Efficacy and safety of trigeminal parasympathetic pathway stimulation for dry eye: A systematic review and meta-analysis.

This study aimed to investigate the efficacy and safety of trigeminal parasympathetic pathway (TPP) stimulation in the treatment of dry eye. A comprehensive search for randomized clinical trials was performed in seven databases (MEDLINE, Embase, CENTRAL, etc.) up to 28 February 2023. After screening the suitable studies, the data were extracted and transformed as necessary. Data synthesis and analysis were performed using Review Manager 5.4, and the risk of bias and quality of evidence were evaluated with the recommended tools. Fourteen studies enrolling 1714 patients with two methods (electrical and chemical) of TPP stimulation were included. Overall findings indicate that TPP stimulation was effective in reducing subjective symptom score (standardized mean difference [SMD], -0.45; 95% confidence interval [CI], -0.63 to -0.28), corneal fluorescence staining (mean difference [MD], -0.78; 95% CI, -1.39 to -0.18), goblet cell area (MD, -32.10; 95% CI, -54.58 to -9.62) and perimeter (MD, -5.90; 95% CI, -10.27 to -1.53), and increasing Schirmer's test score (SMD, 0.98; 95% CI, 0.65 to 1.31) and tear film break-up time (SMD, 0.57; 95% CI, 0.19 to 0.95). Compared to inactive or low-activity stimulation controls, it has a higher incidence of adverse events. Therefore, TPP stimulation may be an effective treatment for dry eye, whether electrical or chemical. Adverse events are relatively mild and tolerable. Due to the high heterogeneity and low level of evidence, the current conclusions require to be further verified.

Do manual therapies have a specific autonomic effect? An overview of systematic reviews.

BACKGROUND: The impact of manual therapy interventions on the autonomic nervous system have been largely assessed, but with heterogeneous findings regarding the direction of these effects. We conducted an overview of systematic reviews to describe if there is a specific autonomic effect elicited by manual therapy interventions, its relation with the type of technique used and the body region where the intervention was applied. METHODS: We conducted an overview according to a publicly registered protocol. We searched the Cochrane Database of Systematic Reviews, MEDLINE, EPISTEMONIKOS and SCOPUS, from their inception to march 2021. We included systematic reviews for which the primary aim of the intervention was to assess the autonomic effect elicited by a manual therapy intervention in either healthy or symptomatic individuals. Two authors independently applied the selection criteria, assessed risk of bias from the included reviews and extracted data. An established model of generalisation guided the data analysis and interpretation. RESULTS: We included 12 reviews (5 rated as low risk of bias according the ROBIS tool). The findings showed that manual therapies may have an effect on both sympathetic and parasympathetic systems. However, the results from included reviews were inconsistent due to differences in their methodological rigour and how the effects were measured. The reviews with a lower risk of bias could not discriminate the effects depending on the body region to which the technique was applied. CONCLUSION: The magnitude of the specific autonomic effect elicited by manual therapies and its clinical relevance is uncertain. We point out some specific recommendations in order to improve the quality and relevance of future research in this field.

Transcutaneous electrical acupoint stimulation applied in lower limbs decreases the incidence of paralytic ileus after colorectal surgery: A multicenter randomized controlled trial.

