Identification of selection and inhibition components in a Go/NoGo task from EEG spectra using a machine learning classifier.

INTRODUCTION: Prior Go/NoGo studies have localized specific regions and EEG spectra for which traditional approaches have distinguished between Go and NoGo conditions. A more detailed characterization of the spatial distribution and timing of the synchronization of frequency bands would contribute substantially to the clarification of neural mechanisms that underlie performance of the Go/NoGo task. METHODS: The present study used a machine learning approach to learn the features that distinguish between ERSPs involved in selection and inhibition in a Go/NoGo task. A single-layer neural network classifier was used to predict task conditions for each subject to characterize ERSPs associated with Go versus NoGo trials. RESULTS: The final classifier accurately identified individual task conditions at an overall rate of 92%, estimated by fivefold cross-validation. The detailed accounting of EEG time-frequency patterns localized to brain regions (i.e., thalamus, pre-SMA, orbitofrontal cortex, and superior parietal cortex) corroborates and also elaborates upon previous findings from fMRI and EEG studies, and expands the information about EEG power changes in multiple frequency bands (i.e., primarily theta power increase, alpha decreases, and beta increases and decreases) within these regions underlying the selection and inhibition processes engaged in the Go and NoGo trials. CONCLUSION: This time-frequency-based classifier extends previous spatiotemporal findings and provides information about neural mechanisms underlying selection and inhibition processes engaged in Go and NoGo trials, respectively. This neural network classifier can be used to assess time-frequency patterns from an individual subject and thus may offer insight into therapeutic uses of neuromodulation in neural dysfunction.

High-Definition Transcranial Direct Current Stimulation to Improve Verbal Retrieval Deficits in Chronic Traumatic Brain Injury.

Chronic verbal retrieval deficits have been noted in traumatic brain injury (TBI), but no U.S. Food and Drug Administration-approved interventions are available. The present study investigated whether 10 sessions of 20 min of 1 mA anodal high-definition transcranial direct current stimulation (HD-tDCS) targeting pre-supplementary motor area/dorsal anterior cingulate cortex (preSMA/dACC) compared with sham HD-tDCS would improve verbal retrieval deficits in TBI patients. Improvements in verbal retrieval processes were observed up to 8 weeks post-treatment. Thus, potential dysfunction to verbal retrieval circuitry in TBI appears amenable to remediation through electromodulation with HD tDCS to the preSMA/dACC. Although further studies clarifying mechanisms by which tDCS brought about these improvements will likely inform refinements in the application of this therapeutic technique, the findings suggest the efficacy of using HD-tDCS to target other systems vulnerable to TBI to improve functioning.

Neurophysiology of threat processing bias in combat-related post-traumatic stress disorder.

Post-traumatic stress disorder (PTSD) is a debilitating condition that may develop after experiencing a traumatic event. Combat exposure increases an individual's chance of developing PTSD, making veterans especially susceptible to the disorder. PTSD is characterized by dysregulated emotional networks, memory deficits, and a hyperattentive response to perceived threatening stimuli. Recently, there have been a number of imaging studies that show structural and functional abnormalities associated with PTSD; however, there have been few studies utilizing electroencephalography (EEG). The goal of this study was to characterize **EEG brain dynamics in individuals with PTSD, in order to better understand the neurophysiological underpinnings of some of the salient features of PTSD, such as threat-processing bias. Veterans of Operation Enduring Freedom/Iraqi Freedom completed an implicit visual threat semantic memory recognition task with stimuli that varied on both category (animals, items, nature, and people) and feature (threatening and nonthreatening) membership, including trauma-related stimuli. Combat veterans with PTSD had slower reaction times for the threatening stimuli relative to the combat veterans without PTSD (VETC). There were trauma-specific effects in frontal regions, with theta band EEG power reductions for the threatening combat scenes in the PTSD patients compared to the VETC group. Additionally, a moderate negative correlation was observed between trauma-specific frontal theta power and hyperarousal symptoms as measured by clinically administered PTSD scale. These findings complement and extend current models of cortico-limbic dysfunction in PTSD. The moderate negative correlation between frontal theta power and hyperarousal endorsements suggests the utility of these measures as therapeutic markers of symptomatology in PTSD patients.

Conjoint differences in inhibitory control and processing speed in childhood to older adult cohorts: Discriminant functions from a Go/No-Go task.

To investigate differences in inhibitory control and processing speed over the life span, participants in 7- to 8-, 10- to 11-, 12- to 15-, 18- to 25-, and 54- to 80-year-old age cohorts completed a Go/No-Go task requiring varying levels of semantic categorization. Discriminant function analysis of correct rejection rates (CRRs), hit rates (HRs), and reaction times (RTs) revealed a function on which CRR loaded positively and RT loaded negatively, across categorization levels. Scores increased from youngest to the younger adult cohort and decreased for the older adult cohort. On a second function, CRR and RT loaded positively and HR loaded negatively across categorization levels. Scores were highest for the older adult cohort and higher for the youngest cohort than for the younger adult cohort. The results suggest change along 2 dimensions might underlie cognitive development: (a) combined increased inhibitory control and processing speed and (b) combined increased speed and decreased biased responding for better inhibitory control. In addition, 2 dimensions might underlie senescence: (a) combined decreased inhibitory control and processing speed and (b) combined decreased speed and increased biased responding for better inhibitory control. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Electrophysiological Correlates of Word Retrieval in Traumatic Brain Injury.

Persons who have had a traumatic brain injury (TBI) often have word retrieval deficits; however, the underlying neural mechanisms of such deficits are yet to be clarified. Previous studies in normal subjects have shown that during a word retrieval task, there is a 750 msec event-related potential (ERP) divergence detected at the left fronto-temporal region when subjects evaluate word pairs that facilitate retrieval compared with responses elicited by word pairs that do not facilitate retrieval. In this study, we investigated the neurophysiological correlates of word retrieval networks in 19 retired professional athletes with TBI and 19 healthy control (HC) subjects. We recorded electroencephalography (EEG) in the participants during a semantic object retrieval task. In this task, participants indicated whether presented word pairs did (retrieval) or did not (non-retrieval) facilitate the retrieval of an object name. There were no significant differences in accuracy or reaction time between the two groups. The EEG showed a significant group by condition interaction over the left fronto-temporal region. The HC group mean amplitudes were significantly different between conditions, but the TBI group data did not show this difference, suggesting neurophysiological effects of injury. These findings provide evidence that ERP amplitudes may be used as a marker of disrupted semantic retrieval circuits in persons with TBI even when those persons perform normally.

Electrophysiological spatiotemporal dynamics during implicit visual threat processing.

Numerous studies have found evidence for corticolimbic theta band electroencephalographic (EEG) oscillations in the neural processing of visual stimuli perceived as threatening. However, varying temporal and topographical patterns have emerged, possibly due to varying arousal levels of the stimuli. In addition, recent studies suggest neural oscillations in delta, theta, alpha, and beta-band frequencies play a functional role in information processing in the brain. This study implemented a data-driven PCA based analysis investigating the spatiotemporal dynamics of electroencephalographic delta, theta, alpha, and beta-band frequencies during an implicit visual threat processing task. While controlling for the arousal dimension (the intensity of emotional activation), we found several spatial and temporal differences for threatening compared to nonthreatening visual images. We detected an early posterior increase in theta power followed by a later frontal increase in theta power, greatest for the threatening condition. There was also a consistent left lateralized beta desynchronization for the threatening condition. Our results provide support for a dynamic corticolimbic network, with theta and beta band activity indexing processes pivotal in visual threat processing.