Although many studies have shed light on the behavioural phenomena associated with visual attention, its neural mechanisms are much less well understood. A study published by Gross et al. in Proceedings of the National Academy of Sciences uses magnetoencephalography (MEG) to investigate how the different areas of the brain that have been implicated in attentional processes might interact, and how this could relate to behaviour.

The authors used a well-established effect — the 'attentional blink' — to investigate brain activity during attentional processes. Subjects have to look at a screen on which they see a stream of letters presented very rapidly (seven letters per second). The task is to spot two 'target' letters embedded in the stream among the non-target (distractor) letters. When the two targets are separated by only one distractor, so that they appear less than 500 ms apart, subjects find it harder to identify the second target. This period of reduced ability to identify the target is called the attentional blink.

Previous functional imaging studies have found several areas of the brain that seem to be involved in attention, including frontal, parietal and temporal regions. Gross and colleagues used MEG to measure the timecourse of activity in these areas, and to identify functional connections between them by looking for periods of long-range synchronization of activity.

Using a form of analysis called time–frequency representation, the authors found that presentation of visual targets, but not distractors, produced strong activity in the beta frequency band (13–18 Hz). The areas of the brain that showed high levels of activity in this band corresponded to those that had previously been implicated in attention by functional imaging studies.

By calculating the synchronization index between the individual regions, Gross et al. tested how the brain areas were connected into a functional network. The connections fell into two groups: in some cases (mainly connections between the occipital cortex and left hemisphere areas), synchronization depended on the presentation of any letter (target or distractor), whereas other connections showed modulation of the synchronization index only by target letters. The latter connections were between the right posterior parietal cortex and the left temporal and frontal cortex.

But is this synchronized activity related to behaviour? To test this, the authors compared trials in which the attentional blink prevented the subject from spotting the second target with those in which the second target was correctly identified, on the grounds that these two types of trial showed different attentional effects. They found that both overall synchronization during the trial and temporal modulation of synchronization (by targets as compared to distractors) were stronger in trials that showed no attentional blink (when subjects successfully identified the second target). The authors suggest that this enhancement of synchronization might reflect a state of higher vigilance, which allows the successful performance of the task.

These findings support the idea that different brain areas that form an 'attentional network' communicate through synchronization (in the beta band, but possibly also at other frequencies). Together with other evidence, this emphasizes the potential importance of synchronized neural activity in cognitive processes.