The influence of hand posture on tactile processing: Evidence from a 7T functional magnetic resonance imaging study

Although behavioral evidence has shown that postural changes influence the ability to localize or detect tactile stimuli, little is known regarding the brain areas that modulate these effects. This 7T functional magnetic resonance imaging (fMRI) study explores the effects of touch of the hand as a function of hand location (right or left side of the body) and hand configuration (open or closed). We predicted that changes in hand configuration would be represented in contralateral primary somatosensory cortex (S1) and the anterior intraparietal area (aIPS), whereas change in position of the hand would be associated with alterations in activation in the superior parietal lobule. Multivoxel pattern analysis and a region of interest approach partially supported our predictions. Decoding accuracy for hand location was above chance level in superior parietal lobule (SPL) and in the anterior intraparietal (aIPS) area; above chance classification of hand configuration was observed in SPL and S1. This evidence confirmed the role of the parietal cortex in postural effects on touch and the possible role of S1 in coding the body form representation of the hand.

Can they touch? A novel mental motor imagery task for the assessment of back pain

Introduction

As motor imagery is informed by the anticipated sensory consequences of action, including pain, we reasoned that motor imagery could provide a useful indicator of chronic back pain. We tested the hypothesis that mental motor imagery regarding body movements can provide a reliable assessment of low back pain.

Methods

Eighty-five subjects with back pain and forty-five age-matched controls were shown two names of body parts and asked to indicate if they could imagine moving so that the named body parts touched. Three types of imagined movements were interrogated: movements of arms, movements of legs and movements requiring flexion and/or rotation of the low back.

Results

Accuracy and reaction times were measured. Subjects with back pain were less likely to indicate that they could touch body parts than age-matched controls. The effect was observed only for those movements that required movement of the low back or legs, suggesting that the effect was not attributable to task difficulty or non-specific effects. There was an effect of pain severity. Compared to subjects with mild pain, subjects with severe pain were significantly less likely to indicate that they could move so that named body parts touched. There was a correlation between pain ratings and impaired performance for stimuli that involved the lower but not upper body.

Discussion

As the Can They Touch task is quick, easy to administer and does not require an explicit judgment of pain severity, it may provide useful information to supplement the assessment of subjects with chronic pain.

B - 84 Changes in Right Pars Triangularis Network Role and Naming Errors in Post-Stroke Aphasia

OBJECTIVE

The goal of the current study was to further clarify the role of right pars trianagularis (rPTr) in persons with aphasia (PWA) by investigating if the structural changes after stroke are associated with language deficits. We hypothesized that boundary controllability (bc), which measures the capacity of a region integrate/segregate brain regions, would be higher in rPTr for PWA than age-matched controls. We also sought to understand whether different types of naming errors corresponded to bc at rPTr. We hypothesized that bc would relate to phonological naming errors.

METHOD

We tested our hypothesis in 60 chronic post-stroke aphasia patients and 62 matched controls. All PWA completed the Western Aphasia Battery (WAB) and the Philadelphia Naming Test (PNT). With PNT data, we calculated the overall accuracy and proportion of error type (phonological, semantic, and mixed).

RESULTS

Consistent with our first hypothesis, we found PWA had higher bc than age-matched controls at rPTr (t(120) = -2.52, p < 0.01). A regression model yielded a statistically significant negative relationship between bc and phonological errors that could not be accounted for by lesion volume (R2 = 0.11, F(1,48) = 6.21, p < 0.05).

CONCLUSION

Our results demonstrate shift in the fundamental anatomical role of rPTr suggests the region becomes more critical for integrating and segregating communication across networks of the brain. Compared to findings in the left PTr in healthy subjects, our data suggest that homotopic recruitment may involve shifts in this anatomical property. and may relate to specific aspects of language processing.

Efficacy of Transcranial Alternating Current Stimulation in the Enhancement of Working Memory Performance in Healthy Adults: A Systematic Meta-Analysis

BACKGROUND

Transcranial alternating current stimulation (tACS)-a noninvasive brain stimulation technique that modulates cortical oscillations in the brain-has shown the capacity to enhance working memory (WM) abilities in healthy individuals. The efficacy of tACS in the improvement of WM performance in healthy individuals is not yet fully understood.

OBJECTIVE/HYPOTHESIS

This meta-analysis aimed to systematically evaluate the efficacy of tACS in the enhancement of WM in healthy individuals and to assess moderators of response to stimulation. We hypothesized that active tACS would significantly enhance WM compared with sham. We further hypothesized that it would do so in a task-dependent manner and that differing stimulation parameters would affect response to tACS.

MATERIALS AND METHODS

Ten tACS studies met the inclusion criteria and provided 32 effects in the overall analysis. Random-effect models assessed mean change scores on WM tasks from baseline to poststimulation. The included studies involved varied in stimulation parameters, between-subject and within-subject study designs, and online vs offline tACS.

RESULTS

We observed a significant, heterogeneous, and moderate effect size for active tACS in the enhancement of WM performance over sham (Cohen's d = 0.5). Cognitive load, task domain, session number, and stimulation region showed a significant relationship between active tACS and enhanced WM behavior over sham.

CONCLUSIONS

Our findings indicate that active tACS enhances WM performance in healthy individuals compared with sham. Future randomized controlled trials are needed to further explore key parameters, including personalized stimulation vs standardized electroencephalography frequencies and maintenance of tACS effects, and whether tACS-induced effects translate to populations with WM impairments.

Glutamate-Weighted Magnetic Resonance Imaging (GluCEST) Detects Effects of Transcranial Magnetic Stimulation to the Motor Cortex

Transcranial magnetic stimulation (TMS) is used in several FDA-approved treatments and, increasingly, to treat neurological disorders in off-label uses. However, the mechanism by which TMS causes physiological change is unclear, as are the origins of response variability in the general population. Ideally, objective in vivo biomarkers could shed light on these unknowns and eventually inform personalized interventions. Continuous theta-burst stimulation (cTBS) is a form of TMS observed to reduce motor evoked potentials (MEPs) for 60 min or longer post-stimulation, although the consistency of this effect and its mechanism continue to be under debate. Here, we use glutamate-weighted chemical exchange saturation transfer (gluCEST) magnetic resonance imaging (MRI) at ultra-high magnetic field (7T) to measure changes in glutamate concentration at the site of cTBS. We find that the gluCEST signal in the ipsilateral hemisphere of the brain generally decreases in response to cTBS, whereas consistent changes were not detected in the contralateral region of interest (ROI) or in subjects receiving sham stimulation.

Lateralized ante mortem and post mortem pathology in a case of Lewy body disease with corticobasal syndrome

Introduction

Methods

Results

Discussion

Virtual Reality Treatment Displaying the Missing Leg Improves Phantom Limb Pain: A Small Clinical Trial

BACKGROUND

Phantom limb pain (PLP) is a common and in some cases debilitating consequence of upper- or lower-limb amputation for which current treatments are inadequate.

