Stimulation Of Inferior Frontal Gyrus Research Articles

Neural mechanisms underlying improved new-word learning with high-density transcranial direct current stimulation

Neurobehavioral studies have provided evidence for the effectiveness of anodal tDCS on language production, by stimulation of the left Inferior Frontal Gyrus (IFG) or of left Temporo-Parietal Junction (TPJ). However, tDCS is currently not used in clinical practice outside of trials, because behavioral effects have been inconsistent and underlying neural effects unclear. Here, we propose to elucidate the neural correlates of verb and noun learning and to determine if they can be modulated with anodal high-definition (HD) tDCS stimulation. Thirty-six neurotypical participants were randomly allocated to anodal HD-tDCS over either the left IFG, the left TPJ, or sham stimulation. On day one, participants performed a naming task (pre-test). On day two, participants underwent a new-word learning task with rare nouns and verbs concurrently to HD-tDCS for 20 min. The third day consisted of a post-test of naming performance. EEG was recorded at rest and during naming on each day. Verb learning was significantly facilitated by left IFG stimulation. HD-tDCS over the left IFG enhanced functional connectivity between the left IFG and TPJ and this correlated with improved learning. HD-tDCS over the left TPJ enabled stronger local activation of the stimulated area (as indexed by greater alpha and beta-band power decrease) during naming, but this did not translate into better learning. Thus, tDCS can induce local activation or modulation of network interactions. Only the enhancement of network interactions, but not the increase in local activation, leads to robust improvement of word learning. This emphasizes the need to develop new neuromodulation methods influencing network interactions. Our study suggests that this may be achieved through behavioral activation of one area and concomitant activation of another area with HD-tDCS.

Treating lexical retrieval using letter fluency and tDCS in primary progressive aphasia: a single-case study

ABSTRACT Background In early stages, individuals with primary progressive aphasia (PPA) report language symptoms while scoring within norm in formal language tests. Early intervention is important due to the progressive nature of the disease. Method We report a single-case study of an individual with logopenic variant PPA (lvPPA). We tested whether letter fluency, used as a therapy task, can improve lexical retrieval when combined with tDCS to either the left inferior-frontal gyrus (IFG) or the left inferior parietal lobe (IPL), administered in two separate therapy phases separated by a wash-out period of 3 months. Outcomes and results We observed increases in number of words retrieved during a letter fluency task in trained and untrained letters, when letter fluency therapy (LeFT) was administered with anodal tDCS. When LeFT was combined with left IFG stimulation, words produced in a letter fluency task were lower frequency and higher age of acquisition after treatment, compared to before treatment and there was also an increase in accuracy and response times in an untrained picture-naming task. Conclusions The results indicate that letter fluency therapy combined anodal tDCS is effective in improving lexical retrieval, particularly when left IFG stimulation was used. Effects generalize beyond the trained task, albeit slowing down of responses in picture naming. This task may provide a useful clinical intervention strategy for patients with mild anomia, who are not challenged enough by traditional naming therapies.

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.

Participation of the classical speech areas in auditory long-term memory.

Accumulating evidence suggests that storing speech sounds requires transposing rapidly fluctuating sound waves into more easily encoded oromotor sequences. If so, then the classical speech areas in the caudalmost portion of the temporal gyrus (pSTG) and in the inferior frontal gyrus (IFG) may be critical for performing this acoustic-oromotor transposition. We tested this proposal by applying repetitive transcranial magnetic stimulation (rTMS) to each of these left-hemisphere loci, as well as to a nonspeech locus, while participants listened to pseudowords. After 5 minutes these stimuli were re-presented together with new ones in a recognition test. Compared to control-site stimulation, pSTG stimulation produced a highly significant increase in recognition error rate, without affecting reaction time. By contrast, IFG stimulation led only to a weak, non-significant, trend toward recognition memory impairment. Importantly, the impairment after pSTG stimulation was not due to interference with perception, since the same stimulation failed to affect pseudoword discrimination examined with short interstimulus intervals. Our findings suggest that pSTG is essential for transforming speech sounds into stored motor plans for reproducing the sound. Whether or not the IFG also plays a role in speech-sound recognition could not be determined from the present results.

38. The effect of repetitive transcranial magnetic stimulation on attention and psychomotor speed in patients with mild cognitive impairment and early Alzheimer’s disease

