The relationship between association responses and activity in the pyramidal tract

1. 1. Correlation coefficients derived from comparison of the amplitude of association responses and the amplitude of the relayed pyramidal volley following auditory, visual and tactile stimuli were all highly significant. There was no correlation between primary auditory and visual responses and the pyramidal volley. Primary somatosensory responses evoked by contralateral tactile stimulation correlated with the pyramidal volley, but not as highly as with cortical responses elicited by ipsilateral stimuli. 2. 2. The responsiveness of the pericruciate cortex to a cortical stimulus was enhanced for 18-80 msec, then diminished for varying periods up to 500 msec following a peripheral stimulus in any of the three modalities. 3. 3. The results indicate that the association cortex of the pericruciate and other cortical association areas and efferent cortico-spinal fibers respond in a unitary fashion to a peripheral stimulus. The possible functional significance of these efferents is discussed.