Patients suffering from functional dizziness (often also called somatoform or psychogenic dizziness) usually recur to different physicians who also have a hard time to identify diagnoses when no organic cause can be identified. An experiment at the Munich Technical University (in German: Technischen Universität München or TUM) has for the first time clarified possible causes of the disease. Patients have problems with sensorimotor processing in the brain that are similar to those of people with organic causes of dizziness.
Several years ago, the Munich-based researchers had already put forward the thesis that functional diseases are based on faulty processing of perceptual stimuli. The team led by Prof. Nadine Lehnen, senior physician in charge of psychosomatics at the TUM, has now been able to support this thesis with an initial experimental pilot study.
Eight people suffering from functional dizziness and eleven healthy people took part as comparison groups. In addition, data from vertigo patients with organic defects who had already undergone the same experiment in previous studies were used. They had either a cerebellar disorder or no functional balance nerves.
During the experiment, the participants sat in a dark room where, in rapid alternation, points of light appeared on the left or right of the wall, to which they were to focus. The eye and head movements during the eye movement were recorded. Then they were given a helmet with weights to change the inertia of the head. When turning, the head wobbled strongly. The experiment was carried out with and without a helmet.
While the healthy adapted their movement fast to the new conditions and the head did not wiggle soon anymore, all test persons with functional dizziness had a hard time. What amazed the research team was the fact that the latter behaved in exactly the same way as the volunteers with massive organic causes of dizziness.
"Our results make it impressively clear that functional dizziness manifested itself in the same way as severe physical diseases, for example after complete loss of the function of the balance nerves. This reflects how severely these people are restricted," said Nadine Lehnen.
On the basis of previous experience, which is stored in the brain in the form of so-called learned models, people form an expectation about the sensory impressions created by a movement. This expectation is compared with the information, for example, from the organs of equilibrium. If the head behaves differently than normal, the two information no longer fit together. There is an imbalance between expectation and reality, which is called a "prediction error".
"Healthy people can easily perceive this error, process it and adapt their movements. In functional vertigo patients, however, sensorimotor impressions do not seem to be correctly processed. They rely primarily on their stored model, which however no longer fits the new reality," she explains and adds: "It was exciting for us that learning was possible with them - but only to a limited extent. It would, therefore, be important for them to treat these people with therapeutic approaches that take this processing deficit into account. In a planned large-scale study, the current results will be put to the test once again.
Nadine Lehnen, Lena Schröder, Peter Henningsen, Stefan Glasauer, Cecilia Ramaioli: Deficient head motor control in functional dizziness: Experimental evidence of central sensory-motor dysfunction in persistent physical symptoms, Progress in Brain Research, 2019, DOI: 10.1016/bs.pbr.2019.02.006