OBJECTIVE

This small clinical trial tested whether game-like interactions with immersive VR activities can reduce PLP in subjects with transtibial lower-limb amputation.

METHODS

Seven participants attended 5-7 sessions in which they engaged in a visually immersive virtual reality experience that did not require leg movements (Cool! ^TM), followed by 10-12 sessions of targeted lower-limb VR treatment consisting of custom games requiring leg movement. In the latter condition, they controlled an avatar with 2 intact legs viewed in a head-mounted display (HTC Vive ^TM). A motion-tracking system mounted on the intact and residual limbs controlled the movements of both virtual extremities independently.

RESULTS

All participants except one experienced a reduction of pain immediately after VR sessions, and their pre session pain levels also decreased over the course of the study. At a group level, PLP decreased by 28% after the treatment that did not include leg movements and 39.6% after the games requiring leg motions. Both treatments were successful in reducing PLP.

CONCLUSIONS

This VR intervention appears to be an efficacious treatment for PLP in subjects with lower-limb amputation.

Virtual Reality Tools for Assessing Unilateral Spatial Neglect: A Novel Opportunity for Data Collection

Unilateral spatial neglect (USN) is a syndrome characterized by inattention to or inaction in one side of space and affects between 23-46% of acute stroke survivors. The diagnosis and characterization of these symptoms in individual patients can be challenging and often requires skilled clinical staff. Virtual reality (VR) presents an opportunity to develop novel assessment tools for patients with USN. We aimed to design and build a VR tool to detect and characterize subtle USN symptoms, and to test the tool on subjects treated with inhibitory repetitive transcranial magnetic stimulation (TMS) of cortical regions associated with USN. We created three experimental conditions by applying TMS to two distinct regions of cortex associated with visuospatial processing- the superior temporal gyrus (STG) and the supramarginal gyrus (SMG) - and applied sham TMS as a control. We then placed subjects in a virtual reality environment in which they were asked to identify the flowers with lateral asymmetries of flowers distributed across bushes in both hemispaces, with dynamic difficulty adjustment based on each subject's performance. We found significant differences in average head yaw between subjects stimulated at the STG and those stimulated at the SMG and marginally significant effects in the average visual axis. VR technology is becoming more accessible, affordable, and robust, presenting an exciting opportunity to create useful and novel game-like tools. In conjunction with TMS, these tools could be used to study specific, isolated, artificial neurological deficits in healthy subjects, informing the creation of VR-based diagnostic tools for patients with deficits due to acquired brain injury. This study is the first to our knowledge in which artificially generated USN symptoms have been evaluated with a VR task.

Virtual image of a hand displaced in space influences action performance of the real hand

The rubber hand illusion (RHI) demonstrates that under some circumstances a fake hand can be regarded as part of one’s body; the RHI and related phenomena have been used to explore the flexibility of the body schema. Recent work has shown that a sense of embodiment may be generated by virtual reality (VR). In a series of experiments, we used VR to assess the effects of the displacement of the virtual image of subjects’ hands on action. Specifically, we tested whether spatial and temporal parameters of action change when participants perform a reaching movement towards the location of their virtual hand, the position of which was distorted on some trials. In different experiments, participants were sometimes provided with incorrect visual feedback regarding the position of the to-be-touched hand (Experiment 1), were deprived of visual feedback regarding the position of the reaching hand when acting (Experiment 2) or reached with the hand, the apparent position of which had been manipulated (Experiment 3). The effect was greatest when participants reached towards (Experiment 1) or with (Experiment 3) the displaced hand when the hand was visible during the reaching, but not when the vision of the hand was removed during the action (Experiment 2). Taken together, these data suggest that visual images of one’s hand presented in VR influence the body schema and action performance.

Ever-ready for action: Spatial effects on motor system excitability

Modulation of excitability in the motor system can be observed before overt movements but also in response to covert invitations to act. We asked whether such changes can be induced in the absence of even covert motor instructions, namely, as a function of the location of the hand with reference to the body. Participants received single-pulse TMS over the motor cortex while they placed their contralateral hand (right hand in Experiment 1, left hand in Experiment 2) to the right or left of their body midline, and looked either at or away from their hand. In both experiments, greater excitability was observed when gaze was directed to the right. This finding is interpreted as a consequence of left brain lateralization of motor attention. Contrary to our expectations, we furthermore consistently observed greater excitability when gaze was directed away from the hand. To account for this finding, we introduce the concept of "surveillance attention" which, we speculate, modulates cortical gain, and thereby cortical excitability. Its function is to increase readiness to act in non-foveated regions of space. Such a process confers an advantage in environments, like those in which humans evolved, in which threatening stimuli may appear unexpectedly, and at any time.

Increasing perceived hand size improves motor performance in individuals with stroke: a home-based training study

Background

Increasing perceived hand size with magnifying lenses improves tactile discrimination and induces changes in action performance. We previously demonstrated that motor skills (tested with grip force, finger tapping, and a reach to grasp tasks) improved when actions were performed with magnified compared to normal vision; twenty-eight percent of 25 participants with stroke exhibited significant improvement on a composite measure of motor performance with magnification as compared to a session without magnification.

Methods

To investigate the potential implications of magnification of vision for motor rehabilitation, we recruited individuals with stroke from the original cohort who exhibited an improvement of at least 10% in grip force and/or finger tapping for a home training protocol. Six individuals with stroke completed a two-week home-based training program in which they performed a range of activities while looking at their hand magnified. Motor skills were measured before, immediately after, and two weeks after the training.

Results

Five of the six participants showed an improvement on motor tasks when tested after the training. In two participants the improvement was evident immediately after the training and persisted in time, while it occurred at two-weeks post-training in the other participants. These results suggest that the magnification of vision is a potential tool for the rehabilitation of post-stroke motor deficits.

