Centrally-mediated sensory information processing is impacted with increased alcohol consumption in college-aged individuals

Changes in processing speed during early abstinence from alcohol dependence

BACKGROUND

Processing speed is a task-independent construct underpinning more complex goal-related abilities. Processing speed is impaired in alcohol dependence (AD) and is linked to relapse, as are the functions it underpins. Reliable measurement of processing speed may allow tracking of AD recovery trajectories and identify patients requiring additional support.

AIMS

To assess changes in reaction time (RT) from baseline (at the start of a detoxification programme) across early abstinence.

METHODS

Vibrotactile RT was assessed in early recovery between days 3 and 7 of treatment in 66 individuals with AD (25 females; aged 19-74, 44.60 ± 10.60 years) and against 35 controls tested on one occasion (19 females; 41.00 ± 13.60), using two multivariate multiple regressions. A mixed multivariate analysis of covariance (MANCOVA) of available AD data (n = 45) assessed change in RT between timepoints and between treatment settings (outpatient vs inpatient).

RESULTS

The group (AD vs control) significantly predicted choice RT at baseline and follow-up but did not significantly predict simple RT or RT variability, which is inconsistent with previous findings. At follow-up, mental fatigue was also predicted by the group, and MANCOVA indicated that this had worsened in inpatients but improved in outpatients.

CONCLUSIONS

Recovery of RT measures so early in the treatment journey was not in line with previous research which indicates persisting deficits. The interaction between setting and timepoint indicates that despite being typically less medically complex, outpatients require ongoing support and monitoring during their recovery.

A pilot study assessing the brain gauge as an indicator of cognitive recovery in alcohol dependence

Alcohol dependence (AD) is associated with multiple cognitive deficits, which can affect treatment outcomes. Current measures of tracking brain recovery (e.g., functional magnetic resonance imaging) can be less accessible for practitioners. This study pilots a novel device (the brain gauge; BG) to assess its utility, and track recovery of cognitive function in residential alcohol treatment.

METHODS

A repeated measures design assessed changes in cognitive function during detoxification. Twenty-one participants with AD (16 Male; Mean age 43.85 ± 6.21) completed a battery of alcohol and memory questionnaires and BG tasks at two time-points (∼days 4 and 10) during a single managed detoxification episode.

RESULTS

Repeated measures ANCOVA revealed that some BG metrics significantly improved, with medium to large effect sizes - processing speed, focus, temporal order judgement and overall cortical metric. However, differences in subjective cognitive function were non-significant after controlling for depression and anxiety change scores. Anxiety change emerged as a significant factor in subjective cognitive function.

CONCLUSIONS

We conclude it is possible that the prefrontal cortex (PFC) recovers more slowly compared to other brain areas, and there are compounding effects of improvements in anxiety and depression, and metacognitive deficits on subjective EF assessments. Future research should seek to validate the clinical utility of the BG by comparing against established neuroimaging methods.

Evaluation of a Field-Ready Neurofunctional Assessment Tool for Use in a Military Environment

INTRODUCTION

The Office of Naval Research sponsored the Blast Load Assessment Sense and Test (BLAST) program to develop a rapid, in-field solution that could be used by team leaders, commanders, and medical personnel to provide a standardized approach to operationally relevant monitoring and analysis of service members exposed to single or repeated low-level blast. A critical piece of the BLAST team's solution was the development of the Brain Gauge technology which includes a cognitive assessment device that measures neurofunctional changes by testing sensory perceptions and a suite of mathematical algorithms that analyze the results of the test. The most recent versions of the technology are easily portable; the device is in the size and shape of a computer mouse. Tests can be administered in a matter of minutes and do not require oversight by a clinician, making Brain Gauge an excellent choice for field use. This paper describes the theoretical underpinnings and performance of a fieldable Brain Gauge technology for use with military populations.

MATERIALS AND METHODS

The methods used by the Brain Gauge have been documented in over 80 peer-reviewed publications. These papers are reviewed, and the utility of the Brain Gauge is described in terms of those publications.

