Weekend bioRxiv.org Preprint Review: Cortical rhythms are modulated by respiration

As most runners who check their pulse know, the pulse rate is strongly influenced by the breathing rate. What is more interesting from a neuroscience perspective is that EEG patterns, including the cortical gamma oscillations, are strongly influenced by respiration as well.

In the paper below, Heck and colleagues report that in both experimental mice subjects and in human subjects undergoing EEG monitoring with implanted electrodes, the EEG gamma activity shows a strong tie in its power to the phases of respiration.

Their findings go a long way to explain the increase in gamma band reported during meditation. Persons experienced with traditional deep meditation techniques often show a marked slowing of breathing rates with meditation, and it seems that it is in that space between inspirations that Heack et al report the rise in gamma power to occur, in both mouse and man.

For me, this paper resonates with some of my memories of residency and fellowship work in Denver in the nineteen-eighties. Dr. James Austin, one of my neurology professors from those years in Colorado, is widely published regarding his neurological interest in Zen meditation. He wrote as far back as 1999 a book, a copy of which sits on my office bookshelf, which discusses from a philosophical and medical perspective the neurological changes which occur in Zen monks during meditation.

Why does this EEG gamma power modulation with respiration occur, and what might be its links to limbic or cognitive functions? Is the change in gamma mediated by a vagal tone influence, as likely explains the changes in heart rate with respiration, or is it via another, perhaps hypothalamic pathway? This remains to be seen.

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Cortical rhythms are modulated by respiration

Detlef H. Heck, Samuel S. McAfee, Yu Liu, Abbas Babajani-Feremi, Roozbeh Rezaie, Walter J. Freeman, James W. Wheless, Andrew C. Papanicolaou, Miklós Ruszinkó, Robert Kozma

bioRxiv preprint first posted online Apr. 16, 2016; doi: http://dx.doi.org/10.1101/049007.

Summary

The brain generates oscillatory neuronal activity at a broad range of frequencies and the presence and amplitude of certain oscillations at specific times and in specific brain regions are highly correlated with states of arousal, sleep, and with a wide range of cognitive processes. The neuronal mechanisms underlying the generation of brain rhythms are poorly understood, particularly for low-frequency oscillations. We recently reported that respiration-locked olfactory bulb activity causes delta band (0.5-4 Hz) oscillatory neuronal activity in the whisker sensory (barrel) cortex in mice. Furthermore, gamma oscillations (30 – 100Hz), which are widely implicated in cognitive processing, were power-modulated in synchrony with the respiratory rhythm. These findings link afferent sensory activity caused by respiration directly to cortical rhythms associated with cognitive functions. Here we review the related literature and present new evidence to propose that respiration has a direct influence on oscillatory cortical activity, including gamma oscillations, and on transitions between synchronous and asynchronous cortical network states (marked by phase transitions). Oscillatory cortical activity, as well as phase transitions, has been implicated in cognitive functions, potentially linking respiratory phase to cognitive processing. We further argue that respiratory influence on cortical activity is present in most, and possibly in all areas of the neocortex in mice and humans. We furthermore suggest that respiration had a role in modulating cortical rhythms from early mammalian evolution. Early mammals relied strongly on their olfactory sense and had proportionately large olfactory bulbs. We propose that to this day the respiratory rhythm remains an integral element of dynamic cortical activity in mammals. We argue that breathing modulates all cortical functions, including cognitive and emotional processes, which could elucidate the well-documented but largely unexplained effects of respiratory exercises on mood and cognitive function.

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