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Earliest attentional effect in the primary auditory and visual cortices

This study addressed a fundamental question about the neural correlates of attention, namely what is the earliest sensory processing stage that attention affects.

Earliest attentional effect in V1

Earliest visual spatial attention related activations (responses to images presented in the left visual field). (On the left) Brain regions modulated by spatial attention for both visual stimulus categories (checkerboards and faces) are shown in three consecutive time intervals. Axial MRI slice that best covers the activations is shown on the upper row. The sagittal view of the first significant activation that was localized in V1 in 55-60 ms interval is shown below. The green lines here indicate the V1/V2 borders (representation of vertical meridian), which were obtained in a separate fMRI experiment. The white dotted line on the axial view shows location of the sagittal slice. Yellow contours encompass the regions of statistically significant (P < 0.005) activations. Red colour indicates the strongest activated regions. Next to the sagittal view, the schematic image of the activation location in V1 is shown. (On the right) Activation time course of right hemisphere V1 generated in response to checkerboards presented in the right visual field, in the attended (blue) and ignored (red) conditions overplotted.

In contrast to earlier accepted view this study demonstrated that the earliest feedforward stimulus-evoked response in the primary visual (auditory) cortex, at ~50 ms (25 ms), is enhanced by spatial attention. Attentional modulation of visual sensory processing starts in V1 and, together with the feedforward volley of activation, spreads through the visual cortex.

V. Poghosyan, A. A. Ioannides, Neuron 58, 802-813 (2008). PDF >>