Primate Basal Ganglia System - Corticostriatal Connection

Corticostriatal Connection

The whole system starts as a major output of the cerebral cortex, about the same size as the corticopontine system opening the cerebellar system. The corticostriatal connection represents a significant portion of the whole cortical output. Almost every part of the cortex, except for the primary olfactory, visual and auditory cortices, sends axons to the striatum. The origin of the connection is in the pyramidal neurons of layer V of the cortex. Corticostriate contributors, of the motor cortex at least, may be collaterals of axons descending lower in the nervous system. However, in primates, the majority of corticostriate axons are monotarget, purely cortico-striate, thin and unbranched until they arrive in the striatum. The corticostriatal connection is glutamatergic and excitatory. This connection is not topologically as simple as was initially described by Kemp and Powell (1970), where the frontal lobe projected anteriorly and the occipitotemporal lobes posteriorly. Part of this distribution grossly remains, but the distribution is much more complex. One small cortical site can send terminal arborisations to several and distal striatal places. The cortico-striatal connection is the substrate of cortical information separation and recombination: axons from distinct cortical areas can systematically end together or separately. There is also a spatial reorganisation, a "remapping".

The corticostriate connection is the first in a chain of strong reduction in numbers between emitter and receiver neurons, i.e. a numerical convergence. The effect of this is that if each striatocortical neuron has its own message, this will be mixed or compressed, leading to lesser definition of the input map.