BACKGROUND: Postoperative paralytic ileus prolongs hospitalization duration, increases medical expenses, and is even associated with postoperative mortality; however, effective prevention of postoperative paralytic ileus is not yet available. This trial aimed to assess the preventative effectiveness of transcutaneous electrical acupoint stimulation applied in the lower limbs on postoperative paralytic ileus incidence after colorectal surgery. METHODS: After ethics approval and written informed consent, 610 patients from 10 hospitals who were scheduled for colorectal surgery between May 2018 and September 2019 were enrolled. Patients were randomly allocated into the transcutaneous electrical acupoint stimulation (stimulated on bilateral Zusanli, Shangjuxu, and Sanyinjiao acupoints in lower limbs for 30 minutes each time, total 4 times) or sham (without currents delivered) group with 1:1 ratio. The primary outcome was postoperative paralytic ileus incidence, defined as no flatus for >72 hours after surgery. RESULTS: Compared to the sham treatment, transcutaneous electrical acupoint stimulation lowered the postoperative paralytic ileus incidence by 8.7% (32.3% vs 41.0%, P = .026) and decreased the risk of postoperative paralytic ileus by 32% (OR, 0.68; P = .029). Transcutaneous electrical acupoint stimulation also shortened the recovery time to flatus, defecation, normal diet, and bowel sounds. Transcutaneous electrical acupoint stimulation treatment significantly increased median serum acetylcholine by 55% (P = .007) and interleukin-10 by 88% (P < .001), but decreased interleukin-6 by 47% (P < .001) and inducible nitric oxide synthase by 42% (P = .002) at 72 hours postoperatively. CONCLUSION: Transcutaneous electrical acupoint stimulation attenuated the postoperative paralytic ileus incidence and enhanced gastrointestinal functional recovery, which may be associated with increasing parasympathetic nerve tone and its anti-inflammatory actions.

Beneficial Effects of Yoga Stretching on Salivary Stress Hormones and Parasympathetic Nerve Activity.

This study aimed to determine the effect of yoga stretching on salivary stress hormones and cardiac autonomic nervous system. To our knowledge, this study is the first to investigate changes in cardiac autonomic nervous system after yoga stretching. In this crossover design study, 10 adult men (age, 26.3 ± 2.5 years) without yoga experience participated in the rest and yoga trials for 90 min. Measurements were carried out before (pre), immediately (post), 60 min, and 120 min after rest or yoga stretching. Saliva samples were collected by chewing a sterile cotton ball at a frequency of 60 cycles per minute. Salivary cortisol and testosterone concentrations were measured using an enzyme-linked immunosorbent assay. With the subjects in the sitting position, heart rate variability was measured using pulse analyzer plus for 150 seconds. As regards rate changes, salivary testosterone level tended to increase (p = 0.088), testosterone/cortisol ratio significantly increased (p < 0.05), and cortisol level significantly decreased (p < 0.05) at 120 min after yoga stretching. The square root of the mean-squared differences of successive normal-to-normal intervals and natural logarithm high-frequency component, which are indicators of parasympathetic nerve activity, increased at 60 min (p < 0.05) and 120 min (p < 0.05) in the yoga trial, respectively. In conclusion, yoga stretching can enhance parasympathetic nerve activity and improve stress hormones. Therefore, yoga stretching may be useful to compensate for physical inactivity and increase life expectancy in the general population.

Moving beyond belief: A narrative review of potential biomarkers for transcutaneous vagus nerve stimulation.

Transcutaneous vagus nerve stimulation (tVNS) is a non-invasive neurostimulation technique that is currently being tested as a potential treatment for a myriad of neurological and psychiatric disorders. However, the working mechanisms underlying tVNS are poorly understood and it remains unclear whether stimulation activates the vagus nerve for every participant. Finding a biological marker of tVNS is imperative, as it can help guide research on clinical applications and can inform researchers on optimal stimulation sites and parameters to further optimize treatment efficacy. In this narrative review, we discuss five potential biomarkers for tVNS and review currently available evidence for these markers for both invasive and tVNS. While some of these biomarkers hold promise from a theoretical perspective, none of the potential biomarkers provide clear and definitive indications that tVNS increases the vagal activity or augments activity in the locus coeruleus-noradrenaline network. We conclude the review by providing several recommendations for how to tackle the challenges and opportunities when researching potential biomarkers for the effects of tVNS.

The mindful attention and awareness scale is associated with lower levels of high-frequency heart rate variability in a laboratory context.

