The Reward System

     

    In neuroscience, the reward system is a collection of brain structures which attempts to regulate and control behaviors by inducing pleasurable effects.
     

    Indeed, humans, in order to survive, have to assure their vital functions (that is to say eating, reproducing, avoiding dangers...). During the human evolution, a circuit developed in the humain brain, which role was to reward the execution of these functions by a pleasurable sensation. By this way, humans were incited to repeat the pleasurable experiences learnt during their life course and so to assure their vital functions.

     

    Three phases can be distinguished in the functioning of the circuit of reward :

  • First, in answer to a sensory stimulus (touch, view, hunger, thirst...), the brain pushes human to act in order to satisfy a need or a desire. For exemple, when glucose rate decreases in the blood, a stimulus of hunger is created and brain pushes human to eat.

  • Second, this action is rewarded by a sensation of pleasure. (It is more the action which is rewarded than the fact to satisfy the need).

  • Lastly, a feeling of satisfaction ends the action, until a new signal provokes a desire.

 

    Thus, this system is essential to survive because it gives the motivation necessary to do these vital functions. It is at the heart of our mental activity and guides all our behaviors.

 

Anatomical level

In brain, the reward circuit corresponds to connections between two groups of neurons, located in the nucleus accumbens and in the ventral tegmental area (VTA). When the brain perceives a pleasurable stimulation, the activity of these neurons increase and a neurotansmitter is produced : dopamine. The release of dopamine create a pleasurable sensation which is lived as a « reward ».

 

Dopamine and euphoria

    As it is explained in « Cannabis on the brain », THC brakes the release of neurotranmitters which leads to stop or to reduce the nerve impulse. There is however a place in the brain where it increases the production of a neurotransmitter : it is dopamine in the Reward Circuit.
    Indeed, all drugs increase the quantity of dopamine in the reward system. This released dopamine produces immediate, but ephemeral, feelings of pleasure and elation.

This paradoxical increase of neurotransmitter is explained by this diagramme :

 

Normally, the dopamine neurons are not activated that is to say, they do not produce dopamine because of the GABAergic neurons which inhibit them. There is no message that travels the dopamine neuron and so, there is no dopamine relase nor a pleasurable sensation.
(GABAergic neurons secrete GABA (gamma-aminobutyric-acid) as their primary neurotransmitter. Their rôle is to inhibit other neurons)

The neurons of dopamine don't have any receptor CB1 but the GABAergic neurons that inhibit them do. Consequently, when there is THC in the brain, THC binds to the GABAergic neurons and inhibit them. By this way, the inhibition provoked by GABA on the dopamine neurons is suppressed and so, dopamine neurons are activated. That is why when a person consumes Cannabis, feels a sensation of euphoria : he feels good and considers that everything is allright, even if he is depressed and his body suffers. The user is in a state of euphoria and relaxation. He is allay and calm.

 

Cannabis provokes also a lot of subjective effects such as an intense enjoyment of taste, flavours, music, humour and arts, along with introspection, philosophical and creative thoughts. These subjective effects obviously differ from the person.

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