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Abstract:
Previous findings indicate that neural activity in the gamma
frequency band (24-60 Hz) plays a role in the representation of
visual feature bindings and their retention in short-term memory.
The purpose of the present experiment was to examine the effect of
short-term memory load on gamma-band activity observed in the human
EEG recorded during the performance of a delayed discrimination
task and assessed through time-windowed Fourier analysis. Five
participants were shown varying nu mbers of unfamiliar sample
objects and prompted to indicate manually, after a fixed delay,
whether the test stimulus matched one of the sample stimuli.
Increased short-term memory load was associated with significantly
increased gamma-band activity at characteristic intervals in the
delay period of the task. Whereas significant increases in gamma
activity observed early in the delay were evenly distributed
between frontal and posterior sites, significant increases in gamma
activity observed late in the delay were concentrated at frontal
recording sites. Significant increases in lower-frequency activity
throughout the delay were observed more often at nonfrontal
recording sites. These results support the hypothesis that
synchronized gamma-band neuronal oscillations are involved in the
maintenance of information in short-term memory and suggest that
gamma activity in frontal cortex figures prominently when
relationships between multiple cognitive representations must be
held in memory.
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