Asymmetry of post-mortem neuropathology in behavioural-variant frontotemporal dementia

Antemortem behavioural and anatomic abnormalities have largely been associated with right hemisphere disease in behavioural-variant frontotemporal dementia, but post-mortem neuropathological examination of bilateral hemispheres remains to be defined. Here we measured the severity of post-mortem pathology in both grey and white matter using a validated digital image analysis method in four cortical regions sampled from each hemisphere in 26 patients with behavioural-variant frontotemporal dementia, including those with frontotemporal degeneration (i.e. tau = 9, TDP-43 = 14, or FUS = 1 proteinopathy) or Alzheimer's pathology (n = 2). We calculated an asymmetry index based on the difference in measured pathology from each left-right sample pair. Analysis of the absolute value of the asymmetry index (i.e. degree of asymmetry independent of direction) revealed asymmetric pathology for both grey and white matter in all four regions sampled in frontototemporal degeneration patients with tau or TDP-43 pathology (P ≤ 0.01). Direct interhemispheric comparisons of regional pathology measurements within-subjects in the combined tauopathy and TDP-43 proteinopathy group found higher pathology in the right orbitofrontal grey matter compared to the left (P < 0.01) and increased pathology in ventrolateral temporal lobe grey matter of the left hemisphere compared to the right (P < 0.02). Preliminary group-wise comparisons between tauopathy and TDP-43 proteinopathy groups found differences in patterns of interhemispheric burden of grey and white matter regional pathology, with greater relative white matter pathology in tauopathies. To test the association of pathology measurement with ante-mortem observations, we performed exploratory analyses in the subset of patients with imaging data (n = 15) and found a direct association for increasing pathologic burden with decreasing cortical thickness in frontotemporal regions on ante-mortem imaging in tauopathy (P = 0.001) and a trend for TDP-43 proteinopathy (P = 0.06). Exploratory clinicopathological correlations demonstrated an association of socially-inappropriate behaviours with asymmetric right orbitofrontal grey matter pathology, and reduced semantically-guided category naming fluency was associated asymmetric white matter pathology in the left ventrolateral temporal region. We conclude that pathologic disease burden is distributed asymmetrically in behavioural-variant frontotemporal dementia, although not universally in the right hemisphere, and this asymmetry contributes to the clinical heterogeneity of the disorder. The basis for this asymmetric profile is enigmatic but may reflect distinct species or strains of tau and TDP-43 pathologies with propensities to spread by distinct cell- and region-specific mechanisms. Patterns of region-specific pathology in the right hemisphere as well as the left hemisphere may play a role in antemortem clinical observations, and these observations may contribute to antemortem identification of molecular pathology in frontotemporal degeneration.

The role of conflict, feedback, and action comprehension in monitoring of action errors: Evidence for internal and external routes

The mechanisms and brain regions underlying error monitoring in complex action are poorly understood, yet errors and impaired error correction in these tasks are hallmarks of apraxia, a common disorder associated with left hemisphere stroke. Accounts of monitoring of language posit an internal route by which production planning or competition between candidate representations provide predictive signals that monitoring is required to prevent error, and an external route in which output is monitored using the comprehension system. Abnormal reliance on the external route has been associated with damage to brain regions critical for sensory-motor transformation and a pattern of gradual error 'clean-up' called conduite d'approche (CD). Action pantomime data from 67 participants with left hemisphere stroke were consistent with versions of internal route theories positing that competition signals monitoring requirements. Support Vector Regression Lesion Symptom Mapping (SVR-LSM) showed that lesions in the inferior parietal, posterior temporal, and arcuate fasciculus/superior longitudinal fasciculus predicted action conduite d'approche, overlapping the regions previously observed in the language domain. A second experiment with 12 patients who produced substantial action CD assessed whether factors impacting the internal route (action production ability, competition) versus external route (vision of produced actions, action comprehension) influenced correction attempts. In these 'high CD' patients, vision of produced actions and integrity of gesture comprehension interacted to determine successful error correction, supporting external route theories. Viewed together, these and other data suggest that skilled actions are monitored both by an internal route in which conflict aids in detection and correction of errors during production planning, and an external route that detects mismatches between produced actions and stored knowledge of action appearance. The parallels between language and action monitoring mechanisms and neuroanatomical networks pave the way for further exploration of common and distinct processes across these domains.

Cognitive and Pathological Influences of Tau Pathology in Lewy Body Disorders

OBJECTIVE

To use digital histology in a large autopsy cohort of Lewy body disorder (LBD) patients with dementia to test the hypotheses that co-occurring Alzheimer disease (AD) pathology impacts the anatomic distribution of α-synuclein (SYN) pathology and that co-occurring neocortical tau pathology in LBDs associates with worse cognitive performance and occurs in a pattern differing from AD.

METHODS

Fifty-five autopsy-confirmed LBD (Parkinson disease with dementia, n = 36; dementia with Lewy bodies, n = 19) patients and 25 AD patients were studied. LBD patients were categorized as having moderate/severe AD copathology (SYN + AD = 20) or little/no AD copathology (SYN-AD = 35). Digital measures of tau, β-amyloid (Aβ), and SYN histopathology in neocortical and subcortical/limbic regions were compared between groups and related to antemortem cognitive testing.

RESULTS

SYN burden was higher in SYN + AD than SYN-AD in each neocortical region (F_{1, 54} = 5.6-6.0, p < 0.02) but was equivalent in entorhinal cortex and putamen (F_{1, 43-49} = 0.7-1.7, p > 0.2). SYN + AD performed worse than SYN-AD on a temporal lobe-mediated naming task (t₂₇ = 2.1, p = 0.04). Antemortem cognitive test scores inversely correlated with tau burden (r = -0.39 to -0.68, p < 0.05). AD had higher tau than SYN + AD in all regions (F_{1, 43} = 12.8-97.2, p < 0.001); however, SYN + AD had a greater proportion of tau in the temporal neocortex than AD (t₄₁ = 2.0, p < 0.05), whereas AD had a greater proportion of tau in the frontal neocortex than SYN + AD (t₄₁ = 3.3, p < 0.002). SYN + AD had similar severity and distribution of neocortical Aβ compared to AD (F_{1, 40-43} = 1.6-2.0, p > 0.1).

INTERPRETATION

LBD patients with AD copathology harbor greater neocortical SYN pathology. Regional tau pathology relates to cognitive performance in LBD dementia, and its distribution may diverge from pure AD. Tau copathology contributes uniquely to the heterogeneity of cognitive impairment in LBD. Ann Neurol 2018; 1-13 ANN NEUROL 2019;85:259-271.

Closing-in Behavior and Parietal Lobe Deficits: Three Single Cases Exhibiting Different Manifestations of the Same Behavior

Closing-in behavior (CIB) is observed in copying tasks (graphic or gestural) when the copy is performed near or on the top of the model. This symptom has been classically considered to be a manifestation of constructional apraxia and is often associated with a visuospatial impairment. More recent work emphasizes the attentional and/or executive nature of the behavior and its association with frontal lobe dysfunction. We describe three patients in whom CIB was associated with posterior parietal deficits of different etiologies (stroke in Patient 1 and dementia in Patients 2 and 3). In copying figures, Patient 1 produced the shape with high accuracy but the rendering overlapped the model, while for Patients 2 and 3 the copies were distorted but overlapping or in close proximity to the target. In gesture imitation, Patient 2 performed the gestures toward the examiner's space, while Patient 1 showed a peculiar form of CIB: when he was asked to place the ipsilesional arm in a position that mirrored the contralesional hand, Patient 1 moved his hand toward his contralesional hand. Patient 3 did not present gestural CIB. While CIB in Patient 1 was associated with selective deficits in executive functions and attention, additional visuospatial deficits were observed in Patients 2 and 3. The latter two patients showed a general visuoconstructional deficit. These case studies support a primary attentional account of CIB but also suggest that visuoconstructional impairments may contribute to the emergence of CIB, in some subjects. This evidence argues for different types of CIB with different cognitive and neural underpinnings. Furthermore, the data support the hypothesis of a differential involvement of fronto-parietal network in CIB.