RESULTS

The Brain Gauge has been demonstrated to be an effective tool for assessing blast-induced neurotrauma and tracking its recovery. Additionally, the method parallels neurophysiological findings of animal models which provide insight into the sensitivity of specific metrics to mechanisms of information processing.

CONCLUSIONS

The overall objective of the work was to provide an efficient tool, or tools, that can be effectively used for (1) determining stand-down criteria when critical levels of blast exposure have been reached and (2) tracking the brain health history until return-to-duty status is achieved. Neurofunctional outcome measures will provide the scientific link between blast sensors and the impact of blast on biological health. This calibration process is strengthened with outcome measures that have a biological basis that are paralleled in animal models. The integrative approach that utilizes the Brain Gauge technology will provide a significant advance for assessing the impact of blast exposure and support rapid, science-based decision-making that will ensure mission success and promote the protection of brain health in service members.

An Experimental Animal Model that Parallels Neurosensory Assessments of Concussion

INTRODUCTION

Tactile-based quantitative sensory assessments have proven successful in differentiating concussed vs. non-concussed individuals. One potential advantage of this methodology is that an experimental animal model can be used to obtain neurophysiological recordings of the neural activity in the somatosensory cortex evoked in response to the same tactile stimuli that are used in human sensory assessments and establish parallels between various metrics of stimulus-evoked cortical activity and perception of the stimulus attributes.

MATERIALS AND METHODS

Stimulus-evoked neural activity was recorded via extracellular microelectrodes in rat primary somatosensory cortex (S1) in response to vibrotactile stimuli that are used in two particular human sensory assessments (reaction time (RT) and amplitude discrimination). Experiments were conducted on healthy control and brain-injured (BI) rats.

RESULTS

Similar to the effects of mild traumatic brain injuries (mTBI) on human neurosensory assessments, comparable experimentally induced brain injuries in rats resulted in the following: (1) elevation of S1 responsivity to vibrotactile stimulation that depended nonlinearly on stimulus amplitude, significantly reducing its capacity to discriminate between stimuli of different amplitudes; (2) 50% reduction in S1 signal-to-noise ratios, which can be expected to contribute to elevation of RT in BI rats; and (3) 60% increase in intertrial variability of S1 responses to vibrotactile stimulation, which can be expected to contribute to elevation of RT variability in BI rats.

CONCLUSIONS

The results demonstrate suggestive similarities between neurophysiological observations made in the experimental rat mTBI model and observations made in post-concussion individuals with regard to three sensory assessment metrics (amplitude discrimination, RT, and RT variability). This is the first successful model that demonstrates that perceptual metrics obtained from human individuals are impacted by mTBI in a manner consistent with neurophysiological observations obtained from rat S1.

Quantification of Mild Traumatic Brain Injury via Cortical Metrics: Analytical Methods

Mild traumatic brain injuries are difficult to diagnose or assess with commonly used diagnostic methods. However, the functional state of cerebral cortical networks can be rapidly and effectively probed by measuring tactile-based sensory percepts (called cortical metrics), which are designed to exercise various components of cortical machinery. In this study, such cortical metrics were obtained from 52 college students before and after they experienced sports-related concussions by delivering vibrotactile stimuli to the index and middle fingertips. Performance on four of the sensory test protocols is described: reaction time, amplitude discrimination, temporal order judgment, and duration discrimination. The collected test performance data were analyzed using methods of uni- and multivariate statistics, receiver operated characteristic (ROC) curves, and discriminant analysis. While individual cortical metrics vary extensively in their ability to discriminate between control and concussed subjects, their combined discriminative performance greatly exceeds that of any individual metric, achieving cross-validated 93.0% sensitivity, 92.3% specificity, 93.0% positive predictive value, and 92.3% negative predictive value. The cortical metrics vector can be used to track an individual's recovery from concussion. The study thus establishes that cortical metrics can be used effectively as a quantitative indicator of central nervous system health status.