Trait mindfulness has been associated with well-being. A key component of trait mindfulness is intentional attention and awareness which is most commonly measured by the Mindful Attention and Awareness Scale (MAAS). This study investigated the relationship between the MAAS and cardiovascular (HF-HRV, heart rate) reactivity to two laboratory stressors that evoked different patterns of change in heart rate (HR). One stressor (viewing a video of a surgery) evoked HR deceleration while the other stressor (mental arithmetic) evoked HR acceleration. Undergraduate students completed the MAAS and were then exposed to the two stressors while ECG (electrocardiography) was recorded. Findings support the reliability of the stressors to induce expected differential cardiovascular responses and explicate the role of parasympathetic activation. Further, a main effect for MAAS was observed indicating that across laboratory conditions, persons scoring higher on the MAAS had lower HF-HRV relative to persons scoring lower on the MAAS. These findings suggest that higher levels of intentional attention and awareness in a laboratory context might promote parasympathetic withdrawal because these participants were more vigilant, experienced higher cognitive load, and detected more threat cues. Implications for the MAAS and cardiovascular responses to stress are discussed.

The Role of Heart Rate Variability in Mindfulness-Based Pain Relief.

Mindfulness meditation is a self-regulatory practice premised on sustaining nonreactive awareness of arising sensory events that reliably reduces pain. Yet, the specific analgesic mechanisms supporting mindfulness have not been comprehensively disentangled from the potential nonspecific factors supporting this technique. Increased parasympathetic nervous system (PNS) activity is associated with pain relief corresponding to a number of cognitive manipulations. However, the relationship between the PNS and mindfulness-based pain attenuation remains unknown. The primary objective of the present study was to determine the role of high-frequency heart rate variability (HF HRV), a marker of PNS activity, during mindfulness-based pain relief as compared to a validated, sham-mindfulness meditation technique that served as a breathing-based control. Sixty-two healthy volunteers (31 females; 31 males) were randomized to a 4-session (25 min/session) mindfulness or sham-mindfulness training regimen. Before and after each group's respective training, participants were administered noxious (49°C) and innocuous (35°C) heat to the right calf. HF HRV and respiration rate were recorded during thermal stimulation and pain intensity and unpleasantness ratings were collected after each stimulation series. The primary analysis revealed that during mindfulness meditation, higher HF HRV was more strongly associated with lower pain unpleasantness ratings when compared to sham-mindfulness meditation (B = -.82, P = .04). This finding is in line with the prediction that mindfulness-based meditation engages distinct mechanisms from sham-mindfulness meditation to reduce pain. However, the same prediction was not confirmed for pain intensity ratings (B = -.41). Secondary analyses determined that mindfulness and sham-mindfulness meditation similarly reduced pain ratings, decreased respiration rate, and increased HF HRV (between group ps < .05). More mechanistic work is needed to reliably determine the role of parasympathetic activation in mindfulness-based pain relief as compared to other meditative techniques. Perspective: Mindfulness has been shown to engage multiple mechanisms to reduce pain. The present study extends on this work to show that higher HRV is associated with mindfulness-induced reductions in pain unpleasantness, but not pain intensity ratings, when compared to sham-mindfulness meditation. These findings warrant further investigation into the mechanisms engaged by mindfulness as compared to placebo.

Radial Pulse and Electrocardiography Modulation by Mild Thermal Stresses Applied to Feet: An Exploratory Study with Randomized, Crossover Design.

OBJECTIVE: To investigate the changes in radial pulse induced by thermal stresses (TSs). METHODS: Sixty subjects were enrolled. Using an open-label, 2×2 crossover randomization design, both feet of each subject were immersed in 15 °C water for cold stress (CS) and in 40 °C water for heat stress (HS) for 5 min each. Radial pulse, respiration and electrocardiogram (ECG) signals were recorded before, during and immediately after the TSs. RESULTS: The analysis of heart rate variability revealed that CS increased the low-frequency (LF) and high-frequency (HF) components (P <0.05) and that HS reduced the LF and HF components (P <0.01). Both TSs reduced the normalized LF, increased the normalized HF, and reduced the LF/HF ratio. The differences in the ECG signals were more dominant during the TS sessions, but those in the radial pulse signals became more dominant immediately after the TS sessions. CS decreased the pulse depth (P <0.01) and increased the radial augmentation index (P <0.1), and HS increased the pulse pressure (P <0.1) and subendocardial viability ratio (P <0.01). There were no significant differences in pulse rate during the three time sequences of each TS. The respiration rate was increased (P <0.1), and the pulse rate per respiration (P/R ratio) was significantly decreased (P <0.05) with CS. The HF region (10-30 Hz) of the pulse spectral density was suppressed during both TSs. CONCLUSIONS: CS induced vasoconstriction and sympathetic reactions, and HS induced vasodilation and parasympathetic reactions. Based on definitions used in pulse diagnosis, we made the novel discoveries that the pulse became slower (decreased P/R ratio), more floating and tenser under CS and that the HF region of the spectral power decreased significantly under both TSs.

