localisation of brain functions
   This is the finding that brain functions could be localised and gave rise to the localisation theory. This theory gains strength through Jackson, Broca and Wernicke.
4. Discovery of the nerve cell
   This is the finding that the brain exists of separate cells. This was aided by better microscopes (1) and improved techniques to stain the brain tissue, which allowed neurons to stand out (Golgi) (2).
5. Disentangling of the communication between neurons
   This is the finding that nerves could be influenced by electricity (Galvani) (1), the finding that neurons communicate using electricity (Bois-Reymond) (2), the finding that electrical signals are based on chemical processes (Von Helmholtz) (3) and the finding that neurotransmitters and synapses exist (4).

The reflex arc refers to the mechanism involved in involuntary movement elicited by sensory stimuli. This led to the notion that higher complex mental functions (e.g. inhibition) are a neuronal reflex.

The localisation theory was held back by the notion that the mind exists independent from the body. Reticularism refers to the idea that the brain is a continuous network and was supported by Golgi.

The equipotentiality theory states that the cortex is a functional whole and that if one part stops working, other parts will compensate for this. Flourens believed that localisation of function occurred in the brainstem but not in the cortex.

Jackson has several important characteristics:

• Proposes a specific relationship between certain brain areas and muscles in specific parts of the body.
• Proposes that the central nervous system has different levels of sensory-motor units; he finds that the evolutionary oldest sensory-motor units are at the bottom of the brain.
• Proposes that higher mental processes (e.g. reason) integrate input from lower brain areas.
• Proposes that higher mental processes found their origin in sensory-motor nervous arrangements.
• Proposes that different behaviour from brain damage rather than a loss of function is due to the brain area experiencing a lack of control from the cortical area.

According to Jackson, the failure of a brain area to work properly due to brain damage leads to a loss of the function. Fritz and Hitzig confirm Jackson experimentally and they find that localization occurs in the cortex. Bartholow experimentally confirms Fritz and Hitzig on a human.

During the enlightenment, the body was seen as a mechanism and empirical research increases. The reflex arc is discovered but the cortex remains poorly understood. Spencer states that in evolution there is survival of the fittest (1) and that all structures evolve from undifferentiated and homogeneous to differentiated and heterogeneous (2). This assumes that organisms become more complex.

James proposed that emotion is a bodily response and that conscious awareness comes later. Later came the idea that the thalamus might be the emotion area in the brain. The hypothalamus took over this position and was later expanded to include the amygdala.

There was a differentiation between the hypothalamus and the cortex:

• Hypothalamus
  Emotions, drives, irrationality and unconsciousness
• Cortex
  Ratio, control and consciousness.

The visceral brain (later: limbic system) was believed to be responsible for aggression, oral and sexual behaviour and was not involved in linguistics. This was used in Freud’s psychoanalysis.

Hebb believed that the brain was a dynamic network and believed that the more a connection between two neurons is used, the stronger this connection becomes, leading to the notion of long-term potentiation. Long-term potentiation allows for the idea of the brain as an evolving network as a function of input from other parts of the brain and the environment. McCulloch and Pitt also believed that the brain consisted of a neural network.

The insights of Hebb, McCulloch and Pitts led to the idea of neural networks and these networks could be tested in computer programmes. The networks appeared to respond to stimulus-response sequences and reinforcement when learning elementary tasks, showing the potential of behaviourism in neuroscience. However, testing models in computer programmes was held back by the limitations of the computers as every extra layer made the model more complex.

Luria employed Romantic science, doing comprehensive case studies on soldiers during and after the second world war. He formulated three laws:

1. Law of hierarchical structure
   This law states that cortical areas have a dominant role in relation to secondary, lower-lying areas.
2. Law of diminishing specificity
   This law states that the further emotion is processed in the brain, the less specific it will be.
3. Law of progressive lateralization
   This law states that more functional lateralization can be found in the cortical areas than in the lower-lying areas.

There are several methods of brain imaging:

1. EEG (electroencephalogram) recording
   This method makes use of electrodes that are placed on the scalp in order to measure the electrical activity of the brain.
2. ERP (event-related potentials)
   This method registers the electrical responses to individual events and is obtained by averaging the EEG signals to stimuli that are repeated a number of times.
3. MEG (magnetoencephalography)
   This method measures the magnetic fields which are produced by electrical signals in the brain.
4. PET (positron emission tomography)
   This method makes use of a radioactive tracer which is injected in the blood which shows which brain areas receive more blood and are, therefore, more active.
5. fMRI
   This method measures the magnetic resonance of the blood, showing which areas of the brain are using more oxygen and are, therefore, more active.
6. TMS (transcranial magnetic stimulation)
   This method makes use of a focussed electrical current which temporarily interferes with the functioning of that brain part.

In EEG, there are slow, regular waves – alpha waves – and fast, irregular waves, beta waves. The waves are large if the neurons fire at a slow pace in synchrony. The waves are small if the neurons fire rapidly and independently. ERP allows researchers to investigate differences in the signal as a function of characteristics of the stimulus. MEG has a high temporal and spatial resolution.

A limitation of fMRI is that oxygen can only be registered a few times per second and, therefore, more detailed processes cannot be measured. It has a high spatial resolution and a low temporal resolution. TMS allows for causal research.

Premature acceptance of biological explanations (e.g. serotonin deficiency causes depression) as a result of neuroscience (e.g. brain imaging) is risky and might lead to modern phrenology. This might be because all brain imaging techniques (except TMS) only give a correlation.

Nowadays, there is functional specialization in the brain although it is believed that most mental processes depend on multiple functional areas and that most areas contribute to different functions and the brain is seen as dynamic. There appears to be a hierarchy in terms of integration and abstraction but not in terms of importance.

Criticism of cognitive neuroscience refers to the fact that it might not be possible to define how the brain computes and encodes psychological processes and it is only possible to localize cognitive functions. However, there are several arguments in defence of cognitive neuroscience:

• There is a difference between empirically demonstrating which brain regions are involved in a particular task and speculating about this.
• Localisation of the brain activity, while a person is performing a task, provides information about the processes that are involved.
• Brain imaging has demonstrated that the brain is compartmentalized into regions with specialized functions and that all tasks require the interaction of several areas distributed over distant parts of the brain.