Tapping, talking and the thalamus: possible influence of the intralaminar nuclei on basal ganglia function.

A patient with a discrete lesion of the left, intralaminar thalamic, nuclei exhibited a paradoxical finding with regard to finger-tapping. Normal subjects typically reduce their tapping rate when performing simultaneous verbal activity. Tapping was impaired in our patient's contralesional hand on baseline trials; however, performing the controlled oral word association (COWA) task, while finger-tapping, normalized her deficit. Subsequent experiments showed that motoric tasks rather than cognitive aspects of the COWA task were critical in potentiating finger-tapping performance. A SPECT study performed at rest revealed focal perfusion asymmetries in motor and premotor cortices. Because the caudal intralaminar nuclei project heavily to the striatum, striatal deafferentiation may account for these asymmetries. These observations provide some insight into the influences of the caudal intralaminar thalamic nuclei on basal ganglia function and the basal ganglia's influence on motor gating.