Digital rhythm training improves reading fluency in children

Musical instrument training has been linked to improved academic and cognitive abilities in children, but it remains unclear why this occurs. Moreover, access to instrument training is not always feasible, thereby leaving less fortunate children without opportunity to benefit from such training. Although music-based video games may be more accessible to a broader population, research is lacking regarding their benefits on academic and cognitive performance. To address this gap, we assessed a custom-designed, digital rhythm training game as a proxy for instrument training to evaluate its ability to engender benefits in math and reading abilities. Furthermore, we tested for changes in core cognitive functions related to math and reading to inform how rhythm training may facilitate improved academic abilities. Classrooms of 8-9 year old children were randomized to receive either 6 weeks of rhythm training (N = 32) or classroom instruction as usual (control; N = 21). Compared to the control group, results showed that rhythm training improved reading, but not math, fluency. Assessments of cognition showed that rhythm training also led to improved rhythmic timing and language-based executive function (Stroop task), but not sustained attention, inhibitory control, or working memory. Interestingly, only the improvements in rhythmic timing correlated with improvements in reading ability. Together, these results provide novel evidence that a digital platform may serve as a proxy for musical instrument training to facilitate reading fluency in children, and that such reading improvements are related to enhanced rhythmic timing ability and not other cognitive functions associated with reading performance. RESEARCH HIGHLIGHTS: Digital rhythm training in the classroom can improve reading fluency in 8-9 year old children Improvements in reading fluency were positively correlated with enhanced rhythmic timing ability Alterations in reading fluency were not predicted by changes in other executive functions that support reading A digital platform may be a convenient and cost-effective means to provide musical rhythm training, which in turn, can facilitate academic skills.

Gamma neuromodulation improves episodic memory and its associated network in amnestic mild cognitive impairment: a pilot study

Amnestic mild cognitive impairment (aMCI) is a predementia stage of Alzheimer's disease associated with dysfunctional episodic memory and limited treatment options. We aimed to characterize feasibility, clinical, and biomarker effects of noninvasive neurostimulation for aMCI. 13 individuals with aMCI received eight 60-minute sessions of 40-Hz (gamma) transcranial alternating current stimulation (tACS) targeting regions related to episodic memory processing. Feasibility, episodic memory, and plasma Alzheimer's disease biomarkers were assessed. Neuroplastic changes were characterized by resting-state functional connectivity (RSFC) and neuronal excitatory/inhibitory balance. Gamma tACS was feasible and aMCI participants demonstrated improvement in multiple metrics of episodic memory, but no changes in biomarkers. Improvements in episodic memory were most pronounced in participants who had the highest modeled tACS-induced electric fields and exhibited the greatest changes in RSFC. Increased RSFC was also associated with greater hippocampal excitability and higher baseline white matter integrity. This study highlights initial feasibility and the potential of gamma tACS to rescue episodic memory in an aMCI population by modulating connectivity and excitability within an episodic memory network.

Intensity-dependent gamma electrical stimulation regulates microglial activation, reduces beta-amyloid load, and facilitates memory in a mouse model of Alzheimer's disease

BACKGROUND

Gamma sensory stimulation may reduce AD-specific pathology. Yet, the efficacy of alternating electrical current stimulation in animal models of AD is unknown, and prior research has not addressed intensity-dependent effects.

METHODS

The intensity-dependent effect of gamma electrical stimulation (GES) with a sinusoidal alternating current at 40 Hz on Aβ clearance and microglia modulation were assessed in 5xFAD mouse hippocampus and cortex, as well as the behavioral performance of the animals with the Morris Water Maze.

RESULTS

One hour of epidural GES delivered over a month significantly (1) reduced Aβ load in the AD brain, (2) increased microglia cell counts, decreased cell body size, increased length of cellular processes of the Iba1 + cells, and (3) improved behavioral performance (learning & memory). All these effects were most pronounced when a higher stimulation current was applied.

CONCLUSION

The efficacy of GES on the reduction of AD pathology and the intensity-dependent feature provide guidance for the development of this promising therapeutic approach.

Stimulus specific cortical activity associated with ignoring distraction during working memory encoding and maintenance

Distraction disrupts Working Memory (WM) performance, but how the brain filters distraction is not known. One possibility is that neural activity associated with distractions is suppressed relative to a baseline/passive task (biased competition). Alternatively, distraction may be denied access to WM, with no suppression. Furthermore, behavioural work indicates separate mechanisms for ignoring distractions which occur (1) while we put information into WM (Encoding Distraction, ED) and (2) while we maintain already encoded information during the WM delay period (Delay Distraction, DD). Here we used fMRI in humans to measure category-sensitive cortical activity and probe the extent to which ED/DD mechanisms involve enhancement/suppression during a WM task. We observed significant enhancement of task-relevant activity, relative to a passive view task, which did not differ according to whether or when distractors appeared. For both ED and DD we found no evidence of suppression, but instead a robust increase in stimulus specific activity in response to additional stimuli presented during the passive view task, which was not seen for the WM task, when those additional stimuli were to be ignored. The results indicate that ED/DD resistance does not necessarily involve suppression of distractor-related activity. Rather, a rise in distractor-associated activity is prevented when distractors are presented, supporting models of input gating, and providing a potential mechanism by which input-gating might be achieved.

