Brain activation during the course of sentence comprehension

Language and the Cerebellum: Structural Connectivity to the Eloquent Brain

Neurobiological models of receptive language have focused on the left-hemisphere perisylvian cortex with the assumption that the cerebellum supports peri-linguistic cognitive processes such as verbal working memory. The goal of this study was to identify language-sensitive regions of the cerebellum then map the structural connectivity profile of these regions. Functional imaging data and diffusion-weighted imaging data from the Human Connectome Project (HCP) were analyzed. We found that (a) working memory, motor activity, and language comprehension activated partially overlapping but mostly unique subregions of the cerebellum; (b) the linguistic portion of the cerebello-thalamo-cortical circuit was more extensive than the linguistic portion of the cortico-ponto-cerebellar tract; (c) there was a frontal-lobe bias in the connectivity from the cerebellum to the cerebrum; (d) there was some degree of specificity; and (e) for some cerebellar tracts, individual differences in picture identification ability covaried with fractional anisotropy metrics. These findings yield insights into the structural connectivity of the cerebellum as relates to the uniquely human process of language comprehension.

The relationship between language ability and brain activity across language processes and modalities

Existing neuroimaging studies on the relationship between language ability and brain activity have found contradictory evidence: On the one hand, increased activity with higher language ability has been interpreted as deeper or more adaptive language processing. On the other hand, decreased activity with higher language ability has been interpreted as more efficient language processing. In contrast to previous studies, the current study investigated the relationship between language ability and neural activity across different language processes and modalities while keeping non-linguistic cognitive task demands to a minimum. fMRI data were collected from 22 healthy adults performing a sentence listening task, a sentence reading task and a phonological production task. Outside the MRI scanner, language ability was assessed with the verbal scale of the Wechsler Abbreviated Scale of Intelligence (WASI-II) and a verbal fluency task. As expected, sentence comprehension activated the left anterior temporal lobe while phonological processing activated the left inferior frontal gyrus. Higher language ability was associated with increased activity in the left temporal lobe during auditory sentence processing and with increased activity in the left frontal lobe during phonological processing, reflected in both, higher intensity and greater extent of activations. Evidence for decreased activity with higher language ability was less consistent and restricted to verbal fluency. Together, the results predominantly support the hypothesis of deeper language processing in individuals with higher language ability. The consistency of results across language processes, modalities, and brain regions suggests a general positive link between language abilities and brain activity within the core language network. However, a negative relationship seems to exist for non-linguistic cognitive functions located outside the language network.

Words in Context: The Effects of Length, Frequency, and Predictability on Brain Responses During Natural Reading

Word length, frequency, and predictability count among the most influential variables during reading. Their effects are well-documented in eye movement studies, but pertinent evidence from neuroimaging primarily stem from single-word presentations. We investigated the effects of these variables during reading of whole sentences with simultaneous eye-tracking and functional magnetic resonance imaging (fixation-related fMRI). Increasing word length was associated with increasing activation in occipital areas linked to visual analysis. Additionally, length elicited a U-shaped modulation (i.e., least activation for medium-length words) within a brain stem region presumably linked to eye movement control. These effects, however, were diminished when accounting for multiple fixation cases. Increasing frequency was associated with decreasing activation within left inferior frontal, superior parietal, and occipito-temporal regions. The function of the latter region—hosting the putative visual word form area—was originally considered as limited to sublexical processing. An exploratory analysis revealed that increasing predictability was associated with decreasing activation within middle temporal and inferior frontal regions previously implicated in memory access and unification. The findings are discussed with regard to their correspondence with findings from single-word presentations and with regard to neurocognitive models of visual word recognition, semantic processing, and eye movement control during reading.

Neural differences in processing of case particles in Japanese: an fMRI study

INTRODUCTION

In subject-object-verb (SOV) languages, such as Japanese, sentence processing proceeds incrementally to the late presentation of the head (verb). Japanese case particles play a crucial role in sentence processing; however, little is known about how these particles are processed. In particular, it is still unclear how the functional difference between case particles is represented in the human brain.

METHODS

In this study, we conducted an fMRI experiment using an event-related design to directly compare brain activity during Japanese case particle processing among the nominative case ga, accusative case o, and dative case ni. Twenty five native Japanese speakers were asked to judge whether the presented character was a particle in a particle judgment task and whether the character ended with a specific vowel in a phonological judgment task, which was used as a control condition.

RESULTS

A particle comparison demonstrated that the processing of ni was associated with significantly weaker brain activity than that of ga and o in the left middle frontal gyrus (MFG) and the inferior frontal gyrus (IFG). Significantly greater brain activity associated with ni relative to ga in the right IFG was also observed.

CONCLUSION

These results suggest that the Japanese case particles ga, ni, and o are represented differently in the brain.

