Common response repertoire of motor cortical neurons in arousal and epicortical activation

Intracellular responses during phasic Electroencephalograph (EEG) arousal were recorded from 229 motor cortical neurons in the cat encéphale isolé preparations. Identified dominant responses were excitatory postsynaptic potentials (EPSPs) in 105 cells (E cells), inhibitory postsynaptic potentials (IPSPs) in 74 cells (I cells), disfacilitation in 48 cells (DF cells), and disinhibition in two cells (DI cells). These responses were comparable with those to near or distant epicortical stimulation (EPICS). thus, most E cells in phasic arousal were EPSP-dominant in response to near (incidence, 104/105) or distant EPICS (51/54), and only a few of the remaining were IPSP-dominant. About two-thirds of I cells were IPSP-dominant (49/74), and the remaining one-third EPSP-dominant (25/74) to near EPICS. However, most I cells became IPSP-dominant (45/49) to distant EPICS. DF and DI cells were initially EPSP- or IPSP-dominant to EPICS, but later responsive with DF in DF cells and DI in DI cells, respectively. In the interaction experiments, the initial negative wave in the direct cortical responses (DCRs) or the EPSPs of dendritic origin elicited by near EPICS and the initial positive wave in DCRs to distant EPICS were all reduced during phasic EEG arousal perhaps due to the occlusion effect. Common response repertoire in EEG arousal and epicortical activation may support the earlier proposed cascade transmission model of phasic EEG arousal, in which the spread of neuronal activities occurs vertically from the superficial to deep cortical layers as well as laterally along various layers.