Individual effects of varying stimulation intensity and response criteria on area of activation for different muscles in humans. A study using navigated transcranial magnetic stimulation

Thordstein, Magnus; Saar, Karin; Pegenius, Göran; Elam, Mikael

doi:10.1016/j.brs.2012.01.004

Cited by 28 publications

(26 citation statements)

References 20 publications

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“…Similarly, a recent study by Thordstein et al [57] showed that lower MEP thresholds could be used to produce a more sensitive RMT estimate (e.g., 50 µV instead of the 100 µV used here). When this data were acquired (~2007) the standard and accepted definition of RMT was followed.…”

Section: Discussionmentioning

confidence: 77%

PET-Based Confirmation of Orientation Sensitivity of TMS-Induced Cortical Activation in Humans

et al. 2013

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Background Currently, it is difficult to predict precise regions of cortical activation in response to transcranial magnetic stimulation (TMS). Most analytical approaches focus on applied magnetic field strength in the target region as the primary factor, placing activation on the gyral crowns. However, imaging studies support M1 targets being typically located in the sulcal banks. Objective/hypothesis To more thoroughly investigate this inconsistency, we sought to determine whether neocortical surface orientation was a critical determinant of regional activation. Methods MR images were used to construct cortical and scalp surfaces for 18 subjects. The angle (θ) between the cortical surface normal and its nearest scalp normal for ~50,000 cortical points per subject was used to quantify cortical location (i.e., gyral vs. sulcal). TMS-induced activations of primary motor cortex (M1) were compared to brain activations recorded during a finger-tapping task using concurrent positron emission tomographic (PET) imaging. Results Brain activations were primarily sulcal for both the TMS and task activations (P < 0.001 for both) compared to the overall cortical surface orientation. Also, the location of maximal blood flow in response to either TMS or finger-tapping correlated well using the cortical surface orientation angle or distance to scalp (P < 0.001 for both) as criteria for comparison between different neocortical activation modalities. Conclusion This study provides further evidence that a major factor in cortical activation using TMS is the orientation of the cortical surface with respect to the induced electric field. The results show that, despite the gyral crown of the cortex being subjected to a larger magnetic field magnitude, the sulcal bank of M1 had larger cerebral blood flow (CBF) responses during TMS.

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Section: Discussionmentioning

confidence: 77%

PET-Based Confirmation of Orientation Sensitivity of TMS-Induced Cortical Activation in Humans

et al. 2013

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“…All neuroimaging modalities have inherent limitations. TMS provides a direct measurement of corticomotor excitability for the muscle of interest, but the properties of the motor map are influenced by coil orientation (Laakso et al 2014), stimulus intensity (Thordstein et al 2013 ) current spread, and by the depth of the stimulated neurons within the complex topography of the motor cortex (Thickbroom et al 1998). Mapping muscle representation with TMS provides a two-dimensional map at the scalp surface that must then be projected onto the cortex if TMS data are to be combined with MRI data.…”

Section: Discussionmentioning

confidence: 99%

The motor cortical representation of a muscle is not homogeneous in brain connectivity

et al. 2017

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Functional connectivity patterns of the motor cortical representational area of single muscles have not been extensively mapped in humans, particularly for the axial musculature. Functional connectivity may provide a neural substrate for adaptation of muscle activity in axial muscles that have both voluntary and postural functions. The purpose of this study was to combine brain stimulation and neuroimaging to both map the cortical representation of the external oblique (EO) in primary motor cortex (M1) and supplementary motor area (SMA), and to establish the resting-state functional connectivity associated with this representation. Motor-evoked potentials were elicited from the EO muscle in stimulation locations encompassing M1 and SMA. The coordinates of locations with the largest motor-evoked potentials were confirmed with task-based fMRI imaging during EO activation. The M1 and SMA components of the EO representation demonstrated significantly different resting-state functional connectivity with other brain regions: the SMA representation of the EO muscle was significantly more connected to the putamen and cerebellum, and the M1 representation of the EO muscle was significantly more connected to somatosensory cortex and the superior parietal lobule. This study confirms the representation of a human axial muscle in M1 and SMA, and demonstrates for the first time that different parts of the cortical representation of a human axial muscle have resting-state functional connectivity with distinct brain regions. Future studies can use the brain regions of interest we have identified here to test the association between resting-state functional connectivity and control of the axial muscles.

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“…This can be clearly observed when constructing recruitment curves, plotting the stimulation intensity versus MEP amplitude (Devanne et al 1997 ). Nonetheless, higher stimulation intensities are associated with a greater area of the cortex resulting in MEPs (Thordstein et al 2013 ), but it remains unclear how stimulation intensity affects the COG and map volume.…”

Section: Introductionmentioning

confidence: 99%

The TMS Map Scales with Increased Stimulation Intensity and Muscle Activation

Ruit

Grey

2015

Brain Topogr

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One way to study cortical organisation, or its reorganisation, is to use transcranial magnetic stimulation (TMS) to construct a map of corticospinal excitability. TMS maps are reported to be acquired with a wide variety of stimulation intensities and levels of muscle activation. Whilst MEPs are known to increase both with stimulation intensity and muscle activation, it remains to be established what the effect of these factors is on the map’s centre of gravity (COG), area, volume and shape. Therefore, the objective of this study was to systematically examine the effect of stimulation intensity and muscle activation on these four key map outcome measures. In a first experiment, maps were acquired with a stimulation intensity of 110, 120 and 130 % of resting threshold. In a second experiment, maps were acquired at rest and at 5, 10, 20 and 40 % of maximum voluntary contraction. Map area and map volume increased with both stimulation intensity (P < 0.01) and muscle activation (P < 0.01). Neither the COG nor the map shape changed with either stimulation intensity or muscle activation (P > 0.09 in all cases). This result indicates the map simply scales with stimulation intensity and muscle activation.

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Individual effects of varying stimulation intensity and response criteria on area of activation for different muscles in humans. A study using navigated transcranial magnetic stimulation

Cited by 28 publications

References 20 publications

PET-Based Confirmation of Orientation Sensitivity of TMS-Induced Cortical Activation in Humans

PET-Based Confirmation of Orientation Sensitivity of TMS-Induced Cortical Activation in Humans

The motor cortical representation of a muscle is not homogeneous in brain connectivity

The TMS Map Scales with Increased Stimulation Intensity and Muscle Activation

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