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Male Sprague-Dawley rats received either radiofrequency lesions of the lateral internal medullary lamina (IML) or ibotenic acid lesions of the lateral intralaminar nuclei (ILN) and midline nuclei (MLN) or sham treatment. Neither lesion group was impaired in the retention of 3 object pair discriminations acquired before surgery nor in the acquisition of a new object pair after surgery. Rats with ILN, but not IML, lesions were impaired in acquiring an initial and 5 subsequent hidden platform locations in a water maze task. These results suggest that damage to both ILN and MLN are needed to produce spatial learning deficits and that extensive damage to the IML or ILN has no detectable effects on retrograde or anterograde memory of object discriminations.