Abstract
Prefrontal cortex activity has been associated with changes to heart rate variability (HRV) via mediation of the cortico-subcortical pathways that regulate the parasympathetic and sympathetic branches of the autonomic nervous system. Changes in HRV due to altered prefrontal cortex functioning can be predicted using the neurovisceral integration model, which suggests that prefrontal hyperactivity increases parasympathetic tone and decreases contributions from the sympathetic nervous system. Working memory (WM) tasks and transcranial direct current stimulation (tDCS) have been used independently to modulate brain activity demonstrating changes to HRV in agreement with the model. We investigated the combined effects of prefrontal tDCS and a WM task on HRV. Bifrontal tDCS was administered for 15 minutes at 2mA to 20 participants in a sham controlled, single-blind study using parallel groups. A WM task was completed by participants at three time points; pre-, during-, and post-tDCS, with resting state data collected at similar times. Frequency-domain HRV was computed for high frequency (HF; 0.15–0.4Hz) and low frequency (LF; 0.04–0.15Hz) power reflecting parasympathetic and sympathetic branch activity, respectively. Response time on the WM task, but not accuracy, improved from baseline to during-tDCS and post-tDCS with sham, but not active, stimulation. HF-HRV was significantly increased in the active tDCS group compared to sham, lasting beyond cessation of stimulation. Additionally, HF-HRV showed a task-related reduction in power during performance on the WM task. Changes in LF-HRV were moderately inversely correlated (r > 0.4) with changes in WM accuracy during and following tDCS compared to baseline levels. Stimulation of the prefrontal cortex resulted in changes to the parasympathetic branch of the nervous system in agreement with a linearly additive interpretation of effects. Sympathetic activity was not directly altered by tDCS, but was correlated with changes in WM performance. This suggests that the parasympathetic and sympathetic branches respond differentially due to similar, but distinct neural pathways. Given the ease of HRV data collection, studies of prefrontal tDCS would benefit from collection of this data as it provides unique insight into tDCS effects resulting from propagation through brain networks.
Highlights
Heart rate variability (HRV), an index of cardiac adaptation to allostatic load, is known to be regulated by the prefrontal cortex such that changes in prefrontal cortex functioning show measurable effects on heart rate variability (HRV) [1]
Whether brain stimulation of the prefrontal cortex alters HRV at rest, whether these effects outlast the period of stimulation, and what the combined effect of both prefrontal cortex brain stimulation and a task known to predominantly engage regions of the prefrontal cortex is on the autonomic nervous system
This study investigated the combined effects of prefrontal transcranial direct current stimulation (tDCS) and a cognitive task known to activate the prefrontal cortex on heart rate variability in healthy participants
Summary
Heart rate variability (HRV), an index of cardiac adaptation to allostatic load, is known to be regulated by the prefrontal cortex such that changes in prefrontal cortex functioning show measurable effects on HRV [1]. The prefrontal cortex is known to modulate brain regions involved in the regulation of autonomic nervous system activity, such as heart rate [4] Both parasympathetic and sympathetic branches of the nervous system are mediated by cortical-subcortical pathways which involve the prefrontal cortex, the anterior cingulate cortex, the insula, the hypothalamus, and the brainstem [5]. Hyper-activation of the prefrontal cortex inhibits the sympathoexcitatory circuit of the amygdala, which is known to have outputs relevant to autonomic regulation [1]. This in turn reduces sympathetic activity and parasympathetic suppression, culminating in a reduction in heart rate
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