SOURCE MEMORY AND HUMAN PREFRONTAL CORTEX

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Many aspects of human memory have been functionally and neuroanatomically dissociated. In the realm of episodic memory, for example, memory for the content of a conversation (item memory) may be more persistent than the memory of who made the comments (source memory). Source memory and item memory have been functionally correlated with the frontal lobes and the medial temporal lobes, respectively. However, the amount of direct neuroanatomical evidence for this hypothesis is limited. This project will compare the electrophysiological and neuroanatomical substrate5 of (1) source memory and (2) item memory in neurological patients with unilateral lesions of prefrontal cortex. Pilot studies will be run in young and elderly control subjects to examine item memory for spoken words and source memory for voice. Then, event-related brain potential (ERP), magnetic resonance imaging (MRI), and behavioral data will be obtained from groups of frontal patients with and without apha5ia and compared to data from age-matched controls. This line of research will provide information on the neural substrates of the observed ERP effects. Our previous results demonstrated that inferior prefrontal cortex and adjacent regions damaged in aphasic stroke patients (the insula and anterior temporal tip) are critical for generating the late positive potentials observed in a lexical decision task. Additionally, we will look at the timing of item and source memory processes by correlating ERPs with behavioral performance. Recent pilot data from controls suggest that source and item memory engage separate neural systems with different temporal characteristics. In the current proposal, we will study groups of patients with MRI-defined damage in subregions of left or right prefrontal cortex. The guiding theoretical framework is that prefrontal cortex plays a greater role in source memory than in item memory, while the medial temporal lobes are more involved in item than source memory. Future research will further evaluate this hypothesis in patients with damage to medial temporal areas including hippocampu5 and entorhinal cortex. This combined ERP, lesion, and behavioral approach will study the contributions of prefrontal cortex to different aspects of verbal memory processing, specifically memory for context (source memory) and memory for content (item memory).