Effects of subcortical ablations on cortical association responses in the cat

The effects of subcortical lesions on cortical polysensory association area responses to peripheral sensory and direct reticular stimulation were investigated in acute chloralosed cats. Large lesions of the mesencephalic reticular formation were followed by a reduction in the amplitude of polysensory association responses to approximately 0–20% of control levels, with little or no reduction of evoked potentials in the primary sensory cortical areas. Unilateral lesions of posterior medial thalamus or the rostral pole of the thalamus had similar effects of polysensory cortical association responses, and also abolished cortical association area responses to direct electrical stimulation of the mesencephalic reticular formation, but only in the ipsilateral cortex. More ventral lesions, in the subthalamic region, reduced nonspecific evoked responses of orbital cortex to both peripheral and reticular stimulation without impairing responses in dorsal cortical association areas. The results are discussed with regard to the pathways of sensory input to the cortical association responses areas.