Magnifying vision improves motor performance in individuals with stroke

Increasing perceived hand size using magnifying lenses improves tactile discrimination and motor performance in neurologically-intact individuals. We tested whether magnification of the hand can improve motor function in individuals with chronic stroke. Twenty-five individuals with a history of stroke more than 6 months prior to testing underwent a series of tasks exploring different aspects of motor performance (grip force, finger tapping, reaching and grasping, and finger matching) under two visual conditions: magnified or normal vision. Performance was also assessed shortly after visual manipulation to test if these effects persisted. Twenty-eight percent of individuals showed an immediate significant improvement averaged across all tasks with magnification; similar beneficial responses were also observed in 32% of individuals after a short delay. These results suggest that magnification of the image of the hand may be of utility in rehabilitation of individuals with stroke.

Apraxia, Neglect, and Agnosia

PURPOSE OF REVIEW

In part because of their striking clinical presentations, disorders of higher nervous system function figured prominently in the early history of neurology. These disorders are not merely historical curiosities, however. As apraxia, neglect, and agnosia have important clinical implications, it is important to possess a working knowledge of the conditions and how to identify them.

RECENT FINDINGS

Apraxia is a disorder of skilled action that is frequently observed in the setting of dominant hemisphere pathology, whether from stroke or neurodegenerative disorders. In contrast to some previous teaching, apraxia has clear clinical relevance as it is associated with poor recovery from stroke. Neglect is a complex disorder with many different manifestations that may have different underlying mechanisms. Neglect is, in the author's view, a multicomponent disorder in which impairment in attention and arousal is a major contributor. Finally, agnosias come in a wide variety of forms, reflecting impairments ranging from low-level sensory processing to access to stored knowledge of the world (semantics).

SUMMARY

The classic behavioral disorders reviewed here were of immense interest to early neurologists because of their arresting clinical phenomenology; more recent investigations have done much to advance the neuroscientific understanding of the disorders and to reveal their clinical relevance.

An Intrinsic Role of Beta Oscillations in Memory for Time Estimation

The neural mechanisms underlying time perception are of vital importance to a comprehensive understanding of behavior and cognition. Recent work has suggested a supramodal role for beta oscillations in measuring temporal intervals. However, the precise function of beta oscillations and whether their manipulation alters timing has yet to be determined. To accomplish this, we first re-analyzed two, separate EEG datasets and demonstrate that beta oscillations are associated with the retention and comparison of a memory standard for duration. We next conducted a study of 20 human participants using transcranial alternating current stimulation (tACS), over frontocentral cortex, at alpha and beta frequencies, during a visual temporal bisection task, finding that beta stimulation exclusively shifts the perception of time such that stimuli are reported as longer in duration. Finally, we decomposed trialwise choice data with a drift diffusion model of timing, revealing that the shift in timing is caused by a change in the starting point of accumulation, rather than the drift rate or threshold. Our results provide evidence for the intrinsic involvement of beta oscillations in the perception of time, and point to a specific role for beta oscillations in the encoding and retention of memory for temporal intervals.

Magnifying the View of the Hand Changes Its Cortical Representation. A Transcranial Magnetic Stimulation Study

Changes in the perceived size of a body part using magnifying lenses influence tactile perception and pain. We investigated whether the visual magnification of one's hand also influences the motor system, as indexed by transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs). In Experiment 1, MEPs were measured while participants gazed at their hand with and without magnification of the hand. MEPs were significantly larger when participants gazed at a magnified image of their hand. In Experiment 2, we demonstrated that this effect is specific to the hand that is visually magnified. TMS of the left motor cortex did not induce an increase of MEPs when participants looked at their magnified left hand. Experiment 3 was performed to determine if magnification altered the topography of the cortical representation of the hand. To that end, a 3 × 5 grid centered on the cortical hot spot (cortical location at which a motor threshold is obtained with the lowest level of stimulation) was overlaid on the participant's MRI image, and all 15 sites in the grid were stimulated with and without magnification of the hand. We confirmed the increase in the MEPs at the hot spot with magnification and demonstrated that MEPs significantly increased with magnification at sites up to 16.5 mm from the cortical hot spot. In Experiment 4, we used paired-pulse TMS to measure short-interval intracortical inhibition and intracortical facilitation. Magnification was associated with an increase in short-interval intracortical inhibition. These experiments demonstrate that the visual magnification of one's hand induces changes in motor cortex excitability and generates a rapid remapping of the cortical representation of the hand that may, at least in part, be mediated by changes in short-interval intracortical inhibition.

Immersive Low-Cost Virtual Reality Treatment for Phantom Limb Pain: Evidence from Two Cases

Up to 90% of amputees experience sensations in their phantom limb, often including strong, persistent phantom limb pain (PLP). Standard treatments do not provide relief for the majority of people who experience PLP, but virtual reality (VR) has shown promise. This study provides additional evidence that game-like training with low-cost immersive VR activities can reduce PLP in lower-limb amputees. The user of our system views a real-time rendering of two intact legs in a head-mounted display while playing a set of custom games. The movements of both virtual extremities are controlled by measurements from inertial sensors mounted on the intact and residual limbs. Two individuals with unilateral transtibial amputation underwent multiple sessions of the VR treatment over several weeks. Both participants experienced a significant reduction of pain immediately after each VR session, and their pre-session pain levels also decreased greatly over the course of the study. Although preliminary, these data support the idea that VR interventions like ours may be an effective low-cost treatment of PLP in lower-limb amputees.

The parietal lobe and language

Although the parietal lobe was considered by many of the earliest investigators of disordered language to be a major component of the neural systems instantiating language, most views of the anatomic substrate of language emphasize the role of temporal and frontal lobes in language processing. We review evidence from lesion studies as well as functional neuroimaging, demonstrating that the left parietal lobe is also crucial for several aspects of language. First, we argue that the parietal lobe plays a major role in semantic processing, particularly for "thematic" relationships in which information from multiple sensory and motor domains is integrated. Additionally, we review a number of accounts that emphasize the role of the left parietal lobe in phonologic processing. Although the accounts differ somewhat with respect to the nature of the linguistic computations subserved by the parietal lobe, they share the view that the parietal lobe is essential for the processes by which sound-based representations are transcoded into a format that can drive action systems. We suggest that investigations of the linguistic capacities of the parietal lobe constrained by the understanding of the parietal lobe in action and multimodal sensory integration may serve to enhance not only our understanding of language, but also the relationship between language and more basic brain functions.

