CORTICAL EVOKED RESPONSES IN AUDITORY AREA AND SIGNIFICANCE OF APICAL DENDRITES

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Abstract
The response to single shock to medial geniculate body in the unanesthetized, curarized cat consisted of initial deflections of short duration, a surface positive and a subsequent surface negative phase. The surface positive wave had a lower threshold than the later negative component. These two components could be recorded separately at different spots on the surface of the auditory cortex. When recording with a penetrating electrode, inversion of polarities of both response components was obtained at approximately the same level. At this level or somewhat deeper the responses to clicks inverted. No systematic continuous change in the latency of the negative peak was found at successive depths. The temporal features of the two components remained rather constant throughout the layers of the cortex. The two components of the response to medial geniculate stimulation interacted in different ways with responses to other stimuli. The results have led to the conclusion that the surface negative phase was due to spread of excitation to neurons located in the cortex and not to propagation up to the surface along the apical dendrites of the neurons responsible for the preceeding surface positive phase.