Transient beneficial effects of excitatory theta burst stimulation in a patient with phonological agraphia after left supramarginal gyrus infarction

We report a patient showing isolated phonological agraphia after an ischemic stroke involving the left supramarginal gyrus (SMG). In this patient, we investigated the effects of focal repetitive transcranial magnetic stimulation (rTMS) given as theta burst stimulation (TBS) over the left SMG, corresponding to the Brodmann area (BA) 40. The patient and ten control subjects performed a dictational words and nonwords writing task before, and 5 and 30 min after they received excitatory intermittent TBS (iTBS) over the left BA 40, the right hemisphere homologous to BA 40, the Wernicke’s area, or the primary visual cortex.ITBS over the left SMG lead to a brief facilitation of phonological non-words writing to dictation. This case study report illustrates that rTMS is able to influence, among other language functions, the phonological loading processes during the written language production in stroke patients.     

Semantic dementia and persisting Wernicke's aphasia: linguistic and anatomical profiles

Few studies have directly compared the clinical and anatomical characteristics of patients with progressive aphasia to those of patients with aphasia caused by stroke. In the current study we examined fluent forms of aphasia in these two groups, specifically semantic dementia (SD) and persisting Wernicke’s aphasia (WA) due to stroke. We compared 10 patients with SD to 10 age- and education-matched patients with WA in three language domains: language comprehension (single words and sentences), spontaneous speech and visual semantics. Neuroanatomical involvement was analyzed using disease-specific image analysis techniques: voxel-based morphometry (VBM) for patients with SD and overlays of lesion digitized lesion reconstructions in patients with WA. Patients with SD and WA were both impaired on tasks that involved visual semantics, but patients with SD were less impaired in spontaneous speech and sentence comprehension. The anatomical findings showed that different regions were most affected in the two disorders: the left anterior temporal lobe in SD and the left posterior middle temporal gyrus in chronic WA. This study highlights that the two syndromes classically associated with language comprehension deficits in aphasia due to stroke and neurodegenerative disease are clinically distinct, most likely due to distinct distributions of damage in the temporal lobe.     

Mechanisms of aphasia recovery after stroke and the role of noninvasive brain stimulation

One of the most frequent symptoms of unilateral stroke is aphasia, the impairment or loss of language functions. Over the past few years, behavioral and neuroimaging studies have shown that rehabilitation interventions can promote neuroplastic changes in aphasic patients that may be associated with the improvement of language functions. Following left hemisphere strokes, the functional reorganization of language in aphasic patients has been proposed to involve both intrahemispheric interactions between damaged left hemisphere and perilesional sites and transcallosal interhemispheric interactions between the lesioned left hemisphere language areas and homotopic regions in the right hemisphere. A growing body of evidence for such reorganization comes from studies using transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), two safe and noninvasive procedures that can be applied clinically to modulate cortical excitability during post-stroke language recovery. We discuss a hierarchical model for the plastic changes in language representation that occur in the setting of dominant hemisphere stroke and aphasia. We further argue that TMS and tDCS are potentially promising tools for enhancing functional recovery of language and for further elucidating mechanisms of plasticity in patients with aphasia.     

Parietal versus temporal lobe components in spatial cognition: Setting the mid‐point of a horizontal line

