Differential control of sympathetic outflow to muscle and skin during physical and cognitive stressors

Abstract

Purpose: Sympathetic nerve activity towards muscle (MSNA) and skin (SSNA) regulates various physiological parameters. MSNA primarily functions in blood pressure and flow, while SSNA operates in thermoregulation. Physical and cognitive stressors have been shown to have effects on both types of sympathetic activity, but there are inconsistencies as to what these effects are. This article aims to address the discrepancies in the literature and compare MSNA and SSNA responses.

Methods: Microelectrode recordings were taken from the common peroneal nerve in 29 participants: MSNA (n = 21), SSNA (n = 16) and both MSNA and SSNA (n = 8). Participants were subjected to four different 2-min stressors: two physical (isometric handgrip task, cold pressor test) and two cognitive (mental arithmetic task, Stroop colour-word conflict test), the latter of which saw participants separated into responders and non-responders to the stressors. It was hypothesised that the physical stressors would have a greater effect on MSNA than SSNA, while the cognitive stressors would operate conversely.

Results: Peristimulus time histogram (PSTH) analysis showed the mental arithmetic task to significantly increase both MSNA and SSNA; the isometric handgrip task and cold pressor test to increase MSNA, but not SSNA; and Stroop test to have no significant effects on changing MSNA or SSNA from baseline. Additionally, stress responses did not differ between MSNA and SSNA in participants who had both sets of data recorded.

Conclusions: This study has provided evidence to support the literature which claims cognitive stressors increase sympathetic activity, and provides much needed SSNA data in response to stressors.

Keywords: Cognitive stress; Peristimulus time histogram; Physical stress; Sympathetic nerve activity.

Fig. 1

MSNA spikes during each stressor. MSNA spikes, as revealed through PSTH analysis, are shown for 50 R-wave time periods before, at the start, at the end and after a the handgrip task (n = 21), b the cold pressor test (n = 18), c the mental arithmetic task (n = 16) and d the Stroop colour–word test conflict (n = 20). Significant differences between time periods are indicated with an asterisk (*P < 0.05; **P < 0.01). Results are presented as mean ± SD

Fig. 2

SSNA spikes during each stressor. SSNA spikes, as revealed through PSTH analysis, are shown for 50 R-wave time periods before, at the start, at the end and after a the handgrip task (n = 16), b the cold pressor test (n = 14), c the mental arithmetic task (n = 12) and d the Stroop colour–word conflict test (n = 16). Significant differences between time periods are indicated with an asterisk (*P < 0.05; **P < 0.01). Results are presented as mean ± SD