Ventral pallidum

The ventral pallidum is a component of the ventral striatopallidal system, which forms part of the basal ganglia circuitry concerned particularly with motivation and reward-related behaviour. Anatomically, it occupies the rostral, subcommissural part of the region historically called the substantia innominata and lies ventral to the anterior commissure.

Afferent/input circuits

The nucleus accumbens (part of the larger ventral striatum) provides the major input to the ventral pallidum, and much of this input is inhibitory and GABAergic.

Importantly, these connections are topographically organised.

• The shell of the nucleus accumbens projects mainly to the ventromedial ventral pallidum (VPvm), whereas

• The core of the nucleus accumbens projects mainly to the dorsolateral ventral pallidum (VPdl).

This organisation allows different components of the ventral pallidum to participate in somewhat different functional circuits.

Efferent/output circuits

The major outputs from ventral pallidum vary between its subregions.

• The VPvm projects to regions including the mediodorsal thalamus, lateral hypothalamus and ventral tegmental area, linking it strongly with limbic, reward and cognitive circuits.

• In contrast, the VPdl projects particularly to motor-related structures such as the subthalamic nucleus and substantia nigra pars reticulata.

Functional correlates

Functionally, the ventral pallidum acts as an important interface between motivation and behaviour. It receives motivational and reward-related information, particularly from the nucleus accumbens, processes this information, and influences thalamic, hypothalamic and motor circuits that help generate an appropriate behavioural response. It can therefore be understood as an important part of the neural circuitry that converts “motivation into action.” Alterations in ventral pallidal circuits are particularly relevant to disorders involving abnormal motivation and reward processing, including addiction and depression.