2.7 Neural circuits

Circuits, not single structures

Functions rarely belong to one structure. They arise from loops of interacting cells.

Reward: the nucleus accumbens

• The nucleus accumbens lies in the ventral striatum and receives mesolimbic dopamine neurones from the ventral tegmental area of the midbrain.

• Cocaine blocks dopamine reuptake, and the dopamine surge in the nucleus accumbens makes it rewarding.

Fear: the amygdala

• Pavlovian fear conditioning depends on the amygdala, which links a neutral cue to an aversive outcome.

• The amygdala triggers fear through its central nucleus, with output to the hypothalamus and periaqueductal grey.

• An amygdala lesion abolishes freezing to the cue.

Orbitofrontal cortex

• The orbitofrontal cortex regulates social conduct and adjusts behaviour when consequences change.

• Damage makes people impulsive, tactless and disinhibited, as in Phineas Gage.

• Formal executive tests may stay normal after orbitofrontal damage.

The dorsolateral prefrontal cortex differs: it holds working memory and maintains goals.

Cerebellar signs

• Intention tremor and past-pointing are cerebellar signs.

• Dysdiadochokinesia, gait ataxia and nystagmus are the other cerebellar signs.

• A lesion of one cerebellar hemisphere gives signs on the same side.

Other circuit nodes

Large-scale networks

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