Neuro-respiratory Synchronization: Connecting Brainwaves and Breath for Cognitive Harmony – Narrative Review

Abstract

The scientific community is actively exploring the effects of breath-related practices on the emotional, physiological, and cognitive functioning of human beings. It is no longer the singular realm of exploration of the spiritual communities. A thorough search of PubMed, Scopus, and Google Scholar was performed to locate pertinent articles on respiratory entrainment of hippocampal waveforms and its relationship with memory. The search utilized terms such as “hippocampal waveforms,” “respiratory entrainment,” and “phase-amplitude coupling (PAC),” which were combined using Boolean operators (AND, OR). There is no dearth of literature indicating consolidation, retrieval, and escalation of memory encoding with breath-related practices. However, the underlying mechanisms linking breath and brain cognition in human beings require further rigorous scientific exploration, which is still in a primitive stage. Nasal airflow during inhalation stimulates various structures in the brain and interferes with hippocampal waves. These hippocampal waves are modified by the nature of respiratory rhythm through hierarchically organized PAC. In addition, research proposes that nasal breathing organizes neuronal activity across the brain and accomplishes intricate behaviors, including memory. Apparently, as hippocampal respiration-induced rhythm tracks breathing, controlled breathing practices can be framed as an active interference mechanism to secure hold over one’s mind and cognition. Hence, in this article, we discuss an overview of the emerging literature on how the physiological regulation of nasal breathing is linked with the neural and cognitive processes.

“Brain waves are the language of brain. These oscillations are shaped by cognition and shape cognition in return.”-Steven Laureys[1]

Introduction

Life dances to the rhythm of countless orchestrations, and among them, the most eminent is the cadence of breath, which endures throughout life, serving to regulate gas exchange, adjust pH, aid olfaction, and maintain homeostasis. However, recent studies illuminate scholars to more expanded roles of breath. Roles spanning from organizing neuronal activity across brain regions to coordinating varied intricate behaviors. Moreover, this respiratory rhythm is predisposed to a variety of host factors, like change in respiratory frequency and depth during sleep-wake, rest-exercise, and cognitive-emotional influences.[2,3] A major goal of this manuscript is to explicate the extent to which respiratory rhythm influences cognitive neural behavior particularly memory, and to review the recent evidence to provide a detailed and insightful analysis of the phenomenon.

Literature Search Strategy

A comprehensive search of PubMed, Scopus, and Google Scholar was conducted to identify relevant articles on the topic of respiratory entrainment of hippocampal waveforms and memory. Search terms included “hippocampal waveforms,” “respiratory entrainment,” and “phase-amplitude coupling (PAC),” combined using Boolean operators (AND, OR). The search focused on articles published between 2000 and 2023. Articles were included if they were peer-reviewed, published in English, and focused on the above topics. Articles not related to these topics, non-English publications, and case reports were excluded. The quality of the studies was assessed using the critical appraisal skills programmed checklist, and only high-quality studies were included in the synthesis. A thematic analysis was conducted, grouping the findings into major themes, including the process of entrainment, detailed analysis of memory circuits, and its clinical implications.

Memory and the Circuitry of Hippocampus

A biologically fundamental function for our survival is the need for retaining and recalling information. The newly encoded information is fragile and susceptible to disruption but becomes more resilient with time by memory consolidation. This process relies significantly on the hippocampus, which undergoes a great deal of processing and network rearrangement, including wakeful replaying of memories during consolidation. This is closely followed by a decline in its critical role when the memory is ready to be stored throughout the cortex.[4] The strength of connections between neuronal synapses is significantly enhanced with each replay. The pattern and strength of this association between cortical structures permit storage and further retrieval of encoded information.[5,6] There is a remarkable overlap in the brain circuitry involving emotions and memory such as the hippocampus, medial prefrontal cortex (mPFC), amygdala, and other limbic regions, including the striatum.[7,8]

