The electroencephalogram of the codfish (Gadus callarias); spontaneous electrical activity and reaction to photic and acoustic stimulation.

Abstract

Summary.1. The electroencephalogram (EEG) has been recorded in the cod (Gadus callarias) both in the awake state and under narcosis. The effects on the EEG of photic and acoustic stimulation have been observed.2. In the awake resting state, when the fish was in the dark, the dominating rhythm recorded was 8–13 c/sec. — especially from the optic lobes (fig. 3 B, fig. 4). When the fish was unsettled or in the light, the EEG was chiefly dominated by higher frequencies, 14‐32 c/sec. (fig. 3 A). Slow rhythms (less than 7 c/sec.) were most pronounced in the telencephalon and were relatively unaffected by surrounding circumstances.3. The arousal reaction, as it occurs in mammals,i. e.a substitution of the dominating 8‐13 c/sec. activity by a faster rhythm of lower amplitude, has been recorded in the cod EEG on sudden illumination of the fish (fig. 5). During acoustic stimulation no arousal reaction was recorded.4. Evoked potentials on photic and acoustic stimulation were recorded from the visual area of the mesencephalon and the acoustic area of the medulla oblongata respectively. On photic stimulation up to a stimulating frequency of 40 c/sec. and on acoustic stimulation up to 100‐140 c/sec., the evoked potentials followed each stimulus.5. It is concluded that the 8‐13 c/sec. activity in the cod corresponds to alpha rhythm of mammals and man, and that in the dorsal thalamus of cod there are parts that are homologous, as regards function, with the midline nuclei and intralaminar system in mammals.