Neurobiology of Language最新文献

Recovery of language function in post-stroke aphasia is affected by many variables, including aphasia severity, age, lesion site and size, and brain health. Semantic and phonological therapies are often used to target naming abilities, and when successful their benefits can extend to discourse production, which has emerged as a promising task to evaluate language processing and recovery in aphasia. Here, after characterizing the lesion and white matter integrity predictors for discourse production before treatment, we asked whether brain integrity at baseline is predictive of treatment generalization to discourse. In a large sample of participants with chronic aphasia (N = 88), we ran region-based lesion-symptom mapping on discourse measures (including fluency, sentence processing abilities, and error types) at baseline, on discourse changes following phonological and semantic treatment separately, and at 1 month and 6 months post-treatment. Discourse productivity at baseline was associated with the integrity of regions and white matter tracts in the dorsal stream. Lesions in the hippocampal system and cortical temporal regions were associated with less improvement in discourse following both phonological and semantic treatment. Long-term improvement was instead predicted by the integrity of the fornix and temporal cortical regions, suggesting that while the hippocampal system is important for learning, learned functions rely on connectivity with cortical areas. The results suggest that the generalization of word-level treatment to discourse production is facilitated by an intact hippocampal system in the medial temporal lobe.

The ability to read relies on the rapid mapping of perceived visual letters and their combinations (i.e., visual word forms) to phonology and meaning. The central role of the left ventral occipito-temporal cortex (VOTC) in processing letter strings, initially suggested by lesion studies, is now widely accepted. Although this brain region has been extensively studied with functional magnetic resonance imaging (fMRI), its causal role as a critical node of a cortical network for reading remains unclear. Here we report a comprehensive case of pure alexia during direct electrical stimulation (DES) of the left VOTC (patient SV, female, 38 yr old, implanted with intracerebral electrodes for refractory epilepsy). During DES of the left posterior occipito-temporal sulcus, but not of neighboring and remote cortical sites, SV was transiently impaired at reading single words while being able to slowly read letter-by-letter. However, SV was impaired when presenting a single letter in a rapid serial visual presentation, which showed that their letter reading is not entirely preserved. In contrast, DES to the same critical sites left performance for oral naming, auditory naming, reading numbers, writing, auditory lexical decision, and semantic matching of pictures unaffected. Intracerebral electrophysiological frequency-tagging investigations showed highly word-selective neural responses at the critical sites. These functional responses were abolished by concurrent DES, which also affected remote word-selective neural activity in the left VOTC. Altogether, these observations provide original evidence for word-selective representations of the left VOTC as a critical node of the cortical reading network.

Upon reading a word, we decompose it into meaningful parts-morphemes. Even if novel, we can derive a likely meaning for it based on how its parts typically behave. Given the typical meaning of affix "-ery," we may guess that a bottlery is a place to make bottles, although we may alternatively guess that it is the craft of bottle making. In this study, we operationalize this feature-an affix's semantic typicality-to investigate affix semantics' role in word processing. Using a lexical decision task and a double dissociative design in an MEG setting, we took advantage of Arabic's highly productive word-pattern derivational system to investigate the role of meaning typicality for derivational morphology. We contrasted one affix typically denoting tools and atypically places with another affix having the reverse denotation pattern. We found higher activity for typical-meaning words in the temporal pole, inferior temporal gyrus, and middle temporal gyrus at an earlier time window than previously associated with semantic processing. Additionally, we replicated results on noun/verb ambiguity, where ambiguous words had higher activity in the fusiform gyrus and throughout the temporal lobe. Our results on lexicality-contrasting words versus nonwords-were also consistent with previous literature. A finer-grained distinction between pseudowords with real roots versus pseudoroots further allowed us to explore the role of affixes in processing in the temporal pole and the inferior frontal cortex. Overall, our study contributes importantly to findings on affix semantic processing and contributes generally to growing findings on different stages of morphological decomposition.

