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Abstract:
Abstract: We analyzed intracranial recordings from epileptic
patients while they performed a working memory task (Sternberg,
1966). In this task, a series of items are presented, followed by a
probe; the subjects task is to indicate whether or not the probe
item was in the series. The excellent spatial and temporal
resolution afforded by intracranially implanted electrodes (depth
electrodes and subdural electrode arrays), enabled us to
simultaneously examine the topography and dynamics of
electroencephalographic activity synchronized to stimulus events
within the task. We analyzed event related potentials (ERPs) in two
variants of the Sternberg working memory task, one using consonants
as stimuli and the other using spatial patterns (two-dimensional
compound sine-wave gratings). Across three subjects, we recorded
from 236 electrode locations. The ERP waveforms for positive and
negative probes were significantly different at 31 of the 236
recording sites, with a number of sites in the left temporal lobe
showing sensitivity to the probe's status as early as 250 ms. In
addition, ERPs at 9 sites were able to distinguish between probes
on the basis of their serial position in the list. The dynamics and
topography of ERPs sensitivity to different stimulus dimensions are
examined and evaluated in the context of current models of working
memory.
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