Acquisition of a new motor skill is accompanied by changes incutaneomuscular reflex responses recorded from finger muscles in man

Cutaneomuscular reflex (CMR) responses and motor unit synchronisation have been recorded to investigate possible reorganisation of central nervous pat hways in six healthy adults learning a novel skill with the non-dominant ha nd. Multi-unit surface EMG signals were recorded from first dorsal inteross eous (1DI) and abductor digiti minimi (ADM) muscles during sustained flexio n of the index finger and abduction of the little finger (flex/ab) and duri ng bilateral controlled finger abduction (ab/ab). CMR responses were elicit ed by concomitant stimulation of the digital nerves of the index finger at 2.5 times threshold for perception. For training purposes the subject pract ised the novel flex/ab task phasically at a rate of 1 Hz for 10 min daily f or 12 days. Cortically mediated components of the CMR responses recorded fr om 1DI and ADM were significantly larger in both muscles during training. T aking the data for all subjects together, when subjects performed sustained flex/ab (novel task), the size of the Il and E2 components were increased by 25 and 55% in 1DI and 192 and 167% in ADM (Mann-Whitney Li-test. P<0.05) . Corresponding values for sustained ab/ab were more modest: 31 and 16% in 1DI and 88 and 54% in ADM. Changes in the size of the spinal Fl component w ere not the same in each muscle: values for sustained flex/ab and ab/ab wer e 33 and 31% Smaller in 1DI and 89 and 59% larger in ADM. No significant ch anges were found in the amount of synchrony of motor unit firing between 1D I and ADM when subjects performed either task during training. These result s suggest that learning a new motor skill produces changes which take place predominantly in the cortical pathways of the CMR and these may be due to changed connectivity within motor and/or sensory cortex which has previousl y been shown in the monkey.