Enhancing cognitive control in amnestic mild cognitive impairment via at-home non-invasive neuromodulation in a randomized trial

Individuals with multi-domain amnestic mild cognitive impairment (md-aMCI) have an elevated risk of dementia and need interventions that may retain or remediate cognitive function. In a feasibility pilot study, 30 older adults aged 60-80 years with md-aMCI were randomized to 8 sessions of transcranial alternating current stimulation (tACS) with simultaneous cognitive control training (CCT). The intervention took place within the participant's home without direct researcher assistance. Half of the participants received prefrontal theta tACS during CCT and the other half received control tACS. We observed high tolerability and adherence for at-home tACS + CCT. Within 1-week, only those who received theta tACS exhibited improved attentional abilities. Neuromodulation is feasible for in-home settings, which can be conducted by the patient, thereby enabling treatment in difficult to reach populations. TACS with CCT may facilitate cognitive control abilities in md-aMCI, but research in a larger population is needed to validate efficacy.

Musical Training Facilitates Exogenous Temporal Attention via Delta Phase Entrainment within a Sensorimotor Network

Temporal orienting of attention plays an important role in our day-to-day lives and can use timing information from exogenous or endogenous sources. Yet, it is unclear what neural mechanisms give rise to temporal attention, and it is debated whether both exogenous and endogenous forms of temporal attention share a common neural source. Here, older adult nonmusicians (N = 47, 24 female) were randomized to undergo 8 weeks of either rhythm training, which places demands on exogenous temporal attention, or word search training as a control. The goal was to assess (1) the neural basis of exogenous temporal attention and (2) whether training-induced improvements in exogenous temporal attention can transfer to enhanced endogenous temporal attention abilities, thereby providing support for a common neural mechanism of temporal attention. Before and after training, exogenous temporal attention was assessed using a rhythmic synchronization paradigm, whereas endogenous temporal attention was evaluated via a temporally cued visual discrimination task. Results showed that rhythm training improved performance on the exogenous temporal attention task, which was associated with increased intertrial coherence within the δ (1-4 Hz) band as assessed by EEG recordings. Source localization revealed increased δ-band intertrial coherence arose from a sensorimotor network, including premotor cortex, anterior cingulate cortex, postcentral gyrus, and the inferior parietal lobule. Despite these improvements in exogenous temporal attention, such benefits were not transferred to endogenous attentional ability. These results support the notion that exogenous and endogenous temporal attention uses independent neural sources, with exogenous temporal attention relying on the precise timing of δ band oscillations within a sensorimotor network.SIGNIFICANCE STATEMENT Allocating attention to specific points in time is known as temporal attention, and may arise from external (exogenous) or internal (endogenous) sources. Despite its importance to our daily lives, it is unclear how the brain gives rise to temporal attention and whether exogenous- or endogenous-based sources for temporal attention rely on shared brain regions. Here, we demonstrate that musical rhythm training improves exogenous temporal attention, which was associated with more consistent timing of neural activity in sensory and motor processing brain regions. However, these benefits did not extend to endogenous temporal attention, indicating that temporal attention relies on different brain regions depending on the source of timing information.

Individual differences in neuroanatomy and neurophysiology predict effects of transcranial alternating current stimulation

BACKGROUND

Noninvasive transcranial electrical stimulation (tES) research has been plagued with inconsistent effects. Recent work has suggested neuroanatomical and neurophysiological variability may alter tES efficacy. However, direct evidence is limited.

OBJECTIVE

We have previously replicated effects of transcranial alternating current stimulation (tACS) on improving multitasking ability in young adults. Here, we attempt to assess whether these stimulation parameters have comparable effects in older adults (aged 60-80 years), which is a population known to have greater variability in neuroanatomy and neurophysiology. It is hypothesized that this variability in neuroanatomy and neurophysiology will be predictive of tACS efficacy.

METHODS

We conducted a pre-registered study where tACS was applied above the prefrontal cortex (between electrodes F3-F4) while participants were engaged in multitasking. Participants were randomized to receive either 6-Hz (theta) tACS for 26.67 min daily for three days (80 min total; Long Exposure Theta group), 6-Hz tACS for 5.33 min daily (16-min total; Short Exposure Theta group), or 1-Hz tACS for 26.67 min (80 min total; Control group). To account for neuroanatomy, magnetic resonance imaging data was used to form individualized models of the tACS-induced electric field (EF) within the brain. To account for neurophysiology, electroencephalography data was used to identify individual peak theta frequency.

RESULTS

Results indicated that only in the Long Theta group, performance change was correlated with modeled EF and peak theta frequency. Together, modeled EF and peak theta frequency accounted for 54%-65% of the variance in tACS-related performance improvements, which sustained for a month.

CONCLUSION

These results demonstrate the importance of individual differences in neuroanatomy and neurophysiology in tACS research and help account for inconsistent effects across studies.

Effects of Transcranial Direct Current Stimulation on Cognition, Mood, Pain, and Fatigue in Multiple Sclerosis: A Systematic Review and Meta-Analysis

Background: The study aimed to evaluate the effects of transcranial direct current stimulation (tDCS) on cognition, mood disturbance, pain, and fatigue in people with multiple sclerosis (PwMS).

Methods: A literature search was performed on articles published between January 1990 and May 2020 in Pubmed, Medline, and Web of Science using the following keywords and their abbreviation in combinations: multiple sclerosis and transcranial direct current stimulation. Mean effect size (ES) and 95% confidence interval were calculated for each domain of interest.

