Key result
Mental concentration and arousal stimuli increased impulse frequency of spontaneously active sympathetic nerve units and initiated firing in previously silent units.
Observational
This physiological study demonstrates that single unit sympathetic nerve activity in human skin responds dynamically to mental and physical arousal stimuli.
Mental arousal may modulate cutaneous vasomotor tone; leaves open its clinical relevance in autonomic testing.
Single unit activity in sympathetic nerve fibres was studied in microelectrode recordings from intact cutaneous nerves in alert man. 4 units exhibited a “spontaneous” discharge of very low frequency (not exceeding 15 imp/min) during resting conditions, whereas 4 other units were silent. Mental concentration and arousal stimuli of different types caused an increase in impulse frequency of spontaneously active units, and previously silent units started firing. In reflex responses to electrical shocks, deep breathing and loud noises, single units often fired repeatedly in bursts, the maximal instantaneous frequency observed being 35 imp/s. Intense reflex responses to electrical stimulation were sometimes followed by a suppression of spontaneous activity for 1–2 s. Some of the units probably had a sudomotor function, since the unit activity correlated well with changes in galvanic skin resistance recorded within the innervation zone of the explored nerve fascicle. The conduction velocity measured for 6 sympathetic units ranged 1.0–0.58 m/s.
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Hallin et al. (1974) reported an observational. Mental concentration and arousal stimuli vs. Resting conditions was evaluated on Single unit activity in sympathetic nerve fibres. Mental concentration and arousal stimuli increased impulse frequency of spontaneously active sympathetic nerve units and initiated firing in previously silent units.
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