FUNCTIONS OF FRONTAL LOBE IN SHORT TERM MEMORY

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The study of electrophysiology of higher brain functions has become possible with the successful development of a 122-channel whole-head MEG (magnetoencephalography) system for non-invasively measuring the magnetic field outside the human head (Lounasmaa et al., IBRO NEWS, 21(2), 1993). In the proposed study we will utilize this whole-head system to detect spontaneous MEG signals from the frontal lobe of healthy volunteers during an alert rest period, during a short-term memory task, and finally again during a rest period. The memory task will consist of a presentation of a set of items to be remembered (i.e. spatial positions of items in the visual field, tone of differing pitches or words presented either visually or auditorily), followed by a retention period, and finally by a test phase where old and new items will be presented to test recognition memory. The coherence of spontaneous MEG activity will be measured to detect activities in the frontal lobe during the rest and retention periods. Localized changes in the coherence pattern will indicate the involvement of the frontal lobe in short-term memory. Asymmetry of the coherence pattern across the hemispheres will be also examined. Temporal kinetics of cortical involvement will be inferred from temporal changes in the coherence pattern during the retention period. Unlikely in previous studies of coherence, we will also examine the source coherence by solving for the source covariance matrix from the MEG covariance maori and test for the source activities in the frontal region during a retention interval. This study may open a new area of application for MEG namely in measuring functions of the associative areas of both healthy people and patients with neurological diseases.