Place navigation engrams acquired with intact brain can be retrieved with either eye and are stored in both hemispheres. The retrieval circuitry was examined by testing an overtrained rat under lidocaine inactivation of the hippocampus, visual cortex, and superior colliculus. Thirty-three hooded rats with implanted cannulae aimed at the above structures were trained to find a target in the southwest quadrant of the pool. Retrieval was tested during occlusion of one eye alone or combined with ipsi- or contralateral blockade (1 microliter 4% lidocaine) of hippocampus, hippocampus and visual cortex, or hippocampus, visual cortex, and superior colliculus. The intact brain escape latencies (9.8 s) were only slightly prolonged by occlusion of one eye (to 12.6 s). Blockade of centers ipsi- or contralateral to the occluded eye increased escape latencies to 12.7 or 15.2 s for hippocampus, to 16.8 or 16.9 s for hippocampus and visual cortex, and to 23.6 or 17.4 s for hippocampus, visual cortex, and superior colliculus, respectively. Significant asymmetry appearing in the last case indicates that the superior colliculus plays an important role in mediation of the crossed visual input supporting place navigation. Residual goal-finding capability in rats with blockade of centers ipsilateral to the occluded eye is probably due to uncrossed visual projections to the intact hemisphere.

Institute of Physiology Czech Academy of Sciences Prague Czech Republic

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