Results: Seventeen articles with a total of 383 PwMS were included in this analysis. For cognition, a strong effect size was found for the trial administering the Symbol Digit Modalities Test (ES: 1.15), whereas trials applying the Attention Network Test showed a negative effect size of −0.49. Moderate to strong effect sizes were observed for mood disturbance (mean ES: 0.92), pain (mean ES: 0.59), and fatigue (mean ES: 0.60). Further subgroup analyses for MS-related fatigue showed that both high and low intensities of stimulation lead to nearly the same degree of favorable effects. More pronounced effects were observed in studies administering the Fatigue Severity Scale compared with studies using other fatigue measures such as the Modified Fatigue Impact Scale.

Conclusion: These results provide preliminary evidence that tDCS has a favorable effect on cognitive processing speed, mood disturbance, pain, and fatigue in MS. However, the effects on cognition and fatigue vary based on the specific assessment used.

Temporal attention is not affected by working memory load

Temporal attention refers to the ability to orient attention in time, which serves to enhance performance such as target detection and discrimination and is a fundamental component of cognitive function. Although some research indicates that temporal attention ability is affected by working memory updating, it is unclear whether temporal attention is also affected by the availability of working memory stores. To address this, participants were presented a dual-task paradigm requiring zero, three, or six digits to be held in working memory while engaged in a temporally cued visual discrimination task. Results show that working memory load did not differentially affect the ability to benefit from predictive temporal cues during the visual discrimination task. This indicates that temporal attention is not affected by available working memory stores. Interestingly, posterior beta band (12-30 Hz) activity was differentially modulated by temporal attention and working memory load, such that it decreased prior to expected targets and increased with load. Analysis across participants indicated that those individuals who exhibited greater temporal attention-based modulation of beta activity (i.e., predictive < neutrally cued) displayed improved discrimination performance, but also yielded lowered working memory accuracy. Thus, the ability to benefit from temporal attention processes while multitasking comes at the cost of lowered secondary task performance. Together, these results indicate that available working memory stores do not affect temporal attention ability. Rather, limitations in divided attention ability result in a performance cost that prioritizes one task over another, which may be indexed by beta band activity.

Multimodal sensory integration: Diminishing returns in rhythmic synchronization

Synchronizing movements with events in the surrounding environment is a ubiquitous aspect of behavior. Experiments studying multimodal integration and rhythmic synchronization tend to focus on how bimodal (e.g., audio-visual) stimuli enhances synchronization performance (i.e., reduced variability) compared with synchronization with its unimodal constituents. As such, it is unclear whether trimodal (i.e., audio-visual-tactile) stimuli may yield additional performance benefits. To address this, we developed a multimodal sensorimotor synchronization assessment that incorporates audio, visual, and vibrotactile stimuli. Results replicate performance improvements with bimodal compared with unimodal stimuli. However, trimodal stimuli yields less, or in some cases no advantage compared with bimodal stimuli. These results demonstrate that in this case, increasing the amount of sensory information beyond bimodal stimuli yields little or no additional performance benefits. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Intracranial alternating current stimulation facilitates neurogenesis in a mouse model of Alzheimer's disease

BACKGROUND

Neurogenesis is significantly impaired in the brains of both human patients and experimental animal models of Alzheimer's disease (AD). Although deep brain stimulation promotes neurogenesis, it is an invasive technique that may damage neural circuitry along the path of the electrode. To circumvent this problem, we assessed whether intracranial electrical stimulation to the brain affects neurogenesis in a mouse model of Alzheimer's disease (5xFAD).

METHODS AND RESULTS

We used Ki67, Nestin, and doublecortin (DCX) as markers and determined that neurogenesis in both the subventricular zone (SVZ) and hippocampus were significantly reduced in the brains of 4-month-old 5xFAD mice. Guided by a finite element method (FEM) computer simulation to approximately estimate current and electric field in the mouse brain, electrodes were positioned on the skull that were likely to deliver stimulation to the SVZ and hippocampus. After a 4-week program of 40-Hz intracranial alternating current stimulation (iACS), neurogenesis indicated by expression of Ki67, Nestin, and DCX in both the SVZ and hippocampus were significantly increased compared to 5xFAD mice who received sham stimulation. The magnitude of neurogenesis was close to the wild-type (WT) age-matched unmanipulated controls.

CONCLUSION

Our results suggest that iACS is a promising, less invasive technique capable of effectively stimulating the SVZ and hippocampus regions in the mouse brain. Importantly, iACS can significantly boost neurogenesis in the brain and offers a potential treatment for AD.

Neural Correlates Underlying the Precision of Visual Working Memory

The neural mechanisms associated with the limited capacity of working memory (WM) has long been studied, but it is still unclear which neural regions are associated with the precision of visual WM. Here, an orientation recall task for estimating the trial-wise precision of visual WM was performed and then repeated two weeks later in an fMRI scanner. Results showed that activity in frontal and parietal regions during WM maintenance scaled with WM load, but not with the precision of WM (i.e., recall error in radians). Conversely, activity in the lateral occipital complex (LOC) during WM maintenance was not affected by memory load, but rather, correlated with WM precision on a trial-by-trial basis. Moreover, activity in LOC also correlated with the individual participant's precision of WM from a separate behavioral experiment. Interestingly, a region within the prefrontal cortex, the inferior frontal junction (IFJ), exhibited greater functional connectivity with LOC when the WM load increased. Together, our findings provide unique evidence that the LOC supports visual WM precision, while communication between the IFJ and LOC varies based on WM load demands. These results suggest an intriguing possibility that distinct neural mechanisms may be associated with general content (load) or detailed information (precision) of WM.