The choice of control conditions can significantly influence the outcomes of functional MRI (fMRI) studies. Moreover, especially in language experiments, the sensory modality (auditory, visual) of stimuli might have an influence on experimental results. In this study we leverage a repository dataset (Mother of Unification Studies; MOUS), to systematically investigate the influence of control condition and stimulation modality on fMRI results during sentence processing. Here, we explored fMRI data of 187 subjects that underwent sentence comprehension with either auditory or visual task presentation (reading or listening). Sentences were either complex, including a relative clause, or simple, not including a relative clause. Control conditions were randomly scrambled words as constructed out of the latter sentence conditions. While auditory stimulation resulted in strong activation changes in the bilateral auditory cortices, visual stimulation revealed stronger activation changes in the anterior temporal lobe if compared to simple and complex words, but not simple sentences. A direct comparison between the auditory and visual modality revealed stronger involvement of the primary auditory cortices for auditory stimulation and left inferior frontal gyrus for visual stimulation over all four conditions (complex sentences, simple sentences, complex words, simple words). The results of this study suggest that stimulation modality and control condition strongly influence sentence processing fMRI results. Future fMRI studies should bear this in mind for study planning.

Dysarthria is a motor speech disorder that is a common symptom of cerebellar dysfunction in people with multiple sclerosis (pwMS). Despite its prevalence, little is known regarding changes in brain functioning associated with dysarthria in this cohort. Management strategies for cerebellar symptoms such as dysarthria are also limited. Fifty-five pwMS and 14 healthy controls participated in this study. We used fMRI to assess changes in speech related functional activation associated with MS, and split our MS cohort into people with and without dysarthria, and with and without cerebellar dysfunction clinically evident as upper limb action tremor. We found that pwMS performed worse on speech production tasks and had overall lower functional activation while preparing for speech than controls. Furthermore, pwMS require additional recruitment of the left Brodmann areas 45 and 46, key motor speech regions, during speech production compared to healthy controls. MS participants presenting with both dysarthria and action tremor performed worst on speech production tasks. These participants had lower functional activation during speech production compared to other MS participants. People with multiple sclerosis display altered functional activation of motor speech areas during speech production, either due to MS injury or reduced activity during preparation. Compensatory activation is reduced in those with both clinical dysarthria and action tremor compared to MS controls and those with tremor only, likely due to more advanced MS.

Transcranial alternating current stimulation (tACS) is a noninvasive neuromodulatory tool that is thought to entrain intrinsic neural oscillations by supplying low electric currents over the scalp. Recent work has demonstrated the efficacy of theta-gamma phase-amplitude coupled tACS over primary motor cortex to enhance motor skill acquisition and motor recovery after stroke. Here, we wished to assess the efficacy of tACS delivered with 75-Hz gamma coupled to the peak of a 6-Hz theta envelope (theta-gamma peak; TGP) at an intensity of 2 mA peak-to-peak to enhance sensorimotor learning during speech production. Sensorimotor learning was measured by shifting the formant frequency of vowels in real-time as speech is produced and measuring the adaptation to this altered feedback. The study was a between-subjects, single-blind, sham-controlled design. We hypothesised that participants who performed the speech task while receiving TGP tACS over the speech motor cortex (N = 30) would show greater adaptation to altered auditory feedback than those receiving sham stimulation (N = 31). Contrary to this hypothesis, there was no effect of TGP tACS on adaptation to the upwards F1 shift in auditory feedback in either the final 30 trials of the learning phase or in the first 15 trials of the after-effect phase. However, a trend emerged in the TGP tACS group for greater retention of the adapted state and slower return to baseline F1 values in the after-effect phase. This finding was not predicted, and highlights the need for further investigation to deepen our understanding of the effects of TGP tACS on speech motor learning.

