The striatum is a large nucleus located deep in the telencephalon in proximity to the lateral brain ventricles. In primates, it is composed of 4 neuronal classes: spiny (96%), leptodendritic (2%), spidery (1%) neurons and microneurons(1%) (Yelnik et al. 1991). In spiny neurons dendritic arborisations are spherical. Most of the dendritic spines in this cell type receive synaptic input from cortical afferents. Their axons have abundant collateral projections participating in local circuitry. The neurons are GABAergic. The leptodendritic neurons (or Deiter's neurons) have all the morphological properties of the pallidal neurons. The spidery neurons are specific to primates. They have a big soma and short dendritic and axonal branches. They are the cholinergic interneurons and are characterized by the fact that they are tonically active. The microneurons are local circuit neurons similar to those found in the thalamus and are GABAergic. Some may be also be dopaminergic (Rochette et al.).
Traditionally, because interval timing depends on the intact striatum but not on the intact cerebellum, the cerebellum has been charged with millisecond timing and the basal ganglia with interval timing. Despite this simplistic dissociation, two recent findings have shed new light on the involvement of the basal ganglia and cerebellum in motor control and interval timing.