Prominence of direct entorhinal-CA1 pathway activation in sensorimotor andcognitive tasks revealed by 2-DG functional mapping in nonhuman primate

The trisynaptic pathway from entorhinal cortex to the hippocampus has long been regarded as the major route of information transfer underlying memory consolidation. Most physiological studies of this pathway involve recording from hippocampal slices. We have used both single- and double-label 2-deox yglucose autoradiographic methods to image the pattern of activation in the hippocampal formation of 14 rhesus monkeys performing cognitive tasks, var ying in content (spatial or nonspatial), process (working memory or associa tive memory), and mode of response (oculomotor or manual). These studies re vealed a highly differentiated pattern of metabolic activation throughout t he rostrocaudal extent of the hippocampal formation that was common to all behavioral conditions examined. This pattern consisted of intense activatio n of the stratum lacunosummoleculare of CA1 and the subiculum, contrasting with barely detectable activity in CA3 and modest activation in the dentate gyrus, which did not include its molecular layer. These findings indicate a remarkable invariance in hippocampal activation under conditions of varie d content, varied process, and varied mode of response and an heretofore-un appreciated preferential engagement of the direct rather than the trisynapt ic pathway during performance of a wide range of behavioral tasks.