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