Prefrontal transcranial direct current stimulation over the right prefrontal cortex reduces proactive and reactive control performance towards emotional material in healthy individuals

The prefrontal cortex plays a crucial role in cognitive processes, both during anticipatory and reactive modes of cognitive control. Transcranial Direct Current Stimulation (tDCS) can modulate these cognitive resources. However, there is a lack of research exploring the impact of tDCS on emotional material processing in the prefrontal cortex, particularly in regard to proactive and reactive modes of cognitive control. In this study, 35 healthy volunteers underwent both real and sham tDCS applied to the right prefrontal cortex in a counterbalanced order, and then completed the Cued Emotion Control Task (CECT). Pupil dilation, a measure of cognitive resource allocation, and behavioral outcomes, such as reaction time and accuracy, were collected. The results indicate that, as compared to sham stimulation, active right-sided tDCS reduced performance and resource allocation in both proactive and reactive modes of cognitive control. These findings highlight the importance of further research on the effects of tDCS applied to the right prefrontal cortex on cognitive engagement, particularly for clinical trials utilizing the present electrode montage in combination with cognitive interventions.

Right prefrontal activation predicts ADHD and its severity: A TMS-EEG study in young adults

OBJECTIVE

Here we bring a neurophysiological diagnostic tool, based on pathophysiologically-relevant brain region, that is critical for reducing the variability between clinicians, and necessary for quantitative measures of ADHD severity.

METHODS

54 healthy and 57 ADHD adults participated in the study. Electroencephalography (EEG) was recorded when combined with transcranial magnetic stimulation (TMS) over the right prefrontal cortex and also recorded during the Stop Signal task.

RESULTS

TMS evoked potentials (TEPs) and the event related potential (ERP) components in the Stop Signal task were found to be significantly reduced in ADHD relative to the matched healthy controls. Stop signal reaction time (SSRT) and stopping accuracy was found to correlate with the ERP signal, and ADHD severity correlated with the TEP signal. Cortical activity (early TEP and Stop Signal ERP) diagnostic model yielded accuracy of 72%.

CONCLUSION

TEPs and ERPs reveal that right PFC excitability was associated with ADHD severity, and with behavioral impulsivity - as a hallmark of ADHD pathology. This electrophysiological biomarker supports the potential of objective diagnosis for ADHD.

SIGNIFICANCE

Such tools would allow better assessment of treatment efficacy and prognosis, may advance understanding of the pathophysiology of the disease and better the public's attitudes and stigma towards ADHD.

TRIAL REGISTRATION

Trial to Evaluate the Efficacy of the HLPFC Coil Deep Transcranial Magnetic Stimulation System in Treating Attention Deficit and Hyperactivity Disorder (ADHD) in Adults, https://clinicaltrials.gov/ct2/show/NCT01737476, ClinicalTrials.govnumberNCT01737476.

Attention and the Cholinergic System: Relevance to Schizophrenia

Traditional methods of drug discovery often rely on a unidirectional, "bottom-up" approach: A search for molecular compounds that target a particular neurobiological substrate (e.g., a receptor type), the refinement of those compounds, testing in animal models using high-throughput behavioral screening methods, and then human testing for safety and effectiveness. Many attempts have found the "effectiveness" criterion to be a major stumbling block, and we and others have suggested that success may be improved by an alternative approach that considers the neural circuits mediating the effects of genetic and molecular manipulations on behavior and cognition. We describe our efforts to understand the cholinergic system's role in attention using parallel approaches to test main hypotheses in both rodents and humans as well as generating converging evidence using methods and levels of analysis tailored to each species. The close back-and-forth between these methods has enhanced our understanding of the cholinergic system's role in attention both "bottom-up" and "top-down"-that is, the basic neuroscience identifies potential neuronal circuit-based mechanisms of clinical symptoms, and the patient and genetic populations serve as natural experiments to test and refine hypotheses about its contribution to specific processes. Together, these studies have identified (at least) two major and potentially independent contributions of the cholinergic system to attention: a neuromodulatory component that influences cognitive control in response to challenges from distractors that either make detection more difficult or draw attention away from the distractor, and a phasic or transient cholinergic signal that instigates a shift from ongoing behavior and the activation of cue-associated response. Right prefrontal cortex appears to play a particularly important role in the neuromodulatory component integrating motivational and cognitive influences for top-down control across populations, whereas the transient cholinergic signal involves orbitofrontal regions associated with shifts between internal and external attention. Understanding how these two modes of cholinergic function interact and are perturbed in schizophrenia will be an important prerequisite for developing effective treatments.