Recent anatomo‐clinical correlation studies have extended to the superior temporal gyrus, the right hemisphere lesion sites associated with the left unilateral spatial neglect, in addition to the traditional posterior‐inferior‐parietal localization of the responsible lesion (supramarginal gyrus, at the temporo‐parietal junction). The study aimed at teasing apart, by means of repetitive transcranial magnetic stimulation (rTMS), the contribution of the inferior parietal lobule (angular gyrus versus supramarginal gyrus) and of the superior temporal gyrus of the right hemisphere, in making judgments about the mid‐point of a horizontal line, a widely used task for detecting and investigating spatial neglect. rTMS trains at 25 Hz frequency were delivered over the inferior parietal lobule (angular gyrus and supramarginal gyrus), the superior temporal gyrus and the anterior parietal lobe of the right hemisphere, in 10 neurologically unimpaired participants, performing a line bisection judgment task. rTMS of the inferior parietal lobule at the level of the supramarginal gyrus brought about a rightward error in the bisection judgment, ipsilateral to the side of the rTMS, with stimulation over the other sites being ineffective. The neural correlates of computing the mid‐point of a horizontal segment include the right supramarginal gyrus in the inferior parietal lobule and do not extend to the angular gyrus and the superior temporal gyrus. These rTMS data in unimpaired subjects constrain the evidence from lesion studies in brain‐damaged patients, emphasizing the major role of a subset of relevant regions.     

Effect of tDCS on Fine Motor Control of Patients in Subacute and Chronic Post-Stroke Stages

Abstract

In this study we compared the effects of transcranial direct current stimulation (tDCS) in the subacute and chronic stages of post-stroke recovery. Anodal/sham tDCS was applied to the primary motor cortex of stroke patients in these stages of recovery in a cross-over design. The Jebsen–Taylor hand function test was employed. The repeated-measure ANOVA showed significant influence of the stimulation type and test performance time (during/after tDCS) with no overall influence of recovery stage. The interaction TYPE*TIME*STAGE was significant. The effect after anodal tDCS in the subacute stage was significantly higher compared to the effects in all relevant conditions including the chronic stage. Therefore, tDCS treatment in the subacute stage of recovery can be superior, at least for some patients, to treatment in the chronic stage.     

The Use of Non-invasive Brain Stimulation Techniques to Facilitate Recovery from Post-stroke Aphasia

Aphasia is a common symptom after left hemispheric stroke. Neuroimaging techniques over the last 10–15 years have described two general trends: Patients with small left hemisphere strokes tend to recruit perilesional areas, while patients with large left hemisphere lesions recruit mainly homotopic regions in the right hemisphere. Non-invasive brain stimulation techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) have been employed to facilitate recovery by stimulating lesional and contralesional regions. The majority of these brain stimulation studies have attempted to block homotopic regions in the right posterior inferior frontal gyrus (IFG) to affect a presumed disinhibited right IFG (triangular portion). Other studies have used anodal or excitatory tDCS to stimulate the contralesional (right) fronto-temporal region or parts of the intact left IFG and perilesional regions to improve speech-motor output. It remains unclear whether the interhemispheric disinhibition model, which is the basis for motor cortex stimulation studies, also applies to the language system. Future studies could address a number of issues, including: the effect of lesion location on current density distribution, timing of the intervention with regard to stroke onset, whether brain stimulation should be combined with behavioral therapy, and whether multiple brain sites should be stimulated. A better understanding of the predictors of recovery from natural outcome studies would also help to inform study design, and the selection of clinically meaningful outcome measures in future studies.     

Augmenting Visual Search Performance With Transcranial Direct Current Stimulation (tDCS)

Military personnel endure rigorous and demanding man-hours designated to monitoring and locating targets in tasks such as cyber defense and Unmanned Aerial Vehicle (UAV) operators. These tasks are monotonous and repetitive, which can result in vigilance decrement. The objective of the study was to implement a form of noninvasive brain stimulation known as transcranial DC stimulation (tDCS) over the left frontal eye field (LFEF) region of the scalp to improve cognitive performance. The participants received anodal and cathodal stimulation of 2 mA for 30 min as well as placebo stimulation on 3 separate days while performing the task. The findings suggest that anodal and cathodal stimulation significantly improves detection accuracy. Also, a correlation was detected between percent of eye closure (PERCLOS) and blinking frequency in relation to stimulation condition. Our data suggest that tDCS over the LFEF would be a beneficial countermeasure to mitigate the vigilance decrement and improve visual search performance.     

