Attentional suppression of activity in the human visual cortex.

We have used fMRI to examine the nature of the changes that occur in the human visual cortex when an observer attends to a particular location in the visual image. Previous studies have shown that the magnitude of the response to a visual stimulus is increased when the observer attends to the stimulus. We show that, in addition, attention to a particular location results in a widespread suppression of activity levels at all other locations. This suggests that a key mechanism of attentional modulation may be that spontaneous (baseline) levels of neural activity are adjusted in a position-dependent manner across the entire visual field.