Modeling the neurophysiology of TMS-induced I-waves
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1
Frankfurt Institute for Advanced Studies (FIAS), Germany
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2
Eberhard Karls Universität Tübingen, Dept. of Neurology, Germany
Transcranial magnetic stimulation (TMS) allows to non-invasively manipulate neural activity via strong magnetic fields and is currently tested for its clinical use for treating depression, stroke, schizophrenia and several other neurological disorders. However, the details of how TMS induces patterns of neural activity in cortical circuits remain poorly understood, which hampers targeted clinical application [1]. Assessing the nature of such patterns or establishing the biophysical basis underlying magnetic stimulation in purely experimental settings remains difficult given the scarce recording opportunities and high variability of results across healthy subjects. Models incorporating anatomically detailed neurons could overcome these limitations and provide valuable insight into the effects of TMS at the cellular and systems level.
We have recently presented a first computational model of how TMS stimulates cortical circuits and produces I-waves, fast rhythmic responses in descending motor pathways [2]. The model consists of a detailed layer 5 (L5) pyramidal cell in primary motor cortex and a population of layer 2 and 3 (L2/3) neurons projecting to it. It parsimoniously explains the mechanisms underlying I-wave generation together with some of their basic properties such as frequency, timing, and size. Here we show how the size of the L5 dendritic trees influences the amplitude of the simulated epidural responses. By removing distal dendritic branches of the L5 cell we show how later I-waves are abolished. This suggests that the complex anatomical structure of L5 neurons plays an important role in the generation of I-waves. We argue that I-waves are a product of synchronized volleys of EPSPs and IPSPs impinging onto L5 cell dendritic trees and the intrinsic membrane properties of L5 cells. This generation mechanism does not require multiple activations of chains of presynaptic elements or complex resonating circuits [1]. Our model additionally reproduces findings from paired-pulse stimulation protocols, pharmacological interventions and behavior modulation of I-waves. In conclusion, our model explains findings from a wide range of experiments and is an important first step towards designing optimized TMS protocols for specific clinical purposes.
Acknowledgements
Supported by the LOEWE-Program “Neuronal Coordination Research Focus Frankfurt” (NeFF).
References
[1] Ziemann U, Rothwell J (2000) I-waves in motor cortex. Journal of Clinical Neurophysiology 17: 397–405.
[2] Rusu CV, Ziemann U, and Triesch J (2012) A Model of I-Wave Generation during Transcranial Magnetic Stimulation (TMS). Computational and Systems Neuroscience (COSYNE), Salt Lake City, USA.
Keywords:
I-wave,
Motor Cortex,
pyramidal cell,
Transcranial Magnetic Stimulation
Conference:
Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012.
Presentation Type:
Poster
Topic:
Neurotechnology and brain-machine interface
Citation:
Rusu
CV,
Murakami
M,
Ziemann
U and
Triesch
J
(2012). Modeling the neurophysiology of TMS-induced I-waves.
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference 2012.
doi: 10.3389/conf.fncom.2012.55.00070
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Received:
20 May 2012;
Published Online:
12 Sep 2012.
*
Correspondence:
Prof. Jochen Triesch, Frankfurt Institute for Advanced Studies (FIAS), Frankfurt am Main, D-60438, Germany, triesch@fias.uni-frankfurt.de