A Tablet-Based Assessment of Rhythmic Ability

The exponential rise in use of mobile consumer electronics has presented a great potential for research to be conducted remotely, with participants numbering several orders of magnitude greater than a typical research paradigm. Here, we attempt to demonstrate the validity and reliability of using a consumer game-engine to create software presented on a mobile tablet to assess sensorimotor synchronization, a proxy of rhythmic ability. Our goal was to ascertain whether previously observed research results can be replicated, rather than assess whether a mobile tablet achieves comparable performance to a desktop computer. To achieve this, younger (aged 18–35 years) and older (aged 60–80 years) adult musicians and non-musicians were recruited to play a custom-designed sensorimotor synchronization assessment on a mobile tablet in a controlled laboratory environment. To assess reliability, participants performed the assessment twice, separated by a week, and an intra-class correlation coefficient (ICC) was calculated. Results supported the validity of this approach to assessing rhythmic abilities by replicating previously observed results. Specifically, musicians performed better than non-musicians, and younger adults performed better than older adults. Participants also performed best when the tempo was in the range of previously-identified preferred tempos, when the stimuli included both audio and visual information, and when synchronizing on-beat compared to off-beat or continuation (self-paced) synchronization. Additionally, high ICC values (>0.75) suggested excellent test–retest reliability. Together, these results support the notion that consumer electronics running software built with a game engine may serve as a valuable resource for remote, mobile-based data collection of rhythmic abilities.

Gyrification abnormalities in presymptomatic c9orf72 expansion carriers

OBJECTIVE

To investigate in-vivo cortical gyrification patterns measured by the local gyrification index (lGI) in presymptomatic c9orf72 expansion carriers compared with healthy controls, and investigate relationships between lGI and cortical thickness, an established morphometric measure of neurodegeneration.

METHODS

We assessed cortical gyrification and thickness patterns in a cohort of 15 presymptomatic c9orf72 expansion carriers (age 43.7 ± 10.2 years, 9 females) compared with 67 (age 42.4 ± 12.4 years, 36 females) age and sex matched healthy controls using the dedicated Freesurfer pipeline.

RESULTS

Compared with controls, presymptomatic carriers showed significantly lower lGI in left frontal and right parieto-occipital regions. Interestingly, those areas with abnormal gyrification in presymptomatic carriers showed no concomitant cortical thickness abnormality. Overall, for both presymptomatic carriers and healthy controls, gyrification and cortical thickness measures were not correlated, suggesting that gyrification captures a feature distinct from cortical thickness.

CONCLUSIONS

Presymptomatic c9orf72 expansion carriers show regions of abnormally low gyrification as early as their 30s, decades before expected symptom onset. Cortical gyrification represents a novel grey matter metric distinctive from grey matter thickness or volume and detects differences in presymptomatic carriers at an early age.

Aging of the frontal lobe

Healthy aging is associated with numerous deficits in cognitive function, which have been attributed to changes within the prefrontal cortex (PFC). This chapter summarizes some of the most prominent cognitive changes associated with age-related alterations in the anatomy and physiology of the PFC. Specifically, aging of the PFC results in deficient aspects of cognitive control, including sustained attention, selective attention, inhibitory control, working memory, and multitasking abilities. Yet, not all cognitive functions associated with the PFC exhibit age-related declines, such as arithmetic, comprehension, emotion perception, and emotional control. Moreover, not all older adults exhibit declines in cognition. Multiple life-course and lifestyle factors, as well as genetics, play a role in the trajectory of cognitive performance across the life span. Thus many adults retain cognitive function well into advanced age. Moreover, the brain remains plastic throughout life and there is increasing evidence that most age-related declines in cognition can be remediated by various methods such as physical exercise, cognitive training, or noninvasive brain stimulation. Overall, because cognitive aging is associated with numerous life-course and lifestyle factors, successful aging likely begins in early life, while maintaining cognition or remediating declines is a life-long process.

Enhancement of multitasking performance and neural oscillations by transcranial alternating current stimulation

Multitasking is associated with the generation of stimulus-locked theta (4–7 Hz) oscillations arising from prefrontal cortex (PFC). Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique that influences endogenous brain oscillations. Here, we investigate whether applying alternating current stimulation within the theta frequency band would affect multitasking performance, and explore tACS effects on neurophysiological measures. Brief runs of bilateral PFC theta-tACS were applied while participants were engaged in a multitasking paradigm accompanied by electroencephalography (EEG) data collection. Unlike an active control group, a tACS stimulation group showed enhancement of multitasking performance after a 90-minute session (F_1,35 = 6.63, p = 0.01, ηp² = 0.16; effect size = 0.96), coupled with significant modulation of posterior beta (13–30 Hz) activities (F_1,32 = 7.66, p = 0.009, ηp² = 0.19; effect size = 0.96). Across participant regression analyses indicated that those participants with greater increases in frontal theta, alpha and beta oscillations exhibited greater multitasking performance improvements. These results indicate frontal theta-tACS generates benefits on multitasking performance accompanied by widespread neuronal oscillatory changes, and suggests that future tACS studies with extended treatments are worth exploring as promising tools for cognitive enhancement.

