Left Posterior Temporal Cortex Research Articles

Alterations in electroencephalographic functional connectivity in individuals with major depressive disorder: a resting-state electroencephalogram study.

Major depressive disorder (MDD) is the leading cause of disability among all mental illnesses with increasing prevalence. The diagnosis of MDD is susceptible to interference by several factors, which has led to a trend of exploring objective biomarkers. Electroencephalography (EEG) is a non-invasive procedure that is being gradually applied to detect and diagnose MDD through some features such as functional connectivity (FC). In this research, we analyzed the resting-state EEG of patients with MDD and healthy controls (HCs) in both eyes-open (EO) and eyes-closed (EC) conditions. The phase locking value (PLV) method was utilized to explore the connection and synchronization of neuronal activities spatiotemporally between different brain regions. We compared the PLV between participants with MDD and HCs in five frequency bands (theta, 4-8 Hz; alpha, 8-12 Hz; beta1, 12-16 Hz; beta2, 16-24 Hz; and beta3, 24-40 Hz) and further analyzed the correlation between the PLV of connections with significant differences and the severity of depression (via the scores of 17-item Hamilton Depression Rating Scale, HDRS-17). During the EO period, lower PLVs were found in the right temporal-left midline occipital cortex (RT-LMOC; theta, alpha, beta1, and beta2) and posterior parietal-right temporal cortex (PP-RT; beta1 and beta2) in the MDD group compared with the HC group, while PLVs were higher in the MDD group in LT-LMOC (beta2). During the EC period, for the MDD group, lower theta and beta (beta1, beta2, and beta3) PLVs were found in PP-RT, as well as lower theta, alpha, and beta (beta1, beta2, and beta3) PLVs in RT-LMOC. Additionally, in the left midline frontal cortex-right temporal cortex (LMFC-RT) and posterior parietal cortex-right temporal cortex (PP-RMOC), higher PLVs were observed in beta2. There were no significant correlations between PLVs and HDRS-17 scores when connections with significantly different PLVs (all p > 0.05) were checked. Our study confirmed the presence of differences in FC between patients with MDD and healthy individuals. Lower PLVs in the connection of the right temporal-left occipital cortex were mostly observed, whereas an increase in PLVs was observed in patients with MDD in the connections of the left temporal with occipital lobe (EO), the circuits of the frontal-temporal lobe, and the parietal-occipital lobe. The trends in FC involved in this study were not correlated with the level of depression. The study was limited due to the lack of further analysis of confounding factors and follow-up data. Future studies with large-sampled and long-term designs are needed to further explore the distinguishable features of EEG FC in individuals with MDD.

Disentangling the neural correlates of semantic and domain-general control: The roles of stimulus domain and task process

Abstract Control processes are critical for the context-appropriate use of meaningful stimuli. Similar definitions have been adopted in two distinct literatures focusing on identifying the neural correlates of “semantic control” and of executive control across domains (the “multiple demand network”). Surprisingly, despite their proposed functions varying only in relation to domain-specificity, these networks appear to differ anatomically. However, prior comparisons are confounded by variations in task design. To what extent might varying task requirements drive differences in activation patterns that are typically attributed to stimulus domain? Here, for the first time, we use functional MRI to disentangle the effects of task process and stimulus domain during cognitively demanding tasks. Participants performed an odd-one-out task requiring rule-switching, inhibition and selection processes, and an n-back working memory task, each with meaningful semantic and non-semantic stimuli, in a factorial design. Both stimulus domain and task process affected the control regions activated, indicating that task process is indeed a key factor confounding prior studies. However, core semantic control regions (left inferior frontal gyrus, left posterior temporal cortex) also showed a preference for semantic stimuli even with matched task processes, while more peripheral semantic control regions, overlapping the multiple demand network (dorsomedial prefrontal cortex, right inferior frontal gyrus), showed little preference across task or stimulus. Conversely, most multiple demand network regions were preferentially engaged for non-semantic stimuli. These results highlight the mutual importance of stimulus domain and task process in driving variation in control region engagement, both across and between semantic control and multiple demand networks.

Semantic-specific and domain-general mechanisms for integration and update of contextual information.