When perception trips action! The increase in the perceived size of both hand and target matters in reaching and grasping movements

Reaching and grasping movements rely on visual information regarding the target characteristics (e.g. size) and the hand position during the action execution. Changes in the visual representation of the body (e.g. increase in the perceived size of the hand) can modify action performance, but it is still unclear how these modifications interact with changes in the external environment. We investigated this topic by manipulating the perceived size of both hand and target objects and the degree of visual feedback available during the movement execution. Ten young adults were asked to reach and grasp geometrical objects in four different conditions: (i) with normal vision with the light on, (ii) with normal vision in the dark, (iii) using magnifying lenses in the light and (iv) using magnifying lenses in the dark. In contrast with previous works, our results show that movement execution is longer in magnified vision compared to normal when the action is executed in the light, but the grasping component was not affected by changes in size in this condition. On the contrary, when the visual feedback of the hand was removed and participants performed the action in the dark, movements were faster and the distances across fingers larger in the magnified than normal vision. This pattern of data suggests that grasping movements adapt rapidly and compensate for changes in vision when this process depends on the degree of visual feedback and/or environmental cues available. In the debate regarding the dissociation between action and perception, our data suggest that action may overcome changes in perception when visual feedback is available, but perception may trick action in situations of reduced visual information.

Baseline Performance Predicts tDCS-Mediated Improvements in Language Symptoms in Primary Progressive Aphasia

Primary Progressive Aphasia (PPA) is a neurodegenerative condition characterized by insidious irreversible loss of language abilities. Prior studies suggest that transcranial direct current stimulation (tDCS) directed toward language areas of the brain may help to ameliorate symptoms of PPA. In the present sham-controlled study, we examined whether tDCS could be used to enhance language abilities (e.g., picture naming) in individuals with PPA variants primarily characterized by difficulties with speech production (non-fluent and logopenic). Participants were recruited from the Penn Frontotemporal Dementia Center to receive 10 days of both real and sham tDCS (counter-balanced, full-crossover design; participants were naïve to stimulation condition). A battery of language tests was administered at baseline, immediately post-tDCS (real and sham), and 6 weeks and 12 weeks following stimulation. When we accounted for individuals' baseline performance, our analyses demonstrated a stratification of tDCS effects. Individuals who performed worse at baseline showed tDCS-related improvements in global language performance, grammatical comprehension and semantic processing. Individuals who performed better at baseline showed a slight tDCS-related benefit on our speech repetition metric. Real tDCS may improve language performance in some individuals with PPA. Severity of deficits at baseline may be an important factor in predicting which patients will respond positively to language-targeted tDCS therapies. Clinicaltrials.gov ID: NCT02928848.

Mechanisms and Effects of Transcranial Direct Current Stimulation

The US Air Force Office of Scientific Research convened a meeting of researchers in the fields of neuroscience, psychology, engineering, and medicine to discuss most pressing issues facing ongoing research in the field of transcranial direct current stimulation (tDCS) and related techniques. In this study, we present opinions prepared by participants of the meeting, focusing on the most promising areas of research, immediate and future goals for the field, and the potential for hormesis theory to inform tDCS research. Scientific, medical, and ethical considerations support the ongoing testing of tDCS in healthy and clinical populations, provided best protocols are used to maximize safety. Notwithstanding the need for ongoing research, promising applications include enhancing vigilance/attention in healthy volunteers, which can accelerate training and support learning. Commonly, tDCS is used as an adjunct to training/rehabilitation tasks with the goal of leftward shift in the learning/treatment effect curves. Although trials are encouraging, elucidating the basic mechanisms of tDCS will accelerate validation and adoption. To this end, biomarkers (eg, clinical neuroimaging and findings from animal models) can support hypotheses linking neurobiological mechanisms and behavioral effects. Dosage can be optimized using computational models of current flow and understanding dose–response. Both biomarkers and dosimetry should guide individualized interventions with the goal of reducing variability. Insights from other applied energy domains, including ionizing radiation, transcranial magnetic stimulation, and low-level laser (light) therapy, can be prudently leveraged.

Transcranial direct current stimulation for the treatment of primary progressive aphasia: An open-label pilot study

Primary progressive aphasia (PPA) is a neurodegenerative condition characterized by gradual deterioration of language function. We investigated whether two weeks of daily transcranial direct current stimulation (tDCS) treatment would improve language abilities in six people with a non-fluent form of PPA. tDCS was applied in an unblinded trial at an intensity of 1.5mA for 20min/day over 10days. At the time of stimulation, patients were engaged in narrating one of several children's wordless picture stories. A battery of neuropsychological assessments was administered four times: at baseline, immediately following the 2-week stimulation period, and then 6-weeks and 12-weeks following the end of stimulation. We observed improvement in linguistic performance in the domains of speech production and grammatical comprehension. Our encouraging results indicate that larger, sham-controlled studies of tDCS as a potential intervention for PPA are warranted.

What can errors tell us about body representations?

In this review, we examine how tactile misperceptions provide evidence regarding body representations. First, we propose that tactile detection and localization are serial processes, in contrast to parallel processing hypotheses based on patients with numbsense. Second, we discuss how information in primary somatosensory maps projects to body size and shape representations to localize touch on the skin surface, and how responses after use-dependent plasticity reflect changes in this mapping. Third, we review situations in which our body representations are inconsistent with our actual body shape, specifically discussing phantom limb phenomena and anesthetization. We discuss problems with the traditional remapping hypothesis in amputees, factors that modulate perceived body size and shape, and how changes in perceived body form influence tactile localization. Finally, we review studies in which brain-damaged individuals perceive touch on the opposite side of the body, and demonstrate how interhemispheric mechanisms can give rise to these anomalous percepts.

Automated segmentation of chronic stroke lesions using LINDA: Lesion identification with neighborhood data analysis

The gold standard for identifying stroke lesions is manual tracing, a method that is known to be observer dependent and time consuming, thus impractical for big data studies. We propose LINDA (Lesion Identification with Neighborhood Data Analysis), an automated segmentation algorithm capable of learning the relationship between existing manual segmentations and a single T1-weighted MRI. A dataset of 60 left hemispheric chronic stroke patients is used to build the method and test it with k-fold and leave-one-out procedures. With respect to manual tracings, predicted lesion maps showed a mean dice overlap of 0.696 ± 0.16, Hausdorff distance of 17.9 ± 9.8 mm, and average displacement of 2.54 ± 1.38 mm. The manual and predicted lesion volumes correlated at r = 0.961. An additional dataset of 45 patients was utilized to test LINDA with independent data, achieving high accuracy rates and confirming its cross-institutional applicability. To investigate the cost of moving from manual tracings to automated segmentation, we performed comparative lesion-to-symptom mapping (LSM) on five behavioral scores. Predicted and manual lesions produced similar neuro-cognitive maps, albeit with some discussed discrepancies. Of note, region-wise LSM was more robust to the prediction error than voxel-wise LSM. Our results show that, while several limitations exist, our current results compete with or exceed the state-of-the-art, producing consistent predictions, very low failure rates, and transferable knowledge between labs. This work also establishes a new viewpoint on evaluating automated methods not only with segmentation accuracy but also with brain-behavior relationships. LINDA is made available online with trained models from over 100 patients.