The effect of increased parasympathetic activity on perceived duration.

Theories of human temporal perception suggest that changes in physiological arousal distort the perceived duration of events. Behavioural manipulations of sympathetic nervous system (SNS) activity support this suggestion, however the effects of behavioural manipulations of parasympathetic (PSNS) activity on time perception are unclear. The current study examined the effect of a paced respiration exercise known to increase PSNS activity on sub-second duration estimates. Participants estimated the duration of negatively and neutrally valenced images following a period of normal and paced breathing. PSNS and SNS activity were indexed by high-frequency heart-rate variability and pre-ejection period respectively. Paced breathing increased PSNS activity and reduced the perceived duration of the negative and neutrally valenced stimuli relative to normal breathing. The results show that manipulations of PSNS activity can distort time in the absence of a change in SNS activity. They also suggest that activities which increase PSNS activity may be effective in reducing the perceived duration of short events.

Chemogenetic manipulation of parasympathetic neurons (DMV) regulates feeding behavior and energy metabolism.

Parasympathetic nervous system (PNS) innervates with several peripheral organs such as liver, pancreas and regulates energy metabolism. However, the direct role of PNS on food intake has been poorly understood. In the present study, we investigated the role of parasympathetic nervous system in regulation of feeding by chemogenetic methods. Adeno associated virus carrying DREADD (designer receptors exclusively activated by designer drugs) infused into the target brain region by stereotaxic surgery. The stimulatory hM3Dq or inhibitory hM4Di DREADD was over-expressed in selective population of dorsal motor nucleus of the vagus (DMV) neurons by Cre-recombinase-dependent manners. Activation of parasympathetic neuron by intraperitoneal injection of the M3-muscarinic receptor ligand clozapine-N-oxide (CNO) (1 mg/kg) suppressed food intake and resulted in body weight loss in ChAT-Cre mice. Parasympathetic neurons activation resulted in improved glucose tolerance while inhibition of the neurons resulted in impaired glucose tolerance. Stimulation of parasympathetic nervous system by injection of CNO (1 mg/kg) increased oxygen consumption and energy expenditure. Within the hypothalamus, in the arcuate nucleus (ARC) changed AGRP/POMC neurons. These results suggest that direct activation of parasympathetic nervous system decreases food intake and body weight with improved glucose tolerance.

A whole-brain map of long-range inputs to GABAergic interneurons in the mouse medial prefrontal cortex.

The medial prefrontal cortex (mPFC) contains populations of GABAergic interneurons that play different roles in cognition and emotion. Their local and long-range inputs are incompletely understood. We used monosynaptic rabies viral tracers in combination with fluorescence micro-optical sectioning tomography to generate a whole-brain atlas of direct long-range inputs to GABAergic interneurons in the mPFC of male mice. We discovered that three subtypes of GABAergic interneurons in two areas of the mPFC are innervated by same upstream areas. Input from subcortical upstream areas includes cholinergic neurons from the basal forebrain and serotonergic neurons (which co-release glutamate) from the raphe nuclei. Reconstruction of single-neuron morphology revealed novel substantia innominata-anteromedial thalamic nucleus-mPFC and striatum-anteromedial thalamic nucleus-mPFC circuits. Based on the projection logic of individual neurons, we classified cortical and hippocampal input neurons into several types. This atlas provides the anatomical foundation for understanding the functional organization of the mPFC.