Spatial working memory and motivational and emotional behaviors are accounted for by the monosynaptic projections from the hippocampus to mPFC. This also contributes to sleep-dependent memory consolidation involving the transfer of novel information to the neocortex. Hence, the hippocampus along with mPFC is aptly referred to as “the hub of infrastructure communication.”[9,10,11,12] Axmacher also reported an increased hippocampal-mPFC synchrony during a working memory task.[13]

Hippocampal Waveforms

The hippocampus exhibits three varied waveforms linked to memory function during active waking, namely theta (4–8 hz), gamma (25–100 hz), and sharp wave ripples (SWR) (110–250 hz). These waveforms are involved in hippocampal-mPFC communication during memory processes. Each wave is observed during a particular behavior, generated by specific mechanisms, and is linked to specific neuronal firing properties.[14] Surprisingly, all these waveforms get influenced by the respiratory rhythm.[3]

Theta waves

These sinusoidal waves are responsible for spatial and episodic memory processing along with temporal coordination and organization of neurons within the hippocampus.[15] Theta waves could be the default mode for hippocampus to establish functional connectivity with mPFC and amygdala.[3]

Gamma waves

These waves are involved in the encoding of current sensory information in memory circuits along with memory retrieval.[16]

Sharp waves

These are large amplitude negative polarity deflections in the apical dendritic layer of cornu ammonis (CA1) hippocampal region. They are mostly, but not always, associated with short-lived fast oscillatory patterns called ripples which together constitute the SWR. These SWRs, which are restricted to the hippocampal network and entorhinal cortex (EC) form the most synchronous event of the mammalian brain and are regarded as the first biomarker for cognitive operations.[14,16]

The two-stage memory consolidation model presented by Gyorgy Buzsaki [Figure 1] posits that, during learning, the neocortex provides the hippocampus with novel information leading to transient synaptic reorganization of its circuits through theta oscillations. This is followed by temporally compressed sequential transfer of modified hippocampal content back to neocortical circuits in the form of SWR when the brain is disengaged from environmental stimuli.[16] Thus, after learning, mostly during slow wave sleep or awake rest periods, the rate of SWR occurrence increases momentarily during consolidation.[3,17] Proving the hypothesis, animal studies by Girardeau et al. have demonstrated suppression of SWR to impair memory consolidation largely.[18]

Figure 1.

Buzsaki’s two stage memory consolidation model[9]

Synchronisation of Neural Activity and Influence of Respiratory Rhythm

Donald Hebb’s cell assembly hypothesis advocates memory to be represented by functional network of distributed ensembles of neurons that are activated concurrently.[13] Multiple mechanisms exist for this dynamic coordination across neurons, but one of the lucidly understood among all is synchronization of neuronal activity by oscillation.[15] Oscillations are ubiquitous phenomenon of the brain and can be observed at multiple scales, from spike times of single neurons, through mesoscopic scale of local field potentials (LFPs), up to more macroscopic electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) recordings.[19] They are intelligent rhythmic electrical activities that reflect the temporo-spatial integration of voltages generated by current flowing in and out of the dendrites of many neurons within an area.[15] This neural activity is spontaneous and often hierarchical, i.e., phase of slower oscillations modulates the power of faster rhythms in a process known as cross-frequency PAC. The ensuing interference is the basis for the perpetually changing electrical landscape of brain, which accounts for the infrastructure that supports neural communication.[16,20] This hierarchical modulation of higher waveforms can be attributable to any low-frequency rhythmic event, including sound waves or even quiet breathing.[21] For effective communication through PAC, spikes in a brain area should arrive at connected brain loci when it is maximally excitable, which is addressed as communication through coherence hypothesis or binding by synchrony.[22,23]

The authority of respiration on cortical activity was unexplored until recently when a series of independent studies unveiled respiratory locked events extensively across various cortical and subcortical structures in both rodents and humans.[2,3] Apparently, a sensory copy of the breathing rhythm propagates to the olfactory system and reaches downstream brain regions, including limbic areas involved in emotion and memory.[24] Thus was borne the idea of perennially existent low-frequency respiratory rhythm working as a common clock, which is deeply intertwined with and influences the faster rhythmic neural activities, especially memory.[25,26,27]

