ATTENTION COORDINATES GAMMA SPINDLES BETWEEN MACAQUE VISUAL AREAS V1 AND V4

Selective visual attention supports behavioral flexibility by gating task-relevant information. Neuronally, this involves selective synchronization of γ-rhythmic activity between upstream neurons representing the attended stimulus (e.g., in V1) and downstream populations receiving competing inputs (e.g., in V4). Selective attention operates discontinuously even under constant task demands, raising the possibility that γ-activity likewise occurs in transient bursts, γ-spindles, rather than as a sustained rhythm. If so, inter-areal synchronization may depend not only on V1-V4 phase-locking but also on spindle coordination, and previous synchrony measures assuming continuous oscillations may underestimate true attentional effects. To investigate whether γ-oscillatory activity is indeed spindle-like and whether attention exploits spindle timing, we analyzed local field potentials recorded from visual areas V1 and V4 in two macaques (macaca mulatta) performing a demanding attention task. We defined γ-spindles as periods of elevated γ-amplitude surpassing a threshold.
We find that γ-activity exhibits transient (~30-100 ms), spindle-like behaviour. When attention was directed to the stimulus in the V1 receptive field, the corresponding V1 population’s spindles occurred preferentially shortly before V4 spindles, whereas no temporal coordination was observed when the competing stimulus was attended. Attention did not modulate individual spindle characteristics (duration, rate), suggesting that information transfer depends primarily on spindles’ temporal coordination rather than their intrinsic characteristics. Accounting for the transient γ structure in V1-V4 phase coherence analysis increased the estimates by 50-100%. The results suggest that 1) interareal spindle coordination may contribute to attention-dependent selective routing; 2) attentional effects on interareal synchrony may have been underestimated.