We investigated whether the difference between chronological and modeled brain age explains individual differences in language performance among healthy older adults. Age-related decline in language abilities is widely documented, with considerable variability among healthy older individuals in both language performance and underlying neural substrate. We derived predicted brain age from grey and white matter using machine learning and used this measure to estimate neurological deviations from chronological age. Using Bayesian mixed-effects modeling, we tested whether brain-age deviations predict language performance in a sample of 86 adults aged 60 years and above. We assessed the effect of brain-age deviations on performance across four well-established language processing tasks, each tapping into linguistic domains known to be vulnerable to ageing and show individual variability in skill levels, in both comprehension and production. Our findings suggest that, in healthy older individuals, predicted deviations of brain age from chronological age do not predict language abilities. This challenges the idea that brain age is a reliable determinant of language processing variability, at least in healthy (as opposed to pathological) ageing and highlights the need to consider other neural and cognitive factors when studying language decline.

Letter processing plays a key role in visual word recognition. However, word recognition models typically overlook or greatly simplify early perceptual processes of letter recognition. We suggest that optimal transport theory may provide a computational framework for describing letter shape processing. We use representational similarity analysis to show that optimal transport cost (Wasserstein distance) between pairs of letters aligns with neural activity elicited by visually presented letters <225 ms after stimulus onset, outperforming an existing approach based on shape overlap. We additionally show that optimal transport can capture the emergence of geometric invariances (e.g., to position or size) observed in letter perception. Finally, we demonstrate that Wasserstein distance predicts neural activity similarly well to features from artificial networks trained to classify images and letters. However, whereas representations in artificial neural networks emerge in a computationally unconstrained manner, our proposal provides a computationally explicit route to modeling the earliest orthographic processes.

Researchers propose that the recovery of language function following stroke depends on the recruitment of perilesional regions in the left hemisphere and/or homologous regions in the right hemisphere. Many investigations of recovery focus on changes in gray matter regions, whereas relatively few examine white matter tracts and none address the role of these tracts in the recovery of verbal working memory. The present study addressed these gaps, examining the role of left versus right hemisphere tracts in the longitudinal recovery of phonological and semantic working memory. For 24 individuals with left hemisphere stroke, we assessed working memory performance within 1 week of stroke (acute time point) and at more than 6 months after stroke (chronic time point). To address whether recovery depends on the recruitment of left or right hemisphere tracts, we assessed whether changes in working memory were related to the integrity of five white matter tracts in the left hemisphere which had been implicated previously in verbal working memory and their right hemisphere analogues. Behavioral results showed significant improvement in semantic but not phonological working memory from the acute to chronic time points. Improvements in semantic working memory significantly correlated with tract integrity as measured by functional anisotropy in the left direct segment of the arcuate fasciculus, inferior fronto-occipital fasciculus and inferior longitudinal fasciculus. The results confirm the role of white matter tracts in language recovery and support the involvement of the left rather than right hemisphere in the recovery of semantic working memory.

Developmental dyslexia is a common learning disability marked by reading and spelling difficulties. While previous imaging studies aiming to elucidate the neurobiological mechanisms of this disorder have reported white matter alterations, they are inconsistent with regards to which specific tracts are implicated and in what way. These inconsistencies might partially stem from methodological limitations such as small sample sizes and the use of outdated diffusion models. To address these issues, we used fixel-based analyses, an advanced diffusion framework, to compare structural white matter organization between 35 adults with dyslexia and 34 controls across three levels of analysis (whole-brain, tract-specific, and tract-averaged). Contrary to expectations, none of the analyses yielded significant group differences. However, within the dyslexic group only, poorer word reading proficiency was linked to greater fiber density and cross-section of the bilateral inferior longitudinal fasciculus. Taken together with the existing literature, our results suggest that white matter structure might not be altered in (adulthood) dyslexia or might be idiosyncratically impacted to such an extent that group-average studies are unable to detect these changes. Future large-scale research and efforts to pool datasets across studies will prove essential for understanding the white matter correlates of dyslexia.