Mechanism of Respiratory Entrainment of Neural Oscillations

Historically, rhythmic neural activity in the brain was observed first as early as 1942, when Lord Adrian recorded waves of activity from the olfactory bulb (OB) in anesthetized hedgehog and reasoned it to uniform mechanical stimulation through inhalation. Yet, after 80 years of eminent research, the contribution of breathing to neural dynamics has not been completely grasped and is critically undervalued.[28]

Even without odor, with each nasal breath, the nasal airflow stimulates mechanoreceptors of olfactory sensory neurons. This generates a breathing-locked rhythmic signal resulting in the entire OB, precisely the mitral and tufted cells becoming entrained to respiratory rhythm and is identified in the form of LFP.[3,29] These olfactory receptor cells (nucleotide-binding subunit of the cyclic nucleotide channel, CNG) are sensitive to both odor as well as mechanical stimulation from nasal airflow. The deletion of CNG Alpha-2 gene results in both general anosmia along with decoupling of OB–LFP from respiration.[30,31] Thus, OB seems to be the cryptic rationale behind respiratory-locked brain activity, and removing or inhibiting the OB or bypassing nasal airflow through tracheostomy or mouth breathing abandons these activities.[5] It is possible that in humans, other respiratory-locked inputs either via sensory input from viscera, including nonnasal somatosensory efferent or from the brain stem respiratory pattern generator, may also substantially contribute to driving respiratory-locked activity, which are discussed further under a separate heading.[3]

A wealth of literature concludes that both the rate and duration of airflow circulating in the nasal cavity and mechanically stimulating the olfactory epithelium determines the respiratory drive in brain.[25] Contrary to the recent research which confirms the presence of respiratory-modulated brain oscillations (RMBO) over diverse brain regions, earlier they were believed to be restricted to areas involved in olfaction such as OB and piriform cortex (PC).[21] Anatomically, the OB neurons project to layer I of lateral EC either directly or through PC [Figure 2]. Further, it synapses on dendrites of EC, progressing to dentate gyrus (DG) which expresses the highest level of respiratory coupled activity.[2] Thus, nasal respiration causes prominent 2–4 Hz LFP in DG, the input region of the hippocampus, which is unique as it is the sole site where adult neurogenesis occurs.[32,33] Spreading further, these oscillations are directed to the hippocampal CA-3 region and are ultimately traced until the somatosensory cortex and prefrontal networks.[32,34] Given the high amplitude of RMBO, which dominate OB, it is not unexpected that LFP in the olfactory tubercle, PC, and medio-dorsal thalamus, all of which receive direct input from OB, are highly correlated with breathing.[2] Herrero et al. demonstrated RMBO in humans at OB, PC, amygdala, hippocampus, insula, medial and lateral olfactory cortex, and gray matter.[34] These RMBO were even traced further as far as the neocortex by Fontani and Bower which were driven almost entirely by OB activity hypothesizing a direct link between respiration and cortical neuronal rhythm.[35] The functional connectivity of the human olfactory cortex with hippocampus may have been retained in the process of mammalian evolution. This functional connection between the olfactory cortex and hippocampal networks is stronger at rest.[36]

Figure 2.

