Novel flexible cap for application of transcranial electrical stimulation: a usability study.

BACKGROUND: Advances in transcranial electrical stimulation (tES) are hampered by the conventional rubber electrodes manually attached to the head with rubber bands. This procedure limits montages to a few electrodes, is error prone with respect to electrode configurations and is burdensome for participants and operators. A newly developed flexible cap with integrated textile stimulation electrodes was compared to the conventional setup of rubber electrodes inserted into sponges fixated by rubber bands, with respect to usability and reliability. Two operators applied both setups to 20 healthy volunteers participating in the study. Electrode position and impedance measures as well as subjective evaluations from participants and operators were obtained throughout the stimulation sessions. RESULTS: Our results demonstrated the superiority of the flexible cap by means of significantly higher electrode configuration reproducibility and a more efficient application. Both, operators and volunteers evaluated the flexible cap as easier to use and more comfortable to wear when compared to the conventional setup. CONCLUSION: In conclusion, the new cap improves existing and opens new application scenarios for tES.

The consequences of the new European reclassification of non-invasive brain stimulation devices and the medical device regulations pose an existential threat to research and treatment: An invited opinion paper.

A significant amount of European basic and clinical neuroscience research includes the use of transcranial magnetic stimulation (TMS) and low intensity transcranial electrical stimulation (tES), mainly transcranial direct current stimulation (tDCS). Two recent changes in the EU regulations, the introduction of the Medical Device Regulation (MDR) (2017/745) and the Annex XVI have caused significant problems and confusions in the brain stimulation field. The negative consequences of the MDR for non-invasive brain stimulation (NIBS) have been largely overlooked and until today, have not been consequently addressed by National Competent Authorities, local ethical committees, politicians and by the scientific communities. In addition, a rushed bureaucratic decision led to seemingly wrong classification of NIBS products without an intended medical purpose into the same risk group III as invasive stimulators. Overregulation is detrimental for any research and for future developments, therefore researchers, clinicians, industry, patient representatives and an ethicist were invited to contribute to this document with the aim of starting a constructive dialogue and enacting positive changes in the regulatory environment.

Benchmarking the effects of transcranial temporal interference stimulation (tTIS) in humans.

Deep brain stimulation (DBS) provides clinical benefits for several neurological and psychiatric conditions. By overcoming the limitations and risks of conventional DBS, transcranial temporal interference stimulation (tTIS) has the potential to offer non-invasive stimulation of deep brain regions. However, research that investigates the efficacy of tTIS is limited to animal studies or computer simulations and its capability to modulate neural oscillations in humans has not been demonstrated so far. The method of tTIS is hypothesized to elicit its effects via neural entrainment, corresponding to the supposed mechanism of action underlying transcranial alternating current stimulation (tACS), another, more established non-invasive brain stimulation technique. Physiological effects of tACS are well established for cortical brain oscillations, but not for deep brain structures. In particular, aftereffects on the power of parieto-occipital alpha oscillations have been shown repeatedly. In a first attempt to test the efficacy of tTIS in the human brain, the current study thus seeks to compare the effects of tTIS to the well-studied aftereffect of tACS in the cortex. To investigate this research question, the current study compared MEG-recorded brain activity during a simple visual change detection task in 34 healthy subjects pre- and post-tTIS. Additionally, the effects of tTIS were contrasted to conventional tACS and a control stimulation. We expected that the parieto-occipital α-power will increase after tTIS and tACS, in contrast to the control stimulation. Overall, no difference between the experimental groups (tTIS, tACS and control stimulation) were found regarding the source-projected increase in α-power. Based on the results of the study two hypothesis can be made: tTIS, tACS and the control stimulation condition don't have an effect on human brain oscillations in the α-band, or, any experimental conditions of the current study can modulate brain oscillations in the α-band. Both hypotheses emphasize the importance of further studies investigating different carrier frequencies, and the comparison to sham stimulation.

Sham tDCS: A hidden source of variability? Reflections for further blinded, controlled trials.