Understanding mind-body disciplines: A pilot study of paced breathing and dynamic muscle contraction on autonomic nervous system reactivity.

Mind-body disciplines such as yoga, Tai Chi, and Qigong have been demonstrated to activate the parasympathetic nervous system, but it remains unclear how these practices achieve these results, whether by breathing, movement, or some combination. This pilot study establishes a model to examine the individual and combined effects of paced breathing and rhythmic skeletal muscle contraction on the activation of the parasympathetic system during a cognitive stressor. Male participants were randomly assigned to one of four preconditioning groups: (a) paced breathing alone, (b) alternating upper extremity muscle contractions, (c) paced breathing synchronized with alternating contractions, or (d) a neutral control task. Autonomic response was assessed by heart rate variability during a standardized cognitive stressor. The alternating contraction group had 71.7% higher activation of parasympathetic signal over respiration alone (p < .001). Alternating contractions synchronized with breathing demonstrated 150% higher parasympathetic activation than control (p < .0001). Comparing the contraction alone and synchronized groups, the synchronized group demonstrated 45.9% higher parasympathetic response during a cognitive stressor (p < .001). In conclusion, paced breathing synchronized with rhythmic muscle contraction leads to more resilient activation of the parasympathetic response than either alternating contractions or breathing alone, which may help explain the stress reducing benefits of mind-body disciplines.

Voluntary upregulation of heart rate variability through biofeedback is improved by mental contemplative training.

Regulation of the parasympathetic nervous system, indexed through high frequency heart rate variability (HF-HRV), is indicative of physical and psychological health. However, little is known about the trainability of this capacity. We investigated the effects of a 9-month mental training program (the ReSource Project; n = 298) on voluntary HF-HRV upregulation, assessed with a novel biofeedback procedure. The program consisted of attentional, interoceptive, socio-affective and socio-cognitive training elements, all of which potentially influence parasympathetic regulation. Based on known links between oxytocin and parasympathetic activity, we also explored the relationship of HF-HRV upregulation to the oxytocin receptor system. We found that HF-HRV during the biofeedback session increased after 3 months of training, concomitant with prolonged respiration cycles. Breathing-controlled changes in HF-HRV upregulation, indicative of improved parasympathetic control, were significantly increased after 6 months of training. Homozygous risk allele carriers (AA) of the oxytocin receptor gene polymorphism rs53576 showed initially lower parasympathetic control, but fully compensated for their initial deficits through the training. No changes were found for HF-HRV at rest. Our data demonstrate that a mental training intervention extending over several months can increase the capacity for voluntary regulation of HF-HRV, with important implications for improving individual and societal health.

Physiological Effects of Viewing Bonsai in Elderly Patients Undergoing Rehabilitation.

The benefits of various nature-derived stimuli that can be used for stress relief and relaxation has recently gained immense attention; however, there are very few studies about their influence on elderly patients. The present study aims to present the effects of viewing bonsai on autonomic nervous activity, prefrontal cortex activity, and subjective assessment findings of psychological relaxation in elderly patients undergoing rehabilitation. Fourteen participants aged 64⁻91 years (mean age ± standard deviation, 78.6 ± 9.6 years) participated in this study. Miniature potted 10-year-old Japanese cypress bonsai trees were used as visual stimuli. Participants viewed the bonsai for 1 min, and the control comprised of no experimental stimulus. Physiological effects on autonomic nervous activity were assessed by measuring the heart rate variability (HRV) and pulse rate. The effects on prefrontal cortex activity were determined using near-infrared spectroscopy, which involved assessment of oxyhemoglobin concentrations in the left and right prefrontal cortices. Subjective evaluations were achieved by the modified semantic differential method. Viewing bonsai resulted in a significant increase in parasympathetic nervous activity, a significant decrease in sympathetic nervous activity, and a significant increase in the perceptions of feeling "comfortable" and "relaxed." In conclusion, our findings indicated that viewing bonsai induces physiological and psychological relaxation.

