Neuroplasticity associated with tactile language communication in a deaf-blind subject

Souzana Obretenova

doi:10.3389/neuro.09.060.2009

Abstract

A long-standing debate in cognitive neuroscience pertains to the innate nature of language development and the underlying factors that determine this faculty. We explored the neural correlates associated with language processing in a unique individual who is early blind, congenitally deaf, and possesses a high level of language function. Using functional magnetic resonance imaging (fMRI), we compared the neural networks associated with the tactile reading of words presented in Braille, Print on Palm (POP), and a haptic form of American Sign Language (haptic ASL or hASL). With all three modes of tactile communication, indentifying words was associated with robust activation within occipital cortical regions as well as posterior superior temporal and inferior frontal language areas (lateralized within the left hemisphere). In a normally sighted and hearing interpreter, identifying words through hASL was associated with left-lateralized activation of inferior frontal language areas however robust occipital cortex activation was not observed. Diffusion tensor imaging -based tractography revealed differences consistent with enhanced occipital-temporal connectivity in the deaf-blind subject. Our results demonstrate that in the case of early onset of both visual and auditory deprivation, tactile-based communication is associated with an extensive cortical network implicating occipital as well as posterior superior temporal and frontal associated language areas. The cortical areas activated in this deaf-blind subject are consistent with characteristic cortical regions previously implicated with language. Finally, the resilience of language function within the context of early and combined visual and auditory deprivation may be related to enhanced connectivity between relevant cortical areas.

Highlights

There is well-documented evidence for extensive crossmodal neuroplastic changes following sensory deprivation in individuals with early onset blindness or deafness
To help disentangle the neural correlates associated with tactile communication from the crossmodal changes related to multiple sensory deprivation, we investigated haptic ASL (hASL) language processing in an individual highly proficient in this form of communication but with normal visual and auditory development
Tactile identification of hASL words for subject A.B. was associated with robust bihemispheric activation that included multiple sensory, motor and language areas

Summary

Introduction

There is well-documented evidence for extensive crossmodal neuroplastic changes following sensory deprivation in individuals with early onset blindness or deafness. It appears that there is functional recruitment of cortical areas normally associated with the processing of the lost sensory modality by the remaining intact senses. These neuroplastic changes can be adaptive and compensatory in nature (Rauschecker, 1995; Bavelier and Neville, 2002; Pascual-Leone et al, 2005). The functional relevance of crossmodal sensory cortical recruitment is supported by evidence of task specific impairment of performance when activity in these regions is disrupted either transiently by repetitive transcranial magnetic stimulation (rTMS) (Cohen et al, 1997; Amedi et al, 2004) or permanently by circumscribed lesions of these cortical areas (Hamilton et al, 2000; Hickok et al, 2002)

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Conclusion