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The maturation of cutaneous reflexes studied in the upper limb in man
Insights
Newborns exhibit powerful cutaneous reflexes in forearm muscles, unlike adults. This study tracks the maturation of these reflexes, linking them to corticospinal tract development in children.
Area of Science:
- Neuroscience
- Developmental Biology
- Human Physiology
Background:
- Cutaneous reflex responses are fundamental neurological pathways.
- Understanding reflex development in infants is crucial for assessing neurological maturation.
- Previous research has not fully detailed the developmental trajectory of cutaneous reflexes in early childhood.
Purpose of the Study:
- To investigate and characterize cutaneous reflex responses in forearm muscles of infants and children.
- To compare reflex patterns in newborns, infants, and children with normal development and those with upper motor neuron lesions.
- To elucidate the relationship between cutaneous reflex maturation and the development of the corticospinal tract.
Main Methods:
- Electrical stimulation of the fingers was used to elicit cutaneous reflex responses.
- Electromyography (EMG) recordings were obtained from forearm flexor and extensor muscles.
- Subjects included premature infants, term infants, and children aged 6 weeks to 11 years, including those with upper motor neuron lesions.
Main Results:
- Newborns displayed potent, synchronous reflex responses in both flexor and extensor muscles.
- Similar synchronous reflex responses were observed in individuals with upper motor neuron lesions, but not in normal adults.
- Reflex latency remained stable, but response amplitude decreased in the first year; long-latency responses emerged by the second year.
Conclusions:
- The developing corticospinal tract significantly influences the maturation of cutaneous reflex responses.
- Abnormal reflex patterns in infants and those with neurological conditions highlight the importance of reflex assessment.
- The study provides insights into the neurodevelopmental timeline of sensorimotor integration in early life.
Abstract:
Cutaneous reflex responses have been recorded from forearm flexor and extensor muscles following electrical stimulation of the fingers. Recordings have been made from premature infants, term infants and children between the age of 6 weeks and 11 years. In the new-born, stimulation of the fingers elicits such a powerful reflex that, in general, individual stimuli will evoke a reflex synchronous action potential in both forearm flexor and extensor muscles. Individual stimuli delivered to the fingers also elicit reflex synchronous muscle action potentials in forearm flexor and extensor muscles in patients with clinical signs of upper motor neurone lesion affecting the upper limb; this has not been observed in normal adult subjects. The latency of the reflex response in the term infant is about 18 msec. Comparison of this value with the latency of the tendon jerk for these muscles would indicate a central delay for the cutaneous reflex of about 3 msec. The latencies of the cutaneous reflex and tendon jerk remain constant over the first 5 years of life. The size of the short-latency cutaneous reflex response decreases progressively over the first year of life. In the second year of life stimulation of the fingers produces long- as well as short-latency increases in recorded muscle electrical activity. The maturation of the cutaneous reflex response is discussed in terms of the maturation of function of the corticospinal tract.