Nasal cycling - not an Olympic sport new for 2012, but the alternating dominance of each nostril. This is a physical phenomenon present in 85% of mammals – and that probably includes you. As we go about our business, one nostril is more open, allowing more air to flow through it than its resting partner. A few hours later, the open nostril rests and the other flares and takes control. Try it. Put a finger under your nose and you will feel a stronger, warmer sensation on one side. Remember to do it again later and you may well find the opposite.
Unsurprisingly, researchers have not been monitoring nasal cycling by sitting around with their fingers under each others’ noses. It has been studied in a number of ways: hot-wire anemometers (ouch) should perhaps remain unpacked; the Zwaardemaker method relies on a calibrated cold mirror and condensation, and a more recent technique involves participants exhaling onto a piece of glass with red dye and then observing the resultant ink bloom. The wonky love hearts which are left behind reveal a striking manifestation of our nasal asymmetry.
This alternating vasodilation and vasoconstriction of the nostrils was first documented by Kayser, a German rhinologist in 1895 and developed by Heetderks in 1927. It has since been embraced by yoga enthusiasts in the meditative practice of Pranayama. Research into nasal cycling was taken up with gusto by David Shannahoff-Khalsa at the University of California in the early 1990s leading to a number of publications, and has more recently been investigated in relation to handedness, autism and early language impairment.
So why this alternation? Looking elsewhere in the body may help explain. It has been suggested that brain lateralisation takes place to make maximum use of neural tissue, avoiding duplication of function. However, nostrils need not multitask, and do not wear out unless they have been regular conduits to substances other than air. The intriguing claim is that the nasal cycle is linked to the rhythm of alternating brain hemispheric activity, and governed by the autonomic nervous system (ANS). Using neural imaging techniques, positive correlations have been found between hemispheric activity and dominance in the opposite nostril. Surprisingly, the nose is called upon as an integral part of cognition!
We even do better in certain kinds of test when forced to breathe through the optimal nostril. Shannahoff-Khalsa and Susan Jella investigated performance in cognitive tests by forcing their undergraduates to breathe through either the left or the right nostril (crocodile-clips, anyone?). When taking the right-brain based spatial tasks, the students did significantly better during left-nostril breathing, whilst on the verbal tasks which are more closely associated with the left hemisphere, they scored higher during right nostril breathing but not significantly so (the asymmetry in significance in this case may be due to multiple brain regions mediating the skills required in the specific types of task).
Although we lag behind dolphins who have nailed the ability to let one half of their brains rest while the other keeps lookout for predators and takes charge of breathing, the evidence from nasal cycling research suggests that there may be some propensity for one side of the human brain to be more active whilst the other takes a back seat, regardless of the task at hand. Half-sleeping has been noted in other species too – we’ve all seen the ‘one-legged’ flamingo, with ducks, geese, storks and herons also making like Maasai tribesmen from time to time. Various theories abound, including the idea that these birds are resting one hemisphere at a time; the resting leg corresponding to the contralateral sleeping hemisphere. The other side supports the body and maintains a degree of alertness when the bird is in a vulnerable state. Evolutionarily, the theory is persuasive.
Although this private life of the nose initially sounds pretty weird, lateralisation of the body is widely observed. Whenever we pick up a pen, put the phone to our ear, cross our legs, interlace our fingers or tilt our heads to be kissed we are demonstrating the body’s inherent lopsidedness. Left- and right-brained tendencies are commonly cited to illustrate our strengths and weaknesses, and lateralisation of the brain is now a major topic within the cognitive sciences; there is even a cross-disciplinary international journal focused exclusively on lateralisation in human and non-human species.
Psychologists and linguists have studied brain regions and lesions in relation to language ability since the 19th century. Such research is widely respected, and what it has in common across the sub-disciplines is the top-down nature of brain governing body. So does our modest air-warming appendage really have the capacity to influence brain function? Shouldn’t it be the other way around? Not necessarily, considering that the ANS and the hypothalamus are ultimately in charge here. It appears that nostril dominance originates from the brain itself, and then in turn affects cortical activity. The evidence suggests that the ANS starts the race, the nostrils cycle and the brain follows behind.
So if the story of nasal cycling is true, how should we best harness it? Plug our left nostril during that work presentation? Stick a finger in the right side during the driving test? Market an airflow detection kit for task/ brain-optimisation? As it seems that achieving ambinasality is beyond us, perhaps we’ve just got to embrace the times when we’re down with a cold, for that is when we are truly cerebrally balanced.
Kayser, R. (1895) Die exakte Messung der Luftdurchgängigkeit der Nase. Arch. Laryng. Rhinol. (Berl.) 8, 101-120
Shannahoff-Khalsa, D. (1993) The ultradian rhythm of alternating cerebral hemispheric activity. Int. J. Neurosci. 70, 285-298
Jella S.A, Shannahoff-Khalsa D.S. (1993) The effects of unilateral forced nostril breathing on cognitive performance. Int J Neurosci. 73, 61-8
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