Cognitive abilities affect everyday life and being able to perform mental tasks efficiently, is important for psychological well-being. These abilities include mental workload, attention, multitasking ability, reasoning, etc. (Tucker-Drob, 2009). Excessive stress affects autonomic and cardiovascular function, which is connected to impaired cognitive and mental functions (da Silva et al., 2009; Delliaux et al., 2019). However, for intended results in task performance, mental faculties and cognitive performance necessitate a certain amount of stress (Atkinson, 1957). Previous research suggested that elevated heart rate variability (HRV) mitigates the effect of mental stress on frontal lobe functions (McIntosh et al., 2021). The HRV is a promising index of cardiac autonomic activity that reflects oscillatory intervals between consecutive heartbeats. The beat-to-beat interactions (i.e., R-R interval) reflect the parasympathetic nervous system (PNS) and the sympathetic nervous system (SNS) input from sinoatrial nodes (Shaffer and Ginsberg, 2017). The dynamic interaction of R-R intervals has frequently been linked with various mind–body interventions that include yoga breathing practices also (Raghuraj and Telles, 2008; Pal et al., 2014; Bhagat et al., 2017). A recent study has shown that slow yoga breathing increases parasympathetic activity and baroreflex sensitivity in yoga practitioners compared to naïve (Anasuya et al., 2020).

Yoga breathing is a three-step method that manipulates nostril breathing: deep inhalation (puraka), complete exhalation (rechaka), and the cessation of breath (khumbhaka). Hatha yogic books have described several slow yoga breathing techniques (Muktibodhananda, 1998; Saraswati, 2012) and in the current study, we focused on the most convenient and popular type of yoga breathing techniques, i.e., (i) alternate nostril breathing (Nadisodhana; ANB), (ii) right nostril breathing (Suryanuloma-viloma; RNB), and (iii) breath awareness (BAW). The manipulations in yoga breathing allow alteration in autonomic activity and higher-order cognitive functions that are yet to be fully understood. The relationship between the R-R interval of autonomic measures following RNB and ANB has been explored in previous investigations (Raghuraj and Telles, 2008; Pal et al., 2014). The authors reported that RNB practice has sympathomimetic effects that were expressed by increased heart rate (HR), metabolism, and O₂ consumption (Telles et al., 1994; Sarang and Telles, 2006), while the practice of ANB at a fixed rate of 5 breaths per min (BPM) showed higher low frequency (LF) power, LF/HF ratio, and a lower high frequency (HF) power of HRV measures (Sharma et al., 2014; Vinay et al., 2016). In contrast, Srivastava et al. reported that practice of 15 min of ANB for 8 weeks reduces HR, indicating a parasympathetic activity (Srivastava et al., 2005). Overall studies suggest that RNB practice increases SNS and ANB increases PNS activity (Lee and Ghiya, 2012; Bhavanani et al., 2014). However, there is a scarcity of research that has explored how slow yoga breathing techniques influence neurocognitive activities. A few research investigations suggest that yoga breathing affects autonomic activity, which may also alter brain functions that include attention and memory (Raghuraj et al., 1998; Santhanam Kumar et al., 2020). A previous investigation has revealed that the practice of ANB improves the performance in the target detection task (evaluated through the P300 oddball task) compared to the BAW session (Telles et al., 2013). According to the studies cited above, yoga breathing not only alters sympathetic or parasympathetic autonomic activity but also enhances mental performance. As far as we know there is no study that has explored the influence of slow yoga breathing (SYB) simultaneously on mental load during working memory and changes in autonomic indices of HRV. Hence, the present study aimed to evaluate the effect of slow yoga breathing practices (SYB) at a fixed rate of approx. 6 bpm simultaneously on: (1) working memory, (2) HRV in different working memory conditions, and (3) HRV during SYB sessions.

To our knowledge, this is the first study to investigate the immediate effect of SYB practice simultaneously on mental workload with working memory tasks and changes in the measures of HRV. The study results revealed that SYB at 6 bpm significantly increases SNS activity and improves mental processes during working memory performance. Our findings indicate that practicing yoga breathing can increase the physiological load, i.e., linked to the significant increase in SNS activity. SNS activity was moderately elevated during the mental load in the present study which is required to complete working memory tasks efficiently (Knight et al., 2020). This has been reflected in the results by faster reaction time (ms) in working memory performance with better accuracy, suggesting that slow yoga breathing through one nostril may improve mental functioning in young adults (Giuliano et al., 2018). Therefore, it can be suggested that the SYB practice may enhance processing speed and the ability to discriminate between target and non-target events in the complex n-back task, particularly in the 2-back condition.

According to previous research, cognitive tasks require significant levels of sympathetic activity or parasympathetic inhibition to complete the task (Berntson et al., 1996; Melis and Van Boxtel, 2001; Melis and van Boxtel, 2007). Parasympathetic withdrawal is associated with “feed-forward” input from higher brain centers to the medullary cardiovascular center that triggers a rapid increase in heart rate which is mediated by temporarily reduced cardiac parasympathetic neural activity. However, sympathetic activation is triggered with moderate to maximal intensity of practice and mediated by the systemic sympathoadrenal activation (Billman, 2013; White and Raven, 2014). During working memory performance, HRV results indicate parasympathetic withdrawal after ANB and RNB breathing practice. That may be linked to improving performance on a task that needs more mental effort. In addition to this, after BAW there was a decrease in reaction time for the 2-back task without any statistically significant changes in accuracy.

