Transcranial direct current stimulation (tDCS) to dorsolateral prefrontal cortex influences perceived pleasantness of food

The ability to regulate the intake of unhealthy foods is critical in modern, calorie dense food environments. Frontal areas of the brain, such as the dorsolateral prefrontal cortex (DLPFC), are thought to play a central role in cognitive control and emotional regulation. Therefore, increasing activity in the DLPFC may enhance these functions which could improve the ability to reappraise and resist consuming highly palatable but unhealthy foods. One technique for modifying brain activity is transcranial direct current stimulation (tDCS), a non-invasive technique for modulating neuronal excitability that can influence performance on a range of cognitive tasks. We tested whether tDCS targeting the DLPFC would influence how people perceived highly palatable foods. In the present study, 98 participants were randomly assigned to receive a single session of active tDCS or sham stimulation. While receiving active or sham stimulation, participants viewed images of highly palatable foods and reported how pleasant it would be to eat each food (liking) and how strong their urge was to eat each food (wanting). We found that participants who received active versus sham tDCS stimulation perceived food as less pleasant, but there was no difference in how strong their urge was to eat the foods. Our findings suggest that modulating excitability in the DLPFC influences “liking” but not “wanting” of highly palatable foods. Non-invasive brain stimulation might be a useful technique for influencing the hedonic experience of eating and might have implications for changing food consumption.

Effect of Percutaneous Electric Stimulation with High Frequency Alternating Currents on the Sensory-Motor System of Healthy Volunteers

BackgroundFormer studies investigated the application, both transcutaneous and with implanted electrodes, of high frequency alternating currents (HFAC) in humans for blocking the peripheral nervous system. The present trial aimed to assess the effect of HFAC on motor response, somatosensory thresholds, and peripheral nerve conduction, when applied percutaneously with ultrasound-guided needles at frequencies of 10 kHz and 20 kHz in healthy volunteers. MethodsA parallel, placebo-controlled, double-blind, randomized clinical trial was conducted. Ultrasound-guided HFAC at 10 kHz and 20 kHz and sham stimulation were delivered to the median nerve of 60 healthy volunteers (n=20 per group) for 20 minutes. The main assessed variables were maximum isometric flexion strength (MFFS) of the index finger, myotonometry, pressure pain threshold (PPT), mechanical detection threshold (MDT), and antidromic sensory nerve action potential (SNAP). Measurements were recorded pre-intervention, during the intervention 15 minutes after its commencement, immediately post-intervention, and at 15 minutes post-intervention.ResultsA decrease in the MFFS was observed immediately post-intervention compared to baseline, both in the 10 kHz group [-8.5 %; 95% confidence interval (CI) -14.9 to -2.1] and the 20 kHz group (-12.0%; 95%CI -18.3 to -5.6). At 15 minutes post-intervention, the decrease in the MFFS was -9.5% (95%CI -17.3 to -1.8) and -11.5% (95%CI -9.3 to -3.8) in the 10 kHz and 20 kHz groups, respectively. No changes over time were found in the sham group. The between-group comparison of changes in MFFS showed a greater reduction of -10.8% (95%CI -19.8 to -1.8) immediately post-intervention in the 20 kHz compared to the sham stimulation group. Muscle tone increased over time in both the 10 kHz and 20 kHz groups, but not in the sham group. The intergroup comparison of myotonometry showed a superior effect in the 20 kHz (6.7%, 95%CI 0.5 to 12.9) versus the sham group. No significant changes were observed in the rest of the assessed variables. ConclusionsThe ultrasound-guided percutaneous stimulation applying 10 kHz and 20 kHz HFAC to the median nerve produced reversible reductions in strength and increases in muscle tone with no adverse effects.

