Modulation of neuronal population receptive fields tuning in Retinitis Pigmentosa: a new imaging approach to study visual function
Otília C. d’Almeida
The concept of visual cortical reorganization or “plasticity” induced by retinal lesions (scotomas) is still one of the most challenging topics discussed in modern neuroscience. It is known that receptive fields (RF) of visual neurons generally increase with convergence. Accordingly, neurons coding central vision have smaller RF than the cells that code for peripheral vision. We asked how the tuning of the populations of visual neurons is affected by a genetically determined perceptual alteration due to peripheral loss of vision (scotomas).
We studied visual cortical plasticity in a model of peripheral visual loss, Retinitis Pigmentosa (RP), using a novel method, Population Receptive Field (pRFs) mapping. This model-driven approach searches the pRF properties that best fit to the fMRI time series data from visual stimulation. Size and eccentricities of pRFs were evaluated in retinotopic cortical visual areas V1, V2 and V3 in 12 RP patients and 13 controls.
The relation between average pRF sizes and eccentricity bins for each early visual area was evaluated. In general, pRF sizes increased along eccentricity. In controls, regarding cortical visual areas, there was a progressively sharper increase from V1 to V2 and later on to V3 in accordance to the known input convergence of regional neuronal populations. Interestingly, this was not the case in the RP group. Slope analysis showed that there was a similar degree of change of pRF sizes with eccentricity across regions suggesting that, in RP patients, there is a loss of input convergence from V1 to V2, and later to V3.
This preliminary analysis shows that there is an alteration of the pRF tuning properties, possibly related with the critical loss of peripheral input in RP patients.
Funding: FCT, ERARE, FEDER COMPETE, BIGDATIMAGE