Behavioural and anatomical studies of the posterior parietal cortex in the rat.

Primates have an area of posterior cortex characterized by multimodal sensory projections to and from the frontal association cortex and a clear behavioural syndrome resulting from lesions to this zone. The posterior association cortex of the rat was examined in two series of experiments, one anatomical and one behavioural, to see if an analogous region could be found. The anatomical connections of Krieg's area 7 in the rat were examined by placing the retrograde tracer, True blue, into the frontal or posterior cortex, and the behaviour of rats with this cortex removed was studied on a variety of tasks. This area appears to be a multimodal sensory association region. It receives projections from striate (area 17), extrastriate (areas 18a and 18b), and somatosensory cortex (area 3). It is also reciprocally connected with the posterior cingulate cortex and two frontal association zones in the medial frontal cortex, namely the anterior cingulate cortex and the frontal eye fields. Lesions produced deficits on tasks of tactile discrimination, and walking a narrow beam, two tasks requiring animals to navigate accurately to a point in space, and a task requiring the association of two spatially discontiguous cues. The animals were not impaired at navigating to a cue or in opening puzzle latches. Overall, the results show that the rat has a sensory association zone that may be analogous to the posterior parietal cortex of primates.