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

Abstract

1) 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 vertical spread of activities across the cortical layers. 2) 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 (EPSPs). 3) Stimuli intensified to evoke both the negative and subsequent positive waves in DCR produced in all tested cells either EPSPs, inhibitory postsynaptic potentials (IPSPs), or both. Direct or axonal antidromic excitation of the cell was observed only infrequently. 4) Cells with EPSPs distributed through all the layers with two peak populations in laminae II and V-VI. Those with IPSPs were located mainly in the upper half of lamina III with a few in more superficial as well as in deeper layers. Both EPSPs and IPSPs showed mono-or oligosynaptic latencies (0.6-10 msec) that tended to become longer in deep than in superficial layers. 5) Some deep layer cells including fast and slow pyramidal tract cells showed slowly rising monosynaptic EPSPs of dendritic origin. 6) Further late responses consisted of EPSPs, IPSPs, disfacilitation (DF), and disinhibition (DI). DF or DI occurred in some deep layer cells. 7) Two modes of vertical spread of activities were postulated : one the cascade transmissions which increased response repertoire toward the depths, and the other the electrotonic spread of EPSPs along dendrites.

Intracortical spread of neuronal activities induced by stimulation of recurrent and thalamic afferent pathways compared with epicortical activation.

“…Open columns there indicate the first EPSPs, hatched the second EPSPs, and filled the summed first and second IPSPs. As has been demonstrated earlier (EzURE et al, 1985), latencies of PSPs evoked by EPICS tend to be increased from superficial to deep layers, whereas those of VL-evoked activities show bidirectional increases from the middle to both superficial and deep layers, as shown in Fig. 9.…”

“…2B-F, Table 2). The latter result contradicted the possibility that the recurrent inhibition well-known since PHILLIPs (1956PHILLIPs ( , 1959 shared any intracortical pathways with the inhibition produced by EPICS particularly in the middle layer cells (EZURE et al, 1985;EZURE and OSHIMA, 1985a). As illustrated in Fig.…”

“…More detailed analysis will be made in this section by using the first and second PSPs by EPICS (cf. EZURE et al, 1985) as well as those from CP and VL. Convergence and no convergence are designated in Table 1 according to the combination of response types from two Vol.…”

“…Experimental procedure and arrangement using the encephale isole cat preparation with an atraumatic apparatus have fully been described in preceding papers (INUBUSHI et al, 1978;EZURE et al, 1985). Bipolar steel needle stimulating electrodes were inserted into CP (A=7.0, L=6.0, H=6.0 in the stereotaxic axes by REINOSO-SUAREZ, 1961) and VL nucleus (A=10.5-11.0, L=3.0-5.0, H= 10.5-12.0).…”

“…EPICS was applied within 0.4 mm of the recording microelectrode (EZURE et al, 1985), and its effects were compared with those of CP and VL stimulation.…”