An earlier study demonstrated that participants practicing yoga breathing at a rate of 6 bpm showed sympathetic arousal which might be due to an increase in physiological load during yogic breathing (Raghuraj and Telles, 2008). Overall, the findings showed that slow breathing considerably raises the LF power and LF/HF ratio, reflecting the predominance of sympathetic activity and sympathovagal balance, respectively. Slow yoga breathing directly influences vagal tone or baroreflex sensitivity that modulate the sinoatrial node, thereby increasing HR oscillation and HRV (Bernardi et al., 2001). The ANB and RNB showed a temporary withdrawal of parasympathetic activity and a concomitant increase in HR that can be linked to higher baroreflex sensitivity and oxygen saturation (Mason et al., 2013). Further, slow breathing studies have demonstrated beneficial effects on cardiorespiratory functions in patients with cardiac surgery, prehypertension, asthma, and major depressive disorder (Karavidas et al., 2007; Lin et al., 2012). The findings of the present study are consistent with the previous study (Lin et al., 2014) which implies that slow yoga breathing practices may be beneficial for the physical and mental health of clinically healthy individuals, mainly due to improvements in the subjective feeling of relaxation. However, the mechanism of action of yoga breathing on autonomic and cognition is not fully understood.

In the neurovisceral integration model, greater parasympathetic activity is linked to selective attention, whereas heightened sympathetic activity is associated with an efficient attention-related processing (Giuliano et al., 2018). In line with the aforementioned findings, we observed that cognitive task performance was improved after slow and controlled SYB (ANB and RNB) sessions, and even after a simple BAW session. The SYB practice may activate specific brain regions such as the dorsal pons, periaqueductal grey matter, cerebellum, hypothalamus, thalamus, lateral and anterior insular cortices in the human brain as revealed in the volitional controlled slow breathing study (Nagai et al., 2015). A recent study reported that yoga breathing and meditation increase synchronization between respiratory and attentional systems via LC activity thereby improving attentional, emotional, and physiological functioning (Melnychuk et al., 2018). Moreover, unilateral yoga breathing at a slow rate (5–8 bpm) demonstrated increased oxygenation and blood volume in the left prefrontal cortex (PFC) after the RNB session as compared to the BAW session (Singh et al., 2015). Though speculation, the above-mentioned brain areas may be associated with the enhancement of autonomic functions during yoga breathing and while performing a neurocognitive task. There might be several other pathways involved in yoga breathing practice that directly or indirectly influence autonomic activity and cognitive functions that needs to be explored in future studies.

A number of limiting factors are likely to account for the current study: the sample size was relatively small, also the lack of a control group (those never exposed to yoga practice), and study outcomes are limited to male yoga practitioners only. Further, during the neurocognitive task, the remnant effect of the practice block could not be ruled out due to technical limitations. The results cannot be extrapolated to generalize the neurocognitive performance as a whole because they are restricted to the immediate impact of yoga breathing practice on neurocognitive function. Moreover, the autonomic changes during pre n-back task might have a carryover effect on HRV in breathing sessions, which should be controlled in a further study. Furthermore, the study findings can only be generalized to healthy individuals and future studies could concentrate on participants with depression or people with mental health issues. Future research should extend the present methodology to a wider array of experimental tasks and examine simultaneous assessments of HRV, and brain imaging techniques (fMRI, fNIRS, or EEG) related to the long-term practice of meditation and yoga breathing. However, within our study, SYB sessions increased parasympathetic withdrawal which was reflected in the improvement of working memory performance when compared with spontaneous breathing in the BAW session.

The present study empirically showed cardiac autonomic arousal during SYB among yoga practitioners. Additionally, moderate SNS activation may support physiological arousal, which is necessary for efficient mental functioning and working memory performance. The outcome of the study suggests that yoga breathing may have the potential to enhance coping abilities by optimizing heightened physiological arousal and facilitating attentional processes. Therefore, SYB may be useful for bringing positive changes in the autonomic activity related to clinical conditions (dysautonomia, attention deficit hyperactive disorder [ADHD], and major depressive disorder [MDD]), which should be investigated in future studies. Furthermore, SYB immediate practice prior to a mental task may facilitate better responses to autonomic activity that is associated with neurocognitive performance.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Institutional Ethics Committee of SVYASA - RES/IEC-SVYASA/009/2015. The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

SD: conceptualization, funding acquisition, methodology, project administration, formal analysis, data curation, validation, interpretation of the data, and writing—original drafting of the work. RB: acquisition, resources, software for analysis, supervision, and validation. All authors contributed to the article and approved the submitted version.

This study was funded by the Science and Engineering Research Board (SERB) [YSS/2015/000734], Department of Science and Technology (DST), New Delhi, Government of India.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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