The feedback loops between brain and body are profound, leading to the possibility that cognition is not simply a function of the brain alone but of brain and body together.
The brain is an open system, evolving based on its interactions with the external environment and, as it turns out, the internal environment as well. As we learn more about human cognition we are beginning to realize that the factors that contribute to cognition extend well beyond the brain. The feedback loops between brain and body are more profound than perhaps we have realized leading to the possibility that cognition is not simply a function of the brain alone but of brain and body together.
What does this mean? Our traditional way of seeing the brain and body as distinct may be completely wrong. Rather cognition may be a full-body experience with multiple systems interacting to produce human thought, reason and behavior.
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The Gut-Brain Connection
For years scientists thought that some mental illnesses, such as depression and anxiety, might be responsible for gut-related illnesses like irritable bowel syndrome. In a classic example of correlation not equaling out to causation, this particular relationship is now thought to also work the other way around. The connection between our brain and gut is not a one-way street. Just as thoughts of food can send signals to prepare your stomach for a meal, changes in your gastrointestinal system can send signals to the brain that influence your mood, choices, and cognitive outcomes.
The anatomy of the human gastrointestinal system makes this embodied cognition connection fit best into our traditional view of thinking neurons and neurotransmitters. The enteric nervous system is also made up of neurons and neurotransmitters, though significantly fewer. This “second brain” extends through the digestive tract, providing the gastrointestinal system with a system of connections similar to the central nervous system, which consists of the brain and spinal cord. Embodied cognition, however, doesn’t stop here.
One area that has garnered significant attention is the microbiome, or the composition of microorganisms living in a person’s gut. In a 2015 study, microbiomes of 46 patients with varying levels of depression were compared to control microbiomes. The depressed patients had two particular organisms in excess, and had unusually low levels of a third. These differences became more sizable with increased levels of depression. Though more research needs to be done, the study points to the importance of gut health. In response to our new understanding of the gut-brain connections, scientists, doctors and even entrepreneurs are beginning to look to the gut as a potential recipient of treatments for seemingly unrelated ailments.
Cognition and the Autonomic Nervous System
The enteric nervous system is one small part of the autonomic nervous system, the part of your body that controls involuntary action such as smooth muscle movement, breathing, and heart rate. If you’ve ever consciously slowed your breathing in an attempt to calm your emotions, then you’ve used your body to moderate your emotions, and the decision-making processes that often accompany strong emotions.
Arguably the most important automatic system in the human body is heart rate. Your heart provides nutrients to your body, pumping oxygenated blood to the cells that need it, and then pumping deoxygenated blood through the lungs for reoxygenation. The brain begins to die within four minutes of heart failure. That’s how important it is. It is therefore not surprising that your heart impacts cognition. Indeed, a study of middle-aged men showed that heart rate variability corresponded with memory performance. Your heart matters.
The Movement-Cognition Connection
Movement matters, too. Studies showing that the brain integrates cognitive and motor tasks suggest that what your body is physically doing impacts thinking and vice versa. Motor imaging, or the act of imagining movement, activates the same areas in the brain as actually moving. This may be why sports players routinely, and successfully, imagine scoring those winning points as a mode on mental practice.
The physiology of movement also helps you think. If you’ve ever taken a walk to clear your head you can attest to this connection. What’s really going on? Your heart is beating faster and your blood is pumping harder. That extra oxygen isn’t limited to cells involved in movement, your brain is also getting an influx of O2 goodness. Walking has been shown to improve memory.and enhance creative thinking. Not bad for the simplest of exercises.
The impact of movement goes beyond this. The brain is often confused when limbs are missing and produces phenomenon such as phantom pain that suggest that appropriate cognition depends on the presence of those body parts.
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A Disembodied Brain
Do these feedback relationships prove that cognition is embodied? While it may be no surprise that our organs are fundamentally coupled to one another, the bigger question is what happens when the brain is disembodied. If these connections are severed, what does it become? We think of the brain’s outputs as thinking, feeling and behavior. It cannot produce behavior without a body or some mechanism of output, but can it still think and feel appropriately, or even at all?
Thin slices of rat brain bubbled with oxygenated artificial cerebrospinal fluid can survive outside the body for several hours and will continue to produce electrical activity with a structure similar to what is seen in the living organism (thin because otherwise the oxygenated fluid could not reach the cells without operational vasculature) (for example see here and here). Brain tissue can grow in a dish and produce electrical activity and it is even conceivable that this could one day be used to drive simple outputs. Does this mean there is thinking going on?
It may be a long time before we know, but in trying to understand our own cognition, we would be well served to better pay closer attention to our bodies.