Previous studies indicated that laser acupuncture (LA) may effectively treat various medical conditions. However, brain responses associated with LA intervention have not been fully investigated. This study is focused on the effect of LA with different energy density (ED) in brain using resting-state functional magnetic resonance imaging (fMRI). We hypothesized that different ED would elicit various brain responses. We enrolled healthy adults participants and selected bilateral PC6 (Neiguan) as the intervention points. LA was applied, respectively, with ED of 0, 7.96, or 23.87 J/cm2. Two 500-s resting-state fMRI scans were acquired before and after intervention, respectively. The functional connectivity (FC) was calculated between autonomic nerve system-regulation associated brainstem structures and other brain regions. Compared to other dosages, the FC between rostral ventrolateral medulla and orbitofrontal cortex has more enhanced; the FC between caudal ventrolateral medulla, nucleus of the solitary tract/nucleus ambiguus, and dorsal motor nucleus of the vagus and somatosensory area has more weakened when ED was 23.87 J/cm2. Different dosages of LA have demonstrated varied regions of FC changes between regions of interest and other brain areas, which indicated that variations in EDs might influence the clinical efficacy and subsequent impacts through distinct neural pathways within the brain.

Blood pressure is tightly controlled by the central nervous system, particularly the brainstem. The aim of this study was to investigate the relationship between mean blood pressure (MBP), muscle sympathetic nerve activity (MSNA) and resting regional brain activity in healthy human subjects. Pseudocontinuous arterial spin labeling and functional magnetic resonance imaging of the brain were performed immediately following a laboratory microneurography recording of MSNA and BP measurement in 31 young, healthy normotensive subjects. Regional cerebral blood flow (CBF) correlated significantly with resting MBP levels in the region encompassing the rostroventrolateral medulla (RVLM), dorsolateral pons, and insular, prefrontal and cingulate cortices. Functional connectivity analysis revealed that the ventrolateral prefrontal cortex displayed greater resting connectivity strength within the RVLM in the lower compared with the higher MBP group. No significant differences in CBF were found when subjects were divided based on their MSNA levels. These results suggest that even subtle differences in resting MBP are associated with significant differences in resting activity in brain regions, which are well known to play a role in cardiovascular function. These data raise the question of the potential long-term consequences of differences in regional brain activity levels and their relationship with systemic blood pressure.

The baroreceptor reflex controls spontaneous fluctuations in blood pressure. One major control variable of the baroreflex is the sympathetic vasoconstrictor activity to muscles [MSNA; burst frequency (BF) and burst incidence (BI)], which can be quantitatively assessed by microneurography. We aimed to investigate the central regions involved in baroreflex regulation of MSNA. Healthy men (mean age 25 years) participated in three experimental sessions. (i) Microneurography recordings of MSNA from the left peroneal nerve during rest and baroreflex unloading, induced by lower body negative pressure (LBNP; -40 mmHg). If MSNA could be reliably recorded throughout this procedure (n = 15), the subjects entered the positron emission tomography (PET) experiments. The two PET sessions took place in a randomised order. Cerebral glucose metabolism (18-fluorodeoxyglucose) was analysed after: (ii) baroreflex unloading (LBNP); and (iii) control condition (lying in the LBNP chamber without suction). The PET data were analysed employing SPM8. LBNP elicited a significant increase in MSNA in all successfully recorded subjects (BI: P = 0.001; F = 5.54; BF: P < 0.001; F = 36.59). As compared with the control condition, LBNP was associated with increased PET regional glucose metabolism bilaterally in the orbitofrontal cortex (OFC; BA 11, 47). Related to the rise of BF, there was increased activation of the left OFC (BA 11); related to the rise of BI there was increased activation of the brainstem corresponding to the rostral ventrolateral medulla. Our data support a role for the ventrolateral medulla and the OFC in baroreflex-mediated control of MSNA in humans.