Response of the Optic Cortex of the Cat. ∗

Abstract

Following a single electric stimulus applied to the optic nerve, electrical potentials of 3 types are recorded from the optic cortex (Fig. 1). The first is a series of 4 or more spikes, each of 1 m.s. duration, comparable to the spikes of peripheral axons. The second is a series of waves, each of 5 to 10 m.s. duration, and the third, a series of waves of much longer duration (Fig. 2), comparable to the alpha waves. These slower potentials do not behave like after-potentials of the spikes. The first spike may follow a stimulus within 1.8 m.s. The following spikes occur at about 1.5 m.s. intervals, and are not simple repetitions of the first, but can be differentiated from it by differences in polarity at different depths in the cortex, by effects of anesthetics, etc. The spikes appear to represent activation of successive groups of elements rather than repetitive activation of one group. These spikes had not previously been recognized in the rabbit cortex, but with improved recording technic can now be seen to be present there also, of relatively lower amplitude. The short waves, 2 or 3 in number, correspond to those identified in the rabbit as the specific visual response. The long waves, often repetitive at 1/5 to 1/8 second intervals, correspond to the response in the rabbit of the alpha mechanism. These 2 series of slower potentials are differentiated characteristically by anesthesia and strychnine, as in the rabbit (Bartley, O'Leary, and Bishop 1 ).

We have investigated the responses of these elements to repetitive stimulation in the cat under different degrees of anesthesia. Magnesium sulphate, 0.25 g/kg or less, with ether as necessary during the preliminary operative procedures