Effect of discharge desynchronization on the size of motor evoked potentials: an analysis

OBJECTIVE: Motor evoked potentials (MEPs) after transcranial magnetic brain stimulation (TMS) are smaller than CMAPs after peripheral nerve stimulation, because desynchronization of the TMS-induced motor neurone discharges occurs (i.e. MEP desynchronization). This desynchronization effect can be eliminated by use of the triple stimulation technique (TST; Brain 121 (1998) 437). The objective of this paper is to study the effect of discharge desynchronization on MEPs by comparing the size of MEP and TST responses. METHODS: MEP and TST responses were obtained in 10 healthy subjects during isometric contractions of the abductor digiti minimi, during voluntary background contractions between 0% and 20% of maximal force, and using 3 different stimulus intensities. Additional data from other normals and from multiple sclerosis (MS) patients were obtained from previous studies. RESULTS: MEPs were smaller than TST responses in all subjects and under all stimulating conditions, confirming the marked influence of desynchronization on MEPs. There was a linear relation between the amplitudes of MEPs vs. TST responses, independent of the degree of voluntary contraction and stimulus intensity. The slope of the regression equation was 0.66 on average, indicating that desynchronization reduced the MEP amplitude on average by one third, with marked inter-individual variations. A similar average proportion was found in MS patients. CONCLUSIONS: The MEP size reduction induced by desynchronization is not influenced by the intensity of TMS and by the level of facilitatory voluntary background contractions. It is similar in healthy subjects and in MS patients, in whom increased desynchronization of central conduction was previously suggested to occur. Thus, the MEP size reduction observed may not parallel the actual amount of desynchronization.

Die tiefgefrorene Lederhose. Sensationelle Geschichten aus dem Gletscher-Eis (von Elisabeth Brückner)

Das Schnidejoch ist ein Gebirgspass 2700 Meter hoch in den Berner Alpen, seit tausenden Jahren von Eis bedeckt. Mittlerweile ist fast alles Eis infolge der globalen Klimaerwärmung geschmolzen. SWR2 Kontext-Radiosendung von Elisabeth Brückner.

Gletscherarchäologie. Steinzeitfunde aus dem Eis (von Elisabeth Brückner)

Der Ötzi ist kein Einzelfall. Immer mehr Hinterlassenschaften der Vorzeit kommen ans Tageslicht, seit die globale Erwärmung nach und nach die alpinen Gletscher zum Schmelzen bringt. Insbesondere am Schnidejoch im Berner Oberland sind Archäologen fündig geworden: Das Eis, das hier jahrtausendelang den Bergsattel bedeckte, ist mittlerweile bis auf einen kleinen Eisfleck geschmolzen und hat rund 900 Artefakte freigegeben. Darunter eine 6.800 Jahre alte Schüssel aus Ulmenholz, eine komplette Jägerausrüstung, römische Schuhnägel aus dem Mittelalter. Und das große Schmelzen geht weiter ...