Introduction Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive tool to study and modulate cortical plasticity and brain processes in healthy and diseased brain. Study objectives The aim of this study was to investigate the effects of one session of high-frequency rTMS on cognitive functions in patients with mild cognitive impairment (MCI) and early stages of Alzheimer's disease (AD). Based on our pilot study results (Eliasova et al., 2014) we were particularly interested in modulating attention and psychomotor speed domain by applying rTMS over the right inferior frontal gyrus (IFG) and the right superior temporal gyrus (STG). Methods Altogether 20 right-handed patients (11 women, 9 men; age 73.0±6.9years; 12 mild AD, 8 MCI) participated in the placebo-controlled study. Each patient received 3 sessions of 10Hz rTMS applied over the IFG, STG and vertex (a control stimulation site). A frameless stereotaxy was used for the coil navigation. A total of 2250 stimuli were delivered per session at 90% intensity of resting motor threshold. The order of stimulation sites was randomized. The Trail making test (TMT) and the Stroop test (ST) were used to evaluate attention and psychomotor speed prior to and immediately after each session. The Wilcoxon paired test and Linear mixed models were used for data analyses. Results rTMS of both IFG and STG induced significant improvement in the Word part of the ST (Wilcoxon paired test; p =0.023 and 0.033, respectively), while the IFG stimulation induced additional enhancement in the TMT A and B (Wilcoxon paired test; p =0.002 and 0.005, respectively). When controlling for placebo effects improvement in the ST (Word part) remained significant after both IFG and STG stimulation. Conclusions rTMS of the right IFG and the right STG enhanced psychomotor speed and attention in patients with early stages of AD and may thus have a therapeutic potential that has to be further tested using a multiple-sessions rTMS protocol.

Transcranial direct current stimulation, implicit alcohol associations and craving

Previous research has shown that stimulation of the left dorsolateral prefrontal cortex (DLPFC) enhances working memory (e.g. in the n-back task), and reduces craving for cigarettes and alcohol. Stimulation of the right inferior frontal gyrus (IFG) improves response inhibition. The underlying mechanisms are not clearly understood, nor is it known whether IFG stimulation also reduces craving. Here, we compared effects of DLPFC, IFG, and sham stimulation on craving in heavy drinkers in a small sample (n=41). We also tested effects of tDCS on overcoming response biases due to associations between alcohol and valence and alcohol and approach, using implicit association tests (IATs). Mild craving was reduced after DLPFC stimulation. Categorization of valence attribute words in the IAT was faster after DLPFC stimulation. We conclude that DLPFC stimulation can reduce craving in heavy drinkers, but found no evidence for tDCS induced changes in alcohol biases, although low power necessitates caution.

Non-invasive brain stimulation of the right inferior frontal gyrus may improve attention in early Alzheimer's disease: A pilot study

IntroductionRepetitive transcranial magnetic stimulation (rTMS) is a noninvasive tool for modulating cortical activity. ObjectivesIn this pilot study, we evaluated the effects of high frequency rTMS applied over the right inferior frontal gyrus (IFG) on cognitive functions in patients with amnestic mild cognitive impairment (MCI) or incipient dementia due to Alzheimer's disease (AD). MethodsTen patients (6 men; 4 women, mean age of 72±8years; MMSE 23±3.56) were enrolled in a randomized, placebo-controlled study with a crossover design. All participants received 2 sessions of 10Hz rTMS over the non-dominant right hemisphere in random order: IFG (active stimulation site) and vertex (control stimulation site). Intensities were adjusted to 90% of resting motor threshold. A total of 2250 pulses were applied in a session. The Trail Making Test (TMT), the Stroop test, and the complex visual scene encoding task (CVSET) were administered before and immediately after each session. The Wilcoxon paired test was used for data analysis. ResultsStimulation applied over the IFG induced improvement in the TMT parts A (p=0.037) and B (p=0.049). No significant changes were found in the Stroop test or the CVSET after the IFG stimulation. We observed no significant cognitive aftereffects of rTMS applied over the vertex. ConclusionsHigh frequency rTMS of the right IFG induced significant improvement of attention and psychomotor speed in patients with MCI/mild dementia due to AD. This pilot study is part of a more complex protocol and ongoing research.

Transcranial direct current stimulation (tDCS) of the inferior frontal gyrus disrupts interpersonal motor resonance

Interpersonal motor resonance (IMR) is presumed to result from activity within the human mirror neuron system, which itself is thought to comprise the inferior parietal lobule (IPL) and inferior frontal gyrus (IFG). Twenty healthy adults underwent anodal, cathodal, and sham transcranial direct current stimulation (tDCS) to either IPL or IFG immediately before the assessment of IMR (using transcranial magnetic stimulation). IMR (i.e., motor-evoked potential amplitude during transitive action observation relative to static observation) was significantly reduced following both anodal and cathodal stimulation of IFG (relative to sham), but there was no effect of stimulation for IPL. These data support the role of IFG, a presumed mirror neuron region, in IMR.

