What are our brains doing in the background? The autonomic circuit sharing theory may unlock the answer
Are our brains working an extra job all this time without telling us? This question is the heart of the autonomic circuit sharing theory. I believe the answer is yes, and our consciousness results from repurposing neural circuits more frequently used to care for our bodies.
Although I am trained to be an objective scientist, I constructed this theory from a very personal perspective. For years, I have known that I have an extreme ability to feel my body and its processes (Building mind-body links for autonomic control). Additionally, I have learned that this connection is not a one-way street, and control over such internal processes is possible. However, based on our current understanding of the brain, such a strong conscious connection to our inner state is inconceivable. The autonomic circuit sharing theory provides a model that can accommodate both internal and external cognition.
The autonomic nervous system controls and monitors internal functions such as heart rate, blood pressure, and digestion. Anatomically, these functions are believed to be handled in smaller and less complex parts of the nervous system. It is categorized as part of the peripheral nervous system, while the central nervous system is thought to be primarily concerned with sensing the external environment and driving behavior.
Compared to the brainstem and spinal cord, the cerebral cortex, the most outer layer of the brain, is thought to house complex cognition, behavior, and consciousness. The vast majority of neuroscience research is focused on the cortex, partly due to its accessibility and association with cognition. For example, the prefrontal cortex is considered to be the CEO of the brain. Similarly, most neuroscientists focus on cognition, behavior, and our interactions with the external environment, while little attention is given to internal processes (Azzalini et al., Trends in Cognitive Sciences).
Although focusing on externally driven cognition and consciousness is understandable, it may be equally important to explore the role of internal cognition in shaping our understanding of the human brain. We are not conscious of the vast majority of our brain activity. During sleep, there is little external input, and humans appear uniquely conscious. I believe internal cognition is fundamental to who we are and how we function but is understudied. Here, I propose the autonomic circuit sharing theory to inspire explorations into our inner selves while expanding our models of the human brain.
The autonomic circuit sharing theory posits that the brain’s computational power is widely used for processing and acting on internal signals. However, we often remain unaware of this internal data processing because it’s done through circuits that also facilitate consciousness and the processing of external signals. My proposition is that, despite the reuse of neurons, these external and internal processes generally operate in orthogonal, or mutually exclusive paths. In this framework, the brain’s computational power is regularly used to monitor and control bodily functions.
While I write this article on my computer, I know that a significant amount of this machine’s calculations are used to manage its memory, temperature, check for updates, block hack attempts from the internet, and scan files for viruses. In spite of this, these processes operate largely unnoticed because they run in the background. A parallel exists within our brains — a large portion of computation is utilized to process signals from our own bodies while remaining largely undetected.
Such background procedures can harness the machine’s full computational power, often taking precedence. For instance, when a virus is detected, a prompt interrupts active processes and displays an urgent alert. However, while a digital computer can cleanly switch contexts, shared neuronal circuits are often interwoven, leading to inadvertent crosstalk when changing tasks. This interference reminds me of a story from a colleague of mine. She received her first flu vaccination upon starting a new position at our hospital. She recounted how the vaccination triggered fever and vivid hallucinations of her mother back in her homeland. Through the lens of autonomic circuit sharing, this can be interpreted as a complex autonomic system taking over circuits used for vision, cognition and perception to orchestrate defense against a viral marker.
As the COVID-19 pandemic has underscored, we are in a constant battle against pathogens. Unlike computer viruses, which were developed long after the advent of computers, biological pathogens such as bacteria have existed long before the first animals. Given our never-ending struggle against infection, it’s reasonable to presume a part of our brain’s computational power is dedicated to protection.
A modern hospital is a testament to the intelligence and computation needed to keep us healthy. The most academically gifted students are selected for medical school, followed by years of further training. Supporting the doctors, a hospital room is filled with machines monitoring vital signs and constantly checking for any sign of something going wrong. Increasingly, these machines send information to complex machine learning algorithms to detect the faintest signature of mortality. Given this high amount of external human and artificial intelligence focused on our bodies, it’s not surprising that our brain is similarly focused on our internal signals.
