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Relationship between stimulus strength and the cutaneous silent period
1Neurophysiology Laboratories, Brigham and Women's Hospital, Boston, MA 02115.
Muscle & Nerve
|March 1, 1993
Summary
A painful electrical stimulus is needed to trigger the cutaneous silent period (CSP) during muscle activity. This study suggests A delta nerve fibers are essential for evoking the CSP, with their potentials detectable in sensory action potentials.
Area of Science:
- Neuroscience
- Human Physiology
- Electrophysiology
Background:
- The cutaneous silent period (CSP) is a brief cessation of muscle activity following a painful cutaneous stimulus.
- Evoking a CSP typically requires a stimulus perceived as painful.
Purpose of the Study:
- To investigate the relationship between stimulus intensity, sensory action potential (SAP) morphology, and subjective experience in evoking the CSP.
- To determine the characteristics of sensory nerve fibers involved in CSP generation.
Main Methods:
- Single sural nerve stimuli were applied to evoke CSP in the soleus muscle.
- Near-nerve electrodes recorded sural SAPs to capture activity from slow-conducting fibers (including A delta fibers) and A alpha fibers.
- Stimulus strength was systematically varied relative to pain and CSP thresholds.
Main Results:
- Stimulus intensities 8-10 times threshold were required to evoke a CSP, with pain threshold slightly lower.
- Sensory action potential (SAP) morphology changed with stimulus strength, showing increased amplitude and more prominent late components at higher intensities.
- Conduction velocities of 15-20 m/s, indicative of A delta fibers, were observed at or below CSP threshold intensities.
Conclusions:
- Activation of sensory axons within the A delta fiber conduction velocity range is necessary for evoking the CSP.
- The potentials generated by these A delta fibers can be identified within the recorded sural SAP, providing insight into CSP mechanisms.