Claustral influence on ipsi- and contralateral motor cortical areas, in the cat.

The electrophysiological relationships between the claustrum and the contralateral motor areas of the cerebral cortex were studied in anaesthetized cats. The extracellular unitary activity of 207 pyramidal tract neurons (PTNs) was recorded from area 4 (125 cells) and area 6 (82 cells). Single shock activation of the contralateral claustrum affected 26% of the total tested PTNs, causing long lasting inhibition (44 PTNs) or long lasting inhibition preceded by early excitation (10 PTNs). Forty-three neurons of the 54 were also influenced by ipsilateral claustrum stimulation. Surgical removal of motor and insular cortices ipsilateral to the stimulated claustrum did not modify claustrum inhibition on contralateral PTNs, whereas section of the corpus callosum abolished this effect, suggesting the existence of a direct claustro-contralateral motor cortex pathway passing through the corpus callosum. These results support the hypothesis that the claustrum may exert a bilateral control on motor coordination.