Path of travel of respiratory coupled oscillations showing the air from nasal cavity to pass to the olfactory bulb, piriform cortex, entorhinal cortex, and further to the hippocampus. In the hippocampus, the waves travel from dentate gyrus to CA3 to CA1 as depicted in the enclosed figure. These nasal oscillations are also transferred from the hippocampus to the neocortex

Due to the same wavelength of theta and respiratory frequency in rodents, earlier hippocampal studies presumed these RMBO as an artifact from breathing. However, humans’ respiratory frequency is much slower than theta rhythm, and moreover, OB-RMBO was found to increase preferentially during inspiration.[3,37] Finally, Ito et al. illustrated respiratory-related signals in hippocampus to be parallel to and distinct from hippocampal theta in widespread brain regions. This RMBO was defined as the hippocampal respiration-induced rhythm (HRR) whose peak frequency perfectly matched with the respiratory rate while the faster component remained as theta rhythm and hippocampal neurons were differently entrained by these two oscillations. Substantiating the fact Yanovsky et al. depicted clear modulation of DG cells by HRR but not by theta waves.[33] Since HRR follows the breathing rate, its peak frequency remains variable and depends upon the animal species and their particular behavioral state, consequently escaping a narrow frequency-based definition.[18] Undeniably, the synchronicity of these oscillations in the brain denotes substantial connotation. “The Proust Phenomenon,” which is the ability of odor to evoke strong emotions and memories, is supported by direct olfactory projections to the amygdala and ED.[2] But what functional significance does entrainment of nonolfactory regions, especially the hippocampus and amygdala, serve remains unresolved completely.[2,21]

Extent and Function of Respiratory Entrained Hippocampal Waves

Apparently, HRR accounts for the hippocampus for modulation of learning and perception through its role in memory encoding, consolidation, and retrieval [Figure 3]. However, the exact mechanism remains elusive.[34,36] HRR has been implicated in the scaffolding and transfer of information between sensory and memory networks and for its further efficient storage in the hippocampus.[5]

Figure 3.

Impact of respiration coupled rhythm on hippocampal waves on learning and memory

Breathing is suggested to exert its system-wide effect through the entrainment of slow cortical rhythms. This, in turn, has the capacity to regulate faster cortical waves, including theta, gamma, and SWR; thus, mediating long-distance brain synchronization through PAC.[26] Long-range PAC is thought to organize brain rhythms and contribute to a variety of higher brain functions, including learning, memory, attention, emotion, and motor behavior, but its technicalities on memory are precisely presented underneath.[38]

As mentioned earlier, PAC is hierarchically organized; delta (1–4 Hz) phase modulates theta (4–10 Hz) amplitude, and theta phase further modulates gamma (30–50 Hz) amplitude.[39] Delta oscillations are characteristic of sleep.[40] Successful consolidation of memories depends on coordinated interplay of slow oscillations (delta), spindles, and SWR during NREM sleep. This enables the transfer of labile information from hippocampus to permanent memory stores in neocortex.[41] Evidently, several neuroscientists consider delta oscillations to be involved in cognition as substantiated by increased EEG delta activity during mental calculation and semantic tasks.[40] During wakefulness and sleep, delta waves have even been shown to mediate hippocampo-mPFC dialogue underlying memory consolidation in the human brain.[42] Zelano et al. reported significant changes in delta and theta range in PC, hippocampus, and amygdala with nasal respiration.[21]

Theta waves form an essential component of neuronal processes underlying memory encoding and retrieval.[3] Research indicates human hippocampal theta activities to undergo PAC with low frequency HRR, and thus any influence of respiration on theta rhythm is likely to influence memory functioning largely.[3,21]

Ito et al. divulged HRR to be specifically modulating the gamma oscillations. The strong connection of gamma oscillations with numerous cognitive processes, including attention, memory, decision-making, and problem-solving, led to speculations that respiration can directly influence cognition.[27,43] Not surprisingly, memory has been argued to be a dynamic data represented by spatiotemporal oscillations of high-frequency gamma-band coherent waveforms in OB and PC gated by respiratory activity.[3] Gamma waves peaked along with the peak of low-frequency RMBO and were modulated both by theta and HRR but strongly by HRR compared to intrinsic theta oscillations.[3,33] The presence of breathing-entained gamma band across regions of the brain suggests that breathing acts as an organizing hierarchical principle for cortical excitability, as proposed by Heck et al.[26]

