Name: transcranial direct current stimulation (tdcs) of wernicke's and broca's areas in studies of language learning and word acquisition
Uploaded: 2019-07-13T13:00:00
Description: Watch this Scientific Journal Video about Transcranial Direct Current Stimulation tDCS of Wernicke's and Broca's Areas in Studies of Language Learning and Word Acquisition at JoVE.com

Supported by RF Government grant contract No.14.W03.31.0010. We wish to thank Ekatarina Perikova and Alexander Kirsanov for their support in preparing this publication. We are grateful to Olga Shcherbakova and Margarita Filippova for their help in stimulus selection and to Anastasia Safronova and Pavel Inozemcev for their assistance in the production of video materials.

All procedures were approved by the local research ethics committee of St. Petersburg State University, St. Petersburg, with consent obtained from all participants.
NOTE: All participants must sign the informed consent and fill in a questionnaire to attest the absence of any contraindications for tDCS stimulation (see Technique and Considerations in the Use of 4 x 1 Ring High-definition Transcranial Direct Current Stimulation (HD-tDCS) by Willamar and colleagues12) and ...

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The results highlight a few important points that need to be taken into account when conducting psycholinguistic research in general, and neurolinguistics tDCS studies in particular. Stimulation of language cortices (exemplified here by Wernicke&#39;s area) produces a complex pattern of behavioral outcomes. Unlike the TMS technique, where it is possible to fully disrupt speech processing (e.g., the so-called &#34;speech arrest&#34; protocol)21, this method enables a possibly more complex, graded a...

The neurobiological mechanisms of human language function are still poorly understood. As the bedrock of our communication ability, this unique human neurocognitive trait plays a particularly important role in our personal and socio-economic lives. Any deficits affecting speech and language are devastating for the sufferers and expensive for the society. At the same time, in the clinic, procedures for treatment of speech deficits (such as aphasia) remain suboptimal, not least due to poor understanding of the neurobiological mechanisms involved1. In research, the recent advent and rapid development of neuroimaging methods have led to multiple discoveries describing activation patterns; yet, causal evidence is often still lacking. Furthermore, language areas of the brain are located somewhat suboptimally for application of mainstream neurostimulation approaches which can provide causal evidence, most importantly the transcranial magnetic stimulation technique (TMS). Whereas offline TMS protocol, such as theta burst stimulation, can cause pain due to the close proximity of the muscles to the point of stimulation, &#34;online&#34; TMS protocols can introduce sound artifacts from stimulation, which is undesirable due to interference&#160;with linguistic stimulus presentation2. Even though TMS is widely used in language studies despite such inconveniences, a welcome alternative may be provided by other stimulation methods, most notably transcranial direct-current stimulation (tDCS). In recent years, tDCS has seen a remarkable growth in its use due to its accessibility, ease of use, relative safety and often rather striking outcomes3. Even though the exact mechanisms underpinning tDCS influence on neural activity are not understood completely, the mainstream view is that, at least at low intensity levels (typically 1-2 mA for 15-60 min), it does not cause any neural excitation or inhibition per se, but instead modulates the resting transmembrane potential in a graded way towards de- or hyperpolarization, shifting the excitation thresholds up or down and thereby making the neural system more or less susceptible to modulations by other events, stimuli, states or behaviors4,5. Whereas most of the applications reported to date have focused on the motor function6 and/or motor system deficits, it has been increasingly applied to higher-level cognitive functions and their respective disabilities. There has been a rise in its application to speech and language, mostly in research aimed at the recovery of post-stroke aphasia7,8,9, even though it has so far led to mixed results with respect to the therapeutic potential, stimulation sites and hemispheres, and optimal current polarity. As this research, and particularly the application of tDCS in cognitive neurobiology of normal language function, is still in its infancy, it is crucial to delineate procedures for stimulating at least the core language cortices (most importantly Wernicke&#39;s and Broca&#39;s areas) using tDCS, which is one of the main aims of the current report.
Here, we will consider application of tDCS to language areas in a word-learning experiment. In general, the case of word learning is taken here as one example of a neurolinguistic experiment, and the tDCS part of the procedure should not change substantially for other types of language experiments targeting the same areas. Yet, we use this opportunity to also highlight major methodological considerations in a word acquisition experiment per se, which is the second main aim of the current protocol description. Brain mechanisms underpinning word acquisition &#8211;&#160;a ubiquitous human capacity at the core of our linguistic communication skill&#160;&#8211;&#160;remain largely unknown10. Complicating the picture, existing literature differs widely in how experimental protocols promote word acquisition, in control over stimulation parameters, and in tasks used to assess learning outcomes (see, e.g., Davis et al.11). Below, we describe a protocol that uses highly controlled stimuli and presentation mode, while ensuring a naturalistic context-driven acquisition of novel vocabulary. Furthermore, we use a comprehensive battery of tasks to assess the outcomes behaviorally at different levels, both immediately after learning and following an overnight consolidation stage. This is combined with sham and cathodal tDCS of language areas (we make a particular example using Wernicke&#39;s area stimulation) which can provide causal evidence on underlying neural processes and mechanisms.

