Eye position-dependent activity in the primary visual area as revealed by fMRI

Abstract

Internal senses of the position of the eye in the orbit may influence the cognitive processes that take into account gaze and limb positioning for movement or guiding actions. Neuroimaging studies have revealed eye position-dependent activity in the extrastriate visual, parietal, and frontal areas, but, at the earliest vision stage, the role of the primary visual area (V1) in these processes remains unclear. Functional MRI (fMRI) was used to investigate the effect of eye position on V1 activity evoked by a quarter-field stimulation using a visual checkerboard. We showed that the amplitude of V1 activity was modulated by the position of the eye, the activity being maximal when both the eye and head positions were aligned. Previous studies gave impetus to the emerging view that V1 activity is a cortical area in which contextual influences take place. The present study suggests that eye position may affect an early stage of visual processing.

Figure 1

Eye tracking measurements observed in one subject for each deviated eye position (7°‐leftward on the top, 0°‐forward in the middle, and 7°‐rightward on the bottom). Both horizontal and vertical eye movements (EM) are represented for each series alternating a 30‐s fixation period and a 30‐s fixation period with visual quarter‐field stimulus (see Subjects and Methods for details). [Color figure can be viewed in the online issue, which is available at www. interscience.wiley.com.]

Figure 2

Definition of the calcarine‐weighted quarter‐field retinotopic VOIs. See Subjects and Methods for details. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 3

Mean amplitude of visually evoked activity in the four weighted‐ calcarine functional VOIs related to their retinotopic visual quarter‐fields. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]