Spatial Attention and the Effects of Frontoparietal Alpha Band Stimulation

A frontoparietal network has long been implicated in top-down control of attention. Recent studies have suggested that this network might communicate through coherence in the alpha band. Here we aimed to test the effect of coherent alpha (8-12 Hz) stimulation on the frontoparietal network. To this end, we recorded behavioral performance and electroencephalography (EEG) data while participants were engaged in a spatial attention task. Furthermore, participants received transcranial alternating current stimulation (tACS) over the right frontal and parietal cortex, which oscillated coherently in-phase within the alpha band. Compared to a group of participants that received sham stimulation, we found that coherent frontoparietal alpha band stimulation altered a behavioral spatial attention bias. Neurally, the groups showed hemispheric-specific differences in alpha coherence between the frontal and parietal-occipital cortex. These results provide preliminary evidence that alpha coherence in the frontoparietal network might play a role in top-down control of spatial attention.

Network degeneration and dysfunction in presymptomatic C9ORF72 expansion carriers

Hexanucleotide repeat expansions in C9ORF72 are the most common known genetic cause of familial and sporadic frontotemporal dementia and amyotrophic lateral sclerosis. Previous work has shown that patients with behavioral variant frontotemporal dementia due to C9ORF72 show salience and sensorimotor network disruptions comparable to those seen in sporadic behavioral variant frontotemporal dementia, but it remains unknown how early in the lifespan these and other changes in brain structure and function arise. To gain insights into this question, we compared 15 presymptomatic carriers (age 43.7 ± 10.2 years, nine females) to matched healthy controls. We used voxel-based morphometry to assess gray matter, diffusion tensor imaging to interrogate white matter tracts, and task-free functional MRI to probe the salience, sensorimotor, default mode, and medial pulvinar thalamus-seeded networks. We further used a retrospective chart review to ascertain psychiatric histories in carriers and their non-carrier family members. Carriers showed normal cognition and behavior despite gray matter volume and brain connectivity deficits that were apparent as early as the fourth decade of life. Gray matter volume deficits were topographically similar though less severe than those in patients with behavioral variant frontotemporal dementia due to C9ORF72, with major foci in cingulate, insula, thalamus, and striatum. Reduced white matter integrity was found in the corpus callosum, cingulum bundles, corticospinal tracts, uncinate fasciculi and inferior longitudinal fasciculi. Intrinsic connectivity deficits were detected in all four networks but most prominent in salience and medial pulvinar thalamus-seeded networks. Carrier and control groups showed comparable relationships between imaging metrics and age, suggesting that deficits emerge during early adulthood. Carriers and non-carrier family members had comparable lifetime histories of psychiatric symptoms. Taken together, the findings suggest that presymptomatic C9ORF72 expansion carriers exhibit functionally compensated brain volume and connectivity deficits that are similar, though less severe, to those reported during the symptomatic phase. The early adulthood emergence of these deficits suggests that they represent aberrant network patterning during development, an early neurodegeneration prodrome, or both.

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Presymptomatic C9ORF72 expansion carriers have brain connectivity deficits.

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These deficits may be a developmental lesion rather than early neurodegeneration.

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Non-carriers and presymptomatic carriers share psychiatric symptomatology.

Predictive cues and age-related declines in working memory performance

Older adults, compared to younger adults, do not benefit from predictive information regarding either what type of stimuli they will see or when to expect them, yet it is unclear whether older adults benefit when given both types of predictive information. Here, electroencephalogram recordings of older (aged 62-87 years) and younger (aged 20-32 years) adults were recorded during a working memory task. Each trial contained 2 faces and 2 scenes presented sequentially, followed by a 5-second delay and a probe stimulus. Participants were told what stimuli to remember/ignore and when they would appear. Predictive cues enabled older adults to remember stimuli as accurately as younger adults, although response times were significantly slower, even when corrected for general age-related slowing. Previously observed reductions in P1/N1 amplitude and latency suppression to irrelevant stimuli were not seen. Rather, older adults exhibited lowered P3 amplitudes to relevant stimuli; those with the greatest declines yielded the lowest accuracy and slowest response times. This shows that predictive information can help maintain accuracy, although not response times, which correspond to age-related declines in neural enhancement to relevant stimuli.

Young-onset frontotemporal dementia in a homozygous tau R406W mutation carrier

Microtubule‐associated protein tau mutations result in 10–20% of cases of genetic frontotemporal lobar degeneration. Tau mutation carriers typically develop behavioral variant frontotemporal dementia with or without parkinsonism. Unlike most frontotemporal dementia gene mutations, heterozygous R406W tau mutation carriers most often develop clinical Alzheimer's disease. We report a homozygous tau R406W mutation carrier with behavioral variant frontotemporal dementia who developed symptoms 20 years before mean family symptom onset. Voxel‐based morphometry showed frontoinsular, frontal, and mesial temporal cortical atrophy. Homozygous tau R406W mutations appear to accelerate symptom onset and drive a behavioral variant frontotemporal dementia syndrome.

Neural sources of performance decline during continuous multitasking

Multitasking performance costs have largely been characterized by experiments that involve two overlapping and punctuated perceptual stimuli, as well as punctuated responses to each task. Here, participants engaged in a continuous performance paradigm during fMRI recording to identify neural signatures associated with multitasking costs under more natural conditions. Our results demonstrated that only a single brain region, the superior parietal lobule (SPL), exhibited a significant relationship with multitasking performance, such that increased activation in the multitasking condition versus the singletasking condition was associated with higher task performance (i.e., least multitasking cost). Together, these results support previous research indicating that parietal regions underlie multitasking abilities and that performance costs are related to a bottleneck in control processes involving the SPL that serves to divide attention between two tasks.

Delayed enhancement of multitasking performance: Effects of anodal transcranial direct current stimulation on the prefrontal cortex

BACKGROUND

The dorsolateral prefrontal cortex (DLPFC) has been proposed to play an important role in neural processes that underlie multitasking performance. However, this claim is underexplored in terms of direct causal evidence.

