ATTENTION-DRIVEN GAMMA-FREQUENCY MODULATIONS IN V1 PREDICT V1–V4 INTER-AREAL SYNCHRONY IN THE MACAQUE’S VISUAL CORTEX

Faced with permanent simultaneous sensory inputs and limited neural resources, attention enables flexible routing of sensory signals through dense neural networks. Such selective routing has been linked to changing patterns of synchrony between local gamma-rhythms of distant neuronal groups; but how such synchrony is set up remains entirely unclear.
It has been proposed that attention mediates selective synchrony by increasing the gamma-frequency of the sender population processing the attended stimulus, thus giving its signals an advantage to reach the receiver area before slower competing inputs. Here, we investigate the relationship between synchronous activity, measured as inter-areal phase coherence (PC), and the frequencies of the local field potentials (LFP) of two nearby V1 populations (competing senders) and one overlapping V4 population (receiver). LFPs were simultaneously recorded from V1 and V4 of two macaque monkeys performing an attentionally demanding delayed match-to-sample task.
We report that attention led to consistently stronger inter-areal synchrony between V1 and V4 and increased gamma-frequency in the attended V1 population. Importantly, the frequency difference between the competing (attended and non-attended) V1 populations predicted inter-areal synchrony for the attended stimuli: greater frequency differences between attended and non-attended V1 populations were associated to greater PC with V4. This relationship was also evident in the trial-averaged time course, where V1–V4 synchrony correlated with V1 frequency differences for the attended population.
These results suggest that a small frequency increase for the sender population processing the attended stimulus might help to selectively synchronize its gamma-band activity with that of the receiver population.