Current Stimulation Protocols Research Articles

The effect of aging on inter-limb coordination: Establishing a novel transcranial alternating current stimulation (tACS) protocol by means of electroencephalography (EEG)

Abstract Healthy aging is a societal challenge with a significant socioeconomic impact. Gaining knowledge about neurodegenerative changes that impact functional independence is thus of high scientific importance. Age-related structural and functional neural changes have consequences for inter-limb coordination, which forms an intrinsic part of everyday life (e.g., driving, buttoning a shirt). Research has demonstrated that transcranial alternating current stimulation (tACS) targeting neural oscillations can alter behavioral performance. Nevertheless, profound understanding of tACS in the context of inter-limb coordination is yet to be achieved. In order to accomplish this, a more thorough understanding of the neural oscillations underlying inter-limb coordination is of utmost importance. The current study used electroencephalography (EEG) in healthy right-handed participants during two inter-limb coordination tasks; the bimanual tracking task (BTT) and the multi-limb reaction time task (MLT). The BTT consists of rotating two dials with both hands in a coordinated fashion. Three conditions were used, differing in left- and right-hand movement frequency. The MLT requires participants to lift multiple limbs in a correct manner. Six conditions were used, differing in required motor response (e.g., lifting right arm and left leg, lifting left arm and both legs). Twenty healthy right-handed young adults (age: 22.3 ± 1.0 (mean ± standard deviation)) and nineteen older adults (age: 70.7 ± 3.0) participated. Laplacian filtered EEG data will be analyzed in the time-frequency domain using morlet wavelet convolution. EEG time-frequency data between 4 and 35 hertz will be analyzed by means of repeated measures ANOVA, investigating differences across conditions and groups for each task respectively. In addition, bivariate channel-level functional connectivity will be analyzed using inter-site phase clustering. Behavioral data will be analyzed with a mixed model approach. These insights will be used to establish novel tACS protocols. If significant differences between young and older adults are present, these findings can lead to age-adapted tACS protocols. Keywords: Electroencephalography, Transcranial alternating current stimulation, Ageing, Functional connectivity

Feasibility of Direct Current stimulation through hair using a dry electrode: potential for transcranial Direct Current Stimulation (tDCS) application.

Conventional transcranial direct current stimulation (tDCS) protocols typically deliver 2 mA for 20-30 minutes. The most common administration uses a wet electrode approach which dries out in ~60 minutes at room temperature. This restricts its application to limited duration electrode-scalp contact use cases unless additional conductive media (saline, gel, or paste) is re-applied. This problem is further compounded by the subject's hair which not only presents administration challenges (interferes with electrode attachment and adhesion) but also acts as a conduit of current flow into the scalp resulting in current hotspots. This non-uniform current injection results in increased skin sensation. The aim of this study was to determine suitability of a commercially available hydrogel for DC delivery through hair. Experiments involved both non-clinical testing on an agar block and clinical testing on subjects' forearms. Electrodes were positioned on the posterior side of the forearm that has hair for the clinical testing. Typical dose as used in tDCS was delivered and pain scores were collected. Results indicate suitable current delivery performance and all subjects tolerated delivery with pain scores ranging between 0-6. Our study paves the way for future testing on the scalp for tDCS application.Clinical Relevance-This study demonstrates the possibility of delivering tDCS through hair via dry electrodes. Specific use cases that cannot use a traditional wet electrode approach stand to benefit from the results of our work.

Baseline Differences in Anxiety Affect Attention and tDCS-Mediated Learning.