Recent research has highlighted the importance of domain-general processes and brain regions for language and semantic cognition. Yet, this has been mainly observed in executively demanding tasks, leaving open the question of the contribution of domain-general processes to natural language and semantic cognition. Using fMRI, we investigated whether neural processes reflecting context integration and context update-two key aspects of naturalistic language and semantic processing-are domain-specific versus domain-general. Thus, we compared neural responses during the integration of contextual information across semantic and non-semantic tasks. Whole-brain results revealed both shared (left posterior-dorsal inferior frontal gyrus, left posterior inferior temporal gyrus, and left dorsal angular gyrus/intraparietal sulcus) and distinct (left anterior-ventral inferior frontal gyrus, left anterior ventral angular gyrus, left posterior middle temporal gyrus for semantic control only) regions involved in context integration and update. Furthermore, data-driven functional connectivity analysis clustered domain-specific versus domain-general brain regions into distinct but interacting functional neural networks. These results provide a first characterisation of the neural processes required for context-dependent integration during language processing along the domain-specificity dimension, and at the same time, they bring new insights into the role of left posterior lateral temporal cortex and left angular gyrus for semantic cognition.

Posterior superior temporal cortex connectivity is related to social communication in toddlers

The second year of life is a time when social communication skills typically develop, but this growth may be slower in toddlers with language delay. In the current study, we examined how brain functional connectivity is related to social communication abilities in a sample of 12-24 month-old toddlers including those with typical development (TD) and those with language delays (LD). We used an a-priori, seed-based approach to identify regions forming a functional network with the left posterior superior temporal cortex (LpSTC), a region associated with language and social communication in older children and adults. Social communication and language abilities were assessed using the Communication and Symbolic Behavior Scales (CSBS) and Mullen Scales of Early Learning. We found a significant association between concurrent CSBS scores and functional connectivity between the LpSTC and the right posterior superior temporal cortex (RpSTC), with greater connectivity between these regions associated with better social communication abilities. However, functional connectivity was not related to rate of change or language outcomes at 36 months of age. These data suggest an early marker of low communication abilities may be decreased connectivity between the left and right pSTC. Future longitudinal studies should test whether this neurobiological feature is predictive of later social or communication impairments.

Gravity matters for the neural representations of action semantics.

The dynamic relationship between the neural representation of action word semantics and specific sensorimotor experience remains controversial. Here, we temporarily altered human subjects' sensorimotor experience in a 15-day head-down tilt bed rest setting, a ground-based analog of microgravity that disproportionally affects sensorimotor experiences of the lower limbs, and examined whether such effector-dependent activity deprivation specifically affected the neural processes of comprehending verbs of lower-limb actions (e.g. to kick) relative to upper-limb ones (e.g. to pinch). Using functional magnetic resonance imaging, we compared the multivoxel neural patterns for such action words prior to and after bed rest. We found an effector-specific (lower vs. upper limb) experience modulation in subcortical sensorimotor-related and anterior temporal regions. The neural action semantic representations in other effector-specific verb semantic regions (e.g. left lateral posterior temporal cortex) and motor execution regions were robust against such experience alterations. These effector-specific, sensorimotor-experience-sensitive and experience-independent patterns of verb neural representation highlight the multidimensional and dynamic nature of semantic neural representation, and the broad influence of microgravity (hence gravity) environment on cognition.

The left inferior frontal gyrus and the resolution of unimodal vs. cross-modal interference in speech production: A transcranial direct current stimulation study

Most neurobiological models of spoken word production propose that multiple lexical candidates are activated in left posterior temporal cortex during word retrieval. Some accounts also propose a role for the left inferior frontal gyrus (LIFG) in selecting the correct word from among these candidates. Evidence for both proposals has come from the picture-word interference (PWI) paradigm, in which participants name pictures (e.g., RABBIT) while ignoring a distractor word. Categorically related distractors (e.g., horse -RABBIT) slow naming latencies compared to unrelated words (e.g., violin -RABBIT), an effect known as semantic interference, whereas congruent distractors (e.g., rabbit -RABBIT) facilitate naming, but the precise conditions in which these effects occur remain a matter of debate. Although the neuroimaging evidence for left temporal cortex engagement in this paradigm is robust, the evidence for LIFG involvement is more equivocal, particularly for semantic interference. A key factor distinguishing LIFG involvement in neuroimaging studies is distractor modality , i.e., activity is more consistently reported for auditory distractors. We therefore applied online anodal transcranial Direct Current Stimulation (atDCS) to LIFG and left posterior temporal cortex in a three-way, cross-over, sham-controlled PWI paradigm involving either written (Experiment 1) or auditory (Experiment 2) distractors. Surprisingly, compared to sham, atDCS over posterior temporal cortex significantly slowed the congruent facilitation effect with written distractors, but did not modulate the semantic interference effect, while atDCS to LIFG did not significantly influence either effect. We also failed to observe any significant modulatory effects of atDCS with auditory distractors. The present results only partially support left temporal lobe engagement during PWI and provide no evidence for LIFG involvement. We recommend future PWI studies systematically investigate different electrode montages in tDCS protocols. • Stimulation to left posterior middle temporal gyrus modulated picture naming with written congruent distractor words. • Stimulation to left posterior middle temporal gyrus did not modulate picture naming with auditory distractors. • Stimulation to left inferior frontal gyrus did not modulate picture naming with written or auditory distractors.