Incongruous oral and written naming: Evidence for a subdivision of the syndrome of Wernicke's aphasia

A 28-year-old man developed the fluent paraphasic speech characteristic of Wernicke's aphasia after an episode of necrotizing temporal lobe encephalitis. He exhibited an unexpected, and heretofore unreported, superiority of written naming over oral naming. His reading comprehension was modestly superior to his auditory comprehension as well. These findings are at variance with the traditional view of Wernicke's aphasia as an undissociable syndrome of defective reading, writing, and speech. They suggest that an appropriately placed lesion can partially spare reading and writing while still producing fluent paraphasic speech.     

Reduction of implicit cognitive bias with cathodal tDCS to the left prefrontal cortex

Implicit associations can interfere with cognitive operations and behavioral decisions without direct intention. Enhancement of neural activity with anodal transcranial direct current stimulation (tDCS) was proposed to reduce implicit associations by means of improved cognitive control. However, a targeted reduction of distractive implicit associations by inhibitory cathodal tDCS, recently shown in spatial–numerical associations, provides an interesting alternative approach to support goal-directed behavior with transcranial brain stimulation. To test this rationale with a sham-controlled cross-over design, a standardized Implicit Association Test (IAT) was performed by 24 healthy participants parallel to 1 mA cathodal or sham tDCS to the left prefrontal cortex. In this double-classification task, insect versus flower pictures and negative versus positive words are mapped together onto two shared response keys with crossed response assignments in separate blocks. Responses were faster when insect + negative and flower + positive stimuli required the same answer (IAT effect). Most critically, the IAT effect was reduced during cathodal tDCS as compared to sham stimulation. Thus, results are consistent with the proposed stimulation rationale, with previous observations, and complementary to previous studies using different tDCS configurations.     

Theodor Meynert′s Contribution to Classical 19th Century Aphasia Studies

Carl Wernicke (1848-1905) is traditionally considered the first to have described the features of, and the brain pathology underlying, impaired auditory comprehension and related symptoms. Although Wernicke (1874) clearly and repeatedly indicates his indebtedness to Theodor von Meynert (1833-1892). this is usually understood as an acknowledgment that Meynert taught Wernicke neuroanatomy (Eggert, 1977); Wernicke′s own words in part support this interpretation. A more sophisticated historical analysis notes that, prior to Wernicke, both Johann Schmidt in 1871 and Charlton Bastian in 1869 had described the concept of receptive aphasia, but neither had supported their analyses with autopsy evidence as did Wernicke, thus not dislodging Wernicke′s claim of priority. However, a virtually unknown work by Theodor von Meynert, published in 1866, has recently been rediscovered by us ["Ein Fall von Sprachstörung, anatomisch begründet." Medizinische Jahrbücher. XII Band der Zeitschrift der K. K. Gesellleschaft der Ärzte in Wien, 22.Jahr. Pp. 152-189]. In this paper Meynert analyzes the anatomical basis for localizing the comprehension of language in the superior temporal gyros, he argues that lesions in this area should (by analogy to Broca′s earlier observations on language expression) cause impairments in language comprehension, and he presents a case of receptive aphasia with autopsy evidence of destruction of the superior temporal gyros in the left hemisphere. The patient′s aphasia was classic: impaired auditory comprehension, and fluent speech with paraphasias. It is clear that Meynert should be given historical credit for his work.     

A proposed regional hierarchy in recovery of post-stroke aphasia

Activation studies in patients with aphasia due to stroke or tumours in the dominant hemisphere have revealed effects of disinhibition in ipsilateral perilesional and in contralateral homotopic cortical regions, referred to as collateral and transcallosal disinhibition. These findings were supported by studies with selective disturbance of cortical areas by repetitive transcranial magnetic stimulation (rTMS) in healthy volunteers and in patients with focal brain lesions. Both, collateral as well as transcallosal disinhibition might be relevant for the compensation of lesions within a functional network. From these data a hierarchical organization of recovery of aphasia after stroke and of compensation of language defects due to brain tumours can be deduced, by which the reactivation of undamaged network areas of the ipsilateral hemisphere usually lead to better outcome than the involvement of homotopic contra-lateral regions. rTMS can be used to identify areas relevant for speech production and might play a role in treatment strategies targeted at modulating the activity of contralateral homotopic areas of the functional network which might interfere with language recovery.     