Variable responses to transcranial direct current stimulation (tDCS) protocols across individuals are widely reported, but the reasons behind this variation are unclear. This includes tDCS protocols meant to improve attention. Attentional control is impacted by top-down and bottom-up processes, and this relationship is affected by state characteristics such as anxiety. According to Attentional Control Theory, anxiety biases attention towards bottom-up and stimulus-driven processing. The goal of this study was to explore the extent to which differences in state anxiety and related measures affect visual attention and category learning, both with and without the influence of tDCS. Using discovery learning, participants were trained to classify pictures of European streets into two categories while receiving 30 min of 2.0 mA anodal, cathodal, or sham tDCS over the rVLPFC. The pictures were classifiable according to two separate rules, one stimulus and one hypothesis-driven. The Remote Associates Test (RAT), Profile of Mood States, and Attention Networks Task (ANT) were used to understand the effects of individual differences at baseline on subsequent tDCS-mediated learning. Multinomial logistic regression was fit to predict rule learning based on the baseline measures, with subjects classified according to whether they used the stimulus-driven or hypothesis-driven rule to classify the pictures. The overall model showed a classification accuracy of 74.1%. The type of tDCS stimulation applied, attentional orienting score, and self-reported mood were significant predictors of different categories of rule learning. These results indicate that anxiety can influence the quality of subjects’ attention at the onset of the task and that these attentional differences can influence tDCS-mediated category learning during the rapid assessment of visual scenes. These findings have implications for understanding the complex interactions that give rise to the variability in response to tDCS.

Intermittent theta burst stimulation over the posterior superior temporal sulcus for children with autism spectrum disorder: A 4-week randomized blinded controlled trial followed by another 4-week open-label intervention.

Intermittent theta burst stimulation is a varied form of repetitive transcranial magnetic non-invasive brain stimulation technique used to treat several neurological and psychiatric disorders. Its feasibility and therapeutic effects on the bilateral posterior superior temporal sulcus in children with autism are unknown. We conducted a single-blind, sham-controlled parallel randomized clinical trial in a hitherto largest sample of intellectually able children with autism (N = 78). Participants randomized to the active group received two-session/week intermittent theta burst stimulation for continuous 8 weeks. Those in the sham group received two-session/week sham stimulations in the first 4 weeks and then active intervention for the following 4 weeks after unblinding. First, we found that continuous 8-week intermittent theta burst stimulation on the bilateral posterior superior temporal sulcus in children with autism is safe and tolerable. Second, we found that 8-week intermittent theta burst stimulation produced greater therapeutic efficacy, although we did not find any significant effects of 4-week intermittent theta burst stimulation on core symptoms and social cognitive performances in autism. Further analysis revealed that participants with higher intelligence and better social cognitive performance, alongside less attention-deficit hyperactivity disorder severity at baseline, were more likely to be responders. This study identified that the factors contribute to responders and the results suggest that longer courses of non-invasive brain stimulation may be needed to produce therapeutic benefits in autism, with consideration of heterogeneous responses.

Neural oscillatory responses to performance monitoring differ between high- and low-impulsive individuals, but are unaffected by TMS.

Higher impulsivity may arise from neurophysiological deficits of cognitive control in the prefrontal cortex. Cognitive control can be assessed by time‐frequency decompositions of electrophysiological data. We aimed to clarify neuroelectric mechanisms of performance monitoring in connection with impulsiveness during a modified Eriksen flanker task in high‐ (n = 24) and low‐impulsive subjects (n = 21) and whether these are modulated by double‐blind, sham‐controlled intermittent theta burst stimulation (iTBS). We found a larger error‐specific peri‐response beta power decrease over fronto‐central sites in high‐impulsive compared to low‐impulsive participants, presumably indexing less effective motor execution processes. Lower parieto‐occipital theta intertrial phase coherence (ITPC) preceding correct responses predicted higher reaction time (RT) and higher RT variability, potentially reflecting efficacy of cognitive control or general attention. Single‐trial preresponse theta phase clustering was coupled to RT in correct trials (weighted ITPC), reflecting oscillatory dynamics that predict trial‐specific behavior. iTBS did not modulate behavior or EEG time‐frequency power. Performance monitoring was associated with time‐frequency patterns reflecting cognitive control (parieto‐occipital theta ITPC, theta weighted ITPC) as well as differential action planning/execution processes linked to trait impulsivity (frontal low beta power). Beyond that, results suggest no stimulation effect related to response‐locked time‐frequency dynamics with the current stimulation protocol. Neural oscillatory responses to performance monitoring differ between high‐ and low‐impulsive individuals, but are unaffected by iTBS.

