Spatial Functions of the Medial Temporal Lobe

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DESCRIPTION (provided by applicant): Nowhere is the significance of neural plasticity more evident than in amnesic patients with damage to the medial temporal lobe. These patients exhibit a profound, selective and long-lasting inability to form or retain new long-term memory for facts and events, termed declarative memory in humans and relational memory in animals. One prototypical form of declarative/relational memory is memory for spatial information. The goal of this proposal is to define the patterns of neural activity that underlie 2 important aspects of memory for spatial information in the macaque monkey hippocampus and entorhinal cortex. First, our preliminary data show that hippocampal and cortical neurons signal learning of new spatial associations (object-place association task) with dramatic changes in neural activity termed "changing cells". Specific Aim 1 will define which aspect/s of the learned object-place association control/s the changing cells. These studies will determine how error trials and systematic manipulations of object identity, place specificity, motor response and behavioral context control the activity of the changing cells. A second key aspect of spatial memory for trajectories or journeys (i.e., how to get from point A to point B) is the ability to remember the temporal order of events in a spatial sequence. Specific Aim 2 will examine both the long-term and working memory signals in the hippocampus and entorhinal cortex during the performance of a delayed sequence recall task where animals must reproduce the order of three-item sequences from memory. Specific Aim 3 will further categorize the task-related and memory-related cells identified in the hippocampus and entorhinal cortex in Specific Aims 1 and 2 into either putative excitatory (PE) or fast spiking (FS) cells. These experiments will also attempt to identify clear theta activity in the monkey hippocampus and superficial entorhinal cortex. Thus, these latter experiments will allow us to 1) link cells with particular task-related or mnemonic signals to specific cell types (i.e., PE or FS cells) and phases of theta and 2) compare the relationship between cell type/theta modulation and neural response observed in monkeys to that described in rats. The results from these studies have implications for understanding a variety of neurological states associated with memory dysfunction including Alzheimer's disease, epilepsy and schizophrenia.