Clinical Neurophysiology Motor Evoked Potentials PDF

Clinical Neurophysiology Part VI Motor Evokd Potentials Karsten Schwerdtfeger Klinik für Neurochirurgie, Universitätsklinikum des Saarlandes. Studiengang: Neural Engineering Master WS 2024/2025 Technical notes  Technical notes Coil Cond...

Clinical Neurophysiology Part VI Motor Evokd Potentials Karsten Schwerdtfeger Klinik für Neurochirurgie, Universitätsklinikum des Saarlandes. Studiengang: Neural Engineering Master WS 2024/2025 Technical notes  Technical notes Coil Condenser discharge Short but high intensity current up to 5,000 A Magnetic field perpendicular to the coil plane Technical notes Coil The magnetic field penetrates skin and skull nearly without any loss In the brain a circular current is induced It has the same plane as the coil but an inverse flow direction The current has ist highest intensity under the innermost loops of the coil Motor Systems Motor cortex – Primary motor cortex Homunculus but Movement not muscles – Premotor cortex Preparing and designing movements – Supplementary motor area Preparing and designing movements – Association cortex Complex information processing in order to prepare complex movements for example speech Motor Pathways Corticospinal (pyramidal) tract – one of several motor systems – Fast execution of movement programs – Homunculus represents movements, no individual muscles – In primates monosynaptic connection to α- motoneurons – No 1:1 transmission Motor Pathways Extrapyramidal system – Historical definition: all neuclei and tracts except the pyramidal system – Polysynaptic cortco- spinal projections – Basal ganglia – Cerebellum  Motor evoked potentials https://www.youtube.com/watch?v= RYTYid9S6Fg Motor evoked potential Stimulation of the motor cortex – Magnetic – Electrical Painful – Stimulation of different cellular elements Motor evoked potential Motor evoked potential Electrically evoked MEP have a shorter latency when compared with magnetic MEP in the same subject. The difference is about 1 – 2 ms  Motor evoked potentials Recording – Surface electrodes – Responding muscle depends upon the coil position and the direction of current Right thenar Right tib. ant Motor evoked potentials Preinnervation of the muscles – Facilitates synaptic transmission – Increases the response – Shortens latency  MEP Spinal stimulation – Usually the distal part of the nerve root or the spinal nerve ist stimulated – Central motor conduction time = T1 – T2  Motor evoked potential Biceps Thenar muscle Clinical application 12,2 ms 20,8 ms – Compression of the right C6-root 14,5 ms 21,2 ms  Technical notes Fig-8 coil Tailored magnetic field More circumscribed cortical stimulation Suited for navigated stimulation https://www.youtube.com/watch?v =MtGMZSwl1Yk  Bereitschaftspotenzial - readiness potential Potential generated before execution of a motor task consists of early and late component – early component: supplementary motor area and premotor cortex activity (~ 1500 - 400 ms prior) – late component: primary motor cortex activity (~ 400 - 0 ms prior) amplitude dependent on task (up to 20 µV)  MEP Bereitschaftspotenzial – Activity of the secondary motor cortex (SMA..) and further association cortex – Internal trigger (movement) – Pretrigger recording  Difference to contingent negative variation (CNV) The contingent negative variation (CNV) is a negative slow surface potential, that occurs during the period between a warning stimulus or signal and an imperative ("go") stimulus.  contingent negative variation (CNV) Different paradigm A relation to motor tasks is not obligatory Increases with the first training runs May decrease if the imperative stimuli alway occurs Transcranial stimulation therapy Historical aspects – Headache (migraine) – Mental illness Transcranial stimulation therapy Stimulation types – rTMS – tACS – tDCS – tRNS – Electroconvulsive Therapy – Tumor Treatment Fields Transcranial stimulation therapy Indications – Migraine – Depression – Other psychiatric disorders – M. Parkinson – Malignant brain tumor Transcranial stimulation therapy TTF – alternating fields (50 – 200 kHz) – Low intensity (1-3 V/cm) – Oscillation of electrically charged molecules – Interference with mitosis – Must be worn for at least 18 hrs/day – Survival improvement for 5 months To be continued