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The Biology Behind 'Psychosomatic' Illness

Bret S. Stetka, MD; Peter L. Strick, PhD|October 07, 2016
Introduction

Editor's Note:
University of Pittsburgh neuroscientist Peter L. Strick, PhD, and colleagues recently published a study[1] in Proceedings of the National Academy of Sciences tracing the neural circuitry connecting various motor and affective regions of the brain to the adrenal medulla and possibly other organs. Dr Strick feels the findings could help explain how so-called "psychosomatic" conditions arise and suggest treatment targets for a variety of disorders. Medscape recently spoke with Dr Strick about his research.

Medscape: Can you give us some background on your new study tracking the link between the brain and adrenal medulla?

Dr Strick: We developed a technique using viruses as tracers to reveal neural networks in monkeys. In the past, I've used this technique to study connections in the motor system, for example, that define the cortical motor areas and how they connect to different muscles. However, in the past, we've been limited to transporting the tracers between just two or three neurons. In our new study, we've successfully gotten the virus to pass through a chain of four to six connected neurons.

In the past, it was thought that one or perhaps two cortical areas might be involved in the control of organs. So we were surprised to see the number of different areas that were involved—locations that included cortical areas involved in motor control and higher-order cognition and affect.

From a broad perspective, it's clear that we can use this tool to look at how the cerebral cortex affects such things as gastrointestinal function and immune function and has cognitive influences on, for example, hypertension, diabetes, and the physical stress response. The findings were interesting not only because of what we found, but also the potential to use this approach in the future to look at other mind/brain interactions.

Medscape: What virus did you use as your tracer?

Dr Strick: We used a strain of rabies virus that is taken up by synapses and transported back to the neuron cell bodies. It's a live virus and replicates in the cell bodies, and then again has the unique property of crossing synapses—of moving transsynaptically to sequentially label neurons in a chain of connections.

Another reason why it's a wonderful tracer is that the nervous system continues to look pristine; there is no obvious cellular damage to the infected neurons.

Some people have said that if you look at six synapses in the brain, you'd get everywhere (like that game "Six Degrees of Kevin Bacon"), and that the data would be highly uninterpretable. But that's not the case. The brain connections and networks are highly specific, as our study showed.

Medscape: What other brain/body connections are you currently studying?

Dr Strick: The second author on the study, David Levinthal, is going to look at the cortical influence on the stomach in the gastrointestinal system as a potential basis for the cognitive influences on irritable bowel syndrome. And there is a student in my lab who is looking at the cortical influences on the heart. There is evidence that strong emotional stimuli, positive or negative, can cause sudden unexpected death—we know that in epilepsy, sudden heart attack is a significant cause of death, possibly influenced by the brain's connection to the heart. Heart attack is also a problem with traumatic brain injury and stroke. We plan to look at connections to the pancreas and spleen as well.

Medscape: In your paper, you speculate that the findings suggest a basis for so-called "psychosomatic" illness. Can you elaborate on this?

Dr Strick: The word "psychosomatic" is loaded and implies that something is all in your head. I think now we can say, "It is in your head, literally!" We showed that there is real neural circuitry that connects cortical areas involved in movement, cognition, and feeling with the control of organ function. So what have been called "psychosomatic disorders" are not imaginary.

In addition to affective and higher cognitive centers, we found that there are motor areas, particularly the primary motor cortex region, that are involved in the control of the adrenal medulla. There are regions in the cortex that control axial body muscles, so it's not a leap to then say that there is something about the core muscles and core exercise that affects stress response.

Also, despite me being one of the least meditative guys I know, functional imaging studies have shown that certain areas of the brain are active during mindfulness meditation. I get the sense that this brain activity might inhibit stress response in part by ultimately acting on the adrenal medulla.

Medscape: Do you see any therapeutic implications of your work?

Dr Strick: Yes, absolutely. In fact, the second author was just trained in transmagnetic stimulation. Now that we have a road map, we can start thinking about stimulating those cortical areas and activating or inactivating them to have an impact on, for example, irritable bowel syndrome. It's not unlike how deep-brain stimulation is used for Parkinson disease and depression.

You could also imagine performing functional imaging studies in someone with post-traumatic stress disorder and then doing a particular cognitive maneuver, or using brain stimulation to alter brain activity and help control symptoms. Hopefully, researchers will use their imaginations to come up with creative therapeutic approaches. I could go on a little sermon here.
References

Dum RP, Levinthal DJ, Strick PL. Motor, cognitive, and affective areas of the cerebral cortex influence the adrenal medulla. Proc Natl Acad Sci U S A. 2016;113:9922-9927. Abstract

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The Biology Behind 'Psychosomatic' Illness. Medscape. Oct 07, 2016.