Event Abstract

Hysteresis Effects of Cortico-Spinal Excitability during Transcranial Magnetic Stimulation

  • 1 Goethe University, Motor Cortex Group, Department of Neurology, Germany
  • 2 Toyama Hospital, Department of Neurology, Japan
  • 3 Frankfurt Institute for Advanced Studies, Germany

Input-output (IO) curves of motor evoked potentials (MEP) are an important and widely used method to assess motor cortical excitability by transcranial magnetic stimulation (TMS). IO curves are measured by applying TMS stimuli at a range of different intensities and the slope and amplitude of the curve is a sensitive marker for excitability changes of neuronal systems under different physiological or pathological conditions. However, it is not known whether the sequence in which the curves are obtained may by itself influence corticospinal activation.

Here, we investigated the effects of history dependence, known also as hysteresis effects on IO curves. To test this IO curves from the first dorsal interosseous (FDI) muscle of 14 healthy volunteers were obtained in three different sequences of stimulus intensity order: Increasing from low to high intensities, decreasing from high to low intensities and randomizing intensities. Intensities ranged from 80% to 170% of the individual resting motor threshold (RMT). At each intensity level 5 trials were recorded and averaged. Sequences were measured with two different inter-trial intervals (ITI, 5s and 20s), and in the resting vs. voluntarily active muscle. All recordings with the resting muscle were carefully checked for voluntary muscle activation to control for unspecific arousal effects. In the resting muscle and at ITI = 5s, IO curves measured with the decreasing sequence were significantly shifted to the left compared to the increasing sequence while the IO curve obtained with the randomized sequence ran in between. Hysteresis was most pronounced in the upper part of the IO curves at intensities of 130% RMT and above. No significant hysteresis was seen at ITI = 20s or in the active FDI.

Our findings implicate that hysteresis could significantly influence IO curves. High intensity stimuli at the beginning of the decreasing sequence seemed to have an enhancing effect on consecutive stimuli during the same recording. As no hysteresis effects were present with the longer ITI of 20s we propose that short-term plasticity may be a possible mechanism to account for this effect.

Conference: Bernstein Conference on Computational Neuroscience, Frankfurt am Main, Germany, 30 Sep - 2 Oct, 2009.

Presentation Type: Poster Presentation

Topic: Learning and plasticity

Citation: Moller C, Arai N, Lucke J and Ziemann U (2009). Hysteresis Effects of Cortico-Spinal Excitability during Transcranial Magnetic Stimulation. Front. Comput. Neurosci. Conference Abstract: Bernstein Conference on Computational Neuroscience. doi: 10.3389/conf.neuro.10.2009.14.124

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Received: 27 Aug 2009; Published Online: 27 Aug 2009.

* Correspondence: Caroline Moller, Goethe University, Motor Cortex Group, Department of Neurology, Frankfurt, Germany, moeller@med.uni-frankfurt.de