Damage to temporoparietal cortex is sufficient for impaired semantic control.

Semantic control allows us to focus semantic activation on currently relevant aspects of knowledge, even in the face of competition or when the required information is weakly encoded. Diverse cortical regions, including left prefrontal and posterior temporal cortex, are implicated in semantic control, however; the relative contribution of these regions is unclear. For the first time, we compared semantic aphasia (SA) patients with damage restricted to temporoparietal cortex (TPC; N=8) to patients with infarcts encompassing prefrontal cortex (PF+; N=22), to determine if prefrontal lesions are necessary for semantic control deficits. These SA groups were also compared with semantic dementia (SD; N=10), characterised by degraded semantic representations. We asked whether TPC cases with semantic impairment show controlled retrieval deficits equivalent to PF+cases or conceptual degradation similar to patients with SD. Independent of lesion location, the SA subgroups showed similarities, whereas SD patients showed a qualitatively distinct semantic impairment. Relative to SD, both TPC and PF+SA subgroups: (1) showed few correlations in performance across tasks with differing control demands, but a strong relationship between tasks of similar difficulty; (2) exhibited attenuated effects of lexical frequency and concept familiarity, (3) showed evidence of poor semantic regulation in their verbal output - performance on picture naming was substantially improved when provided with a phonological cue, and (4) showed effects of control demands, such as retrieval difficulty, which were equivalent in severity across TPC and PF+groups. These findings show that semantic impairment in SA is underpinned by damage to a distributed semantic control network, instantiated across anterior and posterior cortical areas.

영어 통사적 이동의 신경상관물:기능적 자기공명영상 연구

This paper investigated the neural processes of sentence comprehension, focusing on a particular syntactic operation of syntactic movement and utilizing a functional magnetic resonance imaging(fMRI). English constructions (i.e., wh-questions known to undergo syntactic movement) were presented to English native speakers in a visual comprehension task and compared with carefully matched control sentences. We found that wh-questions as compared to yes/no questions induced activation in the left inferior frontal gyrus(or Broca’s area), precentral gyrus, and posterior superior temporal cortex, consistent with a previous study utilizing a Hebrew auditory comprehension task. This finding suggests that the processing of syntactic movement includes a consistent set of brain regions, irrespective of task or language.

Neuromodulation of verb-transitivity judgments

This study aimed to further clarify the roles of the temporal and frontal lobes of the brain in the processing of verb argument structure. Left inferior frontal brain areas have long been considered important for sentence processing, but recent research links left posterior temporal cortex to knowledge of verb argument structure. We applied cathodal High-Definition transcranial Direct Current Stimulation to 45 participants in a between-subjects design, with 15 participants each for inferior-frontal-cortex stimulation, posterior-temporal-cortex stimulation, and sham stimulation. Set up as a training task during stimulation, participants made overt judgments on the number of participant roles associated with individual verbs. Stimulation of posterior temporal cortex did not yield results that were different from sham stimulation, speeding up task responses overall. By contrast, stimulation of inferior frontal cortex yielded differential results for intransitive versus transitive verbs, speeding up responses to intransitive verbs and increasing accuracy to transitive verbs, relative to other conditions. The transitivity effect, specific to inferior frontal stimulation, suggests a role for inferior frontal cortex in access to verb-argument-structure information, possibly specific to situations of high cognitive load and in which participant roles have to be established for production, as opposed to comprehension.

