Limits...
Transcranial magnetic stimulation for individual identification of the best electrode position for a motor imagery-based brain-computer interface.

Hänselmann S, Schneiders M, Weidner N, Rupp R - J Neuroeng Rehabil (2015)

Bottom Line: On an individual level, the MI-induced mu-rhythm modulation was at average found 1.6 cm (standard deviation (SD) = 1.30 cm) lateral and 0.31 cm anterior (SD = 1.39 cm) to the motor hand area and enabled a significantly better online BCI performance than the motor hand areas.On an individual level a trend towards a consistent average spatial distance between motor hand area and mu-rhythm modulation center was found indicating that TMS may be used as a simple tool for quick individual optimization of EEG-recording electrode positions of MI-based BCIs.The study results indicate that motor hand areas of the primary motor cortex determined by TMS are not the main generators of the cortical mu-rhythm.

View Article: PubMed Central - PubMed

Affiliation: Heidelberg University Hospital, Spinal Cord Injury Center, Schlierbacher Landstrasse 200a, 69118, Heidelberg, Germany. s.haenselmann@gmail.com.

ABSTRACT

Background: For the translation of noninvasive motor imagery (MI)-based brain-computer interfaces (BCIs) from the lab environment to end users at their homes, their handling must be improved. As a key component, the number of electroencephalogram (EEG)-recording electrodes has to be kept at a minimum. However, due to inter-individual anatomical and physiological variations, reducing the number of electrodes bares the risk of electrode misplacement, which will directly translate into a limited BCI performance of end users. The aim of the study is to evaluate the use of focal transcranial magnetic stimulation (TMS) as an easy tool to individually optimize electrode positioning for a MI-based BCI. For this, the area of MI-induced mu-rhythm modulation was compared with the motor hand representation area in respect to their localization and to the control performance of a MI-based BCI.

Methods: Focal TMS was applied to map the motor hand areas and a 48-channel high-resolution EEG was used to localize MI-induced mu-rhythm modulations in 11 able-bodied, right-handed subjects (5 male, age: 23-31). The online BCI performances of the study participants were assessed with a single next-neighbor Laplace channel consecutively placed over the motor hand area and over the area of the strongest mu-modulation.

Results: For most subjects, a consistent deviation between the position of the mu-modulation center and the corresponding motor hand areas well above the localization error could be observed in mediolateral and to a lesser degree in anterior-posterior direction. On an individual level, the MI-induced mu-rhythm modulation was at average found 1.6 cm (standard deviation (SD) = 1.30 cm) lateral and 0.31 cm anterior (SD = 1.39 cm) to the motor hand area and enabled a significantly better online BCI performance than the motor hand areas.

Conclusion: On an individual level a trend towards a consistent average spatial distance between motor hand area and mu-rhythm modulation center was found indicating that TMS may be used as a simple tool for quick individual optimization of EEG-recording electrode positions of MI-based BCIs. The study results indicate that motor hand areas of the primary motor cortex determined by TMS are not the main generators of the cortical mu-rhythm.

No MeSH data available.


Related in: MedlinePlus

Electrode positions of the 48-channel high resolution EEG recordings. 48 electrodes were placed over the sensorimotor cortex according to a 10–6.7 system with inter-electrode distances of 23 mm in mediolateral and anterior-posterior direction. Electrode positions C3, Cz and C4 are consistent with the international 10–20 system. The central 24 Laplace channels are outlined by solid circles. Electrode positions adjacent to C3 and C4 were annotated according to their use in this paper. In addition, the area of the TMS stimulation grid is overlaid as a blue rectangle
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4547425&req=5

Fig2: Electrode positions of the 48-channel high resolution EEG recordings. 48 electrodes were placed over the sensorimotor cortex according to a 10–6.7 system with inter-electrode distances of 23 mm in mediolateral and anterior-posterior direction. Electrode positions C3, Cz and C4 are consistent with the international 10–20 system. The central 24 Laplace channels are outlined by solid circles. Electrode positions adjacent to C3 and C4 were annotated according to their use in this paper. In addition, the area of the TMS stimulation grid is overlaid as a blue rectangle

Mentions: This allowed for the stimulation of a 6 cm × 4.5 cm area medial to C3 (and C4 respectively) that was centered at the C3-C4 axis (Fig. 2). Biphasic stimulation pulses were applied according to the safety guidelines for TMS [25] using a MagPro R100 magnetic stimulator (MagVenture GmbH, Hückelhoven, Germany) and a MC-B70 butterfly-shaped coil (MagVenture GmbH, Hückelhoven, Germany). Both hemispheres were stimulated independently. The amplitudes of the MEPs were recorded from the abductor digiti minimi (ADM) muscle of the contralateral hand using Ambu Neuroline 700 self-adhesive Ag/AgCl electrodes (Ambu A/S, Ballerup, Denmark). The reference electrode was placed on the proximal interphalangeal joint of the little finger. Subjects were advised to relax the recorded muscle during stimulation. In order to find the appropriate stimulation intensity, the stimulator output was stepwise increased starting from 40 % of the maximal stimulator output until reproducible MEP amplitudes greater than 0.5 mV could be elicited at the presumed low-threshold site. The maximum intensity was limited to 70 % to avoid unpleasant sensations. For both hemispheres, each of the 20 stimulations points was stimulated four times in a random order. The butterfly-shaped coil was held parallel to the nasion-inion axis and tangential to the scalp surface with the coil handle pointing posterior. For each hemisphere, the MEP amplitudes of each stimulation point were averaged and expressed as value relative to the highest average amplitude observed. Based on the resulting 4 × 5 MEP amplitude matrix the two-dimensional center of gravity (CoG) was calculated using the equationFig. 2


Transcranial magnetic stimulation for individual identification of the best electrode position for a motor imagery-based brain-computer interface.