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique increasingly used to modulate neural activity in the living brain. In order to establish the neurophysiological, cognitive or clinical effects of tDCS, most studies compare the effects of active tDCS to those observed with a sham tDCS intervention. In most cases, sham tDCS consists in delivering an active stimulation for a few seconds to mimic the sensations observed with active tDCS and keep participants blind to the intervention. However, to date, sham-controlled tDCS studies yield inconsistent results, which might arise in part from sham inconsistencies. Indeed, a multiplicity of sham stimulation protocols is being used in the tDCS research field and might have different biological effects beyond the intended transient sensations. Here, we seek to enlighten the scientific community to this possible confounding factor in order to increase reproducibility of neurophysiological, cognitive and clinical tDCS studies.

Novel bifunctional cap for simultaneous electroencephalography and transcranial electrical stimulation.

Neuromodulation induced by transcranial electric stimulation (TES) exhibited promising potential for clinical practice. However, the underlying mechanisms remain subject of research. The combination of TES and electroencephalography (EEG) offers great potential for investigating these mechanisms and brain function in general, especially when performed simultaneously. In conventional applications, the combination of EEG and TES suffers from limitations on the electrode level (gel for electrode-skin interface) and the usability level (preparation time, reproducibility of positioning). To overcome these limitations, we designed a bifunctional cap for simultaneous TES-EEG applications. We used novel electrode materials, namely textile stimulation electrodes and dry EEG electrodes integrated in a flexible textile cap. We verified the functionality of this cap by analysing the effect of TES on visual evoked potentials (VEPs). In accordance with previous reports using standard TES, the amplitude of the N75 component was significantly decreased post-stimulation, indicating the feasibility of using this novel flexible cap for simultaneous TES and EEG. Further, we found a significant reduction of the P100 component only during TES, indicating a different brain modulation effect during and after TES. In conclusion, the novel bifunctional cap offers a novel tool for simultaneous TES-EEG applications in clinical research, therapy monitoring and closed-loop stimulation.

Portable qEEG and HD-tCS Device for Point-of-Injury Traumatic Brain Injury Diagnostics.

Mild Traumatic Brain Injury (mTBI) can cause prolonged or permanent injuries if left undetected and ignored. It is therefore of great interest to lower the threshold for diagnosis of individuals with mTBI injury. We report on the development of a prototype of a portable quantified EEG (qEEG) system intended for in-the-field mTBI diagnostics. The 32-electrode system is fully battery driven, is interfaced with a control unit being part of a telemedicine care system. Electrode montage is a central problem effectively challenging measurements outside clinical environments. The system concept is unique in the sense that it will allow an automated montage process employing a flexible, disposable, one-size-fits-all electrode cap. All electrodes are individually configurable so that they can be used for both wet and dry qEEG electrodes. All electrodes can also be individually configured to allow Trans-Cranial Current Stimulation (tCS) sessions in DC, AC or other current supply modalities. The system has been functionality tested in end-to-end configurations where all control and measurement signals are forwarded between the head device on one side and the user interface and telemedicine system on the other. Tests confirm that the device can acquire and forward EEG data from 32 channels in parallel at target sensitivities up to 1 kHZ sampling frequencies. Additional device clinical evaluation is planned.

A biofeedback intervention to control impulsiveness in a severely personality disordered forensic patient.

Impulsiveness in personality disordered forensic patients is associated with poor treatment completion and high risk of re-offending. A biofeedback training protocol, previously found to reduce impulsiveness and improve attention in children with Attention Deficit Hyperactivity Disorder, was used in an initial attempt to reduce impulsiveness in a severely personality disordered man with borderline, antisocial and histrionic features. Electrocortical, behavioural and self-report measures of impulsiveness were taken before and immediately following 6 weeks of biofeedback training and at 3 months follow-up. The patient successfully engaged with the intervention. His self-reports of reduced impulsiveness and improved attention were corroborated by behavioural and electrocortical measures that indicated reduced impulsiveness and better focused attention. Results suggest this intervention might prove useful in improving behavioural and emotional self-regulation in severely personality disordered patients.