An investigation of cross-modal plasticity of effective connectivity in the blind by dynamic causal modeling of functional MRI data.

To investigate connectivity between primary somatosensory area (S1) and striate cortex (V1) in the blind, we used dynamic causal modeling of functional MRI acquired while 15 blind (9 early-onset and 6 late-onset) and 24 sighted subjects performed a tactile Braille discrimination task with their right hand. Five regions of interest were selected from either the ventral or dorsal pathways: left S1, anterior intraparietal sulcus (aIPS), superior occipital gyrus (SOG), inferior occipital gyrus (IOG), and V1. Bayesian model comparison showed that a cortico-cortical feedback pathway model without direct connections between V1 and S1 performed better than that with direct connections. In the blind, baseline connectivity and its discrimination-specific modulation in aIPS-SOG and aIPS-IOG were positive and bi-directional, while they were negative in the sighted. Thus visual deprivation may induce reorganization of the visual cortical areas due to the competitive shift for tactile inputs. The early blind showed stronger connectivity than the late blind in the dorsal pathway (aIPS-V1 through SOG) and in SOG-IOG bi-directionally. Task performance positively correlated with baseline connectivity of SOG-V1 and SOG-IOG across blind subjects. Therefore, dorsal visual regions are involved in the functional shift in V1 from visual to tactile information processing in blind subjects.