Impact of Anodal High-Definition Transcranial Direct Current Stimulation of Medial Prefrontal Cortex on Stroop Task performance and its electrophysiological correlates. A pilot study

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.

Combined effects of transcranial direct current stimulation and aerobic exercise on inhibitory control function in healthy young adults: An event-related potential study

Transcranial direct current stimulation (tDCS) and aerobic exercise (AE) have been demonstrated to enhance inhibitory control function in healthy individuals separately. However, the potential benefits of combining these two interventions have yet to be fully explored. In this study, we aimed to use multiple event-related potential (ERP) components (P200, N200, and N450) to investigate the combined effects of tDCS and AE on the improvement of inhibitory control ability in healthy young adults. We evaluated the influence of this combined intervention on cognitive tasks involving inhibitory control function and basic information processing by performing the Stroop Word Color task. Our results showed that compared to the application of tDCS or AE alone, the combined intervention of tDCS and AE had a greater effect on improving inhibitory control function in healthy young adults. The amplitude of P200, N200, and N450 ERP components also changed more significantly during the Stroop Word Color task. We concluded that the mechanism of tDCS combined with AE in improving inhibitory control ability may involve synergistic effects on brain structures at different levels, such as regulating interactions at the reticular activating system level and activating corresponding brain regions at the medial frontal lobe and frontal lobe levels.

Neuromodulating the performance monitoring network during conflict and error processing in healthy populations: Insights from transcranial electric stimulation studies

The performance monitoring system is fundamentally important for adapting one’s own behavior in conflicting and error-prone, highly demanding circumstances. Flexible behavior requires that neuronal populations optimize information processing through efficient multi-scale communication. Non-invasive brain stimulation (NIBS) studies using transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (tES) fields to alter the cortical activity promise to illuminate the neurophysiological mechanisms that underpin neuro-cognitive and behavioral processing and their causal relationship. Here, we focus on the transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) that have been increasingly used in cognitive neuroscience for modulating superficial neural networks in a polarity (tDCS) and frequency/phase (tACS) fashion. Specifically, we discuss recent evidence showing how tDCS and tACS modulate the performance monitoring network in neurotypical samples. Emphasis is given to studies using behavioral tasks tapping conflict and error processing such as the Stroop, the Flanker, and the Simon tasks. The crucial role of mid-frontal brain regions (such as the medial frontal cortex, MFC; and the dorsal anterior cingulate cortex, dACC) and of theta synchronization in monitoring conflict and error is highlighted. We also discuss current technological limitations (e.g., spatial resolution) and the specific methodological strategies needed to properly modulate the cortical and subcortical regions.