Towards more reliable TMS studies - How fast can we probe cortical excitability?

Knowledge and attitude toward transcranial magnetic stimulation among rehabilitation specialists in Saudi Arabia

Research has demonstrated the benefits of transcranial magnetic stimulation (TMS) in rehabilitation. TMS has been widely used in clinical and research settings for individuals with and without neurological dysfunctions. Therefore, understanding the knowledge and attitudes of rehabilitation specialists regarding TMS is crucial for its application. To our knowledge, no such studies have previously been conducted in the rehabilitation field. Therefore, this study is the first to assess rehabilitation specialists' knowledge of and attitudes toward TMS. An observational cross-sectional study using a self-administered online survey was conducted among 102 rehabilitation specialists to assess their knowledge and attitudes regarding TMS application in rehabilitation sciences. Descriptive and inferential statistics were used to describe the knowledge and attitudes of rehabilitation specialists toward TMS and examine the impact of different factors such as gender, education level, acceptability, and practice on these outcomes. Rehabilitation specialists who participated in this study showed a limited level of general knowledge of TMS in rehabilitation (7.81 ± 6.20, 37.19%). However, a significant association between educational levels and knowledge was found. Higher knowledge scores were observed for specialists with post-graduate degrees compared to those with only a bachelor's degree. Moreover, knowledge level, experience, and availability of TMS equipment in the workplace led to a positive attitude toward TMS among rehabilitation specialists. A low knowledge level among rehabilitation specialists was attributed to their level of education. Nevertheless, specialists showed an overall positive attitude toward TMS. Therefore, customized medical education is necessary to incorporate TMS theory and applications into neuroscience and rehabilitation courses for rehabilitation specialists as it holds significant promise as a therapeutic tool.

Transcranial magnetic stimulation mapping of the motor cortex: comparison of five estimation algorithms

Background

There are currently five different kinds of transcranial magnetic stimulation (TMS) motor mapping algorithms available, from ordinary point-based algorithms to advanced field-based algorithms. However, there have been only a limited number of comparison studies conducted, and they have not yet examined all of the currently available algorithms. This deficiency impedes the judicious selection of algorithms for application in both clinical and basic neuroscience, and hinders the potential promotion of a potential superior algorithm. Considering the influence of algorithm complexity, further investigation is needed to examine the differences between fMRI peaks and TMS cortical hotspots that were identified previously.

Methods

Twelve healthy participants underwent TMS motor mapping and a finger-tapping task during fMRI. The motor cortex TMS mapping results were estimated by five algorithms, and fMRI activation results were obtained. For each algorithm, the prediction error was defined as the distance between the measured scalp hotspot and optimized coil position, which was determined by the maximum electric field strength in the estimated motor cortex. Additionally, the study identified the minimum number of stimuli required for stable mapping. Finally, the location difference between the TMS mapping cortical hotspot and the fMRI activation peak was analyzed.

Results

The projection yielded the lowest prediction error (5.27 ± 4.24 mm) among the point-based algorithms and the association algorithm yielded the lowest (6.66 ± 3.48 mm) among field-based estimation algorithms. The projection algorithm required fewer stimuli, possibly resulting from its suitability for the grid-based mapping data collection method. The TMS cortical hotspots from all algorithms consistently deviated from the fMRI activation peak (20.52 ± 8.46 mm for five algorithms).

Conclusion

The association algorithm might be a superior choice for clinical applications and basic neuroscience research, due to its lower prediction error and higher estimation sensitivity in the deep cortical structure, especially for the sulcus. It also has potential applicability in various other TMS domains, including language area mapping and more. Otherwise, our results provide further evidence that TMS motor mapping intrinsically differs from fMRI motor mapping.

Limited evidence for reliability of low and high frequency rTMS over the motor cortex

OBJECTIVE

The aim of this study was to investigate the reliability of low-frequency and high-frequency repetitive transcranial magnetic stimulation (rTMS) on healthy individuals over the motor cortex. A secondary outcome was the assessment if low-frequency rTMS results in inhibition and high-frequency rTMS results in facilitation.

METHODS

In this experiment, 30 healthy participants received on four consecutive days one session each with application of 1 Hz or 20 Hz rTMS over the left motor cortex. 1 Hz and 20 Hz were applied in alternating order, whereby the starting frequency was randomized. Motor evoked potentials (MEPs) were measured before and after each session. Reliability measures were intraclass and Pearson's correlation coefficient (ICC and r).

RESULTS

ICCs and r values were low to moderate. Notably, within subgroups of less confounded measures, we found good r values for 20 Hz rTMS. The group-level analysis did not demonstrate a clear low-frequency inhibition and high-frequency facilitation pattern. At the single-subject level, only one participant exhibited significant changes consistent with the expected pattern, with concurrent decreases in MEPs following 1 Hz sessions and increases following 20 Hz sessions.

CONCLUSION

The investigated neuromodulatory protocols show low to moderate reliability. Results are questioning the low-frequency inhibition and high-frequency facilitation pattern.

SIGNIFICANCE

Methodological improvements for the usage of rTMS are necessary to increase validity and reliability of non-invasive brain stimulation.