The intertwining of circuits for external and internal information processing may explain many thoughts we don’t understand. For example, our brain will fire off neurons in our motor cortex that will guide our hand to stop a mosquito that’s biting us. In that case, a signal leads to a clear motor action. While a mosquito may seem like a minor concern, it may carry a deadly disease. In contrast, what happens if an internal signal of utmost significance demands complex computational processing? In such circumstances, our current train of thought should be interrupted to reprioritize our cognitive faculties. A succinct tweet by Lex Fridman encapsulates our perspective on these interruptions:
In this case, the external goals of food and sex are clear to him. In contrast, I propose that his confusing and contradictory thoughts may be triggered by the processing of internal signals that is undertaken by intertwined circuits. As an example, a neural response to an aggressive bacteria in a precise location in his stomach could indirectly trigger a memory from his adolescence. Those ‘Showerthoughts’ or random epiphanies that many experience while having a shower are another example. In the shower the stimulus is clear — many detections of temperature and pressure changes. Concerning design specifications, he neglects our constant struggle against infectious disease and how this probably demands a significant portion of our brain’s computational resources.
There is mounting evidence that some of the same circuits used for external processing and consciousness are also utilized in autonomic function. A prime example of this superpositioning is the insular cortex, a region crucial for processing social emotions such as empathy and compassion. This region is also believed to be a neural correlate of consciousness (A.D. Craig, Nature Reviews Neuroscience). More directly, it helps us understand how we feel (interoception) and receives visceral inputs from our bodies. Activity in the insula is associated with signals of thirst, fatigue, pain, breathing rhythm, and heart rate. A second region, the motor cortex, which drives the swatting response to a mosquito, was found to mobilize infection-fighting cells from the bone marrow in mice (Poller et al., Nature) and pain related immune responses in the spleen (Zhu et al., Nature Neuroscience). Traditionally, the motor cortex is considered to function in planning and control of voluntary movements rather than fighting infections. Another example is the occipital cortex, which is primarily believed to process visual information and not much else. Surprisingly, activity in this region was correlated with the gastric rhythm of the stomach in two recent brain imaging studies (from Dr. Catherine Tallon-Baudry’s lab, Ignacio Rebollo et al., eLife and Journal of Neuroscience). Beyond rhythmic correlation, Mayeli and colleagues discovered that a vibrating pill elicits neural responses in the occipital cortex (preprint). Lastly, experiments on mice from Dr. Asya Rolls’ lab suggest that signals from the gut are processed in the brain to remember and drive local immune responses (Koren et al., Cell). These findings collectively show that multiple cortical regions, thought to exclusively process external signals, also assess and act on internal information from our bodies.
The autonomic circuit sharing theory is greatly aligned with the visceral theory of sleep by the late Dr. Ivan Pigarev. This hypothesis posits that the cerebral cortex switches from processing external information to internal signals during sleep (Ivan Pigarev, Neuroscience and Behavioral Physiology). This theory has been further expanded to explain the observation of ‘local sleep’, where a particular brain region enters a sleep-like state (Pigarev and Pigareva, Frontiers in Systems Neuroscience). The autonomic circuit sharing theory fully supports the switching of circuits across the sleep-wake cycle. If the circuits are shared, external inputs and actions should be restricted while internal signals are processed and acted upon. When internal processing picks up, it’s plausible that the overlapping circuits for external processing also become activated, resulting in dreams. Such inadvertent activations could explain why dreams are often bizarre and nonsensical. There may be exceptions that involve aligned circuits, such as a full bladder causing dream about going to the bathroom. It’s important to remember that these circuits required potty training to be under our consciousness control, allowing us to understand the driver of such dreams. Personally, when I activate autonomic circuits, I often end up falling asleep. A minor divergence in my theory is that I propose that the autonomic circuits, while mostly orthogonal, remain active during wakefulness, even beyond periods of local sleep. Another extension is that I suggest our internal cognition handles events beyond the visceral organs to include the whole body. Just as a computer’s virus scanner is always on the lookout, I believe our bodies are continuously vigilant and responsive to internal problems wherever they arise.
Unexplained spontaneous neural activations in the brain could be evidence of this continuous vigilance. In brain imaging studies, scientists have long pondered over the role of the default mode network. This network is one of the many resting state networks, characterized by the coordinated activation of several brain regions during resting periods, when the participant is not engaged in a specific task. It was once termed the ‘task-negative network’ as it deactivates when subjects perform an external task. At the level of neurons, an extensive study of the mouse visual cortex found that a large group of neurons (34%) did not reliably respond to any presented visual stimuli. The authors labeled this class of neurons as ‘none’, which fits the amount of investigation such ‘spontaneous’ activations receive (de Vries et al., Nature Neurosceince). Most recently, scientists discovered that the mouse neurons that are active without visual stimuli have molecular signature which is linked to acetylcholine, a key neurotransmitter of the autonomic nervous system (Bugeon et al., Nature). I suspect this unexplained neural activity may stem from shared circuits that also process internal or bodily signals. This view was first proposed by Azzalini, Rebollo, and Catherine Tallon-Baudry after they found an overlap between the resting-state and visceral brain networks (Trends in Cognitive Sciences). Thus, internal signal processing could explain the widespread and mysterious brain activity that neuroscientists often observe.