OBJECTIVE

The current study aimed to delineate the causal involvement of the DLPFC during multitasking by modulating neural activity with transcranial direct current stimulation (tDCS) prior to engagement in a demanding multitasking paradigm.

METHODS

The study is a single-blind, crossover, sham-controlled experiment. Anodal tDCS or sham tDCS was applied over left DLPFC in forty-one healthy young adults (aged 18-35 years) immediately before they engaged in a 3-D video game designed to assess multitasking performance. Participants were separated into three subgroups: real-sham (i.e., real tDCS in the first session, followed by sham tDCS in the second session 1 h later), sham-real (sham tDCS first session, real tDCS second session), and sham-sham (sham tDCS in both sessions).

RESULTS

The real-sham group showed enhanced multitasking performance and decreased multitasking cost during the second session, compared to first session, suggesting delayed cognitive benefits of tDCS. Interestingly, performance benefits were observed only for multitasking and not on a single-task version of the game. No significant changes were found between the first and second sessions for either the sham-real or the sham-sham groups.

CONCLUSIONS

These results suggest a causal role of left prefrontal cortex in facilitating the simultaneous performance of more than one task, or multitasking. Moreover, these findings reveal that anodal tDCS may have delayed benefits that reflect an enhanced rate of learning.

Effects of noninvasive brain stimulation on cognitive function in healthy aging and Alzheimer's disease: a systematic review and meta-analysis

The study aimed to evaluate the effects of noninvasive brain stimulation on cognitive function in healthy older adults and patients with Alzheimer's disease. A comprehensive literature search was performed on noninvasive stimulation studies published from January 1990 to November 2014 in Pubmed and Web of Science. Fourteen articles with a total of 331 participants were identified as studies with healthy older adults, and the mean effect size and 95% confidence interval were estimated. A significant effect size of 0.42 was found for the cognitive outcome. Further subgroup analyses demonstrated more prominent effects for studies delivering the stimulation before the execution of the task and studies applying multiple sessions of stimulation. To assess the effects of stimulation on Alzheimer's disease patients, 11 studies with a total of 200 patients were included in the analysis. A significant effect size of 1.35 was found for the cognitive outcomes. Subgroup analyses indicated more pronounced effects for studies applying the stimulation during the execution of the task compared with studies delivering the stimulation before the execution of the task. Noninvasive brain stimulation has a positive effect on cognitive function in physiological and pathological aging.

Expectations of Task Demands Dissociate Working Memory and Long-Term Memory Systems

Many aspects of the complex relationship between working memory (WM) and long-term memory (LTM) remain unclear. Here, we manipulated task demands on a brief delayed-recognition paradigm to reveal behavioral and neural dissociations between these systems. Variations from a Baseline task included 3 challenges: increased delay duration, distraction during maintenance, and more closely matched memory probes, which were presented in behavioral experiments and during functional magnetic resonance imaging. Each of the challenges resulted in a significant decline in WM accuracy, and interestingly, a concurrent improvement in incidental LTM. Neural data revealed that, in task blocks, when participants anticipated, and then experienced, increased demands, they engaged medial temporal lobe (MTL) regions more during both the encoding and delay periods. Overall, these results indicate that distinct memory systems are recruited based on anticipated demands of a memory task, and MTL involvement underlies the observed dissociation between WM and LTM performance.

Structural and functional differences in medial prefrontal cortex underlie distractibility and suppression deficits in ageing

Older adults experience deficits in working memory (WM) that are acutely exacerbated by the presence of distracting information. Human neurophysiological studies have revealed that these changes are accompanied by a diminished ability to suppress visual cortical activity associated with task-irrelevant information. Although this is often attributed to deficits in top-down control from a prefrontal cortical source, this has not yet been directly demonstrated. Here we evaluate the neural basis of distraction’s negative impact on WM and the impairment in neural suppression in older adults by performing structural and functional MRIs while older participants engage in tasks that require remembering relevant visual stimuli in the context of overlapping irrelevant stimuli. Analysis supports both an age-related distraction effect and neural suppression deficit, and extends our understanding by revealing an alteration in functional connectivity between visual cortices and a region in the default network, the medial prefrontal cortex (mPFC). Moreover, within the older population, the magnitude of WM distractibility and neural suppression are both associated with individual differences in cortical volume and activity of the mPFC, as well as its associated white-matter tracts.

Reliability measures of functional magnetic resonance imaging in a longitudinal evaluation of mild cognitive impairment

As the aging population grows, it has become increasingly important to carefully characterize amnestic mild cognitive impairment (aMCI), a preclinical stage of Alzheimer's disease (AD). Functional magnetic resonance imaging (fMRI) is a valuable tool for monitoring disease progression in selectively vulnerable brain regions associated with AD neuropathology. However, the reliability of fMRI data in longitudinal studies of older adults with aMCI is largely unexplored. To address this, aMCI participants completed two visual working tasks, a Delayed-Recognition task and a One-Back task, on three separate scanning sessions over a three-month period. Test-retest reliability of the fMRI blood oxygen level dependent (BOLD) activity was assessed using an intraclass correlation (ICC) analysis approach. Results indicated that brain regions engaged during the task displayed greater reliability across sessions compared to regions that were not utilized by the task. During task-engagement, differential reliability scores were observed across the brain such that the frontal lobe, medial temporal lobe, and subcortical structures exhibited fair to moderate reliability (ICC=0.3-0.6), while temporal, parietal, and occipital regions exhibited moderate to good reliability (ICC=0.4-0.7). Additionally, reliability across brain regions was more stable when three fMRI sessions were used in the ICC calculation relative to two fMRI sessions. In conclusion, the fMRI BOLD signal is reliable across scanning sessions in this population and thus a useful tool for tracking longitudinal change in observational and interventional studies in aMCI.