Intraoperative transcranial facial motor evoked potential monitoring in surgery of cerebellopontine angle tumors predicts early and late postoperative facial nerve function

ObjectiveWe propose a novel method that predicts facial nerve function (FNF) calculated from the drop and recovery of facial motor evoked potential (FMEP) amplitude ratio during the surgery of cerebellopontine angle tumors. MethodsWe enrolled 73 patients with cerebellopontine angle tumor, and used a biphasic, constant current, and suprathreshold stimulation (BCS) protocol to record FMEP of the orbicularis oris. We measured the intraoperative minimum-to-baseline amplitude ratio (MBR), the final-to-baseline amplitude ratio (FBR), and the recovery value (RV). RV was measured by subtracting MBR from FBR. Using those values, we evaluated FNF both at early postoperative (EP) and late postoperative (LP) periods. ResultsWe successfully obtained 62 FMEP readings. Facial palsies occurred in 22 patients during the EP period, and 14 patients recovered during the LP period. Both MBR and FBR showed a significant correlation with FNF in the EP period. RV showed a good predictive power of FNF recovery during the LP period for the first time. ConclusionsRV is a new and useful predictor of FNF recovery. MBR can be an intraoperative predictor of FNF in the EP period. SignificanceFNF outcome in the early and late postoperative periods can be predicted by FMEP.

Parametric study of transcranial alternating current stimulation for brain alpha power modulation.

Transcranial alternating current stimulation, a non-invasive brain stimulation technique, has been used to increase alpha (8–12 Hz) power, the latter being associated with various brain functions and states. Heterogeneity among stimulation parameters across studies makes it difficult to implement reliable transcranial alternating current stimulation protocols, explaining the absence of consensus on optimal stimulation parameters to modulate the alpha rhythm. This project documents the differential impact of controlling for key transcranial alternating current stimulation parameters, namely the intensity, the frequency and the stimulation site (anterior versus posterior). Phase 1:20 healthy participants underwent 4 different stimulation conditions. In each experimental condition, stimulation via 2 electrodes was delivered for 20 min. Stimulation conditions were administered at PO7-PO8 or F3-F4 at individual’s alpha frequency, or at individual’s theta frequency or sham. Stimulation intensity was set according to each participant’s comfort following a standardized unpleasantness scale (≤ 40 out of 100) and could not exceed 6 mA. All conditions were counterbalanced. Phase 2: participants who tolerated higher intensity of stimulation (4–6 mA) underwent alpha-frequency stimulation applied over PO7–PO8 at 1 mA to investigate within-subject modulation of stimulation response according to stimulation intensity. Whether set over posterior or anterior cortical sites, alpha-frequency stimulation showed greater increase in alpha power relative to stimulation at theta frequency and sham stimulation. Posterior alpha-frequency stimulation showed a greater increase in alpha power relative to the adjacent frequency bands over frontal and occipito-parietal brain areas. Low intensity (1 mA) posterior alpha stimulation showed a similar increase in alpha power than at high (4–6 mA) intensity when measured immediately after stimulation. However, when tested at 60 min or 120 min, low intensity stimulation was associated with significantly superior alpha power increase relative to high intensity stimulation. This study shows that posterior individual’s alpha frequency stimulation at higher intensities is well tolerated but fails to increase stimulation aftereffects recorded within 2 h of stimulation on brain oscillations of the corresponding frequency band. In sharp contrast, stimulating at 1 mA (regardless of phosphene generation or sensory perception) effectively and selectively modulates alpha power within that 2-h time window, thus validating that it as a reliable stimulus intensity for future studies. This study also shows that posterior alpha-frequency stimulation preferentially modulates endogenous brain oscillations of the corresponding frequency band. Moreover, our data suggest that posterior alpha-frequency transcranial alternating current stimulation is a reliable and precise non-invasive brain stimulation technique for persistent modulation of both frontal and occipito-parietal alpha power.

