Intracortical origin of recruiting responses in the cat cortex.

Field potentials associated with recruiting responses produced by low-frequency stimulation of non-specific thalamic sites were simultaneously recorded from an intracortical tri-probe and the pial surface. Separation of the tri-probe tips along the probe axis (typically 100 mum) permitted discrimination of spatial field potentials. Analyses were performed on the data to provide estimates of the intracortical locations of the ion sources and sinks giving rise to the surface negative recruiting response. At the peak of a recruiting response event, the results suggest a sink in Brodmann layer II simultaneous with a source in layers III, IV and V. A hypothesis of a simultaneous 'push-pull' spatial modulation of pyramidal cell activity in layer II with the activity of pyramidal cells in layers IV, V and VI is proposed.