Reducing Lethal Force Errors by Modulating Police Physiology.

OBJECTIVES: The aim of this study was to test an intervention modifying officer physiology to reduce lethal force errors and improve health. METHODS: A longitudinal, within-subjects intervention study was conducted with urban front-line police officers (n = 57). The physiological intervention applied an empirically validated method of enhancing parasympathetic engagement (ie, heart rate variability biofeedback) during stressful training that required lethal force decision-making. RESULTS: Significant post-intervention reductions in lethal force errors, and in the extent and duration of autonomic arousal, were maintained across 12 months. Results at 18 months begin to return to pre-intervention levels. CONCLUSION: We provide objective evidence for a physiologically focused intervention in reducing errors in lethal force decision-making, improving health and safety for both police and the public. Results provide a timeline of skill retention, suggesting annual retraining to maintain health and safety gains.

Effects of maternity yoga on the autonomic nervous system during pregnancy.

AIM: To elucidate the changes in the daily variation seen in the autonomic nervous system during pregnancy brought about by maternity yoga and to evaluate how maternal yoga affects stress and sleep. METHODS: A prospective, longitudinal study was conducted between January 2013 and December 2014. Pregnant women who were attending maternity yoga classes at Palmore Hospital between 20 and 23 weeks' gestation were enrolled as the yoga group, and a matched control group was also enrolled. Study participants completed questionnaires, including a perceived stress scale and sleep logs, during their second and third trimesters. Heart rate variability and salivary α-amylase levels were evaluated as stress indices at 20-23 weeks' gestation, 28-31 weeks' gestation and 36-40 weeks' gestation. RESULTS: A total of 38 women were in the yoga group, with 53 in the control group. At 28-31 weeks' gestation, heart rate variability during night and late-night periods was significantly higher in the yoga group than in the control group. At 36-40 weeks' gestation, variability between the morning, afternoon and late night was significantly higher in the yoga group. Salivary α-amylase levels decreased significantly immediately after practicing yoga during all evaluation periods in the yoga group. Night-time sleep duration was significantly longer in the yoga group. CONCLUSION: Our results suggest that practicing yoga activates the parasympathetic nervous system during the third trimester of pregnancy, consolidating sleep during the night and decreasing α-amylase levels, which indicates reduced stress.

Vagal Mediation of Low-Frequency Heart Rate Variability During Slow Yogic Breathing.

OBJECTIVE: Changes in heart rate variability (HRV) associated with breathing (respiratory sinus arrhythmia) are known to be parasympathetically (vagally) mediated when the breathing rate is within the typical frequency range (9-24 breaths per minute [bpm]; high-frequency HRV). Slow yogic breathing occurs at rates below this range and increases low-frequency HRV power, which may additionally reflect a significant sympathetic component. Yogic breathing techniques are hypothesized to confer health benefits by increasing cardiac vagal control, but increases in low-frequency HRV power cannot unambiguously distinguish sympathetic from parasympathetic contributions. The aim of this study was to investigate the autonomic origins of changes in low-frequency HRV power due to slow-paced breathing. METHODS: Six healthy young adults completed slow-paced breathing with a cadence derived from yogic breathing patterns. The paced breathing took place under conditions of sympathetic blockade, parasympathetic (vagal) blockade, and placebo. HRV spectral power was compared under 11 breathing rates during each session, in counterbalanced order with frequencies spanning the low-frequency range (4-9 bpm). RESULTS: HRV power across the low-frequency range (4-9 bpm) was nearly eliminated (p = .016) by parasympathetic blockade (mean (SD) spectral power at breathing frequency = 4.1 (2.1)) compared with placebo (69.5 (8.1)). In contrast, spectral power during sympathetic blockade 70.2 (9.1) and placebo (69.5 (8.1)) was statistically indistinguishable (p = .671). CONCLUSIONS: These findings clarify the interpretation of changes in HRV that occur during slow-paced breathing by showing that changes in low-frequency power under these conditions are almost entirely vagally mediated. Slow-paced breathing is an effective tool for cardiac vagal activation.

