New research published in Scientific Reports suggests that breathing has a crucial role in coordinating brain activity in the prefrontal brain network during wakefulness. The findings provide new insights into the relationship between respiration and cognitive processing, and could have important implications for meditative practices that involve controlled breathing.
Previous studies have indicated that respiration can have significant effects on brain activity and cognitive processes. For example, changes in breathing patterns have been linked to alterations in attention, arousal, and emotional states. The respiratory system also shares neural pathways and connections with brain regions involved in cognition.
For their new study, the researchers focused on a specific structure called the nucleus reuniens (Reu), which acts as a link between the prefrontal cortex and the hippocampus. The researchers wanted to investigate how the synchronization of neural activity, particularly in the gamma rhythm frequency range, is organized in this network.
The gamma rhythm is a specific pattern of electrical activity in the brain characterized by high-frequency oscillations in the gamma frequency range, typically around 30 to 80 cycles per second (Hz). It is a prominent feature of brain activity and is associated with various cognitive processes, including attention, perception, memory, and consciousness.
“We were intrigued by the idea that breathing can cause brain networks to continuously switch between synchronized states and desynchronized states. The synchronization of neural activity is a fundamental brain mechanism that is very closely linked to cognition, particularly when it emerges at the gamma frequency in prefrontal regions,” explained lead author Diellor Basha, a PhD candidate at Laval University and member of the Timofeev Lab.
“It is also well-known that, during waking, much of the variance in neural activity comes from sensations that we evoke by our own movements. Breathing is one of those behaviors that stimulates a surprisingly large set of senses, ranging from mechanical and thermal sensations evoked by air flowing through the nose, olfaction, the feeling of chest expansions, chemosensation from fluctuating CO2 and O2 levels and even hearing, which can be stimulated by the sound of air flow.”
“Unsurprisingly, breathing can drive neuronal activity in numerous brain regions as has been demonstrated in a recent wave of studies. Understanding how breathing affects brain activity helps us understand fundamental questions relating to cognitive experience and the inextricable relationship between body and mind.”
To conduct their study, the researchers used animal models, specifically cats and mice. They implanted electrodes in different brain regions, including the prefrontal cortex, hippocampus, midline thalamus, and various cortical areas. They recorded local field potentials (LFP) and performed intracellular recordings to measure the electrical activity of individual neurons. The researchers also monitored the animals’ respiration by recording temperature changes near the nostrils or using a piezoelectric sensor strip placed on the animal’s thorax.
The researchers found the gamma rhythm played a crucial role in understanding the relationship between respiration and brain activity. There was a coupling or synchronization between gamma oscillations and the respiratory cycle in certain brain regions, specifically the prefrontal cortex and the midline thalamus. This means that the gamma oscillations in these regions were modulated or influenced by the respiratory cycle, with specific phases of the oscillations aligning with different phases of breathing.
“The main takeaway of our study is that breathing is a major pacemaker in cognitive areas of the waking brain,” Basha told PsyPost. “During exhalation, prefrontal regions go into a gamma oscillation and synchronize with the nucleus reuniens of the thalamus, an area which acts as a crucial link between the prefrontal cortex and the hippocampus.”
“By facilitating long-range coordination across this cognitive network, breathing cycles can impose specific time windows that promote cognitive processing. This may explain how breathing exercises or the conscious control of breathing in meditation can modulate cognitive and emotional states.”
Interestingly, the synchronization between breathing and brain activity was mainly observed during wakefulness, indicating that it is specifically related to the conscious state of being awake.
“As animals began to sleep, we observed that gamma oscillations decoupled from breathing cycles and became linked instead to internal sleep oscillations such as spindles,” Basha explained. “We found this observation particularly surprising since breathing continues with regularity even during sleep. It suggests that there is a yet-undiscovered process that controls the coupling of gamma oscillations to breathing in the waking state.”
The researchers also explored where the breathing-related signals in the brain come from. They suggest that a part of the brain called the entorhinal cortex, which receives input from the olfactory (smell) system, might be involved in generating the breathing-related signals.
“One of our findings was that breathing entrained synaptic activity in the nucleus reuniens of the thalamus,” Basha told PsyPost. “However, it is unclear what are the inputs to the thalamus that drive this synaptic activity. As any student of neuroscience knows, the only sensory structure that does not project to the thalamus is the olfactive system, which suggests that an alternative pathway communicates respiration cycles to the thalamus.”
“Secondly, we studied waking behavior in quietly resting animals and we did not study how gamma oscillations change as breathing rate increases during active waking behaviors such as exploration. For this question, we invite readers to read two excellent studies that have comprehensively looked at the link between waking behavior and brain activity: Karalis and Sirota, 2022 Nature Communications and Girin et al. 2021 Scientific Reports.”
“The brain is constantly monitoring the sensations that we evoke by our own behavior,” Basha said. “With every breath you take, every move you make, every bond you break, the brain is watching you š¶ š.”
The study, “Respiration organizes gamma synchrony in the prefronto-thalamic network“, was authored by Diellor Basha, Sylvain Chauvette, Maxim Sheroziya, and Igor Timofeev.
