High-definition transcranial direct current stimulation modulates theta response during a Go-NoGo task in traumatic brain injury

Local effective connectivity changes after transcranial direct current stimulation in obsessive-compulsive disorder patients

AIM

This study investigates the effects of transcranial direct current stimulation (tDCS) on brain network connectivity in individuals with obsessive-compulsive disorder (OCD).

METHODS

In a randomized, double-blind, sham-controlled experimental design anodal tDCS (vs. sham) was applied in a total of 43 right-handed patients with OCD, targeting the right pre-supplementary motor area (pre-SMA). Cathodal reference electrode was put on the left pre-SMA. The current was set as 2 mA, with a stimulation duration of either 30 s (sham) or 1200 s. Concurrent resting-state functional MRI data were collected following tDCS (or sham) stimulation. We employed regression dynamic causal modelling (rDCM) to extract whole brain effective connectivity (EC) matrices subsequently analyzing these matrices through graph theory approaches to examine changes in brain activity across different network scales.

RESULTS

We found that tDCS compared to sham caused significant changes in local effective connectivity. Increased recruitment level was detectable in the sensorimotor network (SMN), indicating enhanced intra-network connectivity after active tDCS. Clustering coefficient and local efficiency were also found to be increased in the same area. No significant changes were detectable with regard to global network connectivity.

CONCLUSIONS

Current findings indicate that single-session tDCS can effectively alter local effective connectivities within the SMN in OCD patients. Given the relevance of the SMN and connected regions for the pathophysiology of OCD we believe that tDCS targeting these areas might constitute an effective intervention to normalize altered network connectivity in the disorder of OCD.

LIMITATION

We used a single tDCS session, which may not reflect long-term effects.

Posttraumatic reexperiencing and alcohol use: Mediofrontal theta as a neural mechanism for negative reinforcement

Over half of U.S. military veterans with posttraumatic stress disorder (PTSD) use alcohol heavily, potentially to cope with their symptoms. This study investigated the neural underpinnings of PTSD symptoms and heavy drinking in veterans. We focused on brain responses to salient outcomes within predictive coding theory. This framework suggests the brain generates prediction errors (PEs) when outcomes deviate from expectations. Alcohol use might provide negative reinforcement by reducing the salience of negatively valenced PEs and dampening experiences like loss. We analyzed electroencephalography responses to unpredictable gain/loss feedback in n = 82 veterans of Operations Enduring and Iraqi Freedom. We used time-frequency principal components analysis of event-related potentials to isolate neural responses indicative of PEs, identifying mediofrontal theta linked to losses (feedback-related negativity) and central delta associated with gains (reward positivity). Intrusive reexperiencing symptoms of PTSD were associated with intensified mediofrontal theta signaling during losses, suggesting heightened negative PE sensitivity. Conversely, increased hazardous alcohol use was associated with reduced theta responses, implying a dampening of these negative PEs. The separate delta-reward positivity component showed associations with alcohol use but not PTSD symptoms. The findings suggest a common neural component of PTSD and hazardous alcohol use involving altered PE processing. We suggest that reexperiencing enhances the intensity of salient negative PEs, while chronic alcohol use may reduce their intensity, thereby providing negative reinforcement by muting posttraumatic distress and associated brain responses. Modifying the mediofrontal theta response could address the intertwined nature of PTSD symptoms and alcohol use, providing new avenues for treatment. (PsycInfo Database Record (c) 2025 APA, all rights reserved).

High definition transcranial direct current stimulation as an intervention for cognitive deficits in Alzheimer's dementia: A randomized controlled trial

BACKGROUND

Recent disease-modifying treatments for Alzheimer's disease show promise to slow cognitive decline, but show no efficacy towards reducing symptoms already manifested.

OBJECTIVES

To investigate the efficacy of a novel noninvasive brain stimulation technique in modulating cognitive functioning in Alzheimer's dementia (AD).

DESIGN

Pilot, randomized, double-blind, parallel, sham-controlled study SETTING: Clinical research site at UT Southwestern Medical Center PARTICIPANTS: Twenty-five participants with clinical diagnoses of AD were enrolled from cognition specialty clinics.

