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Abstract:
Rhythmic synchronization of neural discharges in the gamma
range has been proposed as a dynamic link between areas involved in
the same network during a given task. This mechanism could underly
the construction of an object representation, driven either by
sensory inputs or by internal top-down processes. Visually induced
gamma oscillations has been repeatedly found to increase in
different tasks involving the activation of an object
representation (feature binding, hidden-object detection or
delayed-matching-to-sample memory tasks). We tested here for a
possible role of gamma oscillations during the retention of
acoustic objects in short-term memory. Sixteen subjects were
presented with random sequences of 4 tones (S1). In the "memory
condition", the subjects compared this sequence with a following
one (S2). In the "control condition", a sequence of 2, 3 or 4
shorter tones (S2) is presented after S1 and the subject had to
detect 3-tones sequences. The difficulties of the tasks were
balanced to engage a similar level of attention, while memory is
required in the first condition only. A sustained gamma activity
was observed in the delay period between S1 and S2 and was
significantly larger in the memory condition. After S2, gamma
activity was found with a time-course depending on whether it is a
target or not. This suggests that functionally distinct gamma
oscillatory activities can be involved at different instant during
cognitive processing.
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