Unraveling the Temporal Interplay of Slow-Paced Breathing and Prefrontal
Transcranial Direct Current Stimulation on Cardiac Indices of Autonomic
Activity
Abstract
The neurovisceral integration model proposes that information flows
bidirectionally between the brain and the heart via the vagus nerves and
vagally-mediated heart rate variability (vmHRV) can be used to index
heart-brain interaction. Recent research has shown that voluntary
reduction of breathing rate (slow-paced breathing, SPB) can enhance
cardiac vagal control. Additionally, prefrontal transcranial direct
current stimulation (tDCS) can modulate the excitability of the
prefrontal region and influence the vagus nerve. However, fundamental
research on the combination of SPB and prefrontal tDCS to increase vmHRV
and other physiological indices of the autonomic nervous system is
scarce. Therefore, 200 healthy participants were assigned to four
experimental groups. Each group received either 20 min of active or sham
tDCS combined with 5.5 breath per minute (BPM) or 15 BPM breathing.
Regardless of the tDCS condition, the SPB group showed a significant
increase in vmHRV over 20 minutes, suggesting an increase in
parasympathetic activity. In addition, a significant decrease in HR at
the first and second 5-minute epochs of the intervention. Regardless of
breathing condition, the active tDCS group exhibited higher HR at the
fourth 5-minute epoch of the intervention compared to the sham tDCS
group, suggesting more sympathetic arousal. However, there was no
combined effect on vmHRV, HR, skin conductance, or blood pressure. SPB
is a robust technique for increasing vmHRV, whereas prefrontal tDCS may
produce effects that counteract those of SPB. More research is necessary
to test whether and how top-down and bottom-up approaches can be
combined to improve vagal control.