INTERVENTION

Treatment consisted of high definition transcranial direct current stimulation (HD-tDCS) delivered for 20 min over the medial prefrontal cortex. Ten sessions of sham, 1 mA, or 2 mA stimulation were received.

MEASUREMENTS

Cognitive outcomes were measured at baseline, after the last HD-tDCS session, and 8-weeks post-treatment. The primary outcome was change in total learning and delayed recall on the Rey Auditory Verbal Learning Test (RAVLT) immediately post-treatment and at 8-weeks. Secondary outcomes included measures of language, processing speed, and executive functioning. A multi-stage approach was used to examine cognitive outcomes, which included evaluation of effect sizes, statistical effects, and rate of clinically meaningful responses.

RESULTS

In this pilot trial, no statistically significant differences on cognitive outcomes were found between sham and active HD-tDCS immediately post-treatment (p's > 0.05). However, moderate-to-large effect sizes were identified for enhanced RAVLT total learning (Cohen's d = 0.69-0.93) and phonemic fluency (d = 1.08-1.49) for both active HD-tDCS conditions compared to sham, with rates of clinically relevant improvement between 25 and 33%. Meaningful enhancement persisted to 8 weeks only for the 1 mA condition.

CONCLUSIONS

Multiple sessions of HD-tDCS over the medial prefrontal cortex appears to have potential to produce meaningful cognitive enhancements in a proportion of patients having AD with improvements maintained for at least 8 weeks in some.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov (NCT05270408). Registered December 30, 2021.

A modified neural circuit framework for semantic memory retrieval with implications for circuit modulation to treat verbal retrieval deficits

Word finding difficulty is a frequent complaint in older age and disease states, but treatment options are lacking for such verbal retrieval deficits. Better understanding of the neurophysiological and neuroanatomical basis of verbal retrieval function may inform effective interventions. In this article, we review the current evidence of a neural retrieval circuit central to verbal production, including words and semantic memory, that involves the pre-supplementary motor area (pre-SMA), striatum (particularly caudate nucleus), and thalamus. We aim to offer a modified neural circuit framework expanded upon a memory retrieval model proposed in 2013 by Hart et al., as evidence from electrophysiological, functional brain imaging, and noninvasive electrical brain stimulation studies have provided additional pieces of information that converge on a shared neural circuit for retrieval of memory and words. We propose that both the left inferior frontal gyrus and fronto-polar regions should be included in the expanded circuit. All these regions have their respective functional roles during verbal retrieval, such as selection and inhibition during search, initiation and termination of search, maintenance of co-activation across cortical regions, as well as final activation of the retrieved information. We will also highlight the structural connectivity from and to the pre-SMA (e.g., frontal aslant tract and fronto-striatal tract) that facilitates communication between the regions within this circuit. Finally, we will discuss how this circuit and its correlated activity may be affected by disease states and how this circuit may serve as a novel target engagement for neuromodulatory treatment of verbal retrieval deficits.

Theta oscillations within right dorsolateral prefrontal cortex contribute differently to speech versus limb inhibition

Evidence suggests that speech and limb movement inhibition are subserved by common neural mechanisms, particularly within the right prefrontal cortex. In a recent study, we found that cathodal stimulation of right dorsolateral prefrontal cortex (rDLPFC) differentially modulated P3 event-related potentials for speech versus limb inhibition. In the present study, we further analyzed these data to examine the effects of cathodal high-definition transcranial direct current stimulation (HD-tDCS) over rDLPFC on frontal theta - an oscillatory marker of cognitive control - in response to speech and limb inhibition, during a Go/No-Go task in 21 neurotypical adults. Electroencephalography data demonstrated that both speech and limb No-Go elicited prominent theta activity over right prefrontal electrodes, with stronger activity for speech compared to limb. Moreover, we found that cathodal stimulation significantly increased theta power over right prefrontal electrodes for speech versus limb No-Go. Source analysis revealed that cathodal, but not sham, stimulation increased theta activity within rDLPFC and bilateral premotor cortex for speech No-Go compared to limb movement inhibition. These findings complement our previous report and suggest (1) right prefrontal theta activity is an amodal oscillatory mechanism supporting speech and limb inhibition, (2) larger theta activity in prefrontal electrodes for speech versus limb following cathodal stimulation may reflect allocation of additional neural resources for a more complex motor task, such as speech compared to limb movement. These findings have translational implications for conditions such as Parkinson's disease, wherein both speech and limb movement are impaired.

