Localization and habituation of sensory evoked DC responses in cat cortex

Abstract

Using calomel electrodes and chopper stabilized amplifiers, sensory evoked d-c responses at the cortical surface were recorded from the primary visual, secondary visual, auditory and somatic areas of the left hemisphere in thirty acutely prepared immobilized cats. The stimuli were light from an incandescent bulb, a hissing sound and a mild shock. Responses were quantified on line by automatic computation of area under the response and by waveform averaging. All four cortical loci could respond to all three stimuli, but by an algebraic analysis of response amplitudes the responses could be fractionated into two components, one of which was localized, the other diffuse. The local component is stimulus bound and is distributed such that the response of the classical sensory area relevant to the stimulus is negative to the response of the other sensory areas, regardless of the over-all response polarity. The diffuse component is on the average, negative in polarity and has a longer latency and duration than the local component. It occurs primarily as an aftereffect of stimulation and is more readily evoked by shock and hiss than by light. The diffure component and the local component are, therefore, distinguished from one another both by their localization and their time course. Both the diffuse component and the local component showed considerable habituation during a 1.5 to 2.0 hour long series of fifty stimulations. The responses probably reflect the joint action of both specific and diffuse cortical inputs, but it is unlikely that they influence the production of action potentials in cortical neurons.