Neurophysiology and cognitive functions of the striatum.

The striatum receives inputs from different areas of the cerebral cortex, including association cortical areas far on in the hierarchy of cortical information processing as well as the sensori-motor cortex, and has connections via the globus pallidus and substantia nigra to the thalamus and thence to premotor and prefrontal cortical areas. Recordings of the activity of neurons in different parts of the striatum of primates show that they have the following properties: 1) neurons in much of the putamen, which receives inputs from the sensori-motor cortex, have activity related to movements; 2) neurons in the caudate nucleus, which receives from the association cortex, have activity related for example to environmental stimuli which signal preparation for or initiation of behavioral responses; 3) neurons in the tail of the caudate nucleus, which receives strongly from the inferior temporal visual cortex, respond when a patterned visual stimulus changes; 4) some neurons in the posterior ventral putamen, which receives from the inferior temporal visual cortex and the prefrontal cortex, respond in a visual short term memory task, delayed match to sample. The neurons responded in the delay period, or differentially to match and non-match stimuli. These neurons did not respond in an auditory delayed match to sample task, so that their activity was not related to movement per se, but was instead more closely related to visual inputs relevant to a memory task; 5) some neurons in the ventral striatum (including the nucleus accumbens), which receives from limbic structures such as the amygdala and hippocampus, respond to stimuli associated with reinforcement or to novel stimuli. It is concluded that there is considerable segregation of function within the striatum. It is suggested that there is an opportunity for inputs which originate from different parts of the cerebral cortex to interact, via a first stage of convergence in the striatum, and by a further stage of convergence on the dendrites of single neurons in the globus pallidus and substantia nigra; and that both these parts of the basal ganglia may learn associations between the different signals they receive. The result of this convergence and learning is that the basal ganglia provide a way for cortical areas far on in the hierarchy of information processing to become linked during motor learning to particular sequences of movements, and thus to be involved in the execution of motor programs.