Support vector regression based multivariate lesion-symptom mapping

A novel multivariate lesion-symptom mapping (LSM) methodology was developed in this study. Lesion analysis is a classic model for studying brain functions. Using lesion data, focal brain-behavior associations have been widely assessed using the massive voxel-based lesion symptom mapping (VLSM) method. Assessing each voxel independently, VLSM suffers from low sensitivity after correcting for the enormous number of comparisons. It is also incapable for assessing a spatially distributed association pattern though the brain-behavior associations generally involve a collection of functionally related voxels. To solve these two outstanding problems, we carried out the first multivariate lesion symptom mapping (MLSM) in this study using support vector regression (SVR). In the so dubbed SVR-LSM, the symptom relation to the entire lesion map rather than each isolated voxel is modeled using a non-linear function, so the inter-voxel correlations are intrinsically considered, resulting in a potentially more sensitive way to examine lesion-symptom relationships. Evaluations using synthetic data and real data showed that SVR-LSM gained a much better performance (in terms of sensitivity and specificity) for detecting brain-behavior relations than VLSM. While the method was designed for lesion analysis, extending it to neuroimaging data will be straightforward.

The ins and outs of meaning: Behavioral and neuroanatomical dissociation of semantically-driven word retrieval and multimodal semantic recognition in aphasia

Theories about the architecture of language processing differ with regard to whether verbal and nonverbal comprehension share a functional and neural substrate and how meaning extraction in comprehension relates to the ability to use meaning to drive verbal production. We (re-)evaluate data from 17 cognitive-linguistic performance measures of 99 participants with chronic aphasia using factor analysis to establish functional components and support vector regression-based lesion-symptom mapping to determine the neural correlates of deficits on these functional components. The results are highly consistent with our previous findings: production of semantic errors is behaviorally and neuroanatomically distinct from verbal and nonverbal comprehension. Semantic errors were most strongly associated with left ATL damage whereas deficits on tests of verbal and non-verbal semantic recognition were most strongly associated with damage to deep white matter underlying the frontal lobe at the confluence of multiple tracts, including the inferior fronto-occipital fasciculus, the uncinate fasciculus, and the anterior thalamic radiations. These results suggest that traditional views based on grey matter hub(s) for semantic processing are incomplete and that the role of white matter in semantic cognition has been underappreciated.

The influence of embodiment on multisensory integration using the mirror box illusion

We examined the relationship between subcomponents of embodiment and multisensory integration using a mirror box illusion. The participants' left hand was positioned against the mirror, while their right hidden hand was positioned 12″, 6″, or 0″ from the mirror - creating a conflict between visual and proprioceptive estimates of limb position in some conditions. After synchronous tapping, asynchronous tapping, or no movement of both hands, participants gave position estimates for the hidden limb and filled out a brief embodiment questionnaire. We found a relationship between different subcomponents of embodiment and illusory displacement towards the visual estimate. Illusory visual displacement was positively correlated with feelings of deafference in the asynchronous and no movement conditions, whereas it was positive correlated with ratings of visual capture and limb ownership in the synchronous and no movement conditions. These results provide evidence for dissociable contributions of different aspects of embodiment to multisensory integration.

Improving clinical cognitive testing: report of the AAN Behavioral Neurology Section Workgroup

OBJECTIVE

To evaluate the evidence basis of single-domain cognitive tests frequently used by behavioral neurologists in an effort to improve the quality of clinical cognitive assessment.

METHODS

Behavioral Neurology Section members of the American Academy of Neurology were surveyed about how they conduct clinical cognitive testing, with a particular focus on the Neurobehavioral Status Exam (NBSE). In contrast to general screening cognitive tests, an NBSE consists of tests of individual cognitive domains (e.g., memory or language) that provide a more comprehensive diagnostic assessment. Workgroups for each of 5 cognitive domains (attention, executive function, memory, language, and spatial cognition) conducted evidence-based reviews of frequently used tests. Reviews focused on suitability for office-based clinical practice, including test administration time, accessibility of normative data, disease populations studied, and availability in the public domain.

RESULTS

Demographic and clinical practice data were obtained from 200 respondents who reported using a wide range of cognitive tests. Based on survey data and ancillary information, between 5 and 15 tests in each cognitive domain were reviewed. Within each domain, several tests are highlighted as being well-suited for an NBSE.

CONCLUSIONS

We identified frequently used single-domain cognitive tests that are suitable for an NBSE to help make informed choices about clinical cognitive assessment. Some frequently used tests have limited normative data or have not been well-studied in common neurologic disorders. Utilizing standardized cognitive tests, particularly those with normative data based on the individual's age and educational level, can enhance the rigor and utility of clinical cognitive assessment.

Common neuropathological features underlie distinct clinical presentations in three siblings with hereditary diffuse leukoencephalopathy with spheroids caused by CSF1R p.Arg782His

Hereditary diffuse leukoencephalopathy with spheroids (HDLS) presents with a variety of clinical phenotypes including motor impairments such as gait dysfunction, rigidity, tremor and bradykinesia as well as cognitive deficits including personality changes and dementia. In recent years, colony stimulating factor 1 receptor gene (CSF1R) has been identified as the primary genetic cause of HDLS. We describe the clinical and neuropathological features in three siblings with HDLS and the CSF1R p.Arg782His (c.2345G > A) pathogenic mutation. Each case had varied motor symptoms and clinical features, but all included slowed movements, poor balance, memory impairment and frontal deficits. Neuroimaging with magnetic resonance imaging revealed atrophy and increased signal in the deep white matter. Abundant white matter spheroids and CD68-positive macrophages were the predominant pathologies in these cases. Similar to other cases reported in the literature, the three cases described here had varied clinical phenotypes with a pronounced, but heterogeneous distribution of axonal spheroids and distinct microglia morphology. Our findings underscore the critical importance of genetic testing for establishing a clinical and pathological diagnosis of HDLS.

Neural organization of spoken language revealed by lesion-symptom mapping

Studies of patients with acquired cognitive deficits following brain damage and studies using contemporary neuroimaging techniques form two distinct streams of research on the neural basis of cognition. In this study, we combine high-quality structural neuroimaging analysis techniques and extensive behavioral assessment of patients with persistent acquired language deficits to study the neural basis of language. Our results reveal two major divisions within the language system – meaning vs. form and recognition vs. production – and their instantiation in the brain. Phonological form deficits are associated with lesions in peri-Sylvian regions, whereas semantic production and recognition deficits are associated with damage to the left anterior temporal lobe and white matter connectivity with frontal cortex, respectively. These findings provide a novel synthesis of traditional and contemporary views of the cognitive and neural architecture of language processing, emphasizing dual-routes for speech processing and convergence of white matter tracts for semantic control and/or integration.

