[Laminar analysis of evoked potentials of the cat visual cortex during prenatal ontogenesis]

A laminar analysis of visual evoked potentials recorded from the cortical striate zone in response to stimulation of the optic nerve was made on the cats foeti in the second half of antenatal development and on kittens in the first few days of their life. In all the investigated terms of prenatal ontogenesis, two negativity foci are distinctly revealed in the specific zones of the visual cortex. The first appears with the least latency in the middle cortical layers after an afferent volley inflow to the cortex. The second, which reaches a maximum in 40 to 50 msec appears in the superficial cortical structures. Analysis of the data obtained shows that the first excitation focus is due to the summation of EPSP in the neural elements of the middle cortical layers, while the second is caused by development of depolarization in the apical dendrites of the pyramidal neurones.