August 6, 2019
When life leaves you, literally, “in the lurch”—suffering from functional dizziness that cannot be linked to an organic cause, no matter how many doctors you may visit or tests you may take—is there any hope for recovery?
For the very first time, researchers at the Technical University of Munich (TUM) in Germany say the answer is yes: Results of a study released on August 5 indicate that people who frequently feel light-headed, woozy, or unbalanced may be suffered from perception disorders.
Specifically, they have found symptoms that resemble those associated with dizziness due to organic causes-but that, instead, are caused by a malfunctioning of the processing of sensory-motor signals in the brain.
The Munich researchers already had postulated several years ago that such functional disorders might be caused by faulty processing of sensory stimuli. The team, headed by Professor Nadine Lehnen, senior physician for Psychosomatic Medicine at the TUM University Hospital rechts der Isar [located to the right of the Isar river], was able to provide more support for this theory by conducting an experimental pilot study.
Eight patients with functional dizziness, along with 11 healthy subjects, participated in the study. The researchers also used data from patients whose dizziness had been linked with organic defects—and who had previously taken part in the same experiment. Those patients had either a cerebellar disorder or a complete loss of functioning vestibular (equilibrium) nerves.
During the experiment, the participants sat in a dark room looking straight ahead while lights were flashed to their right and their left. They then were asked to look in the direction of the light points. Their eye and head movements during the gaze shifts were recorded. The subjects then were fitted with a weighted helmet to alter the inertia of their head. This resulted in significant head wobbling. The experiment was performed with and without the helmet.
Whereas the healthy subjects quickly adapted their movements to the new circumstances and managed to stop their head from wobbling, all the subjects with functional dizziness found the task difficult to perform. What surprised the research team was the fact that the latter behaved in exactly the same way as subjects with dizziness due to massive organic defects.
“Our results clearly show that functional dizziness is manifested exactly like severe physical disorders, for example after complete functional loss of the vestibular nerves. This reflects how severely impaired these people are,” Professor Lehnen said in a press release..
Based on previous experience, which is stored in the brain in the form of learned models, people have a certain expectation about the sensory impressions evoked by a movement. This expectation is compared with information from the vestibular organs. If the head behaves differently than normal, the two sets of information no longer match. This creates an imbalance between expectation and reality, a state known as prediction error.
“Healthy people can easily perceive this error, process it and adapt their movements accordingly. Patients with functional dizziness, by contrast, do not appear to process sensory-motor impressions correctly. They rely primarily on their stored model, but it no longer matches the new reality,” Nadine Lehnen explains.
Can the condition be improved? She notes, “We were excited to observe that they are still able to learn—albeit only to a limited degree.” It would therefore be important to treat such patients using therapeutic approaches that take into account this processing deficit. A large-scale study is planned to corroborate the recent findings.
Research contact: Nadine.Lehnen@mri.tum.de