Stimulating somatosensory psychophysics: a double-blind, sham-controlled study of the neurobiological mechanisms of tDCS

The neuromodulation technique transcranial direct current stimulation (tDCS) is thought to produce its effects on behavior by altering cortical excitability. Although the mechanisms underlying the observed effects are thought to rely on the balance of excitatory and inhibitory neurotransmission, the physiological principles of the technique are not completely understood. In this study, we examine the influence of tDCS on vibrotactile adaptation, using a simple amplitude discrimination paradigm that has been shown to exhibit modifications in performance due to changes in inhibitory neurotransmission. Double-blind tDCS (Anodal/Sham) of 1 mA was delivered for 600 s to electrodes positioned in a somatosensory/contralateral orbit montage. Stimulation was applied as part of a pre/post design, between blocks of the behavioral tasks. In accordance with previous work, results obtained before the application of tDCS indicated that amplitude discrimination thresholds were significantly worsened during adaptation trials, compared to those achieved at baseline. However, tDCS failed to modify amplitude discrimination performance. Using a Bayesian approach, this finding was revealed to constitute substantial evidence for the null hypothesis. The failure of DC stimulation to alter vibrotactile adaptation thresholds is discussed in the context of several factors that may have confounded the induction of changes in cortical plasticity.

Percept of the duration of a vibrotactile stimulus is altered by changing its amplitude

There have been numerous studies conducted on time perception. However, very few of these have involved tactile stimuli to assess a subject’s capacity for duration discrimination. Previous optical imaging studies in non-human primates demonstrated that increasing the duration of a vibrotactile stimulus resulted in a consistently longer and more well defined evoked SI cortical response. Additionally, and perhaps more interestingly, increasing the amplitude of a vibrotactile stimulus not only evoked a larger magnitude optical intrinsic signal (OIS), but the return to baseline of the evoked response was much longer in duration for larger amplitude stimuli. This led the authors to hypothesize that the magnitude of a vibrotactile stimulus could influence the perception of its duration. In order to test this hypothesis, subjects were asked to compare two sets of vibrotactile stimuli. When vibrotactile stimuli differed only in duration, subjects typically had a difference limen (DL) of approximately 13%, and this followed Weber’s Law for standards between 500 and 1500 ms, as increasing the value of the standard yielded a proportional increase in DL. However, the percept of duration was impacted by variations in amplitude of the vibrotactile stimuli. Specifically, increasing the amplitude of the standard stimulus had the effect of increasing the DL, while increasing the amplitude of the test stimulus had the effect of decreasing the DL. A pilot study, conducted on individuals who were concussed, found that increasing the amplitude of the standard did not have an impact on the DL of this group of individuals. Since this effect did not parallel what was predicted from the optical imaging findings in somatosensory cortex of non-human primates, the authors suggest that this particular measure or observation could be sensitive to neuroinflammation and that neuron-glial interactions, impacted by concussion, could have the effect of ignoring, or not integrating, the increased amplitude.

Vibrotactile discriminative capacity is impacted in a digit-specific manner with concurrent unattended hand stimulation

A number of perceptual and neurophysiological studies have investigated the effects of delivering unilateral versus bilateral tactile sensory stimulation. While a number of studies indicate that perceptual discrimination degrades with opposite-hand stimulation, there have been no reports that examined the digit specificity of cross-hemispheric interactions to discriminative capabilities. The purpose of this study was to determine whether unattended hand (UH) stimulation significantly degraded or improved amplitude discriminative capacity on the attended hand (AH) in a digit-specific manner. The methods are based on a sensory perceptual task (vibrotactile amplitude discriminative capacity on the tips of the fingers D2 and D3 of the left hand) in the absence and presence of conditioning stimuli delivered to D2 and D3 of the right hand. Non-specific equal-amplitude stimulation to D2 and D3 of the UH significantly worsened amplitude discrimination (AD) performance, while delivering unequal-amplitude stimuli to D2 and D3 of the UH worsened task performance only under the condition in which the unattended stimuli failed to appropriately match the stimulus parameters on the AH. Additionally, delivering single-site stimuli to D2 or D3 of the UH resulted in degraded performance on the AD task when the stimulus amplitude did not match the amplitude of the stimulus applied to homologous digits of the AH. The findings demonstrate that there is a reduction in performance under conditions where UH stimulation least matched stimulation applied to the AH, while there was little or no change in performance when stimulus conditions on the homologous digit(s) of the contralateral sites were similar. Results suggest that bilateral interactions influence perception in a context-dependent manner that is digit specific.