Theta oscillations are thought to provide a common temporal reference for the exchange of information among distant brain networks.[33] Faster gamma oscillations nested within theta cycles are believed to underlie local information processing. Finally, periods of hippocampal theta–prefrontal slow gamma coupling are associated with increased synchronization of neurons within mPFC and organize sequential activation of hippocampal neurons during active waking behavior.[33,38] Research suggests that this coupling between global and local oscillations, as showcased by “theta-gamma coupling,” is the general coding mechanism. Together, this combination of long-range low-frequency phase synchronization and local PAC might serve as a mechanism to coordinate large-scale brain communication for memory processes across distant brain areas.[44,45]

In humans, SWR is phase-locked to hippocampal gamma and delta activity. Yu and Liu provided the first evidence that HRR modulates the probability of SWR through PAC with gamma waves, and reducing this should subsequently reduce SWR.[46] Even modulation of SWR by delta waves was proposed by Buzsaki et al.[16] This phase locking of SWR to respiration might be necessary to create a proper temporal alignment between hippocampal SWR and neocortical excitability to optimize the transfer of memory information.[46] Since it is observed that HRR and SWR are both vital for memory consolidation; hence, nasal respiration modulates the consolidation process, and disturbing the neural process underlying awake consolidation should have a direct negative bearing on memory consolidation.[5,46] Table 1 depicts the outcomes of various studies conducted on respiratory rhythm and cognition

Table 1.

Studies from across the globe coupling respiratory rhythm with cognition

Study		Brain region		Species		Outcome
Karalis and Sirota, 2022[47]		Hippocampus		Mice		Respiratory rhythm provides a unifying global temporal coordination of neuronal firing and network dynamics across cortical and subcortical networks
Girin et al., 2021[25]		Different regions (OB, mPFC, Hippocampus)		Rats		Changes in respiratory regime affect cortical dynamics Respiratory regime at rest is optimal for respiration to drive the brain
Binder et al., 2019[12]		Hippocampus, mPFC		Mice		Monosynaptic projections between hippocampus and mPFC contributes distinctly to memory consolidation
Moberly, 2018[2]		pIPFC		Mouse		Olfactory inputs modulate rhythmic activity in fear circuits and thus suggest a neural pathway that may underlie the behavioural benefits of respiration-entrained olfactory signals
Arshamian et al., 2018[5]		Hippocampus		Humans		Respiration mode during awake consolidation has behaviourally relevant consequences for episodic odour recognition
Tort et al., 2018[19]		Different regions (hippocampus, mPFC etc.)		Mice		RMBO are particularly prominent in the mPFC and coupling between theta and gamma reported in this region corresponds to RR-gamma coupling
Herrero et al., 2018[34]		Different regions (Amygdala, Hippocampus, Insula)		Humans		The organization of neuronal oscillations in brain is influenced by the rhythmic patterns of breathing and detail mechanisms of how cognitive factors impact otherwise automatic neuronal processes duringinteroceptive attention
Kőszeghy et al., 2018[48]		OFC		Mouse		Firing of neurons in the OFC exhibit a strong temporal relationship with the breathing rhythm, providing a temporal framework for high order, multi-dimensional processing of sensory value and internal state information
Zelano et al., 2016[21]		PC, hippocampus		Humans (patient within tractable epilepsy vs. healthy subjects)		Patients: Respiratory entrainment of LFP in human PC, amygdala and hippocampus. These effects diminished when breathing was diverted to the mouth Healthy subjects: Breathing phase systematically influences cognitive tasks related to amygdala and hippocampal functions
Yanovsky et al., 2014[33]		Hippocampus		Mouse		Nasal respiration strongly modulates hippocampal network activity providing a long-range synchronizing signal between olfactory and hippocampal networks

OFC: Orbitofrontal cortex, pIPFC: Prelimbic prefrontal cortex, mPFC: Medial prefrontal cortex, PC: Piriform cortex, LFP: Local field potential, RMBO: Respiratory-modulated brain oscillations, RR: Respiration rate, OB: Olfactory bulb

