retinotopic

Retinotopic refers to the topographic organization by which visual information from the retina is represented in the brain in a way that preserves spatial relationships from the retina. In a retinotopic map, neighboring points on the retina correspond to neighboring neurons in retinorecipient areas, most notably the primary visual cortex (V1) and many higher visual areas.

Anatomy and mechanism: Retinotopic mapping begins with retinal ganglion cells that project to the lateral geniculate nucleus of the thalamus and onward to V1 via the optic radiations. In V1 and many extrastriate areas, the cortical surface contains a continuous map of the contralateral visual field, with the fovea allocated disproportionately large cortical space—a phenomenon known as cortical magnification. Maps are commonly described in terms of polar angle (the direction around the center of gaze) and eccentricity (distance from the center).

Properties and implications: Retinotopy enables precise localization of visual stimuli and supports spatially organized receptive fields across the cortex. While early visual cortex tends to be strongly retinotopic, higher visual areas can show more complex or less strictly retinotopic representations, reflecting increasingly abstract processing.

Measurement and research: Retinotopic maps are studied using functional imaging and electrophysiology. Techniques include fMRI with phase-encoded stimuli such as rotating wedges to map polar angle and expanding rings to map eccentricity, as well as direct neural recordings and optical imaging in animal studies.

Clinical and practical relevance: Retinotopic mapping aids in assessing visual field defects, guides neurosurgical planning, and informs research on visual plasticity following injury or vision loss.