Researchers expand our understanding of how the body and brain communicate

The human brain constantly receives information from the body, specifically from internal organs such as the heart and lungs. This information seldom reaches consciousness but is crucial for maintaining a healthy body and for influencing performance in the brain, including perception, emotion, and cognition. Now, researchers are investigating how exactly the brain processes the incoming stream of information from the heart and lungs, leading to a broader understanding of brain-body integration and the resulting health or disease.

Publishing their work in the Proceedings of the National Academy of Sciences (PNAS), co-senior authors Vibhor Krishna, MD, associate professor of neurosurgery at the UNC School of Medicine; Ali Rezai, MD, director of the Rockefeller Neuroscience Institute and associate dean of neuroscience at the West Virginia School of Medicine; and Olaf Blanke, MD, PhD, director of the laboratory of cognitive neuroscience at the Swiss Federal Institute of Technology, discovered that specific neurons in the thalamus are actively involved in processing cardiac and respiratory signals.

"Each heartbeat and every breath create a rich, incoming stream of sensory information for the human brain," said Krishna. "However, a deeper understanding of how the brain integrates this information has remained elusive. We have been interested in discovering how the human brain achieves the integration of cardio-respiratory information and whether its breakdown is linked to any disorders of the brain, heart, or lungs observed in the clinic."

Over the years, clinical and research teams collaborated to painstakingly study this integration using an established technique of microelectrode recording during deep brain stimulation surgery. Using a new approach to study single neurons in three different thalamic regions, the researchers were able to observe a direct functional involvement of thalamic and subthalamic neurons in processing cardio-respiratory signals. This information can help to better characterize how subcortical regions of the brain process signals through a functional pathway from internal organs.

To complete this work, the research team took advantage of microelectrode recordings during deep brain stimulation for patients undergoing treatment for neurological conditions. The researchers then used these recordings to investigate the activity of single neurons related to cardiac and respiratory functions in three subcortical regions: ventral intermedius nucleus and ventral caudalis nucleus of the thalamus, and the subthalamic nucleus.

They found that about 70% of the recorded neurons were modulated by either the heartbeat, the cardiac inter-beat interval, or the respiration.

These cardiac and respiratory response patterns varied largely across neurons both in terms of timing and their kind of modulation, the authors wrote. A substantial proportion of these visceral neurons -- about 30% -- were responsive to more than one of the tested signals, underlining specialization and integration of cardiac and respiratory signals in subthalamic nucleus and thalamic neurons.

"We think our work will be significant for several medical specializations, including cardiology, pulmonology, neurology, psychiatry, and psychological research," Krishna said.

Rezai added, "Better understanding of the human brain is the next frontier. And interdisciplinary collaborations between functional neurosurgeons and neuroscientists will enable us to gain an unprecedented window into the inner functioning of the human brain."

Applauding this research as a significant step forward, Nelson Oyesiku, MD, PhD, chair of the UNC Department of Neurosurgery, said, "We understand that the brain maintains homeostasis throughout the body through direct neurological and endocrine regulation. This research reveals that the incoming information from the heart and lungs is processed in the thalamic and subthalamic brain regions, besides other regions, enabling our brain to effectively assume its role in regulating bodily functions."