Enhancing the mirror illusion with transcranial direct current stimulation

Visual feedback has a strong impact on upper-extremity movement production. One compelling example of this phenomena is the mirror illusion (MI), which has been used as a treatment for post-stroke movement deficits (mirror therapy). Previous research indicates that the MI increases primary motor cortex excitability, and this change in excitability is strongly correlated with the mirror's effects on behavioral performance of neurologically-intact controls. Based on evidence that primary motor cortex excitability can also be increased using transcranial direct current stimulation (tDCS), we tested whether bilateral tDCS to the primary motor cortices (anode right-cathode left and anode left-cathode right) would modify the MI. We measured the MI using a previously-developed task in which participants make reaching movements with the unseen arm behind a mirror while viewing the reflection of the other arm. When an offset in the positions of the two limbs relative to the mirror is introduced, reaching errors of the unseen arm are biased by the reflected arm's position. We found that active tDCS in the anode right-cathode left montage increased the magnitude of the MI relative to sham tDCS and anode left-cathode right tDCS. We take these data as a promising indication that tDCS could improve the effect of mirror therapy in patients with hemiparesis.

Somatotopic representation of location: evidence from the Simon effect

Representing the locations of tactile stimulation can involve somatotopic reference frames in which locations are defined relative to a position on the skin surface, and also external reference frames that take into account stimulus position in external space. Locations in somatotopic and external reference frames can conflict in terms of left/right assignment when the hands are crossed or positioned outside of their typical hemispace. To investigate the spatial codes of the representation of both tactile stimuli and responses to touch, a Simon effect task, often used in the visual modality to examine issues of spatial reference frames, was deployed in the tactile modality. Participants performed the task with stimuli delivered to the hands with arms in crossed or uncrossed postures and responses were produced with foot pedals. Across all 4 experiments, participants were faster on somatotopically congruent trials (e.g., left hand stimulus, left foot response) than on somatotopically incongruent trials (left hand stimulus, right foot response), regardless of arm or leg position. However, some evidence of an externally based Simon effect also appeared in 1 experiment in which arm (stimulus) and leg (response) position were both manipulated. Overall, the results demonstrate that tactile stimulus and response codes are primarily generated based on their somatotopic identity. However, stimulus and response coding based on an external reference frame can become more salient when both hands and feet can be crossed, creating a situation in which somatotopic and external representations can differ for both stimulus and response codes.

Multivariate lesion-symptom mapping using support vector regression

Lesion analysis is a classic approach to study brain functions. Because brain function is a result of coherent activations of a collection of functionally related voxels, lesion-symptom relations are generally contributed by multiple voxels simultaneously. Although voxel-based lesion-symptom mapping (VLSM) has made substantial contributions to the understanding of brain-behavior relationships, a better understanding of the brain-behavior relationship contributed by multiple brain regions needs a multivariate lesion-symptom mapping (MLSM). The purpose of this artilce was to develop an MLSM using a machine learning-based multivariate regression algorithm: support vector regression (SVR). In the proposed SVR-LSM, the symptom relation to the entire lesion map as opposed to each isolated voxel is modeled using a nonlinear function, so the intervoxel correlations are intrinsically considered, resulting in a potentially more sensitive way to examine lesion-symptom relationships. To explore the relative merits of VLSM and SVR-LSM we used both approaches in the analysis of a synthetic dataset. SVR-LSM showed much higher sensitivity and specificity for detecting the synthetic lesion-behavior relations than VLSM. When applied to lesion data and language measures from patients with brain damages, SVR-LSM reproduced the essential pattern of previous findings identified by VLSM and showed higher sensitivity than VLSM for identifying the lesion-behavior relations. Our data also showed the possibility of using lesion data to predict continuous behavior scores.

Continuous carryover of temporal context dissociates response bias from perceptual influence for duration

Recent experimental evidence suggests that the perception of temporal intervals is influenced by the temporal context in which they are presented. A longstanding example is the time-order-error, wherein the perception of two intervals relative to one another is influenced by the order in which they are presented. Here, we test whether the perception of temporal intervals in an absolute judgment task is influenced by the preceding temporal context. Human subjects participated in a temporal bisection task with no anchor durations (partition method). Intervals were demarcated by a Gaussian blob (visual condition) or burst of white noise (auditory condition) that persisted for one of seven logarithmically spaced sub-second intervals. Crucially, the order in which stimuli were presented was first-order counterbalanced, allowing us to measure the carryover effect of every successive combination of intervals. The results demonstrated a number of distinct findings. First, the perception of each interval was biased by the prior response, such that each interval was judged similarly to the preceding trial. Second, the perception of each interval was also influenced by the prior interval, such that perceived duration shifted away from the preceding interval. Additionally, the effect of decision bias was larger for visual intervals, whereas auditory intervals engendered greater perceptual carryover. We quantified these effects by designing a biologically-inspired computational model that measures noisy representations of time against an adaptive memory prior while simultaneously accounting for uncertainty, consistent with a Bayesian heuristic. We found that our model could account for all of the effects observed in human data. Additionally, our model could only accommodate both carryover effects when uncertainty and memory were calculated separately, suggesting separate neural representations for each. These findings demonstrate that time is susceptible to similar carryover effects as other basic stimulus attributes, and that the brain rapidly adapts to temporal context.

Critical brain regions for tool-related and imitative actions: a componential analysis

Numerous functional neuroimaging studies suggest that widespread bilateral parietal, temporal, and frontal regions are involved in tool-related and pantomimed gesture performance, but the role of these regions in specific aspects of gestural tasks remains unclear. In the largest prospective study of apraxia-related lesions to date, we performed voxel-based lesion-symptom mapping with data from 71 left hemisphere stroke participants to assess the critical neural substrates of three types of actions: gestures produced in response to viewed tools, imitation of tool-specific gestures demonstrated by the examiner, and imitation of meaningless gestures. Thus, two of the three gesture types were tool-related, and two of the three were imitative, enabling pairwise comparisons designed to highlight commonalities and differences. Gestures were scored separately for postural (hand/arm positioning) and kinematic (amplitude/timing) accuracy. Lesioned voxels in the left posterior temporal gyrus were significantly associated with lower scores on the posture component for both of the tool-related gesture tasks. Poor performance on the kinematic component of all three gesture tasks was significantly associated with lesions in left inferior parietal and frontal regions. These data enable us to propose a componential neuroanatomic model of action that delineates the specific components required for different gestural action tasks. Thus, visual posture information and kinematic capacities are differentially critical to the three types of actions studied here: the kinematic aspect is particularly critical for imitation of meaningless movement, capacity for tool-action posture representations are particularly necessary for pantomimed gestures to the sight of tools, and both capacities inform imitation of tool-related movements. These distinctions enable us to advance traditional accounts of apraxia.

