A large number of studies have so far tried to uncover the rules governing the attention-driven
modulation of bottom-up processes [1] and succeeded in identifying areas for the attentional
control of visual processing among which frontal, temporal and parietal areas play
a prominent role. Still, little is known about the mechanism by which these areas
interact. We used magnetoencephalography to study transient long-range neural communication,
by means of phase synchronization among these areas, in a challenging task which induces
deficits of temporal visual attention. Two target letters embedded in a stream of
13 distractor letters were visually presented to 10 healthy subjects at a rate of
seven per second. The targets were separated in time by a single distractor. This
condition leads to a dual-task interference in a well-studied behavioral phenomenon
known as the „attentional blink“ (AB)- the reduced ability to report the second target
when an interval of less than 500 ms separates them. A time-frequency representation
(TFR) was computed, time-locked to the presentation of behaviorally meaningless distractors
and subtracted from the corresponding TFR of correctly detected target letters. The
difference TFR reveals an enhancement in the beta-frequency range (around 15Hz) at
a latency of about 400 ms after target presentation. The neural generators giving
rise to this TFR signature of target processing were localized in each individual
subject using „dynamic imaging of coherent sources“ DICS [2]. Spatial normalization
and permutation analysis were employed and resulted in the identification of eight
significant regions-of-interest across subjects: occipital, frontal left, frontal
right, temporal left, temporal right, posterior parietal left, posterior parietal
right, cingulum. Mean phase synchronization between specific areas was modulated by
the behavioral relevance of the stimuli and the perceptual outcome. Our results demonstrate
that distinct spatio-temporal patterns of transient long-range phase synchronization
in a fronto-parieto-temporal network distinguish the trials in which physically identical
stimuli were perceived or not. Thus synchronization/desynchronization appears to be
a candidate mechanism for enhancing target processing and may define an important
aspect of what we commonly refer to as 'attention'. References: [1] Desimone R, Duncan J. Annu Rev Neurosci 1995; 18: 193–222. [2] Gross J et al.
Proc Natl Acad Sci USA 2001; 98: 694–699.
