Corticocortical Connections Mediate Primary Visual Cortex Responses to Auditory Stimulation in the Blind

Abstract

Blind individuals have to rely on nonvisual information to a greater extent than sighted to efficiently interact with the environment, and consequently exhibit superior skills in their spared modalities. These performance advantages are often paralleled by responses in the occipital cortex, which have been suggested to be essential for nonvisual processing in the blind. However, it is currently unclear through which pathways (i.e., thalamocortical or corticocortical connections) nonvisual information reaches the occipital cortex of the blind. Here, we used functional magnetic resonance imaging to study blind and matched sighted humans with an auditory discrimination paradigm and used dynamic causal modeling to investigate the effective connectivity underlying auditory activations in the primary visual cortex of blind volunteers. Model comparison revealed that a model connecting the medial geniculate nucleus (MGN), primary auditory cortex (A1), and primary visual cortex (V1) in a bidirectional manner outperformed all other models in both groups. Regarding inference on model parameters, we observed that basic auditory mechanisms (i.e., sensory input to MGN and connections from MGN to A1) did not differ significantly between the two groups. In contrast, we found clear evidence for stronger corticocortical connections from A1 to V1 in the blind, whereas results with regard to thalamocortical enhancement (from MGN to V1 and, in a control analysis, from the lateral geniculate nucleus to V1) were not consistent. These results suggest that plastic changes especially in corticocortical connectivity allow auditory information to evoke responses in the primary visual cortex of blind individuals.

Brain circuit–gene expression relationships and neuroplasticity of multisensory cortices in blind children

“…Thus, neural plasticity is driven by multimodal connectivity integration, in areas that seem essentially involved in the catalysis of cross-modal adaptation. For instance, our findings integrate well with previous discoveries of crossmodal integration in congenitally blind individuals (22,23), in which increased connectivity between auditory or somatosensory cortex and specific areas of the occipital lobe is observed. Indeed, we describe similar connectivity increases but at the indirect connectivity level, meaning that a significant amount of cross-modal interactions between visual cortex and other primary systems is likely determined by multimodal relay stations.…”

Direct Structural Connections between Voice- and Face-Recognition Areas

“…The results of our study also integrate well with recent developments in multisensory research showing that information from different modalities interact earlier and on lower processing levels than traditionally thought (Cappe et al, 2010;Kayser et al, 2010;Klinge et al, 2010;Beer et al, 2011; for review see Ghazanfar and Schroeder, 2006;Driver and Noesselt, 2008). We assume that direct connections between FFA and voicesensitive cortices are especially relevant in the context of person identification.…”

“…Direct structural connections between voice-and facesensitive areas would be in line with recent developments in multisensory research suggesting that information from different modalities interacts already at relatively early processing stages (Ghazanfar and Schroeder, 2006;Kayser and Logothetis, 2007;Driver and Noesselt, 2008;Cappe et al, 2010;Kayser et al, 2010;Klinge et al, 2010). Early integration based on direct connections would provide useful constraints for possible interpretations of ambiguous sensory input (von Kriegstein et al, 2008).…”

Functional specialization for auditory–spatial processing in the occipital cortex of congenitally blind humans

“…Klinge et al (52) recently used dynamic causal modeling of an fMRI dataset to investigate the effective connectivity underlying auditory activations in the primary visual cortex of CB. They found clear evidence for stronger corticocortical connections from primary auditory cortex to primary visual cortex in the blind compared with sighted controls, whereas their results regarding thalamocortical tracts (from medial geniculate nucleus to V1) were inconsistent.…”