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Cross-correlation analysis of motor unit activity recorded from two separate thumb muscles during development in man
J Gibbs1, L M Harrison, J A Stephens
1Department of Physiology, University College London, UK.
Insights
Motor unit control of thumb muscles matures through childhood, with common neural drive developing by age 4 and refining until age 15. This neural maturation correlates with improved fine motor skills in children.
Area of Science:
- Neuroscience
- Motor Control
- Developmental Biology
Background:
- The development of fine motor skills, particularly thumb function, is crucial for daily activities.
- Understanding the neural control mechanisms underlying thumb abduction and extension in children is essential for identifying developmental trajectories.
Purpose of the Study:
- To investigate the maturation of motor control in the thumb abductor muscles during childhood.
- To examine the relationship between neural drive to thumb muscles and the development of independent finger movements.
Main Methods:
- Surface electromyography (EMG) was used to record multi-unit activity from the abductor pollicis brevis and abductor pollicis longus muscles in 75 children (4-15 years) and 9 adults.
- Cross-correlation analysis of motor unit discharges was performed to assess common input to motoneurons.
- Sequential finger-to-thumb opposition tasks were timed to evaluate fine motor skill performance.
Main Results:
- A common drive to the motoneurone pools innervating the thumb abductor muscles was prevalent in most subjects, indicated by central peaks in cross-correlograms.
- The prevalence and size of these common drive peaks increased with age from 4 to 15 years, with peak size stabilizing around age 10.
- The duration of the common drive signal decreased with age, and a weak positive correlation was found between common drive strength and the speed of sequential finger movements in children.
Conclusions:
- The neural control of thumb abduction and extension undergoes significant maturation during childhood, characterized by the development and refinement of common input to motoneurons.
- This developmental process of neural maturation is associated with improved fine motor control, specifically in tasks requiring independent finger movements.
- The findings provide insights into the neurophysiological basis of developing hand dexterity in children.
Abstract:
1. Multi-unit surface EMG signals were recorded from the short and long thumb abductor muscles of seventy-five children aged from 4 to 15 years and from nine adults during simultaneous abduction and extension of the left and right thumb. Ability to perform independent finger movements was investigated by timing a series of sequential finger-to-thumb oppositions. 2. Cross-correlograms were constructed from the discharges of motor units recorded from the long and short abductor muscles acting on the same thumb. In the majority of subjects, short duration central peaks were present indicating the presence of a common drive to the motoneurone pools innervating these two muscles. Except for those subjects aged 4 and 5 years, the size of these central correlogram peaks did not differ significantly between the dominant and non-dominant hands. 3. The prevalence of central cross-correlogram peaks in different subjects increased from the age of 4 years to 15 years. The size of the central cross-correlogram peak increased with age up to 10 years but did not alter significantly after this age. The duration of the central peak steadily decreased over the age range of 4 to 15 years. 4. Multilinear regression analysis of data recorded from children revealed that there was a positive, but weak, correlation between the size of the cross-correlogram peak and the rate of performance of sequential finger movements after having controlled for age.