Posttraumatic reexperiencing and alcohol use: mediofrontal theta as a neural mechanism for negative reinforcement

Objective

Over half of US military veterans with posttraumatic stress disorder (PTSD) use alcohol heavily, potentially to cope with their symptoms. This study investigated the neural underpinnings of PTSD symptoms and heavy drinking in veterans. We focused on brain responses to salient outcomes within predictive coding theory. This framework suggests the brain generates prediction errors (PEs) when outcomes deviate from expectations. Alcohol use might provide negative reinforcement by reducing the salience of negatively-valenced PEs and dampening experiences like loss.

Methods

We analyzed electroencephalography (EEG) responses to unpredictable gain/loss feedback in veterans of Operations Enduring and Iraqi Freedom. We used time-frequency principal components analysis of event-related potentials to isolate neural responses indicative of PEs, identifying mediofrontal theta linked to losses (feedback-related negativity, FRN) and central delta associated with gains (reward positivity, RewP).

Results

Intrusive reexperiencing symptoms of PTSD were associated with intensified mediofrontal theta signaling during losses, suggesting heightened negative PE sensitivity. Conversely, increased hazardous alcohol use was associated with reduced theta responses, implying a dampening of these negative PEs. The separate delta-RewP component showed associations with alcohol use but not PTSD symptoms.

Conclusions

Findings suggest a common neural component of PTSD and hazardous alcohol use involving altered PE processing. We suggest that reexperiencing enhances the intensity of salient negative PEs, while chronic alcohol use may reduce their intensity, thereby providing negative reinforcement by muting emotional disruption from reexperienced trauma. Modifying the mediofrontal theta response could address the intertwined nature of PTSD symptoms and alcohol use, providing new avenues for treatment.

Cognitive control subprocess deficits and compensatory modulation mechanisms in patients with frontal lobe injury revealed by EEG markers: a basic study to guide brain stimulation

Background

Frontal lobe injury (FLI) is related to cognitive control impairments, but the influences of FLI on the internal subprocesses of cognitive control remain unclear.

Aims

We sought to identify specific biomarkers for long-term dysfunction or compensatory modulation in different cognitive control subprocesses.

Methods

A retrospective case-control study was conducted. Event-related potentials (ERP), oscillations and functional connectivity were used to analyse electroencephalography (EEG) data from 12 patients with unilateral frontal lobe injury (UFLI), 12 patients with bilateral frontal lobe injury (BFLI) and 26 healthy controls (HCs) during a Go/NoGo task, which included several subprocesses: perceptual processing, anticipatory preparation, conflict monitoring and response decision.

Results

Compared with the HC group, N2 (the second negative peak in the averaged ERP waveform) latency, and frontal and parietal oscillations were decreased only in the BFLI group, whereas P3 (the third positive peak in the averaged ERP waveform) amplitudes and sensorimotor oscillations were decreased in both patient groups. The functional connectivity of the four subprocesses was as follows: alpha connections of posterior networks in the BFLI group were lower than in the HC and UFLI groups, and these alpha connections were negatively correlated with neuropsychological tests. Theta connections of the dorsal frontoparietal network in the bilateral hemispheres of the BFLI group were lower than in the HC and UFLI groups, and these connections in the uninjured hemisphere of the UFLI group were higher than in the HC group, which were negatively correlated with behavioural performances. Delta and theta connections of the midfrontal-related networks in the BFLI group were lower than in the HC group. Theta across-network connections in the HC group were higher than in the BFLI group but lower than in the UFLI group.

Conclusions

The enhancement of low-frequency connections reflects compensatory mechanisms. In contrast, alpha connections are the opposite, therefore revealing more abnormal neural activity and less compensatory connectivity as the severity of injury increases. The nodes of the above networks may serve as stimulating targets for early treatment to restore corresponding functions. EEG biomarkers can measure neuromodulation effects in heterogeneous patients.