Neural changes after training with transcranial direct current stimulation to increase speech fluency in adults who stutter

In a randomised controlled trial, we showed that a five-day intervention combining anodal transcranial direct current stimulation over the left inferior frontal cortex with temporary speech fluency enhancing techniques reduces stuttering. Speech fluency was unchanged by the fluency training alone, as predicted. Here, we report the neural changes associated with the intervention, measured using functional MRI during sentence reading before the training and one-week later. We obtained imaging data in 25 adult men who stutter (median age = 32 y, inter-quartile range = 11) at the pre-intervention baseline and again one-week post-intervention. A control group of 15 adult men who do not stutter (median age = 30 y, inter-quartile range = 10) and did not complete the intervention were scanned on one occasion. In a whole-brain analysis of perceptibly fluent sentence reading, we compared the change in task-evoked neural activity in the sub-group of men who stutter who had received active stimulation during the intervention (N=13) with those who had sham stimulation (N=12). We hypothesised that the combination of anodal stimulation over the left inferior frontal cortex and fluency-enhancing training would result in lasting change to the brain networks supporting fluent speech production. An additional region-of-interest analysis explored effects on basal ganglia nuclei, which are thought to have a key role in the casual mechanism of stuttering, and which we hypothesised would be engaged by the behavioural approach used during training (choral and metronome-timed speaking). One week after the intervention, the group who had received active transcranial stimulation showed increased activity in speech-related brain regions, relative to the group who had received sham stimulation. Cortically, these changes were evident in left inferior frontal cortex (pars opercularis and orbitalis), anterior insula, anterior superior temporal gyrus, anterior cingulate cortex, and supplementary motor area. Subcortically, activation increased in the caudate nuclei and putamen bilaterally, and in right globus pallidus and thalamus. Together these regions form cortico-striatal-thalamo-cortical loops involved in the planning and initiation and control of speech movements.Our findings reveal that the mechanism of action of the tDCS intervention involved increasing activity across the network involved in the production of fluent speech, indicating that tDCS can be used to promote neural plasticity to strengthen networks supporting natural fluency. This study advances the potential of using non-invasive brain stimulation to improve therapy efficacy for those people who stutter who choose to work on increasing fluency.

Effects of electrical brain stimulation on brain indices and presence experience in immersive, interactive virtual reality

The subjective presence experience in virtual reality (VR) is associated with distinct brain activation patterns. Particularly, the dorsolateral prefrontal cortex (DLPFC) seems to play a central role. We investigated the effects of electric brain stimulation (transcranial direct current, tDCS) on the presence experience as well as on brain activity and connectivity. Thirty-eight participants received either anodal (N = 18) or cathodal (N = 20) stimulation of the DLPFC before interacting in an immersive VR as well as sham stimulation. During VR interaction, EEG and heart rate were recorded. After VR interaction, participants rated their subjective presence experience using standardized questionnaires. Cathodal stimulation led to stronger brain connectivity than sham stimulation. Increased brain connectivity was associated with numerically lower levels of subjective presence. Anodal stimulation did not lead to changes in brain connectivity, and no differences in subjective presence ratings were found between the anodal and sham stimulation. These results indicate that cathodal tDCS over the DLPFC leads to a more synchronized brain state, which might hamper the activity in networks, which are generally associated with the evolvement of the subjective presence experience. Our results underline the importance of the DLPFC for the presence experience in VR.

Transcranial Direct Current Stimulation Enhances Muscle Strength of Non-dominant Knee in Healthy Young Males

Transcranial direct current stimulation (tDCS) has been applied in training and competition, but its effects on physical performance remain largely unknown. This study aimed to observe the effect of tDCS on muscular strength and knee activation. Nineteen healthy young men were subjected to 20 min of real stimulation (2 mA) and sham stimulation (0 mA) over the primary motor cortex (M1) bilaterally on different days. The maximal voluntary contraction (MVC) of the knee extensors and flexors, and surface electromyography (sEMG) of the rectus femoris (RF) and biceps femoris (BF) were recorded before, immediately after, and 30 min after stimulation. MVC, rate of force development (RFD), and sEMG activity were analyzed before and after each condition. MVC of the non-dominant leg extensor and flexor was significantly higher immediately after real stimulation and 30 min after stimulation than before, and MVC of the non-dominant leg flexor was significantly higher 30 min after real stimulation than that after sham stimulation (P < 0.05). The RFD of the non-dominant leg extensor and flexor immediately after real stimulation was significantly higher than before stimulation, and the RFD of the non-dominant leg extensor immediately after real stimulation and 30 min after stimulation was significantly higher than that of sham stimulation (P < 0.05). EMG analysis showed the root mean square amplitude and mean power frequency (MPF) of the non-dominant BF and RF were significantly higher immediately after real stimulation and 30 min after stimulation than before stimulation, and the MPF of the non-dominant BF EMG was significantly higher 30 min after real stimulation than that after sham stimulation (P < 0.05). Bilateral tDCS of the M1 can significantly improve the muscle strength and explosive force of the non-dominant knee extensor and flexor, which might result from increased recruitment of motor units. This effect can last until 30 min after stimulation, but there is no significant effect on the dominant knee.