Evidence for Functional and Dysfunctional Alteration in Respiratory Locked Neural Processing

Karalis and Sirota testified memory consolidation to be improved by nasal compared to oral breathing in mice.[3] Arshamian et al., deciphered that recognition of facial fear expression in humans is faster if presented during the inspiratory phase. Perl et al. identified that task-related brain activity was greater during nasal inhalation than exhalation.[49] Participants were better able to discriminate their own versus others voices better during inspiration versus expiration in an experiment by Orepic et al.[50] The enhanced memory consolidation is supposedly due to alteration in SWR and delta waveform induced by nasal breathing. Yet another study reported that even when no instruction for inspiration was given, participants inhaled spontaneously at the beginning of a cognitive task, and this inhalation induces changes in brain network and functional connectivity.[5,25] Hogervorst et al. confirmed that as cognitive workload intensifies, the rate of respiration tends to accelerate and emerges as one of the most reliable single physiological variables for classifying cognitive workload levels.[51] An extensive study revealed that the respiratory cycle affects six varied task paradigms spanning emotional discrimination, sound detection, visual memory, pitch discrimination, and visual motion discrimination, where participants specifically exhibited inhalation during stimulus presentation and exhalation while responding.[52] Further, Zelano et al. demonstrated superior memory encoding and retrieval of visual objects in humans by demonstrating greater intracranial EEG coherence during nasal as opposed to mouth breathing.[21] Researchers have established enhanced retention during a memory task even by applying transcranial currents that mimic slow respiratory oscillations in the frontal cortex during NREM.[53]

Nasal breathing does more than just modulation of waves; it actively influences numerous ongoing activities across diverse cerebral regions. Recent reviews highlight a heightened connectivity between corresponding hemispheres of the brain, notably in areas like the caudate nucleus, which plays a crucial role in working memory as evidenced by fMRI studies conducted during nasal breathing. This advocates that uni-nostril breathing can stimulate increased activity in the contralateral hemisphere, as corroborated by heightened oxygenation and blood volume in the contralateral prefrontal cortex.[54] In addition, nasal breathing is linked to robust functional connections within the cerebellum, accompanied by heightened activation of the inferior parietal gyrus, an area deeply implicated in the storage of phonological memory, further emphasizing the multifaceted impact of nasal breathing on cognitive processes.[55] Results of Nakamura et al. support the concept that memory is notably enhanced during peak inhalation in nasal respiration, as noticed by reduced reaction time and enhanced recall accuracy.[56]

Conditions where RMBO is disrupted, dysfunctions may occur.[21] Kuroshio et al. went on to display that children with mouth breathing had poorer academic achievement, cognitive skills, and phonological working memory compared to nasal breathers.[57] Rhyou and Nam have indicated asthma patients grapple with cognitive impairment. Interestingly, this cognitive dysfunction seems to be particularly linked to extended asthma duration and poorer lung function.[58] COPD patients too have been associated with cognitive decline. In addition, individuals with congenital central hypoventilation syndrome, a disorder with defects in control of breathing are reported to suffer from poor neurocognitive skills. Further establishing the intricate relationship between breathing and cognitive performance is hyperventilation seen in panic disorder or altered respiratory patterns observed in autism spectrum disorder.[59] This highlights the intricate interplay between breathing and cognition. However, the extent to which loss of respiratory entrainment contributes to it is definitely debatable.