Mapping lesion, structural disconnection, and functional disconnection to symptoms in semantic aphasia

Patients with semantic aphasia have impaired control of semantic retrieval, often accompanied by executive dysfunction following left hemisphere stroke. Many but not all of these patients have damage to the left inferior frontal gyrus, important for semantic and cognitive control. Yet semantic and cognitive control networks are highly distributed, including posterior as well as anterior components. Accordingly, semantic aphasia might not only reflect local damage but also white matter structural and functional disconnection. Here, we characterise the lesions and predicted patterns of structural and functional disconnection in individuals with semantic aphasia and relate these effects to semantic and executive impairment. Impaired semantic cognition was associated with infarction in distributed left-hemisphere regions, including in the left anterior inferior frontal and posterior temporal cortex. Lesions were associated with executive dysfunction within a set of adjacent but distinct left frontoparietal clusters. Performance on executive tasks was also associated with interhemispheric structural disconnection across the corpus callosum. In contrast, poor semantic cognition was associated with small left-lateralized structurally disconnected clusters, including in the left posterior temporal cortex. Little insight was gained from functional disconnection symptom mapping. These results demonstrate that while left-lateralized semantic and executive control regions are often damaged together in stroke aphasia, these deficits are associated with distinct patterns of structural disconnection, consistent with the bilateral nature of executive control and the left-lateralized yet distributed semantic control network.

Effective connectivity within the neural system for object-directed action representation during aware and unaware tool processing

Previous brain functional specialization evidence has shown that both aware and unaware visual processing of manipulable objects activate left premotor, parietal, and posterior temporal cortices, which are thought to constitute object-directed action and object-function processing streams. An open question is whether, both under supraliminal and subliminal processing conditions, there is directional spread of activation along these functional streams, leading to causal inter-regional connectivity effects. In this study, we used Dynamic Causal Modelling to estimate the effective connectivity influences within the premotor-parieto-temporal network, as a function of factorial contrasts for Manipulability (manipulable vs non-manipulable objects) and Perceptual Awareness (above vs below perceptual threshold). We modeled forward and backward connections originating from visual area V4, as a region underlying object texture segregation, and spreading through the left premotor-parieto-temporal network. Both above and below perceptual threshold, the visual processing of manipulable objects was associated with a specific increase of reciprocal effective connectivity coupling among left premotor-parieto-temporal regions. Aware and unaware manipulable object processing differed from each other for their distinct patterns of top-down activation enhancement exerted, in the former case, by left premotor-parieto-temporal regions on area V4 and, in the latter case, by left premotor on temporal regions. Although it is only under aware processing conditions that effective connectivity in the action representation system may promote object visual contour segregation in area V4, our results suggest that the encoding of object-action and object-function information can occur through left-hemispheric premotor, parietal, and temporal causal interdependencies, even when the object is not consciously perceived.

Brain Networks Involved in Depression in Patients with Frontotemporal Dementia and Parkinson's Disease: An Exploratory Resting-State Functional Connectivity MRI Study.

Depression is characterized by feelings of sadness, loss, or anger that may interfere with everyday activities. Such a neuropsychiatric condition is commonly reported in multiple neurodegenerative disorders, which are quite different from each other. This study aimed at investigating the brain networks involved in depression in patients with frontotemporal dementia (FTD) and Parkinson’s disease (PD) as compared to healthy controls (HC). Fifty participants were included in the study: 17 depressed FTD/PD patients; 17 non-depressed FTD/PD patients; and 16 non-depressed HCs matched for age and gender. We used the Beck depression inventory (BDI-II) to measure depression in all groups. On the same day, 3T brain magnetic resonance with structural and resting-state functional sequences were acquired. Differences in resting-state functional connectivity (FC) between depressed and non-depressed patients in all the experimental groups were assessed by using seed-to-seed and network-to-network approaches. We found a significant seed-to-seed hyperconnectivity patterns between the left thalamus and the left posterior temporal fusiform cortex, which differentiated FTD/PD depressed patients from the HCs. Network-to-network analysis revealed a significant hyperconnectivity among the default-mode network (left lateral-parietal region), the medial prefrontal cortex and the left lateral prefrontal cortex (i.e., part of the central executive network). We investigated whether such FC patterns could be related to the underlying neurodegenerative disorder by replicating the analyses with two independent samples (i.e., non-depressed PD and non-depressed FTD patients) and adding clinical parameters as covariates. We found no FC differences in these groups, thus suggesting how the FC pattern we found may signal a common depression-related neural pathway implicated in both the neurocognitive disorders.