Reduced Interference and Serial Dependency Effects for Naming in Older but not Younger Adults after 1 Hz rTMS of Right Pars Triangularis

1 Hz rTMS was used to decrease excitability of right pars triangularis (R PTr) to determine whether increased R PTr activity during picture naming in older adults hampers word finding. We hypothesized that decreasing R PTr excitability would reduce interference with word finding, facilitating faster picture naming. 15 older and 16 younger adults received two rTMS sessions. In one, speech onset latencies for picture naming were measured after both sham and active R PTr stimulation. In the other session, sham and active stimulation of a control region, right pars opercularis (R POp), were administered before picture naming. Order of active vs. sham stimulation within session was counterbalanced. Younger adults showed no significant effects of stimulation. In older adults, a trend indicated that participants named pictures more quickly after active than sham R PTr stimulation. However, older adults also showed longer responses during R PTr than R POp sham stimulation. When order of active vs. sham stimulation was modeled, older adults receiving active stimulation first had significantly faster responding after active than sham R PTr stimulation and significantly faster responding after R PTr than R POp stimulation, consistent with experimental hypotheses. However, older adults receiving sham stimulation first showed no significant differences between conditions. Findings are best understood, based on previous studies, when the interaction between the excitatory effects of picture naming and the inhibitory effects of 1 Hz rTMS on R PTr is considered. Implications regarding right frontal activity in older adults and for design of future experiments are discussed.

Predictive Role of Executive Function in the Efficacy of Intermittent Theta Burst Transcranial Magnetic Stimulation Modalities for Treating Methamphetamine Use Disorder—A Randomized Clinical Trial

Background: Repetitive transcranial magnetic stimulation (rTMS) has therapeutic effects on craving in methamphetamine (METH) use disorder (MUD). The chronic abuse of METH causes impairments in executive function, and improving executive function reduces relapse and improves treatment outcomes for drug use disorder. The purpose of this study was to determine whether executive function helped predict patients' responses to rTMS treatment.Methods: This study employed intermittent theta burst stimulation (iTBS) rTMS modalities and observed their therapeutic effects on executive function and craving in MUD patients. MUD patients from an isolated Drug Rehabilitation Institute in China were chosen and randomly allocated to the iTBS group and sham-stimulation group. All participants underwent the Behavior Rating Inventory of Executive Function - Adult Version Scale (BRIEF-A) and Visual Analog Scales (VAS) measurements. Sixty-five healthy adults matched to the general condition of MUD patients were also recruited as healthy controls.Findings: Patients with MUD had significantly worse executive function. iTBS groups had better treatment effects on the MUD group than the sham-stimulation group. Further Spearman rank correlation and stepwise multivariate regression analysis revealed that reduction rates of the total score of the BRIEF-A and subscale scores of the inhibition factor and working memory factor in the iTBS group positively correlated with improvements in craving. ROC curve analysis showed that working memory (AUC = 87.4%; 95% CI = 0.220, 0.631) and GEC (AUC = 0.761%; 95% CI = 0.209, 0.659) had predictive power to iTBS therapeutic efficacy. The cutoff values are 13.393 and 59.804, respectively.Conclusions: The iTBS rTMS had a better therapeutic effect on the executive function of patients with MUD, and the improved executive function had the potential to become a predictor for the efficacy of iTBS modality for MUD treatment.Clinical Trial Registration:ClinicalTrials.gov, identifier: ChiCTR2100046954.

