PT  - JOURNAL ARTICLE
AU  - Georgios Spyropoulos
AU  - Conrado A. Bosman
AU  - Pascal Fries
TI  - A theta rhythm in awake macaque V1 and V4 and its attentional modulation
AID  - 10.1101/117804
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 117804
4099  - http://biorxiv.org/content/early/2017/03/17/117804.short
4100  - http://biorxiv.org/content/early/2017/03/17/117804.full
AB  - Theta-rhythmic neuronal synchronization has been described in hippocampus and high-level visual areas. Recent studies suggest that theta in visual areas might originate in V1. We analyzed simultaneous electrocorticographic (ECoG) grid recordings of local field potentials from areas V1 and V4 of two macaque monkeys performing a selective visual attention task. We found a ≈4 Hz theta rhythm, which was strongest at sites showing visually induced gamma-band activity. This theta rhythm was coherent between V1 and V4, with a predominant V1-to-V4 Granger causal influence. Locally, theta phase was correlated with power in a narrow gamma-frequency band. These theta-rhythmic processes were reduced by selective attention to a visual stimulus contralateral to the recorded visual areas. This attentional effect was substantial, particularly compared to other reported effects of attention in area V1. We also investigated, whether microsaccades (MSs) play a role in the generation or attentional modulation of theta. Stratification of MS rate between attention conditions, or elimination of MS-affected data epochs left the main results essentially unchanged. Thus, we find an MS-independent theta rhythm in the visually driven part of V1, which rhythmically modulates local gamma and entrains V4, and which is strongly reduced by attention.