Introduction

Functional magnetic resonance imaging (fMRI) of early and late blind participants is used to localize the processes involved in phonological processing for noun pair antonyms and synonyms. Cortical reorganization takes place due to neurological or ophthalmological disorders, which may be compensated by other senses [3,5]. This study is to assess cross-modal plasticity related to two age groups 6-12 years and 13-19 years if any, for auditory reorganization prevalence in visually-impaired children.

Objective

To evaluate the performance of auditory perception and language processing in early and late blind subjects in comparison to sighted controls for two age range (6-12 years and 13-19 years) by using functional magnetic resonance imaging.

Materials and method

Twenty early blind (EB) and Twenty late blind (LB) subjects and fifteen sighted controls (SC) (all right handed) in two age groups 6-12 years and 13-19 years were recruited from the clinics of our institute (Table 1). Standard diagnostic and exclusion criteria were followed. Functional MRI scans were conducted on standard clinical 3T whole body MR scanner (Achieva 3.0T TX, Philips, Netherlands) with the subjects in supine position. For Phonological processing: Patients were presented with antonyms and synonym noun pairs, through auditory cue with the help of E-prime and MR compatible headphone and microphones (NordicNeuroLab, Norway). Single-shot echo planar imaging (EPI) sequence was used for the functional MRI studies to study the Blood oxygen level dependent (BOLD) effects in the whole brain. (Number of slices: 30, slice thickness 4.5 mm; TR: 2000 ms, TE: 30 ms, FOV: 231.7 mm, flip angle: 90°, Number of Dynamics: 192, resolution: 64 x 64) was used for the BOLD sessions. Pre- and post-processing was carried out using SPM8 (Wellcome Department of Cognitive Neurology, London, UK). The BOLD clusters were converted from MNI template to the Talairach and Tornoux coordinates, for estimation of anatomical areas. One-way Anova test (p<0.001, cluster threshold 10) was used for group analysis.

Results

During synonyms task EB1, EB2, LB2 subjects showing bilateral activation in visual cortical areas, primary and auditory association cortex, dorsal posterior cingulate cortex, somatosensory association cortex. Also right hemisphere found in area including , thalamus, superior temporal gyrus, brainstem, superior frontal gyrus, and precentral gyrus, while left hemisphere response in inferior parietal lobule, insula, precuneus, cerebellum, associative visual cortex (v3,v4,v5), premotor cortex and supplementary motor area, medial frontal gyrus.LB1, EB1 showed BOLD response prominently in left hemisphere cerebellum, middle frontal gyrus, parahippocampal gyrus, precuneus, superior temporal gyrus, thalamus and in right cingulate gyrus, medial frontal gyrus. During antonyms task EB2, LB2, and EB1 show bilateral activation in superior temporal gyrus but cerebellum, precuneus was active in LB1. Right lentiform nucleus, brainstem and left inferior parietal lobule, parahippocampal gyrus was also active in both groups (EB and LB), however right in, and left medial frontal gyrus, parahippocampal gyrus, middle occipital gyrus, precuneus, thalamus, cerebellum, middle frontal gyrus, superior middle frontal gyrus, inferior middle frontal gyrus was active in early blind (EB1, EB2). For antonyms task bold activation in late blind (LB1 and LB2) was located in right cuneus, inferior frontal gyrus, middle frontal gyrus, parahippocampal gyrus, precentral gyrus, superior frontal gyrus, superior temporal gyrus and left activity in fusiform gyrus, inferior parietal lobule, lingual gyrus, medial frontal gyrus, middle temporal gyrus, parahippocampal gyrus.

Discussion

The lexical semantic task, activate peripheral regions of visual cortex in all age range 6-12 and 13-19 years age range in both early blind and late blind groups. EB1<EB2 and LB2 subjects attended to sound sources suggesting functional connections between auditory cortex and visual cortex required to process language associated with sound sources. Blood oxygen- level dependent (BOLD) activity in 6-12 years age range in EB1 and LB1 suggesting auditory association areas are involved in the auditory processing of language suggesting that phonological processing does not always necessarily recruit Broca’s area. The involvement of Broca’s area in phonological processing may be a function of task demands [3]. Semantically associated antonyms noun pair word evoked robust activity throughout visual cortical regions for blind people; The lexical semantic task elicited greater activity in medial cortical areas that have been possible due to participants may be covertly vocalized heard words when trying to remember common meanings or antonyms [1]. In late and early blind groups of 13-19 years age range, the lexical semantic task elicited stronger activity in the posterior left inferior frontal gyrus adjoining the middle frontal gyrus, and nearby inferior parts of the pre-central gyrus helping in finding the level of difficulty [2]. Recently, it has also been suggested that the cerebellum is involved in purely sensory tasks, such as visual and auditory motion perception [4].

Acknowledgements

DST funding agency