The idea that respiration and attention interact with each other has been central to yogic practices for millennia. Contemporary research in cognitive neuroscience is beginning to unravel remarkable ways in which respiration modulates, and is modulated by, cognitive processes. Mounting evidence is suggesting that our ongoing respiratory rhythm may act as a physiological pacemaker for higher order functions to be entrained by. Despite many sensory-cognitive domains being investigated from this perspective, the area of ‘attention’ specifically has been sparsely researched. However, one dynamical systems model (Melnychuk et al 2018) has attempted to bridge the gap between respiration and attention via the locus coeruleus- noradrenaline (LC-NA) system, due to the crucial simultaneous roles that the LC has in the arousal and attentional system as well as the brainstem respiratory network. The present thesis aimed to corroborate initial supporting evidence for synchronisation between these systems and test predictions of this model.
Empirical Chapter 1 aimed to test whether decreasing respiratory frequency would stabilise both behavioural attention and pupil diameter (PD) oscillatory activity, compared to a spontaneously breathing control group. PD was used as a proxy measure for LC activity. A novel task was designed, the Paced Auditory Cue Entrainment (PACE) task, in which participants responded rhythmically to auditory cues, providing a continuous measure of sustained attention, and additionally, the breathing group used the cues as a breath guide, breathing in the range of 0.1 – 0.15 Hz. Despite no group differences in the variation of the timing of responses, the control group committed significantly more frequent response rhythm inversions – an exploratory accuracy variable of pressing the wrong key at the right time. The breathing group barely committed any of such errors compared to the control group. Additionally, the PD activity of the breathing group closely followed the frequency of the breathing, such that they were oscillating in the same range, implying that PD and therefore possibly LC activity was entrained by the breath intervention. From this we conclude that decreasing respiratory frequency did indeed stabilise attention, mitigating lapses, possibly through stabilising fluctuations in LC activity.
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Empirical Chapter 2 was an investigation into how attention is modulated over the respiratory cycle in a sustained attention task with no explicit respiration instructions. We used younger (YAs) and older adults (OAs) as a natural division of attentional strategy, since OAs were previously seen to show less mind wandering and more stable psychophysiological signatures of attention on this task than the YAs, however the groups sustained attention performance did not differ. We discovered here that both groups showed evidence of entraining their respiratory cycle to events in the task, however, the OAs did this to a significantly greater degree. Analysis of task performance, subjective attentional state, PD, and EEG oscillatory power, showed that all these attentional signatures were significantly modulated over the respiratory cycle. We were further able to utilise the differing attentional strategies, as well as the degree of respiratory-task entrainment, to infer the relative contributions from top-down and bottom-up influences respectively on these modulatory patterns. There appeared to be a fluctuation in attention so that conditions were optimal for task focus during the respiratory phases which were most entrained to task events, and less optimal for task focus and more geared towards mind wandering outside of the entrainment window. We interpret these findings to be evidence of respiration as an ‘attentional metronome’ of sorts, interacting with each other via the LC-NA system.
Empirical Chapter 3 utilised the data from the prior chapters to investigate how sighs (infrequent, deep breaths) are implicated in resetting suboptimal respiratory variability, corroborating previous findings, as well as testing for implications in transitioning between attentional and arousal states. Sighs here did play a significant role in resetting respiratory variability; however, no evidence was found that behavioural or experiential measures of attention were influenced. A significant association was discovered between the degree of respiratory-task entrainment and sighs, suggesting that sighs may in part function to reset entrainment-induced random respiratory variability, and facilitate further entrainment. PD was seen to undergo large changes over the course of sighs, implicating the LC-NA arousal system in sigh behaviour in humans.