Lesion analysis of the brain areas involved in language comprehension

The cortical regions of the brain traditionally associated with the comprehension of language are Wernicke's area and Broca's area. However, recent evidence suggests that other brain regions might also be involved in this complex process. This paper describes the opportunity to evaluate a large number of brain-injured patients to determine which lesioned brain areas might affect language comprehension. Sixty-four chronic left hemisphere stroke patients were evaluated on 11 subtests of the Curtiss-Yamada Comprehensive Language Evaluation - Receptive (CYCLE-R; Curtiss, S., & Yamada, J. (1988). Curtiss-Yamada Comprehensive Language Evaluation. Unpublished test, UCLA). Eight right hemisphere stroke patients and 15 neurologically normal older controls also participated. Patients were required to select a single line drawing from an array of three or four choices that best depicted the content of an auditorily-presented sentence. Patients' lesions obtained from structural neuroimaging were reconstructed onto templates and entered into a voxel-based lesion-symptom mapping (VLSM; Bates, E., Wilson, S., Saygin, A. P., Dick, F., Sereno, M., Knight, R. T., & Dronkers, N. F. (2003). Voxel-based lesion-symptom mapping. Nature Neuroscience, 6(5), 448-450.) analysis along with the behavioral data. VLSM is a brain-behavior mapping technique that evaluates the relationships between areas of injury and behavioral performance in all patients on a voxel-by-voxel basis, similar to the analysis of functional neuroimaging data. Results indicated that lesions to five left hemisphere brain regions affected performance on the CYCLE-R, including the posterior middle temporal gyrus and underlying white matter, the anterior superior temporal gyrus, the superior temporal sulcus and angular gyrus, mid-frontal cortex in Brodmann's area 46, and Brodmann's area 47 of the inferior frontal gyrus. Lesions to Broca's and Wernicke's areas were not found to significantly alter language comprehension on this particular measure. Further analysis suggested that the middle temporal gyrus may be more important for comprehension at the word level, while the other regions may play a greater role at the level of the sentence. These results are consistent with those seen in recent functional neuroimaging studies and offer complementary data in the effort to understand the brain areas underlying language comprehension.     

Cerebellum and processing of negative facial emotions: cerebellar transcranial DC stimulation specifically enhances the emotional recognition of facial anger and sadness

Some evidence suggests that the cerebellum participates in the complex network processing emotional facial expression. To evaluate the role of the cerebellum in recognising facial expressions we delivered transcranial direct current stimulation (tDCS) over the cerebellum and prefrontal cortex. A facial emotion recognition task was administered to 21 healthy subjects before and after cerebellar tDCS; we also tested subjects with a visual attention task and a visual analogue scale (VAS) for mood. Anodal and cathodal cerebellar tDCS both significantly enhanced sensory processing in response to negative facial expressions (anodal tDCS, p=.0021; cathodal tDCS, p=.018), but left positive emotion and neutral facial expressions unchanged (p>.05). tDCS over the right prefrontal cortex left facial expressions of both negative and positive emotion unchanged. These findings suggest that the cerebellum is specifically involved in processing facial expressions of negative emotion.     

