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Lower limb cutaneous polysynaptic reflexes in the child, according to age and state of waking or sleeping
Insights
This study shows how infant reflex responses change with age and sleep state. Muscle reflex patterns in children evolve significantly from birth to three years, differing between awake and sleeping states.
Area of Science:
- Neuroscience
- Developmental Biology
- Physiology
Background:
- Understanding developmental changes in human reflexes is crucial for assessing neurological maturation.
- Electromyographic studies provide objective measures of neural pathway function.
Purpose of the Study:
- To investigate age- and state-dependent changes in lower limb reflex responses in infants and young children.
- To characterize the development of polysynaptic reflexes (R II and R III) in the tibialis anterior and short head of the femoral biceps muscles.
Main Methods:
- Electromyography (EMG) was used to record muscle activity in response to electrical stimulation of the skin in the lower limb.
- Studies were conducted on children aged 3 days to 3 years, both awake and asleep (REM and non-REM stages).
- Stimulation targeted the cutaneous area around the toes, with recordings from tibialis anterior and short head of the femoral biceps muscles.
Main Results:
- In awake infants, stimulation evoked polysynaptic discharges (R II and R III) in both muscles.
- From birth to one year, the tibialis anterior showed a lower activation threshold, with a predominant flexion reflex pattern.
- After 20 months, the tibialis anterior threshold increased, surpassing that of the short head of the biceps, mirroring adult patterns.
- Sleep significantly altered reflex responses: R II responses were depressed, and R III responses were also depressed or absent in non-REM sleep.
- R III responses persisted in REM sleep in infants but were abolished in older children.
Conclusions:
- Lower limb reflex patterns undergo significant maturation from infancy through early childhood.
- Sleep state profoundly influences the excitability and expression of spinal reflexes in developing humans.
- These findings provide normative data for developmental changes in human motor control and reflex pathways.
Abstract:
An electromyographic study of reflex responses elicited by stimulation of an area of skin in the lower limb was undertaken in awake or sleeping children from 3 days to 3 years of age. Recordings were made on the tibialis anterior and the short head of the femoral biceps. In the awake child, electrical stimulation of the cutaneous area around the toes evoked polysynaptic discharges (R II and R III) in both muscles. From birth to one year of age, the threshold for the tibialis anterior was much lower than for the short head of biceps, and the flexion reflex pattern predominated. After 20 months of age, the recruitment pattern for polysynaptic responses was different: the threshold for tibialis anterior increased and became higher than for the short head of biceps, as in the adult. In sleeping children, the most striking feature was the depression of R II responses. In non-REM sleep, R III responses also were depressed, with a similar threshold in both muscles, and even disappeared during deep sleep. In REM sleep, R III responses were present in babies, but seemed to be abolished in older children.