Vertical spread of neuronal activity within the cat motor cortex investigated with epicortical stimulation and intracellular recording.

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Abstract
In the encephale isole cat preparation the surface of precruciate cortex was electrically stimulated. Intracellular responses underneath the stimulated site were recorded to assess the verticle spread of activities across the cortical layers. To the epicortical stimulation (EPICS) with intensity adjusted to evoke a pure negative wave in the direct cortical response (DCR), only some neurons in relatively superficial layers responded with excitatory postsynaptic potentials (EPSP). Stimuli intensified to evoke both the negative and subsequent positive waves in DCR produced in all tested cells either EPSP, inhibitory post-synaptic potentials (IPSP) or both. Direct or axonal antidromic excitation of the cell was observed only infrequently. Cells with EPSP distributed through all the layers with 2 peak populations in laminae II and V-VI. Those with IPSP were located mainly in the upper half of lamina III with a few in more superficial as well as in deeper layers. Both EPSP and IPSP showed mono- or oligosynaptic latencies (0.6-10 ms) that tended to become longer in deep than in superficial layers. Some deep layer cells including fast and slow pyramidal tract cells showed slowly rising monosynaptic EPSP of dendritic origin. Further late responses consisted of EPSP, IPSP, disfacilitation (DF), and disinhibition (DI). DF or DI occurred in some deep layer cells. Two models of verticle spread of activities were postulated: cascade transmissions which increased response repetoire toward the depths, and electrotonic spread of EPSP along dendrites.

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