Anxiety and negative emotions reduced by brain circuit that consciously slows breathing

By Dr. Chinta SidharthanReviewed by Danielle Ellis, B.Sc.Nov 22 2024

Researchers at the Salk Institute have discovered a brain pathway that connects the frontal cortex to the brainstem, offering potential therapeutic targets for anxiety, panic, and PTSD.

In a recent study published in Nature Neuroscience, researchers investigated the neural pathways linking the dorsal anterior cingulate cortex (dACC) and the pontine reticular nucleus caudalis (PnC) in mice to understand the neuronal pathways that slow breathing and alleviate negative emotions such as anxiety.

By exploring this corticopontine circuit, the study provided insights into how slow breathing influences emotional regulation, offering new perspectives on the mechanisms of stress regulation.

Background

Breathing is vital for maintaining oxygen levels and plays a key role in emotional and behavioral regulation. Humans can consciously adjust their breathing, often employing slower rhythms to reduce stress and anxiety. While the brainstem controls automatic respiratory patterns, higher brain areas such as the anterior cingulate cortex (ACC) contribute to voluntary breathing, especially during activities such as speaking and swallowing.

Furthermore, cortical control of breathing may also impact emotional states, as anxiety is often associated with rapid, shallow breathing, whereas slow breathing promotes relaxation. However, despite the established link between respiration and emotion, the mechanisms through which cortical inputs influence the breathing centers in the brainstem remain unclear.

Hitherto, research on this subject has largely focused on brainstem pathways, leaving significant gaps in understanding how top-down control integrates with emotional responses. Investigating these mechanisms could help understand the biological basis for using slow breathing techniques in managing stress and anxiety.

About the study

In the present study, the researchers investigated a corticopontine circuit connecting dACC to the PnC in mice. Using retrograde tracing with cholera toxin subunit B, they identified the neurons in the dACC that project to the PnC.

Furthermore, light-sensitive proteins — channelrhodopsin-2 for activation and halorhodopsin for inhibition — were expressed in these neurons using adeno-associated viral vectors. The study then used optogenetics, which is the use of light to control the activity of cells, such as neurons, to perform selective manipulation of these circuits.

The breathing patterns were recorded using inductance plethysmography and nasal thermistor sensors under light anesthesia and during conditions where the mice were behaving freely. Additionally, the neural activity in the pathway linking dACC to PnC (dACC→PnC) was monitored using calcium imaging, using GCaMP indicators, which are genetically encoded calcium indicators containing calmodulin and green fluorescent protein.

The neural activity monitoring was conducted during specific behaviors such as drinking and exploring anxiety-inducing environments. The study involved behavioral experiments such as the elevated plus maze and light-dark preference tests to evaluate anxiety-like behaviors.

The researchers also identified downstream targets of the dACC→PnC corticopontine pathway that project to brainstem respiratory centers and forebrain regions implicated in emotional regulation. These projections were mapped using anterograde tracing and optogenetic activation of specific axon terminals.

Additionally, the dependence of the dACC→PnC circuit on synchronizing breathing during purposeful actions, such as drinking, was also assessed. This involved manipulating the circuit’s activity and analyzing changes associated with respiratory patterns and behavioral outcomes.

Results

The researchers found that the dACC communicates with the PnC to regulate breathing and anxiety, and the activation of the dACC→PnC circuit reduced breathing rates and alleviated anxiety-like behaviors without altering emotional valence, which determines whether an emotion is negative or positive.

This pathway included neurons in the PnC that used gamma-aminobutyric acid (GABA) to inhibit brainstem respiratory centers and project to the forebrain regions involved in emotional regulation, which enabled simultaneous modulation of breathing and anxiety.

Furthermore, during behaviors requiring respiratory coordination, such as drinking, the dACC→PnC circuit showed increased activity, correlating with slower breathing. In anxiety-inducing situations, the activation of the circuit promoted slower breathing patterns and reduced anxiety-related behaviors.

For instance, the optogenetic activation of the dACC→PnC pathway increased exploration in anxiety tests such as the elevated plus maze and light-dark preference task, indicating reduced anxiety. Conversely, inhibiting this circuit reduced exploration, heightened anxiety-like behaviors, and impaired breathing coordination during purposeful activities.

Moreover, mapping the circuit’s connectivity revealed that dACC→PnC neurons influence both brainstem respiratory centers and the forebrain structures critical for emotional responses. This dual role highlighted the circuit’s capacity to synchronize respiratory and emotional states.

Meanwhile, optogenetic manipulation confirmed that the activity of the pathway directly regulates anxiety relief through its effect on breathing rhythms, establishing a neural link between slow breathing practices and emotional regulation.

Conclusions

Overall, the study identified the dACC→PnC circuit as a key regulator of breathing and emotional states. The results indicated that this pathway modulated brainstem and forebrain connections to slow breathing and bring about anxiety relief, which offers important insights into how deliberate respiratory practices reduce stress.

These findings revealed potential targets for therapies addressing anxiety and related conditions and emphasized the importance of cortical control in respiratory and emotional integration.