The neural substrates associated with attentional resources and difficulty of concurrent processing of the two verbal tasks

The kana pick-out test has been widely used in Japan to evaluate the ability to divide attention in both adult and pediatric patients. However, the neural substrates underlying the ability to divide attention using the kana pick-out test, which requires participants to pick out individual letters (vowels) in a story while also reading for comprehension, thus requiring simultaneous allocation of attention to both activities, are still unclear. Moreover, outside of the clinical area, neuroimaging studies focused on the mechanisms of divided attention during complex story comprehension are rare. Thus, the purpose of the present study, to clarify the neural substrates of kana pick-out test, improves our current understanding of the basic neural mechanisms of dual task performance in verbal memory function. We compared patterns of activation in the brain obtained during performance of the individual tasks of vowel identification and story comprehension, to levels of activation when participants performed the two tasks simultaneously during the kana pick-out test. We found that activations of the left dorsal inferior frontal gyrus and superior parietal lobule increase in functional connectivity to a greater extent during the dual task condition compared to the two single task conditions. In contrast, activations of the left fusiform gyrus and middle temporal gyrus, which are significantly involved in picking out letters and complex sentences during story comprehension, respectively, were reduced in the dual task condition compared to during the two single task conditions. These results suggest that increased activations of the dorsal inferior frontal gyrus and superior parietal lobule during dual task performance may be associated with the capacity for attentional resources, and reduced activations of the left fusiform gyrus and middle temporal gyrus may reflect the difficulty of concurrent processing of the two tasks. In addition, the increase in synchronization between the left dorsal inferior frontal gyrus and superior parietal lobule in the dual task condition may induce effective communication between these brain regions and contribute to more attentional processing than in the single task condition, due to greater and more complex demands on voluntary attentional resources.

Near-infrared spectroscopic study and the Wada test for presurgical evaluation of expressive and receptive language functions in glioma patients: with a case report of dissociated language functions

Near-infrared spectroscopy (NIRS) has proven to be useful for the evaluation of language lateralization in healthy subjects, infants, and epileptic patients. This study for the first time investigated the expressive and receptive language functions separately, using NIRS in presurgical glioma patients. We also describe a special case with dissociated pattern of language functions. Ten glioma patients were examined. Using NIRS, the hemodynamic changes during a verb generation task or story listening task were measured in the cerebral hemisphere on either side covering the language areas. Following the NIRS study, the Wada test was performed in all the patients. The NIRS study revealed increases of oxyhemoglobin and decreases of deoxyhemoglobin in the language areas elicited by both tasks. In 9 patients, who were all right-handed, the expressive and receptive language functions were lateralized to the left hemisphere. The results of the NIRS study were completely consistent with those of the Wada test. In the remaining 1 patient with a right sided insular glioma, who was right-handed, the NIRS study revealed stronger activation of the right inferior frontal region during the verb generation task, and stronger activation of the left superior temporal region during the story listening task. This dissociated language function was validated by the Wada test and the postoperative neurological course. These results demonstrate that a NIRS study using our technique is extremely valuable for preoperative assessment of the language functions and exemplifies how a preoperative NIRS study can allow detection of unforeseen language lateralization.

Spatiotemporal Analysis of Brain Activity During Understanding Honorific Expressions

This paper discusses brain activity during the understanding of sentences from the perspective of Systemic Functional Linguistics. We focus on ideational meaning (propositional meaning in an ordinary sense) and interpersonal meaning (as is typically seen in honorific expressions). The present study is an experimental exploration of the spatiotemporal pathways of neuronal activation. Japanese sentences containing and not containing honorific expressions are compared in electroencephalography experiments. In these experiments, the sentences without honorific expressions have ideationalmeaning, but those with honorific expressions have both ideational and interpersonal meanings. Through the use of the equivalent current dipole source localization method, the spatiotemporal processes of activation of the brain are analyzed. There is a single pathway during the understanding of the sentences without honorific expressions; this pathway is mainly observed in the left hemisphere. On the other hand, there are three pathways in the case of the sentences with honorific expressions, two of which are observed in the right hemisphere. The remaining pathway is the same as the aforementioned single pathway. This fact strongly suggests that the common pathway is concerned with processing ideational meaning. The other two pathways observed during understanding of the sentences with honorific expressions are considered to be related to processing interpersonal meaning.

