Habituation of cutaneomuscular reflexes recorded from the first dorsal interosseous and triceps muscle in man

Cutaneomuscular reflexes have been recorded from the first dorsal interosse ous muscle during a sustained abduction of the index finger of 20 subjects (25 recordings) following stimulation of the digital nerves at the followin g frequencies: 2 Hz, 3 Hz, 5 Hz, 7 Hz and 9 Hz, presented in random order. Five hundred stimuli were given at each frequency. EMG was rectified and co nsecutive batches of 100 sweeps of each set of 500 responses were averaged time locked to the stimulus. All reflex components, E1, I1 and E2, exhibit habituation with the E1 component habituating the most and the I1 component the least. There was considerable variation in the rate of habituation bet ween subjects. The rate of habituation was independent of the frequency of stimulation. Reflex responses were recorded from the triceps brachii muscle in eight subjects; this reflex response habituated at a faster rate than t he E2 component recorded from the first dorsal interosseous muscle. These r esults are discussed in relation to the choice of stimulus parameters for t he clinical testing of cutaneous reflexes. We conclude that it is important to consistently average the same number of responses. (C) 2000 Elsevier Sc ience B.V. All rights reserved.