Linking Respiration and Locus Coeruleus

A group of researchers, including Sirota et al. have held a contrarian view where they detected respiration to continue to influence SWR even after olfactory deafferentation. They proposed the role of an alternative respiratory modulation pathway distinct from HRR; hypothesizing an intriguing link between respiration and cognition. An excitatory pathway from pre-Botzinger complex (PBC) connects to locus coeruleus (LC), by which automatic breathing pattern sets an intrinsic rhythm in LC and was equally supported by Yackle and et al.[26,60,61] They postulated brain activity to be modulated by a dual mechanism of respiratory entrainment, one through HRR and the other through LC. With each inspiration, PBC sends signals in diametrically opposite directions. A descending motor signal is transmitted to the diaphragm and an ascending respiratory corollary to the brain, specifically to LC. This ascending respiratory discharge modulates brain activity alone during mouth breathing and along with HRR in nasal breathing, although this does not sync completely with the theory of augmented memory consolidation during nasal breathing. Analogous findings of respiratory corollary discharge were reported by Perl et al.[49] LC is the principal site of noradrenergic synthesis in the brain, and its role in attention, arousal, and memory is well documented. The activity of LC is even shown to increase with inhalation and decrease with exhalation, involving targets throughout the cortex. On this precontext, Melnychuk et al. framed that increased excitatory input from inspiratory PBC neurons during fast and irregular breathing could result in increased arousal and attention and comparable changes in neural activity throughout the brain.[26,61,62]

Breath Modulation and Cognition

Throughout history, in varied cultures, slow nasal deep breathing and voluntary pacing of breath have been followed in yoga and meditation practices as a means to de-stress and encourage physical and emotional well-being.[34] Interest in these practices has spread from East to West and, now, from spiritual to scientific domain.[26] There is substantive evidence that consciously attending to respiratory behavior offers a means of regulating emotional states and cognitive processes.[63] Herrero et al. illustrated that faster breathing in humans was associated with HRR greater in power, which continued to follow breathing frequency at a faster pace particularly in premotor, motor cortex, insula, and amygdala. As breathing returned to normalcy, HRR tracked at a lower frequency.[34] Similar “tracking effect” was reported in rodents by Ito et al.[43] Hence, modulating the breath means modulating the circuitry and physiological responses associated with it. Controlled breath can be framed as an active interference mechanism to enhance cognitive performance and, also, to meet the ever-changing environmental requirements especially to gain hold over one’s mind.[26]

Recent anatomical studies reveal a two-way communication between breath and cortex, citing that it is not only the breath that controls cortex, but the cortex also communicates with the respiratory network.[26] A study by Feinstein et al. proposed electrical activation of the amygdala to elicit apneic episodes.[64] The fact that the rate of breathing can be influenced by stimulation of hippocampus, amygdala, and insula in situations of fear and anxiety in humans suggests a more complex breathing circuitry above the brainstem level propelled by limbic and cortical areas.[34]

Clinical Implications and Future Research

Voluntarily increasing breathing rate can trigger mechanisms similar to those activated during anxiety and stress. On the other hand, long and deep inhalation can be an ideal regime for large areas of brain entrainment. Hence, respiratory rate and route can be a roadmap to regulate emotional responses, as evidenced by varied yogic practices. Entrainment of large areas of the brain by lower frequency sound or light can enhance memory, and this mechanism can be used in children or geriatric population suffering from memory deficit issues. Most ADHD patients have an abundance of slow brain waves (delta and theta), which may be targeted by controlled breathing patterns for modulation of memory performance.

The connection between respiratory rhythms and brain oscillations holds promise as a potential biomarker across various disorders characterized by distinct neural signatures. This insight opens future research avenues for using breathing patterns and practices as a noninvasive measure to aid in diagnosis and management of emotional responses such as anxiety and stress. Furthermore, the neurophysiological correlations of effects of mindful breathing practices on patients with memory disorders may give valuable insights. Further research is required to provide insights into the neurophysiological correlations of various yogic breathing techniques (pranayamas) with cognitive functions.

Conclusion

Breathing and its rhythm exert a meaningful influence on cognition, especially memory. As signatures of respiration are found in cortical and subcortical regions that do not receive direct input from the olfactory bulb, breathing rhythm seems like a universal gesture in the brain instead of just being an olfactory sensory processor. Thus, controlling breath has the potential that can be established as an easily accessible and effective tool that shapes emotional, physiological, and especially cognitive processes.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.