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Pleasure and pain
Sub-Topics
Pleasure and Drugs
Avoiding Pain

Linked
HelpThe Hypothalamus and the Pleasure-Pain AxisThe Role of the HypothalamusLE SYSTÈME DE RÉCOMPENSE DU CERVEAU
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Original modules
Tool Module : A Neuroanatomical and Psychological Model of AnxietyA Neuroanatomical and Psychological Model of Anxiety

“Centres” of Cognitive Functions in the Brain: A Misleading Concept


The same parts of the human brain that are involved in positive reinforcement of behaviour are also involved in the sensation of pleasure.

The radical behaviourists’ explanation of positive reinforcement ignored the concept of pleasure.
But these two ideas can be applied almost synonymously to human beings, who when asked why they engage in reinforced behaviours, will usually spontaneously cite the subjective experience of pleasure that these behaviours provide.

The expression "pleasure centres of the brain", introduced by Olds in a 1956 article, is still a good way to describe the neuronal substrates of rewards for behaviour. As researchers have discovered new neural pathways involved in pleasure and rewards, however, the term “centre” which suggests a single locus, has gradually been replaced by the word “system,” which stresses the involvement of multiple groups of neurons.

THE PLEASURE CENTRES

Researchers have found that the main centres of the brain’s reward circuit are located along the medial forebrain bundle (MFB). The ventral tegmental area (VTA) and the nucleus accumbens are the two major centres in this circuit, but it also includes several others, such as the septum, the amygdala, the prefrontal cortex, and certain parts of the thalamus. Each of these structures appears to participate in its own way in various aspects of behavioural response.

Moreover, all of these centres are interconnected and innervate the hypothalamus (red arrows), informing it of the presence of rewards. The lateral and ventromedial nuclei of the hypothalamus are especially involved in this reward circuit.
 

The hypothalamus then acts in return not only on the ventral tegmental area, but also on the autonomic and endocrine functions of the entire body, through the pituitary gland.

Aversive stimuli that provoke fight or flight responses activate the brain’s punishment circuit (the periventricular system, or PVS), which enables us to cope with unpleasant situations. The PVS was identified by De Molina and Hunsperger in 1962. It includes various brain structures, such as the hypothalamus, the thalamus, and the central grey substance surrounding the aqueduct of Sylvius. Some secondary centres of this circuit are found in the amygdala and the hippocampus.

The punishment circuit functions by means of acetylcholine, which stimulates the secretion of adrenal cortico-trophic hormone (ACTH). ACTH in turn stimulates the adrenal glands to release adrenalin to prepare the body’s organs for fight or flight.

Interestingly, stimulation of the punishment circuit can inhibit the reward circuit, which supports the common observation that fear and punishment can drive out many pleasures.

The MFB and the PVS are thus two major systems of motivation in human beings. These systems encourage people to behave so as to suppress their instinctive impulses and avoid painful experiences.

The situation is quite different for the third circuit, the behavioural inhibition system (BIS). This system was identified by Henri Laborit in the early 1970s. It is associated with the septo-hippocampal system, the amygdala, and the basal nuclei. It receives inputs from the prefrontal cortex and transmits its outputs via the noradrenergic fibres of the locus coeruleus and the serotininergic fibres of the medial Raphe nuclei. Some authors believe that serotonin plays a major role in this system.

The BIS is activated when both fight and flight seem impossible and the only remaining behavioural option is to submit passively. The pathological consequences of this behavioural inhibition have provided an understanding of how destructive chronic stress can be to people’s health.

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