Single-unit analysis of binocular neurons in the frog optic tectum.

Abstract Responses of single, postsynaptic neurons in the deeper cellular layers of the frog optic tectum were recorded with glass-coated metal microelectrodes. Particular emphasis was placed upon the analysis of input and response properties of binocularly driven neurons. Section of the posterior and tectal commissures did not affect binocular response activity. However, removal of the contralateral tectal lobe or section of the deep tegmental commissures eliminated the ipsilateral component of binocular unit activity. The pathway of visual information from the ipsilateral retina is probably via the contralateral tectum, through the tegmental commissures to the ipsilateral tectum. The majority of tectal neurons observed could be activated by visual, tactile, and occasionally, auditory stimuli. Such multisensory units showed a spontaneous level of activity, whereas purely visual neurons did not. Visual receptive fields of binocular neurons were larger than those of monocular neurons in the intact preparation. Tectal neurons responded only to moving stimulus targets and often showed rapid adaptation to a repeated stimulus. However, some units showed little stimulus adaptation and the majority of units observed fell between those two extremes. Tectal neurons showed a greater response to vertical than to horizontal stimulus motion, which may be related to the predominance of vertical eye movements in the frog.

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