Interaction between Cortico-tectal and Retino-tectal Inputs as Revealed by Analysis of Field Potentials of the Cat's Superior Colliculus

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  • TAMAI MAKOTO
    Department of Physiology, Tohoku University School of Medicine Department of Ophthalmology, Tohoku University School of Medicine
  • OGAWA TETSURO
    Department of Physiology, Tohoku University School of Medicine Department of Physiology, Akita University School of Medicine

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In chloralose-anesthetized cats, electrical stimulation of the optic tract evoked a negative-positive field potential wave at the surface of the ipsilateral superior colliculus which reversed to a positive-negative wave at the deeper part of the superficial gray layer. The maximal amplitude of the deep positivity was reached at the optic layer. Cortical stimulation of visual and surrounding areas elicited similar field potentials in the ipsilateral superior colliculus. Reversal in polarity occurred at the same depth as did for the tract-evoked field potential. In general, stimulation of cortical areas surrounding the visual cortex, for example, the posterior suprasylvian gyrus, gave rise to a larger response than stimulation of the visual cortex. Reversible inactivation of the cortical visual and adjacent areas by cooling resulted in a reduction of the tract-evoked field potential with a gradual recovery to the initial amplitude after removal of the cooling agent. This finding indicates that the geniculocortico-tectal pathway contributes the generation of collicular response to stimulation of the retinotectal pathway. Topographical interrelationships between the effective cortical area and the superior colliculus were examined with the amplitude of cortically evoked collicular responses as an index. It was revealed that the junctional part between the lateral and postlateral gyri was related to the posterior part of the superior colliculus and that the upper part of the postsuprasylvian gyrus was associated with the anterior part of the superior colliculus. As to interaction between cortico-tectal and retino-tectal inputs, it was found that preceding stimulation of the effective cortical areas produced an initial facilitation from 50 to 200 msec followed by a depression of collicular response to optic tract stimulation lasting for as long as 500 msee.

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