Cutaneous reflex responses and their central nervous pathways studied in man

Area of Science:

• Neuroscience
• Human Physiology
• Motor Control

Background:

• Cutaneous reflexes are involuntary responses to skin stimulation.
• Understanding these reflexes aids in diagnosing neurological disorders.
• The pathways and central processing of cutaneous reflexes are not fully elucidated.

Purpose of the Study:

• To investigate the neurophysiological pathways of cutaneous reflex responses in human muscles.
• To differentiate between spinal and supraspinal contributions to cutaneous reflexes.
• To correlate reflex alterations with specific central nervous system lesions.

Main Methods:

• Recorded cutaneous reflex responses in the first dorsal interosseous and extensor digitorum brevis muscles.
• Stimulated digital nerves of the index finger and second toe, respectively.
• Compared responses in healthy subjects and patients with central nervous system lesions.

Main Results:

• Cutaneous reflexes exhibited distinct short and long latency components.
• Short latency excitation and inhibition in the first dorsal interosseous muscle appear to have spinal origins.
• Long latency excitation in the first dorsal interosseous muscle is dependent on supraspinal pathways, including the dorsal columns and motor cortex.

Conclusions:

• Short latency cutaneous reflexes have spinal pathways, with inhibitory interneurons under descending extrapyramidal control.
• Long latency cutaneous reflexes originate supraspinally, requiring dorsal column transmission, sensori-motor cortex relay, and corticospinal tract descending pathways.
• Lesions in the dorsal columns, motor cortex, or corticospinal tract significantly alter specific components of these cutaneous reflexes.