Fronto-parietal network: flexible hub of cognitive control

A recent study shows that the fronto-parietal network (FPN), and subregions therein, alters its functional connectivity with nodes of other networks based on task goals. Moreover, FPN patterns of connectivity not only reflect engagement of specific tasks, but also serve as a code that can be transferred to facilitate learning novel tasks.

Reconciling the influence of task-set switching and motor inhibition processes on stop signal after-effects

Executive response functions can be affected by preceding events, even if they are no longer associated with the current task at hand. For example, studies utilizing the stop signal task have reported slower response times to “GO” stimuli when the preceding trial involved the presentation of a “STOP” signal. However, the neural mechanisms that underlie this behavioral after-effect are unclear. To address this, behavioral and electroencephalography (EEG) measures were examined in 18 young adults (18–30 years) on “GO” trials following a previously “Successful Inhibition” trial (pSI), a previously “Failed Inhibition” trial (pFI), and a previous “GO” trial (pGO). Like previous research, slower response times were observed during both pSI and pFI trials (i.e., “GO” trials that were preceded by a successful and unsuccessful inhibition trial, respectively) compared to pGO trials (i.e., “GO” trials that were preceded by another “GO” trial). Interestingly, response time slowing was greater during pSI trials compared to pFI trials, suggesting executive control is influenced by both task set switching and persisting motor inhibition processes. Follow-up behavioral analyses indicated that these effects resulted from between-trial control adjustments rather than repetition priming effects. Analyses of inter-electrode coherence (IEC) and inter-trial coherence (ITC) indicated that both pSI and pFI trials showed greater phase synchrony during the inter-trial interval compared to pGO trials. Unlike the IEC findings, differential ITC was present within the beta and alpha frequency bands in line with the observed behavior (pSI > pFI > pGO), suggestive of more consistent phase synchrony involving motor inhibition processes during the ITI at a regional level. These findings suggest that between-trial control adjustments involved with task-set switching and motor inhibition processes influence subsequent performance, providing new insights into the dynamic nature of executive control.

Age-related changes in expectation-based modulation of motion detectability

Expecting motion in some particular direction biases sensitivity to that direction, which speeds detection of motion. However, the neural processes underlying this effect remain underexplored, especially in the context of normal aging. To address this, we examined younger and older adults' performance in a motion detection task. In separate conditions, the probability was either 50% or 100% that a field of dots would move coherently in the direction a participant expected (either vertically or horizontally). Expectation and aging effects were assessed via response times (RT) to detect motion and electroencephalography (EEG). In both age groups, RTs were fastest when motion was similar to the expected direction of motion. RT tuning curves exhibited a characteristic U-shape such that detection time increased with an increasing deviation from the participant's expected direction. Strikingly, EEG results showed an analogous, hyperbolic curve for N1 amplitude, reflecting neural biasing. Though the form of behavioral and EEG curves did not vary with age, older adults displayed a clear decline in the speed of detection and a corresponding reduction in EEG N1 amplitude when horizontal (but not vertical) motion was expected. Our results suggest that expectation-based detection ability varies with age and, for older adults, also with axis of motion.

Anticipatory alpha phase influences visual working memory performance

Alpha band (8-12 Hz) phase dynamics in the visual cortex are thought to reflect fluctuations in cortical excitability that influences perceptual processing. As such, visual stimuli are better detected when their onset is concurrent with specific phases of the alpha cycle. However, it is unclear whether alpha phase differentially influences cognitive performance at specific times relative to stimulus onset (i.e., is the influence of phase maximal before, at, or after stimulus onset?). To address this, participants performed a delayed-recognition, working memory (WM) task for visual motion direction during two separate visits. The first visit utilized functional magnetic resonance (fMRI) imaging to identify neural regions associated with task performance. Replicating previous studies, fMRI data showed engagement of visual cortical area V5, as well as a prefrontal cortical region, the inferior frontal junction (IFJ). During the second visit, transcranial magnetic stimulation (TMS) was applied separately to both the right IFJ and right V5 (with the vertex as a control region) while electroencephalography (EEG) was simultaneously recorded. During each trial, a single pulse of TMS (spTMS) was applied at one of six time points (-200, -100, -50, 0, 80, 160 ms) relative to the encoded stimulus onset. Results demonstrated a relationship between the phase of the posterior alpha signal prior to stimulus encoding and subsequent response times to the memory probe two seconds later. Specifically, spTMS to V5, and not the IFJ or vertex, yielded faster response times, indicating improved WM performance, when delivered during the peak, compared to the trough, of the alpha cycle, but only when spTMS was applied 100 ms prior to stimulus onset. These faster responses to the probe correlated with decreased early event related potential (ERP) amplitudes (i.e., P1) to the probe stimuli. Moreover, participants that were least affected by spTMS exhibited greater functional connectivity between V5 and fronto-parietal regions. These results suggest that posterior alpha phase indexes a critical time period for motion processing in the context of WM encoding goals, which occurs in anticipation of stimulus onset.

