The timing of an individual’s inhalation and exhalation cycle can influence various abilities, such as detecting a light touch and distinguishing three-dimensional objects. A study revealed that individuals tend to inhale right before a cognitive task, and doing so often improves performance. Some researchers have noted that only nasal breathing has these effects; mouth breathing does not.
A new emerging idea about how this works focuses on the harmonic oscillations recorded from electrical brain activity. These waves, typically measured by electrodes placed on the scalp, capture the cumulative activity of thousands of neurons. For decades, some neuroscientists have argued that they reflect communication between distant brain regions that may shape critical aspects of cognition.
For instance, they may represent how the brain integrates sensory information processed separately in the auditory and visual parts of the brain to create what we experience as a seamless perception of sounds and visuals in a scene. Some scientists have even suggested that such synchronous activity could be the basis of consciousness itself, although proving this is quite challenging.
In experiments with rodents, some research groups have found that the rhythm of breathing affects wave activity in the hippocampus, a critical area for learning and memory. While awake, the collective electrical activity of neurons in the hippocampus increases and decreases at a consistent rate—typically 6 to 10 times per second. This theta brain rhythm, as it’s called, occurs in all studied animal species, including humans.
In a 2016 study, neuroscientist Adriano Tort at the Federal University of Rio Grande do Norte in Brazil and colleagues began investigating theta oscillations but found that their electrodes also synced to a different rhythm, a slower rhythm with about three peaks per second, roughly resembling the resting breathing rate of a mouse. Initially, they were concerned that this might be due to unstable electrodes or movement of the animal. However, additional experiments convinced them that not only was the rhythmic activity real and synchronized with breathing, but it also functioned like a metronome to set the pace for faster theta waves in the hippocampus.
The breathing rhythm affects people’s performance on tasks related to emotion and memory.
During this time, neuroscientist Christina Zelano and colleagues reported similar findings in humans. Utilizing data from electrodes placed on the brains of epilepsy patients by neurosurgeons to monitor their seizures, the researchers discovered that natural breathing synchronized oscillations in several brain regions, including the hippocampus and the amygdala, a key player in emotional processing. This synchronization effect diminished when researchers asked subjects to breathe through their mouths, indicating that sensory feedback from nasal airflow plays a crucial role.
Zelano and her colleagues found that the breathing rhythm not only synchronized activity in brain regions related to emotion and memory but could also influence people’s performance on emotion and memory-related tasks. In one experiment, they monitored the breathing of subjects and asked them to identify emotions expressed in a set of images developed by psychologists to test emotion recognition ability. During this process, subjects identified fearful faces faster while inhaling than while exhaling. In another test, results showed that subjects recalled details of an image more accurately when they took a deep nasal breath.
Recent studies have shown that the breathing rhythm can synchronize activity not only within but also between brain regions. In one study, neuroscientists Nikolaos Karalis and Anton Sirota found that the breathing rate synchronized activity between the hippocampus and the prefrontal cortex in sleeping mice. This synchronization could play a role in the formation of long-term memories, Karalis and Sirota suggested in a paper published earlier this year in Nature Communications. Many neuroscientists believe that initial memory formation occurs in the hippocampus before being transferred to the cortex during sleep for long-term storage—a process thought to require synchronized activity between the hippocampus and the cortex.
What are the effects of breath-focused meditation?
For millennia, yoga practitioners and other ancient meditation traditions have practiced breath control as a means to influence their mental states. In recent years, researchers have become increasingly interested in the biological mechanisms behind these effects and how they might be applied to help those with anxiety and mood disorders.
Helen Lavretsky, a psychiatrist at UCLA, has collaborated for years with neuroscientists and others to investigate how different types of meditation affect the brain and biological markers of stress, as well as immune function. Among other findings, Lavretsky discovered that meditation can improve performance in laboratory memory tests and alter brain connectivity in older adults with mild cognitive impairment, a potential precursor to Alzheimer’s disease and other forms of dementia. In more recent, yet unpublished studies, Lavretsky has shifted her focus to exploring whether simple breath control methods can be beneficial.
Lavretsky, who is also a certified yoga instructor, states, “Although I am a psychiatrist, my research is about how to avoid medication. I think breathing exercises could be a good alternative for many people, especially with more research into which breathing techniques work best for which conditions and how they can be tailored to individuals.
The impact on human speech
Neuroscientist Kevin Yackle and colleagues recently used mice to investigate the interaction between breathing and vocalization. When separated from the nest, newborn mice emit ultrasonic squeaks, which have a frequency too high for human hearing. Yackle, currently at the University of California, San Francisco, noted, “Typically, there are some regular squeaks within a breath, unlike the syllables in human speech.
To understand how this works, the researchers traced back from the larynx, the throat portion involved in sound production. They used anatomical tracking tools to identify the neurons controlling the larynx and traced their connections back to a cluster of cells in the brainstem, an area they named the intermediate rhythmic oscillatory network (iRO). Using various techniques, the researchers found that destroying or inhibiting iRO neurons eliminated the ability to squeak, while stimulating them increased the number of squeaks in each breath.
When the researchers dissected brain tissue slices containing iRO neurons, the cells continued to fire in a typical pattern. Yackle remarked, “These neurons generate a rhythm identical to the animal’s squeaks but faster.”
Further experiments showed that iRO neurons help integrate vocalization with breathing by requiring the preBötzinger complex (the respiratory rhythm generator located in the brainstem) to produce small breaths that interrupt exhalation—allowing a series of short squeaks to fit within a single exhalation. In other words, the rhythmic squeaking is not produced by a series of exhales, but from one long exhalation interspersed with many interruptions.
These findings, reported earlier this year in the journal Neuron, may have implications for exploring human language. Yackle noted that the number of syllables per second falls within a relatively narrow range across all human languages. He suggests that this may be due to constraints posed by the need to coordinate vocalization with breathing.