Functional deficits in carpal tunnel syndrome reflect reorganization of primary somatosensory cortex

Carpal tunnel syndrome, a median nerve entrapment neuropathy, is characterized by sensorimotor deficits. Recent reports have shown that this syndrome is also characterized by functional and structural neuroplasticity in the primary somatosensory cortex of the brain. However, the linkage between this neuroplasticity and the functional deficits in carpal tunnel syndrome is unknown. Sixty-three subjects with carpal tunnel syndrome aged 20-60 years and 28 age- and sex-matched healthy control subjects were evaluated with event-related functional magnetic resonance imaging at 3 T while vibrotactile stimulation was delivered to median nerve innervated (second and third) and ulnar nerve innervated (fifth) digits. For each subject, the interdigit cortical separation distance for each digit's contralateral primary somatosensory cortex representation was assessed. We also evaluated fine motor skill performance using a previously validated psychomotor performance test (maximum voluntary contraction and visuomotor pinch/release testing) and tactile discrimination capacity using a four-finger forced choice response test. These biobehavioural and clinical metrics were evaluated and correlated with the second/third interdigit cortical separation distance. Compared with healthy control subjects, subjects with carpal tunnel syndrome demonstrated reduced second/third interdigit cortical separation distance (P < 0.05) in contralateral primary somatosensory cortex, corroborating our previous preliminary multi-modal neuroimaging findings. For psychomotor performance testing, subjects with carpal tunnel syndrome demonstrated reduced maximum voluntary contraction pinch strength (P < 0.01) and a reduced number of pinch/release cycles per second (P < 0.05). Additionally, for four-finger forced-choice testing, subjects with carpal tunnel syndrome demonstrated greater response time (P < 0.05), and reduced sensory discrimination accuracy (P < 0.001) for median nerve, but not ulnar nerve, innervated digits. Moreover, the second/third interdigit cortical separation distance was negatively correlated with paraesthesia severity (r = -0.31, P < 0.05), and number of pinch/release cycles (r = -0.31, P < 0.05), and positively correlated with the second and third digit sensory discrimination accuracy (r = 0.50, P < 0.05). Therefore, reduced second/third interdigit cortical separation distance in contralateral primary somatosensory cortex was associated with worse symptomatology (particularly paraesthesia), reduced fine motor skill performance, and worse sensory discrimination accuracy for median nerve innervated digits. In conclusion, primary somatosensory cortex neuroplasticity for median nerve innervated digits in carpal tunnel syndrome is indeed maladaptive and underlies the functional deficits seen in these patients.

A vibrotactile behavioral battery for investigating somatosensory processing in children and adults

The cortical dynamics of somatosensory processing can be investigated using vibrotactile psychophysics. It has been suggested that different vibrotactile paradigms target different cortical mechanisms, and a number of recent studies have established links between somatosensory cortical function and measurable aspects of behavior. The relationship between cortical mechanisms and sensory function is particularly relevant with respect to developmental disorders in which altered inhibitory processing has been postulated, such as in ASD and ADHD. In this study, a vibrotactile battery consisting of nine tasks (incorporating reaction time, detection threshold, and amplitude- and frequency discrimination) was applied to a cohort of healthy adults and a cohort of typically developing children to assess the feasibility of such a vibrotactile battery in both cohorts, and the performance between children and adults was compared. These results showed that children and adults were both able to perform these tasks with a similar performance, although the children were slightly less sensitive in frequency discrimination. Performance within different task-groups clustered together in adults, providing further evidence that these tasks tap into different cortical mechanisms, which is also discussed. This clustering was not observed in children, which may be potentially indicative of development and a greater variability. In conclusion, in this study, we showed that both children and adults were able to perform an extensive vibrotactile battery, and we showed the feasibility of applying this battery to other (e.g., neurodevelopmental) cohorts to probe different cortical mechanisms.