For adaptive behaviour, it is necessary to estimate what is happening in the environment around us well. This applies not only to the external environment but also to what is happening inside our bodies. However, patients with neuropsychiatric disorders, including those suffering from functional movement disorders, are known to fail to properly evaluate information coming from the body's internal environment and to attach too much or too little importance to it. Even such a simple task as to correctly count the beats of one's own heart can be a real challenge for a person with an interoception disorder. The number of beats they would count usually does not match the number of beats measured by the ECG or other heart rate monitors.
It was these patients with a functional movement disorder that were included in the study of Dr Sojka. Functional movement disorder is a relatively common but little-studied disease in which there is a sudden onset of tremor or paralysis of the limbs without an obvious neurological cause. The research team questioned whether the discrepancy in the perception and evaluation of perceptions from one's own body could be related to changes in the white matter structure of patients' brains. As DDrSojka explained in the interview, “Today, the notion that the brain is organized into many networks with different functions is prevalent in neuroscience. White matter forms the pathways that connect the various parts of the brain and therefore constitutes the basis of every network."
In Dr Sojka's study, the structure of white matter in patients was monitored by special neuroimaging methods, using which they were able to compare the cohesion of white matter between patients with functional movement disorders and healthy individuals. They used the previously mentioned heart rate counting test and simultaneous heart rate measurement using an ECG to measure the interoception. They then compared the results of measuring interoception with neuroimaging. They found that in patients with a functional movement disorder, there is a connection between a reduced ability to perceive information from the body's internal environment and the structure of the interoceptive network, which is responsible for processing this information. On the contrary, this association has not been demonstrated in healthy individuals.
Research on white matter in patients with functional movement disorders is still in its infancy. However, according to Dr Sojka, the hypothesis of a disturbed interoceptive network has been discussed for some time in the community of researchers dealing with this disease. Dr Sojka's team's findings provided empirical evidence for this hypothesis for the first time and therefore present a significant contribution to the knowledge about the disease's pathophysiology. We asked Mgr. Petr Sojka, PhD about the details of the research.
You focused on patients with motor functional neurological disorders, abbreviated mFND. It is a relatively common diagnosis that neurologists encounter in their clinical practice. In some patients, besides other symptoms, non-epileptic seizures also occur. How do these seizures differ from epileptic ones?
Even for the eye of an experienced neurologist, it can be difficult to distinguish a non-epileptic seizure from an epileptic one. For this reason, video-EEG monitoring is the gold standard for diagnosing non-epileptic seizures, where we can record the EEG during the seizure. Patients with non-epileptic seizures do not have the same pattern of activity seen in epilepsy when captured in the EEG recordings. Suppose we cannot register a seizure for a prolonged period during video-EEG monitoring. Then so-called induction tests are used, where, for example, the seizure is induced by a suggestion. The patient is given a placebo and told that it is a seizure-inducing substance. These suggestions do not work in patients with epilepsy.
The existence of grey matter is known to the general public, while white matter is relatively in its shadow. As you mention in your paper, white matter research, especially in mFND, is still in its infancy. What led you to this pioneering approach?
mFND is a complex disease in which we do not expect one or a few gray cortex areas to be responsible for the onset and maintenance of symptoms. Instead, we believe that disruption of whole neural networks that connect multiple brain areas is the leading cause. Today, the notion that the brain is organized into many networks with different functions is prevalent in neuroscience. E.g., the default mode network is active during introspection or when dealing with memories. On the other hand, the central executive network is activated when the brain solves a task. White matter forms the pathways that connect the various parts of the brain and therefore constitutes the basis of every network. In magnetic resonance imaging, we can measure which pathways have lower integrity and use this information to make inferences about dysfunctional communication between different brain areas within one network or between multiple networks.
In the article, you mention studies that describe the different responses of the body and the emotional reaction to a particular perception, such as stress, in patients with mFND. How does current science explain this contradiction between body and mind? How are differences in perception and physiological responses tested?
The brain's main task is to estimate accurately how the surrounding environment works. Based on the estimation, the brain can then act effectively through the body. Just like in a darkened room, we try to estimate the shapes and distances of things so that we can reach the switch safely and turn on the light. For the brain, the body is such a darkened room, i.e., space from which a lot of incomplete information comes, and the brain tries to guess their origin. In neuropsychiatric diseases, including mFND, the brain may stop estimating information from the body's internal environment correctly and attach too much importance to certain sensations - for example, an increased heart rate after climbing stairs begins to be interpreted by the brain as a signal of the disease.
The easiest way to measure the difference between physiological response and the subjective perception of that response is to count one's heart rate, which we simultaneously record using an ECG or other device that measures heart activity. Suppose the number of heartbeats measured and counted by a person differs significantly. Then we can conclude that the person is not so much aware of the signals coming from the body or that he or she is more aware of them than usual - the latter scenario can occur in people suffering from anxiety or panic attacks. But we can also find the difference between the subjective perception of how unpleasant an image is for a person using a numerical scale and at the same time measure the stress response using skin resistance. Other ways of measurement are recordings of people's complaints about memory and testing their objective performance in memory tasks. A significant difference between the subjective report and the measured values may mean that the brain puts too much importance on some perceptions or, conversely, is not aware of some information.
In the article, you describe your observations of the connection between the white matter anatomy of patients with mFND and interoception, i.e., the ability to perceive their bodies. What did you manage to find out?
We found that only in patients with mFND their reduced ability to perceive information from the body's internal environment is related to the disruption of the interoceptive network structure, i.e., the network that processes interoceptive information. We did not observe this association in the healthy control subjects. The community of researchers dealing with mFND has been discussing the hypothesis of disruption of the interoceptive network in this group of patients for some time. For the first time, our team provided empirical evidence for this hypothesis.