The hippocampus is crucial for episodic memory, although the mechanisms underlying its contributions are not fully understood. A major obstacle for understanding hippocampal function is the difficulty in linking neural activity to rapidly occurring memory processes that unfold with millisecond time scales. For instance, viewing behavior influences memory formation and retrieval, with ~4 visual fixations on average occurring every second during feats of memory. To address this challenge, the proposed research combines records of viewing behavior obtained via eye-movement tracking with recordings of hippocampal activity from depth electrodes implanted chronically in human subjects for the treatment of epilepsy. This approach yields spatially and temporally precise measurement of hippocampal activity corresponding to the rapid series of visual fixations that occurs during memory formation and retrieval. The primary goal is to identify hippocampal neural activity associated with viewing behavior that reflects novelty detection versus retrieval processes during memory formation. We focus on novelty detection and retrieval because these are two fundamental aspects of hippocampal function that have not been adequately segregated in previous experiments due to their rapid and interactive nature. By linking intracranial recordings of hippocampal neural activity with eye movements that reflect novelty detection versus retrieval in a tightly controlled experimental memory task, the proposed project would advance knowledge of how specific memory functions that occur dynamically during memory formation are supported by the hippocampus. The mechanistic knowledge provided by this proposed research would advance understanding of normal memory function and memory abnormalities in individuals with impairments, including epilepsy and other neurological and psychiatric disorders. Furthermore, establishing relationships between memory-related eye movements and hippocampal function could motivate novel diagnostics for specific hippocampal abnormalities in individuals with memory impairments.
Memory impairments are common in individuals with hippocampal dysfunction due to epilepsy and other neurological and psychiatric disorders. The proposed research uses eye movements to measure memory processing in people with chronically implanted electrodes to understand how hippocampus contributes to memory. This research could advance understanding of memory impairment and motivate development of highly sensitive memory tests to measure hippocampal dysfunction.