New Approaches Based on Non-Invasive Brain Stimulation and Mental Representation Techniques Targeting Pain in Parkinson's Disease Patients: Two Study Protocols for Two Randomized Controlled Trials.

Pain is an under-reported but prevalent symptom in Parkinson’s Disease (PD), impacting patients’ quality of life. Both pain and PD conditions cause cortical excitability reduction and non-invasive brain stimulation. Mental representation techniques are thought to be able to counteract it, also resulting effectively in chronic pain conditions. We aim to conduct two independent studies in order to evaluate the efficacy of transcranial direct current stimulation (tDCS) and mental representation protocol in the management of pain in PD patients during the ON state: (1) tDCS over the Primary Motor Cortex (M1); and (2) Action Observation (AO) and Motor Imagery (MI) training through a Brain-Computer Interface (BCI) using Virtual Reality (AO + MI-BCI). Both studies will include 32 subjects in a longitudinal prospective parallel randomized controlled trial design under different blinding conditions. The main outcomes will be score changes in King’s Parkinson’s Disease Pain Scale, Brief Pain Inventory, Temporal Summation, Conditioned Pain Modulation, and Pain Pressure Threshold. Assessment will be performed pre-intervention, post-intervention, and 15 days post-intervention, in both ON and OFF states.

Cortical current density magnitudes during transcranial direct current stimulation correlate with skull thickness in children, adolescent and young adults.

Transcranial direct current stimulation protocols are often applied with a fixed parameter set to all subjects participating in an interventional study. This might lead to considerable effect variation in inhomogeneous subject groups or when transferring stimulation protocols to different age groups. The aim of this study was to evaluate magnitude differences of the electric current density distribution on the gray matter surface in children, adolescent and adults in correlation with the individual volume conductor geometry. We generated individual six compartment finite element models from structural magnetic resonance images of four children (age: 10.95 a±1.32 a), eight adolescents (age: 15.10 a±1.16 a) and eight young adults (age: 21.62 a±2.45 a). We determined the skull thickness in the models as Euclidean distance between the surface of the cerebrospinal fluid compartment and outer skull boundary. For tDCS simulations, we modeled 5×7cm patch electrodes impressing 1mA current intensity as anode and cathode over the left M1 and the right fronto-polar orbit, respectively. The resulting current density was analyzed on the gray matter surface. Our results demonstrate higher cortical current density magnitudes in children compared to adults for a given tDCS current strength. Above the evaluated cortex, the skull thickness increased with age. In conclusion, we underline the importance of age-dependent and individual models in tDCS simulations.

Implicit visual sensitivity towards slim versus overweight bodies modulates motor resonance in the primary motor cortex: A tDCS study

Motor resonance (MR) can be influenced by individual differences and similarity in the physical appearance between the actor and observer. Recently, we reported that action simulation is modulated by an implicit visual sensitivity towards normal-weight compared with overweight bodies. Furthermore, recent research has suggested the existence of an action observation network responsible for MR, with limited evidence whether the primary motor cortex (M1) is part of this. We expanded our previous findings with regards to the role of an implicit normal-weight-body preference in the MR mechanism. At the same time, we tested the functional relevance of M1 to MR, by using a transcranial direct current stimulation (tDCS) protocol. Seventeen normal-weight and 17 overweight participants were asked to observe normal-weight or overweight actors reaching and grasping a light or heavy cube, and then, at the end of each video-clip to indicate the correct cube weight. Before the task, all participants received 15 min of sham or cathodal tDCS over the left M1. Measures of anti-fat attitudes were also collected. During sham tDCS, all participants were better in simulating the actions performed by normal-weight compared with overweight models. Surprisingly, cathodal tDCS selectively improved the ability in the overweight group to simulate actions performed by the overweight models. This effect was not associated with scores of fat phobic attitudes or implicit anti-fat bias. Our findings are discussed in the context of relevance of M1 to MR and its social modulation by anti-fat attitudes.

