Publication:

Functional asymmetry in sensory discrimination in visually blind and its association to braille reading

Background In health, human somatosensory modality is symmetrically distributed. But highly specialised functions like skilled movements, visual sensation while reading show lateralisation. In visually blind population somatosensory modality is used for specialised function like braille reading. Thus present study was undertaken to assess somatosensory modality in visual blind & to find out its association to braille reading.

Methods 60 visually blind participants were assessed. Detailed history about motor dominance, preferred braille finger was asked. 2 point discrimination (2PD) test was done in all 10 fingers using weber compass. 30 normal visioned controls were assessed for comparison. Unpaired t-test was used for analysis.

Results Most participants (n=44) chose finger from right hand as preferred finger for braille reading; this was unrelated to motor handedness. In visually blind population average values of 2PD in right hand was significantly (p<0.001) less than right. In normal visioned subjects there was no significant difference in sensory discrimination between right and left hand.

Conclusions Due to presence of language areas in left hemisphere (90-92% of people), all our language related modalities are inclined toward left hemisphere. Here we proved that blind people prefer right hand over left hand while reading written braille language and thus have better sensory discrimination for same. Previous studies have shown that blindness itself acts as stimulus to activate latent pathways (cross-modal plasticity) between somatosensory cortex, visual cortex and language areas. Overall we tried to prove brain is hardwired to do all language related activities preferably with right hand.