Layer-by-layer analysis of visual cortical evoked potentials during prenatal development of the cat

Conclusions

• 1. Layer-by-layer analysis of potentials arising in the striate cortex in response to electrical stimulation of the optic nerve was carried out on cat fetuses and kittens during the first days after birth.

• 2. Layer-by-layer analysis of the distribution of potentials and the discovery of the location of their “source” and “sink” showed that during the last 3 weeks of intrauterine life and in early postnatal ontogeny the application of a single stimulus to the optic nerve causes the appearance of two negative potentials in the cortex, located in different layers.

• 3. After the arrival of a volley of afferent impulses in the cortex the first high-amplitude negative potential arises in the middle layers of the cortex. It is evidently a combined EPSP of a population of pyramidal and stellate neurons lying in the middle layers of the cortex.

• 4. The second focus of excitation arises 40–50 msec after the first. Layer-by-layer analysis shows that it is due to excitation of neurons located in the upper layers of the cortex, most probably in the apical dendrites of pyramidal neurons.

• 5. The results of this layer-by-layer analysis of EP of the primary visual projection cortex show that the characteristic temporal and spatial sequence of activation of neurons found in the visual cortex of adult animals is formed during the second half of the intrauterine period of development.