Cerebellar transcranial alternating current stimulation in the gamma range applied during the acquisition of a novel motor skill

The development of novel strategies to augment motor training success is of great interest for healthy persons and neurological patients. A promising approach is the combination of training with transcranial electric stimulation. However, limited reproducibility and varying effect sizes make further protocol optimization necessary. We tested the effects of a novel cerebellar transcranial alternating current stimulation protocol (tACS) on motor skill learning. Furthermore, we studied underlying mechanisms by means of transcranial magnetic stimulation and analysis of fMRI-based resting-state connectivity. N = 15 young, healthy participants were recruited. 50 Hz tACS was applied to the left cerebellum in a double-blind, sham-controlled, cross-over design concurrently to the acquisition of a novel motor skill. Potential underlying mechanisms were assessed by studying short intracortical inhibition at rest (SICIrest) and in the premovement phase (SICImove), intracortical facilitation at rest (ICFrest), and seed-based resting-state fMRI-based functional connectivity (FC) in a hypothesis-driven motor learning network. Active stimulation did not enhance skill acquisition or retention. Minor effects on striato-parietal FC were present. Linear mixed effects modelling identified SICImove modulation and baseline task performance as the most influential determining factors for predicting training success. Accounting for the identified factors may allow to stratify participants for future training-based interventions.

Effects of transcranial direct current stimulation on cortex modulation by stimulation of the primary motor cortex and parietal cortex in humans

Aim of the study Transcranial magnetic stimulation (TMS) is used to measure corticospinal excitability (CSE) from the primary motor cortex (M1) in humans through motor-evoked potentials (MEPs). The variability of CSE responses to transcranial direct current stimulation (tDCS) protocols is high and needs to be reproduced in the healthy population. The M1 and posterior parietal cortex (PPC) are anatomically and functionally connected and could play a role in understanding the variability in CSE responses. We tested the individual MEPs following a common cathodal (ctDCS) protocol over the M1 and PPC. Materials and methods Twenty-eight healthy subjects were randomized for a ctDCS stimulation over the left M1 and PPC for 20 min on a separate days. The first dorsal interosseous muscle (FDI) contralateral stimulation of the left M1 was used as the resting motor threshold (RMT), while 15 single pulses 4–8 s apart at an intensity of 120% RMT were used to determine the baseline MEP amplitude and at T0, 5, 10, 20, 30, 40, 50, and 60 min after ctDCS stimulation in both sessions. Results A 20 min duration of ctDCS stimulation significantly deceased the CSE only at T0 (p = 0.046 at M1, p = 0.010 at PPC). Conclusion Our results suggested that PPC stimulation can modulate M1 excitability and PPC–M1 connectivity, but a significant effect is only observed immediately post ctDCS. The tDCS showed variability in response to the tDCS protocol is consistent with other non-invasive brain stimulation studies.

