Visually-released, pain-induced defensive boxing in the rat was abolished by lesions which destroyed the ventrobasal thalamus. The visually-released boxing was produced by facial anesthesia of one of a pair of rats which were administered footshock in a small chamber; the rat with facial anesthesia was forced to rely upon visual stimuli rather than the facial tactile stimuli which normally release the behavior. The abolition of the visually-released boxing was specifically related to destruction of the ventrobasal thalamus rather than adjoining structures. A particularly effective control procedure involved abolition of the response by unilateral lesions confined to the ventrobasal thalamus and removal of visual input to the contralateral side of the brain by closure of the ipsilateral eye. Since visually-released boxing is a learned behavior dependent upon the visual cortex, it would appear that cortical mechanisms incorporate higher levels of the tactile projection system into an alternative system which releases the behavior after facial anesthesia.
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