Parameterization of transcranial magnetic stimulation

A recent study (Di Lazzaro et al. J Neurophysiol 105: 2150-2156, 2011) describes the findings from a rigorous comparison on the effects of several popular variations of transcranial magnetic stimulation (TMS) protocols. The results demonstrate that excitatory and inhibitory neural networks may be independently modulated based on TMS protocol selection. Moreover, the within-group replication of multiple between-group experiments suggests that independent evaluations of TMS parameters will continue to inform and guide future TMS research.

The influence of perceptual training on working memory in older adults

Normal aging is associated with a degradation of perceptual abilities and a decline in higher-level cognitive functions, notably working memory. To remediate age-related deficits, cognitive training programs are increasingly being developed. However, it is not yet definitively established if, and by what mechanisms, training ameliorates effects of cognitive aging. Furthermore, a major factor impeding the success of training programs is a frequent failure of training to transfer benefits to untrained abilities. Here, we offer the first evidence of direct transfer-of-benefits from perceptual discrimination training to working memory performance in older adults. Moreover, using electroencephalography to evaluate participants before and after training, we reveal neural evidence of functional plasticity in older adult brains, such that training-induced modifications in early visual processing during stimulus encoding predict working memory accuracy improvements. These findings demonstrate the strength of the perceptual discrimination training approach by offering clear psychophysical evidence of transfer-of-benefit and a neural mechanism underlying cognitive improvement.

Top-down modulation of visual feature processing: the role of the inferior frontal junction

Distinct areas within the visual association cortex are specialized for representing specific stimulus features, such as V4 for color and V5/hMT+ for motion. Recent studies have demonstrated that areas associated with attended features exhibit enhanced cortical activity, whereas those associated with ignored features elicit reduced activity. However, the source of this attentional (or top-down) modulation remains uncertain. A network of fronto-parietal cortical regions has been proposed as the prime candidate underlying this top-down modulation. Here, we evaluate whether there are distinct or overlapping top-down network regions for attention to different stimulus features. To this end, we explored functional magnetic resonance imaging (fMRI) functional connectivity data, electroencephalographic (EEG) source localization, and phase coherence that were obtained while participants attended or ignored motion and color stimuli. Functional connectivity analysis indicated that attention to color relies strongly on prefrontal regions, whereas attention to motion recruits both prefrontal and parietal areas. Although these networks are generally topologically segregated, both color and motion processes recruit right inferior frontal junction (IFJ). However, the IFJ may be more critical for color processing, as only connectivity with V4 predicted the degree of attentional modulation. Source localization at the time range of attentional modulation of the event related potential corroborated the role of the right IFJ and indicated that feature-based, top-down modulation occurs early during processing (< 200ms post-stimulus onset). Furthermore, long-distance alpha (8-12Hz) phase coherence between the IFJ and visual cortices may serve as a mechanism underlying anticipatory, top-down modulation of color feature processing.

Predictive knowledge of stimulus relevance does not influence top-down suppression of irrelevant information in older adults

Our ability to focus attention on task-relevant stimuli and ignore irrelevant distractions is reflected by differential enhancement and suppression of neural activity in sensory cortices. Previous research has shown that older adults exhibit a deficit in suppressing task-irrelevant information, the magnitude of which is associated with a decline in working memory performance. However, it remains unclear if a failure to suppress is a reflection of an inability of older adults to rapidly assess the relevance of information upon stimulus presentation when they are not aware of the relevance beforehand. To address this, we recorded the electroencephalogram (EEG) in healthy older participants (aged 60-80 years) while they performed two different versions of a selective face/scene working memory task, both with and without prior knowledge as to when relevant and irrelevant stimuli would appear. Each trial contained two faces and two scenes presented sequentially followed by a 9 sec delay and a probe stimulus. Participants were given the following instructions: remember faces (ignore scenes), remember scenes (ignore faces), remember the xth and yth stimuli (where x and y could be 1st, 2nd, 3rd or 4th), or passively view all stimuli. Working memory performance remained consistent regardless of task instructions. Enhanced neural activity was observed at posterior electrodes to attended stimuli, while neural responses that reflected the suppression of irrelevant stimuli was absent for both tasks. The lack of significant suppression at early stages of visual processing was revealed by P1 amplitude and N1 latency modulation indices. These results reveal that prior knowledge of stimulus relevance does not modify early neural processing during stimulus encoding and does not improve working memory performance in older adults. These results suggest that the inability to suppress irrelevant information early in the visual processing stream by older adults is related to mechanisms specific to top-down suppression.

Practice-related improvement in working memory is modulated by changes in processing external interference

Working memory (WM) performance is impaired by the presence of external interference. Accordingly, more efficient processing of intervening stimuli with practice may lead to enhanced WM performance. To explore the role of practice on the impact that interference has on WM performance, we studied young adults with electroencephalographic (EEG) recordings as they performed three motion-direction, delayed-recognition tasks. One task was presented without interference, whereas two tasks introduced different types of interference during the interval of memory maintenance: distractors and interruptors. Distractors were to be ignored, whereas interruptors demanded attention based on task instructions for a perceptual discrimination. We show that WM performance was disrupted by both types of interference, but interference-induced disruption abated across a single experimental session through rapid learning. WM accuracy and response time improved in a manner that was correlated with changes in early neural measures of interference processing in visual cortex (i.e., P1 suppression and N1 enhancement). These results suggest practice-related changes in processing interference exert a positive influence on WM performance, highlighting the importance of filtering irrelevant information and the dynamic interactions that exist between neural processes of perception, attention, and WM during learning.