MODIFICATION OF CORTICAL ACTIVITY BY MEANS OF INTERMITTENT PHOTIC STIMULATION IN THE MONKEY

Abstract

Evidence of a driving effect of intermittent photic stimulation upon the cortical activity (EEG) was found in the record of each of 12 monkeys (Macaca mulatto). This effect was reflected over a range of several cycles: 1) by increased amplitude per unit of time of the cortical activity, 2) by regularization or increased stability of the cortical rhythm, and 3) by the not uncommon appearance of cortical frequencies exactly double or triple that of a given flash frequency. The effect was present on an avg. of 55% of the total time of stimulation for the group as a whole and ranged from 28-78% for individual monkeys. The range of frequencies at which driving occurred varied from 7.5 cycles-2.0 cycles in individual monkeys and averaged 5.0 cycles for the group as a whole. Amplitude maxima produced during driving tended to cluster in a very limited range. For the 12 monkeys (plus a repeat record made on one animal) 9 amplitude maxima fell within a frequency range of one cycle per sec., i.e., 10.5 to 11.5 flashes per sec. Amplitude maxima produced during non-driving were distributed over a range of 7-29 cycles per sec. with no suggestion of clustering. Control records were obtained which eliminated the auditory component of the apparatus as being effective in producing driving. The driving effect in monkey is similar to that demonstrated in rabbit and in cat (Bartley) (Bishop) and in man (Adrian and Matthews). Its relation to the Brucke effect and to the Bartley effect (both of which are brightness enhancement effects occurring in the range of flicker) needs to be explored.