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Electrophysiological analysis of cortico-tectal connections in the turtle

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Abstract

Two types of evoked potentials are recorded in the tectum mesencephali in response to electrical stimulation of the forebrain surface of the turtleEmys orbicularis. The results of a layer-by-layer analysis show that evoked potentials of type I in response to stimulation of the hippocampal and piriform cortex are generated outside the tectum. Evoked potentials of type II, consisting of two surface-negative components, are recorded in the tectum in response to stimulation of the rostro-central surface of the forebrain. The first component appeared after a latent period of 20 msec and lasted 40–60 msec; the second component appeared after 80–100 msec and lasted 100–300 msec. Layer-by-layer and pharmacological analysis showed that the first component of the type II evoked potential is generated in the tegmental structures of the mesencephalon, whereas the second (long-latency) is generated in the tectum. The tectal origin of the second component is confirmed by its interaction with the tectal response to photic stimulation or to electrical stimulation of the optic nerve, evidence that these evoked potentials are generated by common structures. The efferent pathway from the dorsal cortex to the primary visual center is unilateral and has features of polysynaptic projections (long latent period, low lability).

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Additional information

A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 6, No. 2, pp. 127–134, March–April, 1974.

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Isabekova, S.B. Electrophysiological analysis of cortico-tectal connections in the turtle. Neurophysiology 6, 97–103 (1974). https://doi.org/10.1007/BF01062744

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Keywords

  • Electrical Stimulation
  • Optic Nerve
  • Latent Period
  • Common Structure
  • Analysis Show