Effects of different transcranial direct current stimulation protocols on visuo-spatial contextual learning formation: evidence of homeostatic regulatory mechanisms

In the present study we tested the effects of different transcranial direct current stimulation (tDCS) protocols in the formation of visuo-spatial contextual learning (VSCL). The study comprised three experiments designed to evaluate tDCS-induced changes in VSCL measures collected during the execution of a visual search task widely used to examine statistical learning in the visuo-spatial domain. In Experiment 1, we probed for the effects of left-posterior parietal cortex (PPC) anodal-tDCS (AtDCS) at different timings (i.e. offline and online) and intensities (i.e. 3 mA and 1.5 mA). The protocol producing the more robust effect in Experiment 1 was used in Experiment 2 over the right-PPC, while in Experiment 3, cathodal-tDCS (CtDCS) was applied over the left-PPC only at a high intensity (i.e. 3 mA) but varying timing of application (offline and online). Results revealed that high intensity offline AtDCS reduced VSCL regardless of the stimulation side (Experiment 1 and 2), while no significant behavioral changes were produced by both online AtDCS protocols (Experiment 1) and offline/online CtDCS (Experiment 3). The reduced VSCL could result from homeostatic regulatory mechanisms hindering normal task-related neuroplastic phenomena.

Modelling of the Temperature Changes Induced by Transcutaneous Spinal Direct Current Stimulation (tsDCS)

Transcutaneous spinal direct current stimulation is a neuromodulation technique recently exploited to regulate the activity and enhance plasticity of spinal neural structure. Despite the few side-effects reported by clinical studies, the assessment of potential localized temperature increases in tissues is still not solved. In this study, the temperature increase induced by a 3 mA stimulation in the tissue target (i.e., the spinal cord), in its surrounding tissues and in other tissues possibly more vulnerable to temperature increase were assessed through a computational approach. That solves Laplace equation and BioHeat equation for electric field and temperature distribution, respectively, on six whole body high resolution anatomical models, including three models of pregnant women at different gestational ages. Results show that temperature increase distribution in those targets is guided by a complex interaction between different mechanism in which electric stimulation plays a secondary role, in particular when blood perfusion is active. The very low heating assessed (below 1.5 m °C) is not consistent with the hypothesis that the induced temperature increase would critically activate metabolic changes in the target tissues here considered or would contribute to the few side effect that the applications of spinal direct current stimulation protocols have shown.

Delivering Transcranial Direct Current Stimulation Away From Clinic: Remotely Supervised tDCS.

To demonstrate the broad utility of the remotely supervised transcranial direct current stimulation (RS-tDCS) protocol developed to deliver at-home rehabilitation for individuals with multiple sclerosis (MS). Stimulation delivered with the RS-tDCS protocol and paired with adaptive cognitive training was delivered to three different study groups of MS patients to determine the feasibility and tolerability of the protocol. The three studies each used consecutively increasing amounts of stimulation amperage (1.5, 2.0, and 2.5mA, respectively) and session numbers (10, 20, and 40 sessions, respectively). High feasibility and tolerability of the stimulation were observed for n=99 participants across three tDCS pilot studies. RS-tDCS is feasible and tolerable for MS participants. The RS-tDCS protocol can be used to reach those in locations without clinic access and be paired with training or rehabilitation in locations away from the clinic. This protocol could be used to deliver tDCS paired with training or rehabilitation activities remotely to service members and veterans.

Neoadjuvant Treatment With Müllerian-Inhibiting Substance Synchronizes Follicles and Enhances Superovulation Yield.

Müllerian-inhibiting substance (MIS), also known as anti-Müllerian hormone, is thought to be a negative regulator of primordial follicle activation. We have previously reported that treatment with exogenous MIS can induce complete ovarian suppression within 5 weeks of treatment in mice. To investigate the kinetics of the return of folliculogenesis following the reversal of suppression, we treated animals with recombinant human MIS (rhMIS) protein for 40 days in adult female Nu/Nu mice and monitored the recovery of each follicle type over time. Following cessation of MIS therapy, secondary, and antral follicles returned within 30 days, along with the normalization of reproductive hormones, including LH, FSH, MIS, and Inhibin B. Furthermore, 30 days following MIS pretreatment, the number of antral follicles were significantly higher than controls, and superovulation with timed pregnant mare serum gonadotropin and human chorionic gonadotropin stimulation at this time point resulted in an approximately threefold increased yield of eggs. Use of the combined rhMIS-gonadotropin superovulation regimen in a diminished ovarian reserve (DOR) mouse model, created by 4-vinylcyclohexene dioxide treatment, also resulted in a twofold improvement in the yield of eggs. In conclusion, treatment with rhMIS can induce a reversible ovarian suppression, following which a rapid and synchronized large initial wave of growing follicles can be harnessed to enhance the response to superovulation. Therapies modulating MIS signaling may therefore augment the response to current ovarian stimulation protocols and could be particularly useful to women with DOR or poor responders to controlled ovarian hyperstimulation during in vitro fertilization.