Robotic Kinematic measures of the arm in chronic Stroke: part 1 – Motor Recovery patterns from tDCS preceding intensive training

Background Effectiveness of robotic therapy and transcranial direct current stimulation is conventionally assessed with clinical measures. Robotic metrics may be more objective and sensitive for measuring the efficacy of interventions on stroke survivor’s motor recovery. This study investigated if robotic metrics detect a difference in outcomes, not seen in clinical measures, in a study of transcranial direct current stimulation (tDCS) preceding robotic therapy. Impact of impairment severity on intervention response was also analyzed to explore optimization of outcomes by targeting patient sub-groups. Methods This 2020 study analyzed data from a double-blind, sham-controlled, randomized multi-center trial conducted from 2012 to 2016, including a six-month follow-up. 82 volunteers with single chronic ischemic stroke and right hemiparesis received anodal tDCS or sham stimulation, prior to robotic therapy. Robotic therapy involved 1024 repetitions, alternating shoulder-elbow and wrist robots, for a total of 36 sessions. Shoulder-elbow and wrist kinematic and kinetic metrics were collected at admission, discharge, and follow-up. Results No difference was detected between the tDCS or sham stimulation groups in the analysis of robotic shoulder-elbow or wrist metrics. Significant improvements in all metrics were found for the combined group analysis. Novel wrist data showed smoothness significantly improved (P < ·001) while submovement number trended down, overlap increased, and interpeak interval decreased. Post-hoc analysis showed only patients with severe impairment demonstrated a significant difference in kinematics, greater for patients receiving sham stimulation. Conclusions Robotic data confirmed results of clinical measures, showing intensive robotic therapy is beneficial, but no additional gain from tDCS. Patients with severe impairment did not benefit from the combined intervention. Wrist submovement characteristics showed a delayed pattern of motor recovery compared to the shoulder-elbow, relevant to intensive intervention-related recovery of upper extremity function in chronic stroke. Trial registration http://www.clinicaltrials.gov. Actual study start date September 2012. First registered on 15 November 2012. Retrospectively registered. Unique identifiers: NCT01726673 and NCT03562663.

The influence of somatosensory and auditory evoked potentials on concurrent transcranial-magnetic stimulation electroencephalography recordings

Background: Transcranial magnetic stimulation (TMS) evoked potentials (TEPs) can be used to index cortical excitability. However, it remains unclear to what extent TEPs reflect somatosensory and auditory-evoked potentials which arise from the scalp sensation and click of the TMS coil, as opposed to transcranial stimulation of cortical circuits. Objectives: The present study had two aims; a) to determine the extent to which sensory potentials contaminate TEPs using a spatially matched sham condition, and b) to determine whether sensory potentials reflect auditory or somatosensory potentials alone, or a combination of the two. Methods: Twenty healthy participants received active or sham stimulation, with the latter consisting of the click of a sham coil combined with scalp electrical stimulation. Earplugs/headphones were used to suppress the TMS click noise. Two additional control conditions i) electrical stimulation alone and ii) auditory stimulation alone were included in a subset of 13 participants. Results: Signals from active and sham stimulation were correlated in spatial and temporal domains, especially >70ms post-stimulation. Relative to auditory or electrical stimulation alone, combined (sham) stimulation resulted in a) larger evoked responses b) stronger correlations with active stimulation and c) a signal that could not be explained by the linear sum of electrical and auditory stimulation alone. Conclusions: Sensory potentials can confound data interpretations of TEPs at timepoints >70ms post-TMS, while earlier timepoints appear reflective of cortical excitability. Furthermore, contamination of TEPs cannot be explained by auditory or somatosensory potentials alone, but instead reflects a non-linear interaction between both sources. Future studies may benefit from controlling for sensory contamination using sham conditions that are spatially matched to active TMS, and which consist of combined auditory and somatosensory stimulation.

10-Hz tACS Over The Prefrontal Cortex Improves Phonemic Fluency

Verbal fluency is an important indicator of human verbal ability. Methods to improve fluency is an interesting issue necessitating investigation. To do this, the current study required participants to randomly receive transcranial alternating current stimulation (tACS) at 10 Hz, 40 Hz (control frequency), and sham stimulation over the prefrontal cortex before a phonemic fluency task. It was found that 10-Hz tACS significantly improved phonemic fluency relative to sham stimulation. This result demonstrates the modulatory effect of 10-Hz tACS on language ability.