Alexia due to ischemic stroke of the visual word form area

The visual word form area (VWFA) is a region in the posterior left occipitotemporal cortex adjacent to the fusiform gyrus hypothesized to mediate word recognition. Evidence supporting the role of this area in reading comes from neuroimaging studies of normal subjects, case-controlled lesion studies, and studies of patients with surgical resection of the VWFA for tumors or epilepsy. Based on these prior reports, a small discrete lesion to the VWFA would be expected to cause alexia in a literate person without prior brain process, but such a case has not previously been reported to our knowledge. Here, we report the case of a previously-healthy 63-year-old man with the acute onset of alexia without other significant impairments. Magnetic resonance imaging (MRI) of the brain revealed a small ischemic stroke localized to the inferior left occipitotemporal cortex, corresponding to the approximate location of the putative VWFA. Characteristic of pure alexia, testing in the weeks following the stroke revealed a letter-by-letter reading strategy and a word length effect on single word reading. Formal visual field testing was normal. There was no color anomia, or object or face recognition deficits, although a mild agraphia may have been present. This case of acute-onset alexia in a previously normal individual due to a small stroke restricted to the VWFA and sparing occipital cortex and white matter pathways supports the conclusion that the VWFA is crucial for reading.

Individual differences in the morphometry and activation of time perception networks are influenced by dopamine genotype

Individual participants vary greatly in their ability to estimate and discriminate intervals of time. This heterogeneity of performance may be caused by reliance on different time perception networks as well as individual differences in the activation of brain structures utilized for timing within those networks. To address these possibilities we utilized event-related functional magnetic resonance imaging (fMRI) while human participants (n=25) performed a temporal or color discrimination task. Additionally, based on our previous research, we genotyped participants for DRD2/ANKK1-Taq1a, a single-nucleotide polymorphism associated with a 30-40% reduction in striatal D2 density and associated with poorer timing performance. Similar to previous reports, a wide range of performance was found across our sample; crucially, better performance on the timing versus color task was associated with greater activation in prefrontal and sub-cortical regions previously associated with timing. Furthermore, better timing performance also correlated with increased volume of the right lateral cerebellum, as demonstrated by voxel-based morphometry. Our analysis also revealed that A1 carriers of the Taq1a polymorphism exhibited relatively worse performance on temporal, but not color discrimination, but greater activation in the striatum and right dorsolateral prefrontal cortex, as well as reduced volume in the cerebellar cluster. These results point to the neural bases for heterogeneous timing performance in humans, and suggest that differences in performance on a temporal discrimination task are, in part, attributable to the DRD2/ANKK1 genotype.

Cognitive neuroscience of bodily representations: Psychological processes and neural mechanisms

The past decade has seen increasing interest within the cognitive neuroscience community in understanding the psychological processes involved in representing the body, and in learning how these processes may be implemented within the brain. This special issue of Cognitive Neuroscience presents six new empirical papers that contribute to this rapidly developing literature, together with two theoretical discussion papers that are accompanied by peer commentaries.

Gone in a flash: manipulation of audiovisual temporal integration using transcranial magnetic stimulation

While converging evidence implicates the right inferior parietal lobule in audiovisual integration, its role has not been fully elucidated by direct manipulation of cortical activity. Replicating and extending an experiment initially reported by Kamke et al. (2012), we employed the sound-induced flash illusion, in which a single visual flash, when accompanied by two auditory tones, is misperceived as multiple flashes (Wilson, 1987; Shams et al., 2000). Slow repetitive (1 Hz) TMS administered to the right angular gyrus, but not the right supramarginal gyrus, induced a transient decrease in the Peak Perceived Flashes (PPF), reflecting reduced susceptibility to the illusion. This finding independently confirms that perturbation of networks involved in multisensory integration can result in a more veridical representation of asynchronous auditory and visual events and that cross-modal integration is an active process in which the objective is the identification of a meaningful constellation of inputs, at times at the expense of accuracy.

Topography of FUS pathology distinguishes late-onset BIBD from aFTLD-U

Background

Multiple neurodegenerative diseases are characterized by the abnormal accumulation of FUS protein including various subtypes of frontotemporal lobar degeneration with FUS inclusions (FTLD-FUS). These subtypes include atypical frontotemporal lobar degeneration with ubiquitin-positive inclusions (aFTLD-U), basophilic inclusion body disease (BIBD) and neuronal intermediate filament inclusion disease (NIFID). Despite considerable overlap, certain pathologic features including differences in inclusion morphology, the subcellular localization of inclusions, and the relative paucity of subcortical FUS pathology in aFTLD-U indicate that these three entities represent related but distinct diseases. In this study, we report the clinical and pathologic features of three cases of aFTLD-U and two cases of late-onset BIBD with an emphasis on the anatomic distribution of FUS inclusions.

Results

The aFTLD-U cases demonstrated FUS inclusions in cerebral cortex, subcortical grey matter and brainstem with a predilection for anterior forebrain and rostral brainstem. In contrast, the distribution of FUS pathology in late-onset BIBD cases demonstrated a predilection for pyramidal and extrapyramidal motor regions with relative sparing of cerebral cortex and limbic regions.

Conclusions

The topography of FUS pathology in these cases demonstrate the diversity of sporadic FUS inclusion body diseases and raises the possibility that late-onset motor neuron disease with BIBD neuropathology may exhibit unique clinical and pathologic features.

Transcranial direct current stimulation accelerates allocentric target detection

BACKGROUND

Previous research on hemispatial neglect has provided evidence for dissociable mechanisms for egocentric and allocentric processing. Although a few studies have examined whether tDCS to posterior parietal cortex can be beneficial for attentional processing in neurologically intact individuals, none have examined the potential effect of tDCS on allocentric and/or egocentric processing.

OBJECTIVE/HYPOTHESIS

Our objective was to examine whether transcranial direct current stimulation (tDCS), a noninvasive brain stimulation technique that can increase (anodal) or decrease (cathodal) cortical activity, can affect visuospatial processing in an allocentric and/or egocentric frame of reference.

METHODS

We tested healthy individuals on a target detection task in which the target--a circle with a gap--was either to the right or left of the viewer (egocentric), or contained a gap on the right or left side of the circle (allocentric). Individuals performed the task before, during, and after tDCS to the posterior parietal cortex in one of three stimulation conditions--right anodal/left cathodal, right cathodal/left anodal, and sham.

RESULTS

We found an allocentric hemispatial effect both during and after tDCS, such that right anodal/left cathodal tDCS resulted in faster reaction times for detecting stimuli with left-sided gaps compared to right-sided gaps.

CONCLUSIONS

Our study suggests that right anodal/left cathodal tDCS has a facilitatory effect on allocentric visuospatial processing, and might be useful as a therapeutic technique for individuals suffering from allocentric neglect.