Cerebellum and processing of negative facial emotions: Cerebellar transcranial DC stimulation specifically enhances the emotional recognition of facial anger and sadness

Some evidence suggests that the cerebellum participates in the complex network processing emotional facial expression. To evaluate the role of the cerebellum in recognising facial expressions we delivered transcranial direct current stimulation (tDCS) over the cerebellum and prefrontal cortex. A facial emotion recognition task was administered to 21 healthy subjects before and after cerebellar tDCS; we also tested subjects with a visual attention task and a visual analogue scale (VAS) for mood. Anodal and cathodal cerebellar tDCS both significantly enhanced sensory processing in response to negative facial expressions (anodal tDCS, p=.0021; cathodal tDCS, p=.018), but left positive emotion and neutral facial expressions unchanged (p>.05). tDCS over the right prefrontal cortex left facial expressions of both negative and positive emotion unchanged. These findings suggest that the cerebellum is specifically involved in processing facial expressions of negative emotion.     

左右侧颞顶联合区对道德意图信息加工能力的共同作用——基于经颅直流电刺激技术

行为人的意图动机是我们对日常行为的对错做出判断的重要依据。以往研究表明,左右侧颞顶联合区(TPJ)都可能与信念意图的整合加工能力相关,尤其是近年来越来越多的神经刺激研究为TPJ区域与心理状态归因能力之间的因果关系提供了证据。然而,这些研究在实验任务的选取,实验设计的优化,实验结论的稳健性上仍然有改进的空间。基于此,本研究开展了两个在设计上互相补充的实验。实验中被试的TPJ区域会接受一段时间的经颅直流电刺激,并完成一系列的道德判断任务,任务是由意图和结果,以及负性和中性2×2双变量构成的4种条件的故事:无伤人、伤人未遂、意外伤人和伤人成功,被试要对故事主角的行为做出谴责程度的道德判断。结合道德判断的谴责程度和决策时间数据发现,当人们在处理信念意图信息时,左右侧TPJ区域可能是协同互动、共同发挥作用的。在激活右侧TPJ并限制左侧TPJ的情况下,人们对负性结果的谴责程度变高,人们变得更加依赖于行为结果做出道德判断;而在限制右侧TPJ并激活左侧TPJ的情况下,人们对负性意图的谴责程度变高,人们变得更加依赖于行为者的动机做出道德判断。     

Can brain stimulation improve semantic joke comprehension?

ABSTRACT

Semantic humour involves a deviation from lexico-semantic rules that introduces ambiguity into interpretation of a situation. The left Inferior Frontal Gyrus (IFG) has been implicated in humour processing (e.g. semantic puns, ambiguity resolution). The present study aimed to examine whether transcranial direct current stimulation (tDCS) over the left IFG would enhance semantic ambiguity resolution. In two sessions, fifteen participants aged 20–35 years received either offline anodal tDCS or sham stimulation for 20?min, after which they read semantically ambiguous humorous sentences, literal (non-ambiguous) sentences, and meaningless sentences, and then performed a semantic judgment task relating to each sentence’s final word. Results showed that ambiguity resolution requires longer processing than literality. However, left IFG stimulation was ineffective in increasing ambiguity resolution. Researchers should target different brain areas in both hemispheres to further explore humour comprehension.     

Theories of spoken word recognition deficits in aphasia: evidence from eye-tracking and computational modeling

We used eye-tracking to investigate lexical processing in aphasic participants by examining the fixation time course for rhyme (e.g., carrot-parrot) and cohort (e.g., beaker-beetle) competitors. Broca’s aphasic participants exhibited larger rhyme competition effects than age-matched controls. A re-analysis of previously reported data (Yee, Blumstein, & Sedivy, 2008) confirmed that Wernicke’s aphasic participants exhibited larger cohort competition effects. Individual-level analyses revealed a negative correlation between rhyme and cohort competition effect size across both groups of aphasic participants. Computational model simulations were performed to examine which of several accounts of lexical processing deficits in aphasia might account for the observed effects. Simulation results revealed that slower deactivation of lexical competitors could account for increased cohort competition in Wernicke’s aphasic participants; auditory perceptual impairment could account for increased rhyme competition in Broca’s aphasic participants; and a perturbation of a parameter controlling selection among competing alternatives could account for both patterns, as well as the correlation between the effects. In light of these simulation results, we discuss theoretical accounts that have the potential to explain the dynamics of spoken word recognition in aphasia and the possible roles of anterior and posterior brain regions in lexical processing and cognitive control.     