A key characteristic of our brains is plasticity, the ability of neurons to rewire to facilitate learning new languages or how to play a musical instrument. If neural circuits are shared, plasticity resulting from external signals could disrupt autonomic circuits that process internal signals
For instance, leading a sedentary life devoid of exercise could result in circuits optimized for external signals but not internal ones. This could explain the massive health benefits of exercise and may also clarify why character-skill training programs that enhance self-control reduce physical health. Researchers have quantified this trade-off in teenagers, whose brains are highly plastic. They discovered that although training increased self-control, it caused their blood cells to age faster than expected (Miller et al., PNAS). Learning self-control, which teaches one to restrain their thoughts, may inadvertently lead to blocking overlapping autonomic circuits, resulting in poorer health. Antipsychotic medications, more intense tool of behavioral change, significantly elevate the chances of developing diabetes, obesity, and cardiovascular disease. Circuit sharing may also explain why brain regions dedicated to specific tasks in experts are smaller than in non-experts. For instance, the brain region controlling the foot in professional football players is thinner than in average individuals. This smaller size might result from the pruning of overlapping autonomic circuits to prevent an autonomic signal from interfering with a shot on goal. This scenario suggests that plasticity is competitive, and learning should accommodate internal information processing. At a high level, the competitive plasticity from shared autonomic circuits provides explanations for clear yet poorly understood observations.
Apart from broadening our comprehension of the human brain, the autonomic circuit sharing theory could have practical implications in mental health. Although speculative, it offers a new framework for understanding psychiatric diseases and neurodevelopmental disorders.
For example, the autism spectrum could be attributed to variable overlaps between circuits for internal autonomic processes and social cognition. In this context, both molecular (Gandal et al., Nature) and neuroimaging studies (Hong et al. Nature Communications) of autism have found that the borders of cortical brain regions are blurred. Experiments have shown that autistic individuals perceive a stronger connection between the mind and body, in contrast to neurotypical individuals who tend to view them as more distinct and separate (Berent et al., PNAS).
Schizophrenia may also be typified by inappropriate crosstalk or interference between circuits that process internal and external sensory information. For example, a minor disruption in gut homeostasis could trigger a visual hallucination in the occipital cortex, where gut and visual processing overlap. Depression might result from circuits becoming inundated with external information, causing rumination that robs computational power needed for processing of internal visceral signals. This could explain why depressed individuals experience persistent aches and pains, changes in appetite, and other bodily symptoms that autonomic circuits should manage. This is supported by a study of over 150,000 people that split health measures between the brain and body. They found that poor body health was a stronger marker of individuals diagnosed with depression than signals from the brain (Tian et al., JAMA Psychiatry).
Furthermore, electroshock therapy is an effective treatment for depression; however, it does lead to memory loss. Similarly, exercise has been found to alleviate depression, but it also induces forgetting (in mice — Epp et al., Journal of Neuroscience). I hypothesize that this forgetting process might free up synapses for autonomic control or cause us to forget how to block autonomic signals. At an extreme, individuals who have attempted suicide have been observed to have blunted or numbed interoception (DeVille et al., eLife). While these connections are highly speculative, they could shed light on ailments that urgently need new treatment strategies.
In conclusion, the autonomic circuit sharing theory provides a model to understand what our brain is doing in the background. Although the high-level processing of internal signals is understudied, evidence of autonomic circuit sharing appears at multiple levels in both mice and humans. As someone with an extreme level of autonomic self-awareness and control, I hope to serve as a case study to stimulate research in this field. By writing this article, my main goal is to find scientists interested in investigating individuals like me and find others that can deeply connect with their autonomic selves. If you are interested in talking to me, please do not hesitate to email me at bodymindbook@gmail.com. I believe that by studying and sharing our experiences, we can better understand autonomic cognition and find new ways to improve mental and physical health.
Joe Somata is a pseudonym for an inquisitive scientist that holds a Ph.D. degree and has first and senior authored several biomedical publications in peer-reviewed journals. He authored this article with the help of OpenAI’s GPT-3 and GPT-4. He’s on Twitter, and you can find his guide for Building mind-body links for autonomic control on Amazon.