Effects of anodal transcranial direct current stimulation on motor evoked potentials variability in humans.

Motor evoked potentials (MEPs) obtained from transcranial magnetic stimulation (TMS) allow corticospinal excitability (CSE) to be measured in the human primary motor cortex (M1). CSE responses to transcranial direct current stimulation (tDCS) protocols are highly variable. Here, we tested the reproducibility and reliability of individual MEPs following a common anodal tDCS protocol. In this study, 32 healthy subjects received anodal tDCS stimulation over the left M1 for three durations (tDCS‐T5, tDCS‐T10, and tDCS‐T20 min) on separate days in a crossover‐randomized order. After the resting motor threshold (RMT) was determined for the contralateral first dorsal interosseous muscle, 15 single pulses 4–8 sec apart at an intensity of 120% RMT were delivered to the left M1 to determine the baseline MEP amplitude at T0, T5, T10, T20, T30, T40, T50, and T60 min after stimulation for each durations. During TMS delivery, 3D images of the participant's cortex and hot spot were visualized for obtaining MEPs from same position. Our findings revealed that there was a significant MEPs improvement at T0 (P = 0.01) after 10 min of anodal stimulation. After the 20‐min stimulation duration, MEPs differed specifically at T0, T5, T30 min (P < 0.05). This indicates that tDCS is a promising tool to improve MEPs. Our observed variability in response to the tDCS protocol is consistent with other noninvasive brain stimulation studies.

Comparison of the Effectiveness of Different transcranial direct current stimulation Protocols (tDCS) with Cognitive Exercises in Improving Response Inhibition in Normal Individuals

Comparison of the Effectiveness of Different transcranial direct current stimulation Protocols (tDCS) with Cognitive Exercises in Improving Response Inhibition in Normal Individuals

Hiccups amelioration following a transcranial direct current stimulation protocol targeting central structures

Hiccups amelioration following a transcranial direct current stimulation protocol targeting central structures

Bilateral Prefrontal Cortex Anodal tDCS Effects on Self-reported Aggressiveness in Imprisoned Violent Offenders

Reduced activity of the frontal lobes, and particularly of the prefrontal cortex, has been related with violent behavior, aggression and crime. The causal importance of prefrontal cortex activity for aggressive behaviors and the self-perception of aggressiveness needs however to be clarified. The aim of this study was to explore the effect of an anodal transcranial direct current stimulation protocol (tDCS, 1.5 mA, 15 min), which, according to previous studies, enhances cortical excitability, applied bilaterally over the prefrontal cortex on self-reported aggressiveness. Two imprisoned violent offender cohorts, discerned by the degree of aggressiveness (murderers vs. non-murderers), were included in this single-blind sham-controlled study. Self-reported aggressiveness was recorded before and after 3 tDCS sessions (one session per day). Four dimensions of aggression were evaluated by means of the standardized Buss–Perry Aggression Questionnaire (BAQ). In both inmate groups the results revealed an aggression-reducing effect of tDCS on the Physical aggression, Anger, and Verbal aggression dimensions of the BAQ. In the Hostility dimension, tDCS significantly reduced aggression only in the group of murderers. These results suggest that modulation of prefrontal cortex excitability by 3 consecutive sessions of tDCS reduces self-reported aggressiveness similarly in murderer and non-murderer samples.