A search for the spatial engram within the frontal lobes of monkeys

Four investigations were conducted concerning the relationship between sulcus principalis and the monkey's spatial capacities. The results of the first two studies indicated that lesions limited to the middle third of sulcus principalis but including both the superior and inferior banks resulted in severe deficits on spatial delayed-alternation and plsace reversal learning. Lesions of the anterior or posterior sectors of principalis or of the periarcuate region produced only mild, if any, impairments on the same spatial tasks. The third study demonstrated that the midprincipalis sector could be differentiated from the anterior and posterior sectors of principalis on anatomical as well as functional bases. The midprincipalis sector had heavy projections to the cingulate and retrosplenial regions while the posterior third had many efferent connections with the parietal lobe. The anterior third had limited projections to the cingulate region and none to the parietal lobe. The fourth investigation demonstrated that intact neural structures could assume some spatial functions after sequential destruction of sulcus principalis. Monkeys with serial, in comparison to one-stage, bilateral ablations of sulcus principalis demonstrated normal performance on a delayed-response task and on some place reversals, and partial recovery of delayed-alternation.