Focal transcranial magnetic stimulation (TMS) was used to map the motor cortical outputs to the right and left first dorsal interosseous (FDI) and right abductor digiti minimi (ADM) muscles of the reading hand in 6 blind proficient Braille readers studied at the National Institute of Neurological Disorders and Stroke, NIH, Bethesda, MD. All subjects had learned Braille before age 13, using the right index finger for character recognition and the left index for line keeping. Comparison of cortical output maps obtained on working days and off days showed that the maps for the FDI of the reading hand were significantly larger in the evening after the working shift than in the morning after having not worked for 2 days. The map shrunk following vacation days and enlarged following a return to work. On control days, the motor threshold for the muscles stayed constant, whereas on the work day, the motor thresholds for the right FDI were significantly lower in the evening study session after practice than in the morning test before practice. The results illustrate the rapid modulation in motor cortical outputs effected by Braille reading. [1]

COMMENT. The authors emphasize the critical importance of timing when looking for changes in neural networks associated with learning skills. Learning a new skill requires plastic changes and rapid modulation of intracortical connections that result in temporary enlargement of the cortical motor output. These neurophysiological changes are supported by PET scanning studies in the same laboratory, showing that Braille reading is associated with an increased activation of the sensorimotor and striate cortex contralateral to the reading hand. (Sadato N et al. 1995).