Pleasure Center

selfstim

Pleasure center is the general term used for the brain regions involved in pleasure. Discoveries made in the 1950s initially suggested that rodents could not stop electrically stimulating parts of their brain, mainly the nucleus accumbens, which was theorized to produce great pleasure.

Further investigations revealed that the septum pellucidium and the hypothalamus can also be targets for self-stimulation. Yet, more recent research has shown that such ‘pleasure’ electrodes do not, in fact, lead to pleasure but only a form of ‘wanting’ or motivation to obtain the stimulation. Instead, the weight of the evidence suggests that the pleasure center of the human brain is not a single center but rather a distributed system of brain regions of which important nodes include subcortical regions (such as the nucleus accumbens and ventral pallidum) and cortical regions (orbitofrontal cortex and anterior cingulate cortex).

The pleasure center was discovered in the 1950s by two brain researchers named James Olds and Peter Milner who were investigating whether rats might be made uncomfortable by electrical stimulation of certain areas of their brain, particularly the limbic system. In the experiment, an electrical current was given to rats if they entered a certain corner of a cage, with the hypothesis that they would stay away from that corner if the effect was uncomfortable. Instead, they came back quickly after the first stimulation and even more quickly after the second. In later experiments, they allowed the rats to press the stimulation lever themselves, to the effect that they would press it as much as seven-hundred times per hour.

This region soon came to be known as the ‘pleasure center.’ Rats in Skinner boxes with metal electrodes implanted into their nucleus accumbens will repeatedly press a lever which activates this region, and will do so in preference over food and water, eventually dying from exhaustion. In rodent physiology, scientists reason that the medial forebrain bundle is the pleasure center of rats. If a rat is given the choice between stimulating the forebrain or eating, it will choose stimulation to the point of exhaustion. The nucleus accumbens, part of the limbic system, plays a role in sexual arousal and the ‘high’ derived from certain recreational drugs.

These responses are heavily modulated by dopaminergic projections from the limbic system. The limbic system is also tightly connected to the prefrontal cortex. Some scientists contend that this connection is related to the pleasure obtained from solving problems. In a now-obsolete practice to cure severe emotional disorders, this connection was sometimes surgically severed, a procedure of psychosurgery, called a prefrontal lobotomy. Patients who underwent this procedure often became passive and lacked all motivation.

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