Cognitive operations in the human caudate nucleus.

We have addressed the role of the head of caudate nucleus in taks of lexical decision, semantic categorization, reading aloud, memory retrieval and object naming by recording neuronal activity from depth electrodes in parkinsonism patients. The firing rate of cells was increased within 400-600 ms when semantic processing was required. Phonological differences increased firing from 1000 to 1200 ms. These responses were similar to those described earlier in Broca's area. Both reading aloud and explicit memory retrieval tasks elicited an inhibition in firing of the same cells with an onset around 800 ms. The results confirm earlier lesion and stimulation studies, and provide a basis for relating cellular activity to studies of blood flow and scalp electrical activity in similar cognitive tasks thus helping us to understanding the cellular mechanisms involved in human cognition.