Proceedings of The Physiological Society
King's College London (2009) Proc Physiol Soc 14, C19
Developmental changes and functional role of 6-12 Hz oscillatory modulation of human slow hand movements
S. F. Farmer1,2, J. A. Stephens3, K. M. Deutsch3
1. Institute of Neurology, University College London, London, United Kingdom. 2. Clinical Neuroscience, Imperial College Healthcare NHS Trust, London, United Kingdom. 3. Department of Physiology, University College London, London, United Kingdom.
In humans slow hand and finger movements are characterized by 6-12 Hz discontinuities visible in raw records and spectra of motion signals such as acceleration (Valbo & Wessberg, 1993; Kakuda et al., 1999). This pulsatile behavior is correlated with motor unit synchronization at 6-12 Hz as shown by significant coherence at these frequencies between pairs of motor units and between the motor units/surface EMG and the acceleration recorded from the limb part controlled by the muscle. We have studied the developmental profile of 6-12 Hz oscillations during static contraction and slow wrist extension and flexion movements though spectral analysis of EMG and acceleration signals. We recorded simultaneous extensor carpi radialis (ECR) EMG and wrist acceleration from 67 subjects aged between 4 and 25 years during either a steady wrist extension task or slow externally paced wrist flexion and extension movements. Subjects were divided into 4 age ranges: 4-6 years (n=21), 7-9 years (n=15), 10-14 years (n=11) and adults (20-25 years, n= 20). In all subjects we compared the EMG-acceleration coherence recorded during slow wrist movements to that recorded during steady wrist extension against gravity. We also measured the speed of repetitive fine finger movements. During steady wrist extension and slow movement, EMG-acceleration coherence increases with age. In adults and older children, compared to steady muscle contraction, wrist movement produced greater additional 6-12 Hz oscillatory drive. In adults, there was significant coherence between ECR EMG and wrist acceleration in the range 6-12 Hz, maximal at 8-9 Hz (see Figure 1). In the age ranges 7-9 years and 10-14 years coherence magnitude values were less than those of the adult subjects. EMG-acceleration data from children aged 4-6 years showed little movement related coherence in the frequency range 6-12 Hz. Statistical comparison using ANOVA and the Chi2 difference of coherence test revealed statistically significant (P<0.05) increases in movement induced coherence with increasing age. The strength of 6-12 Hz EMG-acceleration slow movement-induced coherence was positively correlated with age (see Figure 2) and speed of fine finger movements. We have shown that 6-12 Hz coherence and the pulsatile control of human movement increase with maturity. This study provides further evidence that oscillations in the human motor system increase with development. We suggest that with age peripheral oscillations are incorporated into a developing oscillatory neural network, which may have implications for normal human motor development and age-related increases in movement velocity.
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