transcranial direct current stimulation (tdcs) of wernicke's and broca's areas in studies of language learning and word acquisition

Language is a highly important yet poorly understood function of the human brain. While studies of brain activation patterns during language comprehension are abundant, what is often critically missing is causal evidence of brain areas&#39; involvement in a particular linguistic function, not least due to the unique human nature of this ability and a shortage of neurophysiological tools to study causal relationships in the human brain noninvasively. Recent years have seen a rapid rise in the use of transcranial direct current stimulation (tDCS) of the human brain, an easy, inexpensive and safe noninvasive technique that can modulate the state of the stimulated brain area (putatively by shifting excitation/inhibition thresholds), enabling a study of its particular contribution to specific functions. While mostly focusing on motor control, the use of tDCS is becoming more widespread in both basic and clinical research on higher cognitive functions, language included, but the procedures for its application remain variable. Here, we describe the use of tDCS in a psycholinguistic word-learning experiment. We present the techniques and procedures for application of cathodal and anodal stimulation of core language areas of Broca and Wernicke in the left hemisphere of the human brain, describe the procedures of creating balanced sets of psycholinguistic stimuli, a controlled yet naturalistic learning regime, and a comprehensive set of techniques to assess the learning outcomes and tDCS effects. As an example of tDCS application, we show that cathodal stimulation of Wernicke&#39;s area prior to a learning session can impact word learning efficiency. This impact is both present immediately after learning and, importantly, preserved over longer time after the physical effects of stimulation wear off, suggesting that tDCS can have long-term influence on linguistic storage and representations in the human brain.

While the data were analyzed for the specific set of tasks, it should be emphasized that the developed set of tests and the paradigm could be adapted to a variety of psycholinguistic experiments. The results were analyzed in terms of accuracy scores (number of correct answers) and the reaction time (RT) using non-parametric Wilcoxon signed rank&#160;test and Mann-Whitney U test across groups (cathodal and sham stimulation conditions). Significant differences for tasks within each group ar...

Watch this Scientific Journal Video about Transcranial Direct Current Stimulation tDCS of Wernicke's and Broca's Areas in Studies of Language Learning and Word Acquisition at JoVE.com

Transcranial Direct Current Stimulation tDCS of Wernicke's and Broca's Areas in Studies of Language Learning and Word Acquisition

Here, we describe a protocol for using transcranial direct current stimulation for psycho- and neurolinguistic experiments aimed at studying, in a naturalistic yet fully controlled way, the role of cortical areas of the human brain in word learning, and a comprehensive set of behavioral procedures for assessing the outcomes.

Transcranial Direct Current Stimulation (tDCS) of Wernicke's and Broca's Areas in Studies of Language Learning and Word Acquisition

Language is a highly important yet poorly understood function of the human brain. While studies of brain activation patterns during language comprehension ...

