Abstract:
The oscillation of neuronal circuits reflected in the EEG gamma frequency may be
fundamental to the perceptual process referred to as binding (the integration of various thoughts
and perceptions into a coherent picture). The aim of our study was to expand our knowledge of
the developmental course ofEEG gamma in the auditory modality.
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We investigated EEG 40 Hz gamma band responses (35.2 to 43.0 Hz) using an auditory
novelty oddball paradigm alone and with a visual-number-series distracter task in 208
participants as a function of age (7 years to adult) at 9 sites across the sagital and lateral axes (F3,
Fz, F4, C3, Cz, C4, P3, Pz, P4). Gamma responses were operationally defined as change in
power or a change in phase synchrony level from baseline within two time windows. The evoked
gamma response was defined as a significant change from baseline occurring between 0 to 150
ms after stimulus onset; the induced gamma response was measured from 250 to 750 ms after
stimulus onset.
A significant evoked gamma band response was found when measuring changes in both
power and phase synchrony. The increase in both measures was maximal at frontal regions.
Decreases in both measures were found when participants were distracted by a secondary task.
For neither measure were developmental effects noted. However, evoked gamma power was
significantly enhanced with the presentation of a novel stimulus, especially at the right frontal
site (F4); frontal evoked gamma phase synchrony also showed enhancement for novel stimuli but
only for our two oldest age groups (16-18 year olds and adults).
Induced gamma band responses also varied with task-dependent cognitive stimulus
properties. In the induced gamma power response in all age groups, target stimuli generated the highest power values at the parietal region, while the novel stimuli were always below baseline.
Target stimuli increased induced synchrony in all regions for all participants, but the novel
stimulus selectively affected participants dependent on their age and gender. Adult participants,
for example, exhibited a reduction in gamma power, but an increase in synchrony to the novel
stimulus within the same region. Induced gamma synchrony was more sensitive to the gender of
the participant than was induced gamma power. While induced gamma power produced little
effects of age, gamma synchrony did have age effects.
These results confirm that the perceptual process which regulates gamma power is
distinct from that which governs the synchronization for neuronal firing, and both gamma power
and synchrony are important factors to be considered for the "binding" hypothesis. However,
there is surprisingly little effect of age on the absolute levels of or distribution of EEG gamma in
the age range investigated.