EFFECTS OF CONVERSATIONAL HYPNOSIS ON RELATIVE PARASYMPATHETIC TONE AND PATIENT COMFORT DURING AXILLARY BRACHIAL PLEXUS BLOCKS FOR AMBULATORY UPPER LIMB SURGERY:A Quasiexperimental Pilot Study.

This two-center quasiexperimental pilot study was to determine the effect of conversational hypnosis on patient comfort and parasympathetic tone, which may represent a quantitative measure of hypnotic depth, during regional anesthesia. The patients received conversational hypnosis in one center and oral premedication in the other. The patients' subjective comfort (0-10 rating scale) and objective parasympathetic tone, as assessed by the Analgesia/Nociception Index (ANI), were measured before and after regional anesthesia. The parasympathetic tone and comfort scores evidenced a significantly greater increase in the hypnosis patients than in controls. These findings suggest that using conversational hypnosis during regional anesthesia may be followed by a subjective increase in patient comfort and an objective increase in parasympathetic tone, monitored by ANI.

Physiological Effects of Visual Stimulation with Forest Imagery.

This study was aimed to clarify the physiological effects of visual stimulation using forest imagery on activity of the brain and autonomic nervous system. Seventeen female university students (mean age, 21.1 ± 1.0 years) participated in the study. As an indicator of brain activity, oxyhemoglobin (oxy-Hb) concentrations were measured in the left and right prefrontal cortex using near-infrared time-resolved spectroscopy. Heart rate variability (HRV) was used as an indicator of autonomic nervous activity. The high-frequency (HF) component of HRV, which reflected parasympathetic nervous activity, and the ratio of low-frequency (LF) and high-frequency components (LF/HF), which reflected sympathetic nervous activity, were measured. Forest and city (control) images were used as visual stimuli using a large plasma display window. After sitting at rest viewing a gray background for 60 s, participants viewed two images for 90 s. During rest and visual stimulation, HRV and oxy-Hb concentration in the prefrontal cortex were continuously measured. Immediately thereafter, subjective evaluation of feelings was performed using a modified semantic differential (SD) method. The results showed that visual stimulation with forest imagery induced (1) a significant decrease in oxy-Hb concentrations in the right prefrontal cortex and (2) a significant increase in perceptions of feeling "comfortable," "relaxed," and "natural."

Parasympathetic activation enhanced by slow respiration modulates early auditory sensory gating.

Sensory gating is a preattentional mechanism to filter irrelevant information from the environment. It is typically reflected as a suppression of the event-related P50 component for successive sounds in the auditory modality. Although stress-induced sympathetic activation has been reported to disrupt P50 suppression, little is known about the modulatory effect of parasympathetic activation on early auditory sensory gating. We determined the parasympathetic effect on the magnetic P50 (P50m) suppression by controlling the respiratory rhythm and recording data simultaneously with magnetoencephalography and electrocardiography, using three successive click sounds as stimulus and ten normal individuals as study participants. The respiratory rhythm was guided by visual cues and set at 0.3, 0.25, or 0.2 Hz for distinct auditory stimulus sequence blocks. Heart rate variability analysis showed that slow respiration leads to significantly large high-frequency power, which is known as the parasympathetic index, whereas low-frequency/high-frequency ratio, known as the sympathetic index, did not differ with the respiratory rhythm. Although P50m suppression was observed in the left and right primary auditory areas for every respiratory condition, the left P50m intensity for the first sound was significantly decreased in the case of slow respiration, thereby indicating disruption of the left P50m suppression. Since background alpha oscillatory power, reflecting the arousal level, was similar for every respiratory rhythm, it is concluded that parasympathetic activation enhanced by slow respiration modulates P50m gating by reducing the initial neural sensitivity for an auditory input. Not only sympathetic but also parasympathetic effects should be considered in the evaluation of P50/P50m biomarkers.