In this video, we describe a simple time and cost efficient protocol for using transcranial direct current stimulation for psycho and neurolinguistic experiments aimed at studying in a naturalistic, yet fully controlled way the role of the cortical areas of the human brain in word learning, and a comprehensive set of behavioral procedures for assessing the outcomes. Language is a highly important, yet poorly understood, function of the human brain. While studies of brain activation patterns during language comprehension are abundant what is often critically missing is causal evidence of brain areas'involvement in a particular function, not least due to the unique human nature of this ability, and a shortage of neurophysiological tools to study causal relationships in the brain non-invasively.Recent years have seen a rapid rise in the use of transcranial direct current stimulation, or tDCS, which is an easy, inexpensive, and safe non-invasive technique that can modulate the state of the stimulated brain area which it does putatively by shifting the excitation and inhibition thresholds, and thus enables the study of its particular contribution to specific functions. Here, we will describe the use of tDCS in a psycholinguistic word learning experiment. Here, we will consider application of tDCS to language areas in a word learning experiment.In general, the case of word learning is taken here as one example of a neurolinguistic experiment, and the tDCS part of the procedure should not change substantially for other types of language experiments which target the same areas. Yet, we use this opportunity to also highlight major methodological considerations in the word acquisition experiment per se, which is the second main aim of the current report. It is important to obtain all legal and ethical permissions for studies on human subjects that are required by your local legislation.In our study, the permission was granted by the University of St.Petersburg Research Ethics Committee. Conduct all measurements in a soundproof, or at least sound attenuated, camera. Sound insulation is very important, since any extraneous sound, noise, human speech, and so on can significantly affect the performance, and thus influence the data.To avoid interference by unnecessary subject experimenter contact, only the screen, headphones, or speakers, and any input devices, such as keyboard or button boxes are to be located inside the camera. Interaction with the experimenter is to be held over intercom, unless personal contact is required. The optimal parameters for text presentation are black text on gray background.We use font face Arial size 27. To reduce delays and jitter in visual presentation, we recommend using a video card and a monitor with a refresh rate of 100 hertz and higher. To measure reaction times, use research grade response pads which have been ergonomics and more precise timing in comparison with conventional keyboards.We have chosen words of Russian language which were controlled for their length and overall structure to avoid any basic effect of surface properties on higher level processing. To create multiple lists, we divided the word into sets which didn't differ statistically on their and syllabic frequency. This was established using T-tests.Novel word forms were created by transposing the alternate syllables within each set of words. So, thus the novel words resembled existing words in terms of orthographic and phonological structure. As a result, we created a list of word forms to be learned and a list of similar unlearned pseudo words from one set of existing words.All three stimulus types that shared one set would therefore potentially enter into lexical competition as neighbors after the learning stage. Further control list of words and pseudo words that didn't share this similarity were also prepared. The sets were counterbalanced around the subject groups in the way that they played different experimental roles to minimize any effects of surface form on newly acquired semantics.We also created novel meanings associated with the new words in the process of learning. They were made of obsolete or real concepts not present in the participants'language. For contextual learning of novel semantics, we created five sentences for each of the new concept describing situations through which one could understand the meaning of the novel words gradually from general to more specific context.Novel words were represented in their base form. The length of the sentences and the number of words were controlled and balance between conditions. Each sentence consisted of eight words according to the minimal length of sentences in Russian, which allow you to understand the context.As you are reading these sentences, you can understand that circunal is a kind of negative feeling which appears when you have to remember too many passwords from your accounts. To assess acquisition and comprehension of word forms and semantics we use several tasks, free recall, cue recognition, lexical decisions, semantic definition, and semantic judgment. In the free recall task, participants had to reproduce as many new word forms as they could remember by typing them into the prepared spreadsheet.The recognition and lexical decisions tasks were used the same stimuli and speed of presentation and differ only in instructions. The items were presented sequentially and randomly. In the recognition task participants had to press button one if they encountered the word during the experiment or press two if they didn't.In the lexical decision, they had to press button one if presented what made sense or press two if it didn't. Semantic tasks were used to estimate the acquisition of normal meanings and the correspondence between that meaning and the surface form. In the semantic definition task, participants are given a list of the items, those presented previously in the learning phase.They should try to define each of them and type their definitions into the spreadsheet. In the semantic judgment task, participants were presented with a word and three definitions. They should choose one correct definition for each word by pressing the corresponding button.Only one of the definitions were correct. In addition, we suggest including none of this or not sure option. Transcranial direct current electrical stimulation, tDCS, generates neuro modulations and spontaneous and neuronal activity.Dependent on the orientation of the cells with respect to current, the membrane potential can be shifted slightly towards hyperpolarization. For instance, for motor system it happens during anodal stimulation, or depolarization for cathodal stimulation. This change in your neural excitability will lead to various temporary alterations in the brain function, including the motor sensory and high level cognitive functions.Here, we will consider application of tDCS to language areas such as Wernicke's and Broca's areas of human in a word learning experiment. It's important to remember the main difference between tDCS and other non-invasive brain stimulation methods, such as transcranial magnetic stimulation, first, since there is not a simpler way to determine sensitivity to tDCS by threshold assessment, a single protocol is applied for all subjects. Second, it's very difficult to accurately estimate the stimulation area.One can only speak about the hypothetical area. Third, it's also difficult to estimate the duration of offline stimulation effects. Presumably, the main effect of stimulation are observed up to one hour after the termination of stimulation.However, the effect of stimulation can sometimes be detected even one day after stimulation. There are three types of stimulation, cathodal, with a cathode electrode over target area, anodal, with the anode over target area, and placebo, or sham stimulation. Use sponge electrodes measuring five by five centimeters.The electrodes should be soaked in physiological saline solution for five minutes before application. In order to minimize the effect of stimulation on other areas of the brain put the anodal electrode at the base of the neck on the right side. We use spongy electrodes measuring two by five centimeters.Particular attention should be paid to prevent spreading of the solution beyond the boundaries of the electrode application zone. Special care should be taken to keep the surrounding electrode area dry. The optimal protocol for cathode stimulation is the stimulation by one milliamp current for 10 minutes.First, the current rises to one milliamp over the initial 20 seconds, and at the end of the stimulation it decreases to zero in the last 20 seconds of the stimulation. The sets with contextual sentences containing the novel words are presented in a random order. Each sentence starts with a word by word presentation.After this, the entire sentence appears on the screen to ensure its full understanding. Participants have to press an indicated response button with their index finger of the left hand after reading the whole sentence. The left hand is used to reduce interference with the language errors of the left hemisphere.Duration of sentence presentation is five seconds. Then a crosshair appears at the center of the screen for 500 milliseconds and the next sentence begins. The sets of the sentences are separated from each other by appearance of three crosshairs for two seconds.Each new concept presentation starts with another crosshair present for 500 milliseconds before the sentence words are flashed. Each word is presented for 500 milliseconds, the empty screen and the background color between the words within one sentence for 300 milliseconds. We used a battery of different tests since tDCS effects on language processing are not well known.To assess learning effects both immediately and following the overnight consolidation stage we recommend breaking the stimulus set into two subset, equally distributed across stimulus conditions and counterbalanced across the subject group. We are running the assessment tasks immediately after the learning protocol and after a 24 hour delay. This protocol allows data analysis using different tests comparing two sets of samples coming from continuous distributions with equal medians, like Wilcox and Rank Sum test, or Mann-Whitney U test, or medians to sample T-test if the distribution is normal.Within each group, there were notable differences in accuracy scores and reaction times between the two assessment sessions. In the sham group novel word recognition was significantly better on the first day than on the second one. In the cathodal group reaction time latency in the recognition task was significantly faster for novel words than for competitor pseudo words on the first day, but not on the second one.The results of lexical decision task showed that after cathodal stimulation both on the first and on the second day there was significantly better performance for novel words than for pseudo word competitors. In the sham group, however, this effect was significant on the second day only. tDCS of language cortices exemplified here by Wernicke's area produces a complex pattern of behavioral outcomes.Contextual presentation of new words after tDCS significantly expands the possibilities of simultaneous study of acquisition of word form per se and of its semantics. To disengage the various effects a battery of different tests is needed, which could test the processes at different levels of short and long term memory, lexical access, semantic processing, and so on. The cognitive effects achieved during the transient stimulation phase are maintained over a longer period and may therefore be possibly used for modulating word acquisition and processing in practical settings.

