Laminar differences in gamma and alpha coherence in the ventral stream

TLDR

Attention enhances neuronal responses and gamma synchrony in V4, boosting the influence of attended stimuli on downstream neurons. The authors recorded from superficial and deep layers of V1, V2, and V4 in two rhesus monkeys to test whether gamma synchrony is common throughout the ventral stream. Gamma synchrony was largely confined to superficial layers across V1, V2, and V4, while deep layers exhibited low‑frequency (alpha) coherence; attention enhanced gamma in superficial layers but reduced alpha in deep layers, with firing rates and noise correlations largely unchanged, suggesting synchrony serves distinct roles in feedback versus feedforward projections.

Abstract

Attention to a stimulus enhances both neuronal responses and gamma frequency synchrony in visual area V4, both of which should increase the impact of attended information on downstream neurons. To determine whether gamma synchrony is common throughout the ventral stream, we recorded from neurons in the superficial and deep layers of V1, V2, and V4 in two rhesus monkeys. We found an unexpected striking difference in gamma synchrony in the superficial vs. deep layers. In all three areas, spike-field coherence in the gamma (40–60 Hz) frequency range was largely confined to the superficial layers, whereas the deep layers showed maximal coherence at low frequencies (6–16 Hz), which included the alpha range. In the superficial layers of V2 and V4, gamma synchrony was enhanced by attention, whereas in the deep layers, alpha synchrony was reduced by attention. Unlike these major differences in synchrony, attentional effects on firing rates and noise correlation did not differ substantially between the superficial and deep layers. The results suggest that synchrony plays very different roles in feedback and feedforward projections.