THE BRAIN FROM TOP TO BOTTOM

The Quest for Pleasure

Pleasure and Drugs

If a sensory stimulus does not provide us with any reward or any punishment, we quickly ignore and forget it. This phenomenon is called habituation. It is what makes us stop being aware of the feeling of clothes against our skin, or the ticking of the clock on the office wall.

Since these stimuli are not associated with anything positive or negative, we simply ignore them, thus freeing up our attention for any actual rewards or dangers that may come our way.

This mechanism lets us select, out of all the information that reaches our senses, the particular information that is of value to us as organisms. Generally, this is only a tiny proportion of all the information that our senses perceive.

THE PLEASURE CENTRES

For a species to survive, its members must carry out such vital functions as eating, reproducing, and responding to aggression. Evolution has therefore developed certain areas in our brain whose role is to provide a pleasurable sensation as a “reward” for carrying out these vital functions.

These areas are interconnected with one another to form what is known as the “reward circuit”.

The ventral tegmental area (VTA), a group of neurons at the very centre of the brain, plays an especially important role in this circuit. The VTA receives information from several other regions that tell it how well various fundamental needs, and more specifically human needs, are being satisfied.

The VTA then forwards this information to another structure further forward in the brain: the nucleus accumbens. To send this information to the nucleus accumbens, the VTA uses a particular chemical messenger: dopamine. The increase in the level of dopamine in the nucleus accumbens, and in other brain regions, reinforces the behaviours by which we satisfy our fundamental needs.