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Behavior

Simultaneous EEG Monitoring During Transcranial Direct Current Stimulation

Transcranial  direct current stimulation (tDCS) is a technique that delivers weak electric  currents through the scalp. This constant electric current ...

Transcranial Direct Current Stimulation and Simultaneous  Functional Magnetic Resonance Imaging

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that uses weak electrical currents administered to the scalp ...

Modulating Cognition Using Transcranial Direct Current Stimulation of the Cerebellum

Numerous studies have emerged recently that demonstrate the possibility of modulating, and in some cases enhancing, cognitive processes by exciting brain ...

Concurrent Electroencephalography Recording During Transcranial Alternating Current Stimulation (tACS)

Concurrent Electroencephalography Recording During Transcranial Alternating Current Stimulation tACS

Oscillatory brain activities are considered to reflect the basis of rhythmic changes in transmission efficacy across brain networks and are assumed to ...

Repetitive Transcranial Magnetic Stimulation to the Unilateral Hemisphere of Rat Brain

Previous rodent models of repetitive transcranial magnetic stimulation (rTMS) adopted whole-brain stimulation instead of unilateral hemispheric rTMS, ...

Simultaneous Transcranial Alternating Current Stimulation and Functional Magnetic Resonance Imaging

Transcranial alternating current stimulation (tACS) is a promising tool for noninvasive investigation of brain oscillations. TACS employs ...

Eye Tracking During Visually Situated Language Comprehension: Flexibility and Limitations in Uncovering Visual Context Effects

The present work is a description and an assessment of a methodology designed to quantify different aspects of the interaction between language processing ...

Dissociation of the Confounding Influences of Expectancy and Integrative Difficulty Residing in Anomalous Sentences in Event-related Potential Studies

The confounding factors of unexpectedness and semantic integration difficulty naturally residing in anomalous sentences in language studies make it ...

Brain State-dependent Brain Stimulation with Real-time Electroencephalography-Triggered Transcranial Magnetic Stimulation

The effect of a stimulus to the brain depends not only on the parameters of the stimulus but also on the dynamics of brain activity at the time of the ...

Lexical Decision Task for Studying Written Word Recognition in Adults with and without Dementia or Mild Cognitive Impairment

Older adults are slower at recognizing visual objects than younger adults. The same is true for recognizing that a letter string is a real word. People ...