Attention-dependent suppression of metabolic activity in the early stages of the macaque visual system

In this study we used a modified double-label deoxyglucose procedure to investigate attention-dependent modulations of deoxyglucose uptake at the earliest stages of the macaque visual system. Specifically, we compared activity levels evoked during two tasks with essentially identical visual stimulation requiring different attentional demands. During a featural-attention task, the subjects had to discriminate the orientation of a grating: during a control spatial-attention task, they had to localize the position of a target point. Comparison of the resulting activity maps revealed attention-dependent changes in metabolic activity in portions of the magnocellular layers of the lateral geniculate nucleus, and the magnocellular-recipient layers 4C alpha and 4B of the striate cortex. In these early stages of the visual system, attention to the orientation of the grating suppressed the metabolic activity in a retinotopically specific band peripheral to the representation of the stimulus. These results favor an early selection model of attention. After a thalamic attention dependent gating mechanism, irrelevant visual information outside the focus of attention may be suppressed at the level of the striate cortex, which would then result in an increased signal-to-noise ratio for the processing of the attended feature in higher-tier, less retinotopically organized, extrastriate visual areas.