Evaluating the roles of the inferior frontal gyrus and superior parietal lobule in deductive reasoning: An rTMS study

This study used off-line repetitive transcranial magnetic stimulation (rTMS) to examine the roles of the superior parietal lobule (SPL) and inferior frontal gyrus (IFG) in a deductive reasoning task. Subjects performed a categorical syllogistic reasoning task involving congruent, incongruent, and abstract trials. Twenty four subjects received magnetic stimulation to the SPL region prior to the task. In the other 24 subjects, TMS was administered to the IFG region before the task. Stimulation lasted for 10min, with an inter-pulse frequency of 1Hz. We found that bilateral SPL (Brodmann area (BA) 7) stimulation disrupted performance on abstract and incongruent reasoning. Left IFG (BA 45) stimulation impaired congruent reasoning performance while paradoxically facilitating incongruent reasoning performance. This resulted in the elimination of the belief-bias. In contrast, right IFG stimulation only impaired incongruent reasoning performance, thus enhancing the belief-bias effect. These findings are largely consistent with the dual-process theory of reasoning, which proposes the existence of two different human reasoning systems: a belief-based heuristic system; and a logic-based analytic system. The present findings suggest that the left language-related IFG (BA 45) may correspond to the heuristic system, while bilateral SPL may underlie the analytic system. The right IFG may play a role in blocking the belief-based heuristic system for solving incongruent reasoning trials. This study could offer an insight about functional roles of distributed brain systems in human deductive reasoning by utilizing the rTMS approach.

Contributions to singing ability by the posterior portion of the superior temporal gyrus of the non-language-dominant hemisphere: First evidence from subdural cortical stimulation, Wada testing, and fMRI

IntroductionAlthough the substrates that mediate singing abilities in the human brain are not well understood, invasive brain mapping techniques used for clinical decision making such as intracranial electro-cortical testing and Wada testing offer a rare opportunity to examine music-related function in a select group of subjects, affording exceptional spatial and temporal specificity. MethodsWe studied eight patients with medically refractory epilepsy undergoing indwelling subdural electrode seizure focus localization. All patients underwent Wada testing for language lateralization. Functional assessment of language and music tasks was done by electrode grid cortical stimulation. One patient was also tested non-invasively with functional magnetic resonance imaging (fMRI). Functional organization of singing ability compared to language ability was determined based on four regions-of-interest (ROIs): left and right inferior frontal gyrus (IFG), and left and right posterior superior temporal gyrus (pSTG). ResultsIn some subjects, electrical stimulation of dominant pSTG can interfere with speech and not singing, whereas stimulation of non-dominant pSTG area can interfere with singing and not speech. Stimulation of the dominant IFG tends to interfere with both musical and language expression, while non-dominant IFG stimulation was often observed to cause no interference with either task; and finally, that stimulation of areas adjacent to but not within non-dominant pSTG typically does not affect either ability. Functional fMRI mappings of one subject revealed similar music/language dissociation with respect to activation asymmetry within the ROIs. ConclusionDespite inherent limitations with respect to strictly research objectives, invasive clinical techniques offer a rare opportunity to probe musical and language cognitive processes of the brain in a select group of patients.

Action Understanding Requires the Left Inferior Frontal Cortex

Numerous studies have established that inferior frontal cortex is active when hand actions are planned, imagined, remembered, imitated, and even observed. Furthermore, it has been proposed that these activations reflect a process of simulating the observed action to allow it to be understood and thus fully perceived. However, direct evidence for a perceptual role for left inferior frontal cortex is rare, and linguistic or motor contributions to the reported activations have not been ruled out. We used repetitive transcranial magnetic stimulation (rTMS) over inferior frontal gyrus during a perceptual weight-judgement task to test the hypothesis that this region contributes to action understanding. rTMS at this site impaired judgments of the weight of a box lifted by a person, but not judgements of the weight of a bouncing ball or of stimulus duration, and rTMS at control sites had no impact. This demonstrates that the integrity of left inferior frontal gyrus is necessary to make accurate perceptual judgments about other people's actions.

Role of the Contralateral Inferior Frontal Gyrus in Recovery of Language Function in Poststroke Aphasia

Functional neuroimaging studies have demonstrated right inferior frontal gyrus (IFG) activation in poststroke aphasia. It remains unclear whether this activation is essential for language performance. We tested this hypothesis in a positron emission tomography (PET) activation study during a semantic task with repetitive transcranial magnetic stimulation (rTMS) on right-handed patients experiencing poststroke aphasia and examined whether rTMS stimulation over the right and left IFG would interfere with language performance. Eleven patients with left-sided middle cerebral arterial infarction, 50 to 75 years of age, were tested with the Aachen Aphasia Test Battery and underwent (15)O-H2O PET activation during a semantic task within 2 weeks after stroke. PET activation images were coregistered to T1-weighted MRIs. Stimulation sites were determined on renderings of head and brain over the maximum activation within left and right IFG. rTMS was performed with 20% maximum output (2.1 T), 10-s train duration, at 4 Hz frequency. A positive rTMS effect was defined as an increased reaction time latency or error rate in the semantic task. PET activations of the IFG were observed on the left (3 patients) and bilaterally (8 patients). Right IFG stimulation was positive in 5 patients with right IFG activation, indicating essential language function. In a verbal fluency task, these patients had a lower performance than patients without right-sided TMS effect. In some poststroke aphasics, right IFG activation is essential for residual language function. However, its compensatory potential seems to be less effective than in patients who recover left IFG function. These results suggest a hierarchy in recovery from poststroke aphasia and a (limited) compensatory potential of the nondominant hemisphere.