Rhinal and Dorsolateral Prefrontal Cortex Lesions Produce Selective Impairments in Object and Spatial Learning and Memory in Canines

To examine the effects of rhinal and dorsolateral prefrontal cortex lesions on object and spatial recognition memory in canines, we used a protocol in which both an object (delayed nonmatching to sample, or DNMS) and a spatial (delayed nonmatching to position or DNMP) recognition task were administered daily. The tasks used similar procedures such that only the type of stimulus information to be remembered differed. Rhinal cortex (RC) lesions produced a selective deficit on the DNMS task, both in retention of the task rules at short delays and in object recognition memory. By contrast, performance on the DNMP task remained intact at both short and long delay intervals in RC animals. Subjects who received dorsolateral prefrontal cortex (dlPFC) lesions were impaired on a spatial task at a short, 5-second delay, suggesting disrupted retention of the general task rules; however, this impairment was transient, and long-term spatial memory performance was unaffected in dlPFC subjects. The present results provide support for the involvement of the RC in object, but not visuospatial, processing and recognition memory, whereas the dlPFC appears to mediate retention of a nonmatching rule. These findings support theories of functional specialization within the medial temporal lobe and frontal cortex and suggest that rhinal and dorsolateral prefrontal cortices in canines are functionally similar to analogous regions in other mammals. J. Comp. Neurol. 511:257-270, 2008. (C) 2008 Wiley-Liss, Inc.