Induced γ-Band Activity during the Delay of a Visual Short-Term Memory Task in Humans

Abstract

It has been hypothesized that visual objects could be represented in the brain by a distributed cell assembly synchronized on an oscillatory mode in the ␥-band (20-80 Hz). If this hypothesis is correct, then oscillatory ␥-band activity should appear in any task requiring the activation of an object representation, and in particular when an object representation is held active in short-term memory: sustained ␥-band activity is thus expected during the delay of a delayed-matching-to-sample task. EEG was recorded while subjects performed such a task. Induced (e.g., appearing with a jitter in latency from one trial to the next) ␥-band activity was observed during the delay. In a control task, in which no memorization was required, this activity disappeared. Furthermore, this ␥-band activity during the rehearsal of the first stimulus representation in short-term memory peaked at both occipitotemporal and frontal electrodes. This topography fits with the idea of a synchronized cortical network centered on prefrontal and ventral visual areas. Activities in the ␣ band, in the 15-20 Hz band, and in the averaged evoked potential were also analyzed. The ␥-band activity during the delay can be distinguished from all of these other components of the response, on the basis of either its variations or its topography. It thus seems to be a specific functional component of the response that could correspond to the rehearsal of an object representation in short-term memory.

Processing of affective pictures modulates right-hemispheric gamma band EEG activity

“…In humans, non-invasive electro-(EEG) and magnetoencephalographic (MEG) recordings have provided evidence that cortical activity in the gamma band range (above 20 Hz) is modulated by (a) the features of a stimulus (Mu Èller et al, 1996;Tallon et al, 1995;Mu Èller et al, 1997;Tallon-Baudry et al, 1997b), by (b) visual spatial attention (Mu Èller, 1998;Gruber et al, 1999), and (c) may represent the perception of a Gestalt (Tallon-Baudry et al, 1997a,b;Keil et al, 1999). In addition, power in the gamma band was enhanced during the active representation of an object in short-term memory during the delay of a delayed-matching-to-sample task (Tallon-Baudry et al, 1998). Since this activity was found at occipito-temporal and frontal leads, the authors interpreted the ®nding as supportive for the idea of a synchronized cortical network involving prefrontal and ventral visual areas.…”

“…As of today, research on cortical emotional responses in the frequency domain was mainly focused on alpha desynchronization (see Davidson, 1995, for an overview). Alpha desynchronization, however, is a poor predictor for measuring the activity of cortical networks since topographical distributions of alpha and high frequency responses are not inversely related in an one-by-one fashion (Mu Èller et al, 1996;Mu Èller et al, 1997;Mu Èller, 1998;Tallon-Baudry et al, 1998). Ray and Cole (1985), for instance reported higher beta activity (16± 24 Hz) in right hemisphere temporal and parietal areas, whereas no effect was found in the alpha band to re¯ect emotional processes.…”

Human cortical EEG rhythms during long-term episodic memory task. A high-resolution EEG study of the HERA model

“…On the contrary, the retrieval process needs a full activation of right frontoparietal network. Gamma band synchronization seems to support this higher cognitive demand, binding frontal and parietal areas in an integrated activation (Lutzenberger et al, 2002;Niedermayer, 2003;Tallon-Baudry et al, 1998).…”

Parametric analysis of oscillatory activity as measured with EEG/MEG

“…To compare parametric and nonparametric tests we used the same epoched data as Tallon-Baudry et al [1998]. We applied their processing steps to derive, for each subject, baseline-corrected power between 230 -330 ms and 24 -60 Hz.…”