Hänselmann S, Schneiders M, Weidner N, Rupp R - J Neuroeng Rehabil (2015)

Electrode positions of the 48-channel high resolution EEG recordings. 48 electrodes were placed over the sensorimotor cortex according to a 10–6.7 system with inter-electrode distances of 23 mm in mediolateral and anterior-posterior direction. Electrode positions C3, Cz and C4 are consistent with the international 10–20 system. The central 24 Laplace channels are outlined by solid circles. Electrode positions adjacent to C3 and C4 were annotated according to their use in this paper. In addition, the area of the TMS stimulation grid is overlaid as a blue rectangle
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4547425&req=5

Fig2: Electrode positions of the 48-channel high resolution EEG recordings. 48 electrodes were placed over the sensorimotor cortex according to a 10–6.7 system with inter-electrode distances of 23 mm in mediolateral and anterior-posterior direction. Electrode positions C3, Cz and C4 are consistent with the international 10–20 system. The central 24 Laplace channels are outlined by solid circles. Electrode positions adjacent to C3 and C4 were annotated according to their use in this paper. In addition, the area of the TMS stimulation grid is overlaid as a blue rectangle
Mentions: This allowed for the stimulation of a 6 cm × 4.5 cm area medial to C3 (and C4 respectively) that was centered at the C3-C4 axis (Fig. 2). Biphasic stimulation pulses were applied according to the safety guidelines for TMS [25] using a MagPro R100 magnetic stimulator (MagVenture GmbH, Hückelhoven, Germany) and a MC-B70 butterfly-shaped coil (MagVenture GmbH, Hückelhoven, Germany). Both hemispheres were stimulated independently. The amplitudes of the MEPs were recorded from the abductor digiti minimi (ADM) muscle of the contralateral hand using Ambu Neuroline 700 self-adhesive Ag/AgCl electrodes (Ambu A/S, Ballerup, Denmark). The reference electrode was placed on the proximal interphalangeal joint of the little finger. Subjects were advised to relax the recorded muscle during stimulation. In order to find the appropriate stimulation intensity, the stimulator output was stepwise increased starting from 40 % of the maximal stimulator output until reproducible MEP amplitudes greater than 0.5 mV could be elicited at the presumed low-threshold site. The maximum intensity was limited to 70 % to avoid unpleasant sensations. For both hemispheres, each of the 20 stimulations points was stimulated four times in a random order. The butterfly-shaped coil was held parallel to the nasion-inion axis and tangential to the scalp surface with the coil handle pointing posterior. For each hemisphere, the MEP amplitudes of each stimulation point were averaged and expressed as value relative to the highest average amplitude observed. Based on the resulting 4 × 5 MEP amplitude matrix the two-dimensional center of gravity (CoG) was calculated using the equationFig. 2

Bottom Line: On an individual level, the MI-induced mu-rhythm modulation was at average found 1.6 cm (standard deviation (SD) = 1.30 cm) lateral and 0.31 cm anterior (SD = 1.39 cm) to the motor hand area and enabled a significantly better online BCI performance than the motor hand areas.On an individual level a trend towards a consistent average spatial distance between motor hand area and mu-rhythm modulation center was found indicating that TMS may be used as a simple tool for quick individual optimization of EEG-recording electrode positions of MI-based BCIs.The study results indicate that motor hand areas of the primary motor cortex determined by TMS are not the main generators of the cortical mu-rhythm.

View Article: PubMed Central - PubMed

Affiliation: Heidelberg University Hospital, Spinal Cord Injury Center, Schlierbacher Landstrasse 200a, 69118, Heidelberg, Germany. s.haenselmann@gmail.com.

ABSTRACT

Background: For the translation of noninvasive motor imagery (MI)-based brain-computer interfaces (BCIs) from the lab environment to end users at their homes, their handling must be improved. As a key component, the number of electroencephalogram (EEG)-recording electrodes has to be kept at a minimum. However, due to inter-individual anatomical and physiological variations, reducing the number of electrodes bares the risk of electrode misplacement, which will directly translate into a limited BCI performance of end users. The aim of the study is to evaluate the use of focal transcranial magnetic stimulation (TMS) as an easy tool to individually optimize electrode positioning for a MI-based BCI. For this, the area of MI-induced mu-rhythm modulation was compared with the motor hand representation area in respect to their localization and to the control performance of a MI-based BCI.

Methods: Focal TMS was applied to map the motor hand areas and a 48-channel high-resolution EEG was used to localize MI-induced mu-rhythm modulations in 11 able-bodied, right-handed subjects (5 male, age: 23-31). The online BCI performances of the study participants were assessed with a single next-neighbor Laplace channel consecutively placed over the motor hand area and over the area of the strongest mu-modulation.

Results: For most subjects, a consistent deviation between the position of the mu-modulation center and the corresponding motor hand areas well above the localization error could be observed in mediolateral and to a lesser degree in anterior-posterior direction. On an individual level, the MI-induced mu-rhythm modulation was at average found 1.6 cm (standard deviation (SD) = 1.30 cm) lateral and 0.31 cm anterior (SD = 1.39 cm) to the motor hand area and enabled a significantly better online BCI performance than the motor hand areas.

Conclusion: On an individual level a trend towards a consistent average spatial distance between motor hand area and mu-rhythm modulation center was found indicating that TMS may be used as a simple tool for quick individual optimization of EEG-recording electrode positions of MI-based BCIs. The study results indicate that motor hand areas of the primary motor cortex determined by TMS are not the main generators of the cortical mu-rhythm.

No MeSH data available.


Related in: MedlinePlus