Characteristics of event-related potentials in recognition processes of Japanese kanji and sentences for Chinese bilinguals

This paper investigates the recognition process of Japanese kanji and sentences for Chinese bilinguals and Native Japanese speakers (NJS), by analyzing the event-related potential (ERP) differences between the two groups while they visually recognized Japanese kanji and sentences. The results showed that no significant differences were found between the two groups while they recognized Japanese kanji, but significant differences were found in the Japanese sentences condition. The results demonstrated that the neural mechanisms of recognition processes of Japanese sentences including kana between the two groups were not identical. When recognizing ambiguous sentences, Chinese bilinguals' P600 only appeared over the right frontal lobe, reflecting that syntactic integration and revision of ambiguous sentences for Chinese bilinguals was related with the right hemisphere. The results showed, for Chinese bilinguals, the difficulty of Japanese language learning was the recognition and understanding of Japanese sentences with kana, not Japanese kanji. We would like to provide a scientific learning method for Chinese bilinguals to enhance their Japanese language learning efficiency from the aspect of brain science.

A comparison of brain activity evoked by single content and function words: an fMRI investigation of implicit word processing

Content and function words have different roles in language and differ greatly in their semantic content. Although previous research has suggested that these different roles may be mediated by different neural substrates, the neuroimaging literature on this topic is particularly scant. Moreover, fMRI studies that have investigated differences between content and function words have utilized tasks that focus the subjects' attention on the differences between these word types. It is possible, then, that task-related differences in attention, working memory, and decision-making contribute to the differential patterns of activation observed. Here, subjects were engaged in a continuous working memory cover task while single, task-irrelevant content and function words were infrequently and irregularly presented. Nonword letter strings were displayed in black font at a fast rate (2/s). Subjects were required to either remember or retrieve occasional nonwords that were presented in colored fonts. Incidental and irrelevant to the memory task, content and function words were interspersed among nonwords at intervals of 12 to 15 s. Both word types strongly activated temporal-parietal cortex, middle and anterior temporal cortex, inferior frontal gyrus, parahippocampal gyrus, and orbital frontal cortex. Activations were more extensive in the left hemisphere. Content words elicited greater activation than function words in middle and anterior temporal cortex, a sub-region of orbital frontal cortex, and the parahippocampal region. Words also evoked extensive deactivation, most notably in brain regions previously associated with working memory and attention.

Neural basis of sentence processing in which incoming words form a sentence

This study examined the neural basis underlying the sequential involvement of sentence processing and determined the point at which the processing cost for an object-initial sentence was observed. We presented each phrase in a Japanese object-initial sentence to Japanese participants one by one using an event-related functional MRI technique and compared with our previous subject-initial experiment. We found that the left lingual gyrus was activated upon presentation of the first noun phrases, and the left inferior frontal gyrus upon presentation of the second noun phrases. The processing cost for an object-initial sentence was observed during verb recognition. Our results suggest that the syntactic complexity of an object-initial sentence is processed by the human brain upon verb recognition.

Neural mechanisms underlying the processing of Chinese and English words in a word generation task: an event-related potential study

Event-related brain potentials (ERPs) were used to examine the spatiotemporal cortical activation patterns underlying Chinese and English word generation (forming a new word by adding a stroke or a letter to an old Chinese or English word) for low- and high-proficiency Chinese-English bilinguals. The results revealed that early visual perceptual processing and word identification were similar between the two languages for the N120 and P220 waveforms. However, a greater negative potential (N250-350) was associated with Chinese words than with English words between 250 and 350 ms. Subsequently, for fluent Chinese bilinguals, Chinese words elicited a more positive ERP deflection (LPC) than did English words between 350 and 800 ms. The differences in ERP components between Chinese and English words indicates that there might be a real difference in the processing demands between these languages, and that the processing of English might be affected by the proficiency of the second language.

Neural basis of syntactic processing of simple sentences in Japanese

This study used event-related functional magnetic resonance imaging to investigate the neural basis underlying the sequential involvement of syntactic processing in the course of sentence comprehension. In experiments, a noun, case particle, and verb were presented one by one, constituting simple sentences in Japanese. Participants judged whether the sentence was syntactically correct (syntactic judgment) or whether the particle and verb had the same vowel (phonological judgment). During particle presentation, greater activation in the left inferior frontal gyrus was observed during syntactic judgment than during phonological judgment. Presentation of verbs subsequently activated the left dorsal prefrontal cortex and medial superior frontal areas in the same comparison. Our findings indicate that these regions are sequentially recruited in the syntactic processing of simple sentences in Japanese.

Role of left inferior frontal gyrus in the processing of particles in Japanese

Particles are a crucial component of sentences in Japanese. They mainly follow nouns, and indicate their thematic role in the sentence, such as agent or patient. This study used functional MRI to investigate the neural basis of the processing of particles. We compared brain activity when participants were required to judge whether a presented character was a particle or whether the character as spoken ended with a specific vowel sound. Differential brain activity during particle judgment was found only in the left inferior frontal gyrus. We further confirmed that this activity was not a feature of categorical judgments in general. Our results indicate that the left inferior frontal gyrus is involved in the processing of thematic role indicated by Japanese particles.