ELECTRICAL ACTIVITY OF THE CEREBRAL CORTEX IN THE UNANESTHETIZED CAT

Abstract

Small Ag electrodes were fixed in the skull so as to make contact on the dura over the motor, sensory, auditory, and visual cortical areas. Flexible leads were brought out through the skin in such a manner as to permit the animals to recover completely from the operation and engage in normal unrestrained activities while at the same time records'' could be taken directly from the cortex over a period of several days. Histological studies of the brain regions over which the electrodes were placed served to control the accuracy of localization and histological structure of the areas used as well as to show that records were taken from normal brain tissue. The results from simultaneous records of the activity of 4 cortical areas with both monopolar and bipolar recording showed that the pattern of cortical activity in the partialy dialized and in the normal undisturbed cat was characterized by more or less regular rhythmic potential changes at frequencies from 3 to 15 per sec. Bilaterally homologous areas showed essentially similar bioelectrical activity. Some fairly consistent differences in pattern of activity from the anesthetized animal could be identified with different cortical fields, but the variations in activity of each region in the normal cat were so great that bioelectric differentiation appeared to be primarily related to differential states of activation rather than to specific cyto-architectonic structure. The greatest similarity of resting activity and response to afferent stimulation was found between the sensory and motor areas. The electogram from all regions was characterized by low amplitude higher frequency potentials when the animal showed behavioral indications of being generally aroused or activated due either to controlled external stimuli or internal organic states. Relaxation was associated with a return of the slower rhythms while the pattern characteristic of sleep was similar to that descr. for man during sleep. The electrical response of the cortex to afferent stimulation included "on" and "off" effects and slow positive and negative after-potentials associated with depressions of rhythmic activity as well as changes in frequency and amplitude of the spontaneous potentials. Changes in the electrical activity of all regions of the cortex usually followed a single effective afferent stimulus although the changes in a given region could be more intense and of a different form than those in other regions.