Abstract
In congenitally blind individuals, the occipital cortex responds to various nonvisual inputs. Some animal studies raise the possibility that a subcortical pathway allows fast re-routing of tactile information to the occipital cortex, but this has not been shown in humans. Here we show using magnetoencephalography (MEG) that tactile stimulation produces occipital cortex activations, starting as early as 35 ms in congenitally blind individuals, but not in blindfolded sighted controls. Given our measured thalamic response latencies of 20 ms and a mean estimated lateral geniculate nucleus to primary visual cortex transfer time of 15 ms, we claim that this early occipital response is mediated by a direct thalamo-cortical pathway. We also observed stronger directed connectivity in the alpha band range from posterior thalamus to occipital cortex in congenitally blind participants. Our results strongly suggest the contribution of a fast thalamo-cortical pathway in the cross-modal activation of the occipital cortex in congenitally blind humans.
Highlights
In congenitally blind individuals, the occipital cortex responds to various nonvisual inputs
To test for the contribution of a thalamo-cortical pathway in the rerouting of tactile information to the occipital cortex in congenitally blind (CB) humans, we combined MEG source imaging and directed functional connectivity to resolve the spatiotemporal dynamics of brain activation in response to tactile stimulation
Detected around 20 ms in the posterior aspect of the thalamus by using both a full cortically distributed source model in individual subjects and a linear regression model constrained to thalamus and the other two regions of interest (ROIs)
Summary
The occipital cortex responds to various nonvisual inputs. Evidence supporting a strengthened corticocortical route for nonvisual afferents is derived from brain imaging studies showing stronger functional connectivity of auditory and somatosensory cortices with the occipital cortex in blind subjects[5,6,7,8,9,10,11]. Our results show that tactile stimulation produces early occipital cortex activations in CB individuals, starting as early as 35 ms, and increases directed connectivity in the alpha-band range from posterior thalamus to occipital cortex Together, these observations indicate a fast thalamo-cortical pathway in the cross-modal activation of the occipital cortex in CB humans
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