Thalamocortical Dysrhythmia and functional brain disorders
Despite international research and various scientific publications, the mechanisms of functional brain disorders remain rather elusive. Parkinson’s disease, essential tremor, neurogenic pain as well as some forms of Epilepsy and Tinnitus have been proven to be triggered by a similar dysfunction in the brain named thalamocortical dysrhythmia. (Reference 1)
Two central structures of the brain, the thalamus and the cortex, are connected in loops with each other. Their organization and function can be compared to the ones of an orchestra. The thalamus in the center plays the role of the conductor and leads the cortical areas around him as the players. Together they produce rhythms, which can be recorded as the electroencephalogram.
A deficient area as small as few millimeters in the brain may dysbalance the fine and complex equilibrium of this thalamocortical orchestra and lead to a functional brain disorder. Depending on where this area is located, it will result in one of the mentioned disorders due to overactivity of the corresponding sector. To illustrate it in a simplified way, it is as if something would pull constantly on the arm of the conductor. He is therefore not able to lead the orchestra correctly anymore. Because of this, different sectors of the orchestra play too loud, causing the appearance of the different functional brain disorders.
Treating functional brain disorders with Ultrasound Functional Neurosurgery
A method, which has been investigated and published several times (References 2 and 3), consists in regulating the functional brain disorders by deactivating the deficient brain area, which is only 3-4 millimeters small and has lost its normal functions long before the intervention. This will allow the system to get back to its natural balance, without causing neurological deficits.
To pick up the picture of the orchestra, this operation deactivates the troublemaker who was pulling on the arm of the conductor. This allows him to take up his normal function and to lead and coordinate the cortical areas without having to reduce the thalamic and the cortical functions. The rhythm is regulated and the troubles decline.
For 30 years this intervention has been done with electrodes, which were introduced into the brain through a small hole in the skull, to reach the intended area and deactivate it.
Since a few years, it is now even possible to perform this neurosurgical intervention with focused ultrasound, without having to open the skull of the patient.
The technique of the incisionless, transcranial, MR-guided focused ultrasound (FUS) allows high-precision (half-millimeter) heating (54-60° Celsius) of the target tissue and a most significant reduction of the interventional risks (infections and bleeding). This is made possible thanks to the application of the ultrasound energy through skin and bone, without mechanical penetration of the skull and the brain. Furthermore the performed therapeutic heating of the chosen target tissue is controlled continuously thanks to MR-thermal imaging.
Focused ultrasound means that around thousand ultrasound waves, each of them innocuous for the brain, converge in the target, where sonic energy gets transformed in thermal energy. The targets measure only 3-4 mm diameter.
The procedure is performed without general anesthesia. To guarantee the accuracy of the target, the head of the patient has to remain static. A ring is therefore fixed under local anesthesia around the patients head. Afterwards he is installed in the MR machine, the target is calculated, and finally the ultrasound energy is applied. This neurosurgical procedure is called a „sonication“.
References:
1: Jeanmonod, D. Magnin, M. Morel, A. (1996). Low-threshold calcium spike bursts in the human thalamus. Common physiopathology for sensory, motor and limbic positive symptoms. Brain, Apr;119 (Pt 2):363-75.
2: Aufenberg, C. Sarnthein, J. Morel, A. Rousson, V. Gallay, M. Jeanmonod, D. (2005). A revival of Spiegel’s campotomy: long term results of the stereotactic pallidothalamic tractotomy against the parkinsonian thalamocortical dysrhythmia. Thalamus & Related Systems, 3(2):121-132.
3: Jeanmonod, D. Morel, A. (2009) The Central Lateral Thalamotomy for Neuropathic Pain. In: Lozano, A.M. Gildenberg, P.L. Tasker, R.R. eds. Textbook of Stereotactic and Functional Neurosurgery, 2nd Edition. Berlin Heidelberg: Springer-Verlag, pp. 2081-2096.