Working memory improvement with non-invasive brain stimulation of the dorsolateral prefrontal cortex: A systematic review and meta-analysis

Recent studies have used non-invasive brain stimulation (NIBS) techniques, such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), to increase dorsolateral prefrontal cortex (DLPFC) activity and, consequently, working memory (WM) performance. However, such experiments have yielded mixed results, possibly due to small sample sizes and heterogeneity of outcomes. Therefore, our aim was to perform a systematic review and meta-analyses on NIBS studies assessing the n-back task, which is a reliable index for WM. From the first data available to February 2013, we looked for sham-controlled, randomized studies that used NIBS over the DLPFC using the n-back task in PubMed/MEDLINE and other databases. Twelve studies (describing 33 experiments) matched our eligibility criteria. Active vs. sham NIBS was significantly associated with faster response times (RTs), higher percentage of correct responses and lower percentage of error responses. However, meta-regressions showed that tDCS (vs. rTMS) presented only an improvement in RT, and not in accuracy. This could have occurred in part because almost all tDCS studies employed a crossover design, possibly due to the reliable tDCS blinding. Study design was also associated with no improvement in correct responses in the active vs. sham groups. To conclude, rTMS of the DLPFC significantly improved all measures of WM performance whereas tDCS significantly improved RT, but not the percentage of correct and error responses. Mechanistic insights on the role of DLPFC in WM are further discussed, as well as how NIBS techniques could be used in neuropsychiatric samples presenting WM deficits, such as major depression, dementia and schizophrenia.     

Alteration of hypnotic experience following transcranial electrical stimulation of the left prefrontal cortex

BackgroundRecent studies of neurostimulation reported alteration of hypnotizability and hypnotic phenomena after inhibition of the dorsolateral prefrontal cortex (DLPFC), but the different assessments of hypnosis and the stimulation parameters still left open many questions about the role of this brain region in hypnotizability. We aimed to administer inhibitory transcranial direct current stimulation (tDCS) over the left DLPFC to observe effects of stimulation on the hypnotic experience and the feeling of agency.Methodsa procedure of hypnotic induction with suggestions was repeated twice: before and after the unilateral cathodal tDCS over the left DLPFC. The experience was assessed through a phenomenological assessment of hypnosis and sense of agency in thirty-three participants randomly assigned to the sham or the active group.Resultsactive (inhibitory) tDCS enhanced the hypnotizability by 15.4% and altered a few dimensions of consciousness such as self-awareness and absorption. No changes emerged on the feeling of agency and pass rates for suggestions.ConclusionstDCS reflects a promising tool to alter the hypnotic phenomena and the responsiveness to hypnotic procedures. Neurocognitive implications are discussed for the construct of hypnotizability as well as for the role of the left DLPFC in the dimensions of consciousness such as self-awareness.     

From the left to the right: How the brain compensates progressive loss of language function

In normal right-handed subjects language production usually is a function oft the left brain hemisphere. Patients with aphasia following brain damage to the left hemisphere have a considerable potential to compensate for the loss of this function. Sometimes, but not always, areas of the right hemisphere which are homologous to language areas of the left hemisphere in normal subjects are successfully employed for compensation but this integration process may need time to develop. We investigated right-handed patients with left hemisphere brain tumors as a model of continuously progressive brain damage to left hemisphere language areas using functional neuroimaging and transcranial magnetic stimulation (TMS) to identify factors which determine successful compensation of lost language function. Only patients with slowly progressing brain lesions recovered right-sided language function as detected by TMS. In patients with rapidly progressive lesions no right-sided language function was found and language performance was linearly correlated with the lateralization of language related brain activation to the left hemisphere. It can thus be concluded that time is the factor which determines successful integration of the right hemisphere into the language network for compensation of lost left hemisphere language function.