TEMPORAL STRUCTURE OF WORKING MEMORY ACTIVITY

California Institute Of Technology, Pasadena CA

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Abstract

DESCRIPTION (Adapted from Applicant's abstract): The aim of this research project is to determine the temporal correlation structure of neuronal activity within and between local and distant cortical areas in a fronto-parietal network during working memory tasks. The research will be performed via simultaneous multiple tetrode recordings from the relevant cortical areas in macaque monkeys performing saccade and reach memory tasks. Multivariate spectral analysis tools will be used to analyze and interpret the neuronal activity. These tools were applied to the data collected during preliminary recording from parietal area LIP during a memory saccade task and revealed a spatially tuned increase in power spectrum in both single unit and local field potentials between 40-90 Hz during the memory period. This is the first demonstration of temporal coding during a memory task. The specific aims will test hypothesis relating to correlations in temporal structure in both single units and local field potentials activity (as compared to the spike rates). The first aim will complete the preliminary study testing the hypothesis that SU and LFP spectra in area LIP show memory fields in 40-90 Hz band by recording from multiple tetrodes during a memory saccade task and characterizing the correlation between SU and LFP activity. The second aim will test the hypothesis that the activity in the FEF in prefrontal cortex and also activated by a memory saccade task, show similar dynamic memory fields of SU and LIP spectra. This will be tested by recording from multiple tetrodes in FEF during the same task. The third aim will test the hypothesis that the temporal structure during working memory is correlated across areas LIP and FEF using multiple tetrode recordings from these areas. The fourth aim will test the hypothesis that the temporal structure and correlation observed in areas LIP and FEF are reflected by analogous activity in reach circuitry during a memory-reach task. This hypothesis will be tested using data recording from parietal reach region (PPR) and dorsal premotor area (PMd) following methodology of the first three aims. Elucidating the organization of temporal structure and correlations in neuronal activity during a working memory task is necessary to determine the underlying functional architecture. The instrumental and analytical techniques developed in this proposal, particularly in the context of LFP, have fundamental significance for development of neural prosthetics. The experiments will promote understanding of short-term memory, which is often affected with aging and neurological disease.