Sympathetic activity is influenced by task difficulty and stress perception during mental challenge in humans.

Abstract

SUMMARY1. Our aim was to determine the influence of the type of task, the absolute and relative difficulty of the task, and the perceived stress associated with performance of the task on sympathetic circulatory regulation during cognitive challenge in humans.2. Sympathetic nerve activity to skeletal muscle (MSNA) determined from peroneal microneurography, heart rate and arterial blood pressure were recorded continuously in twelve subjects during a modified Stroop colour word test (CWT) and mental arithmetic (MA), each performed over six levels of increasing absolute task difficulty. Performance (percentage correct) on each task was assessed and ratings of perceived stress obtained. Responses to CWT and MA were compared at similar levels of performance and perceived stress. 3. MSNA decreased at task onset, remained below baseline levels at low levels of difficulty which were not perceived as stressful, increased above baseline levels at higher levels of difficulty which were perceived as stressful, and increased further during recovery. Thus, the regulation of MSNA was stress dependent. At similar levels of stress perception there were no differences in MSNA between CWT and MA. Although performance declined as task difficulty increased, there was no particular 'threshold' level of performance associated with the stimulation of MSNA.4. Arterial pressure and heart rate were elevated above baseline levels throughout the mental tasks. Arterial pressure increased over the first 3-4 levels of each task and then plateaued whereas heart rate did not vary across increasing levels of task difficulty. Heart rate and arterial pressure responses to CWT were higher than those to MA.5. These data demonstrate that during cognitive challenge the stimulation of MSNA is governed primarily by perceived stress which is dependent, in part, on the absolute level of task difficulty. In contrast, neither performance nor the type of cognitive task appear to be important determinants of MSNA. Arterial pressure is influenced by the task and level of difficulty. Heart rate is independent of task difficulty but may be task dependent.

Effects of cognitive challenge on self‐directed behaviors by chimpanzees (Pan troglodytes)

“…The present study tested the generality of the ethological model described above by investigating the influence of task difficulty on SDBs by chimpanzees, in a nonsocial context. Research with humans has demonstrated that manipulations of such factors as uncertainty and task difficulty increase sympathetic nervous system (SNS) activation [Callister et al, 1992;Esler et al, 1989;Gotthardt et al, 1995;Sausen et al, 1991]. Physiological measures such as plasma cortisol, plasma ACTH, catechoamines, heart rate, and blood pressure have been demonstrated to increase with increases in task difficulty.…”

Rate of cardiovascular recovery to combined or separate orthostatic and mental challenges

“…Thus, inefficient recovery may eventually result in unfavorable physical sequelae. On the other hand, the observation of bradycardia below pre-stimulus levels after the removal of mental challenge (Callister et al, 1992) might also have cardiological implications, because myocardial infarction often occurs at low heart rates (Deanfield et al, 1984). In this connection, it seems relevant to also describe typical patterns of recovery in young and healthy individuals.…”

Individual Differences in Physiological Responses and Type A Behavior Pattern.

“…Typical cardiovascular responses are elevation of heart rate, blood pressure, and respiration rate. Mental stress also induces several autonomic responses (Callister et al, 1992), and modify immune and endocrine functions. It is well known that there are individual differences in magnitude and/or direction of stress responses.…”