Are alpha and beta oscillations spatially dissociated over the cortex in context-driven spoken-word production?

Decreases in oscillatory alpha‐ and beta‐band power have been consistently found in spoken‐word production. These have been linked to both motor preparation and conceptual‐lexical retrieval processes. However, the observed power decreases have a broad frequency range that spans two “classic” (sensorimotor) bands: alpha and beta. It remains unclear whether alpha‐ and beta‐band power decreases contribute independently when a spoken word is planned. Using a re‐analysis of existing magnetoencephalography data, we probed whether the effects in alpha and beta bands are spatially distinct. Participants read a sentence that was either constraining or non‐constraining toward the final word, which was presented as a picture. In separate blocks participants had to name the picture or score its predictability via button press. Irregular‐resampling auto‐spectral analysis (IRASA) was used to isolate the oscillatory activity in the alpha and beta bands from the background 1‐over‐f spectrum. The sources of alpha‐ and beta‐band oscillations were localized based on the participants’ individualized peak frequencies. For both tasks, alpha‐ and beta‐power decreases overlapped in left posterior temporal and inferior parietal cortex, regions that have previously been associated with conceptual and lexical processes. The spatial distributions of the alpha and beta power effects were spatially similar in these regions to the extent we could assess it. By contrast, for left frontal regions, the spatial distributions differed between alpha and beta effects. Our results suggest that for conceptual‐lexical retrieval, alpha and beta oscillations do not dissociate spatially and, thus, are distinct from the classical sensorimotor alpha and beta oscillations.

Epileptic opsoclonus due to cortical dysplasia of the left posterior temporal cortex: A simultaneous electroencephalogram and electrooculogram study

This is the first report of opsoclonus seizures due to left posterior cortex epilepsy, which was documented with oculogram (see supplementary discussion) [1], scalp, and subdural EEG. The child has been seizure free for 44 months after resection of the left posterior temporal cortex. Review of literature and the index case support posterior cortex as the epileptogenic zone of ictal opsoclonus.

Task modulation of spatiotemporal dynamics in semantic brain networks: An EEG/MEG study

How does brain activity in distributed semantic brain networks evolve over time, and how do these regions interact to retrieve the meaning of words? We compared spatiotemporal brain dynamics between visual lexical and semantic decision tasks (LD and SD), analysing whole-cortex evoked responses and spectral functional connectivity (coherence) in source-estimated electroencephalography and magnetoencephalography (EEG and MEG) recordings. Our evoked analysis revealed generally larger activation for SD compared to LD, starting in primary visual area (PVA) and angular gyrus (AG), followed by left posterior temporal cortex (PTC) and left anterior temporal lobe (ATL). The earliest activation effects in ATL were significantly left-lateralised. Our functional connectivity results showed significant connectivity between left and right ATL, PTC and right ATL in an early time window, as well as between left ATL and IFG in a later time window. The connectivity of AG was comparatively sparse. We quantified the limited spatial resolution of our source estimates via a leakage index for careful interpretation of our results. Our findings suggest that the different demands on semantic information retrieval in lexical and semantic decision tasks first modulate visual and attentional processes, then multimodal semantic information retrieval in the ATLs and finally control regions (PTC and IFG) in order to extract task-relevant semantic features for response selection. Whilst our evoked analysis suggests a dominance of left ATL for semantic processing, our functional connectivity analysis also revealed significant involvement of right ATL in the more demanding semantic task. Our findings demonstrate the complementarity of evoked and functional connectivity analysis, as well as the importance of dynamic information for both types of analyses.

Temporo-cerebellar connectivity underlies timing constraints in audition.

The flexible and efficient adaptation to dynamic, rapid changes in the auditory environment likely involves generating and updating of internal models. Such models arguably exploit connections between the neocortex and the cerebellum, supporting proactive adaptation. Here, we tested whether temporo-cerebellar disconnection is associated with the processing of sound at short timescales. First, we identify lesion-specific deficits for the encoding of short timescale spectro-temporal non-speech and speech properties in patients with left posterior temporal cortex stroke. Second, using lesion-guided probabilistic tractography in healthy participants, we revealed bidirectional temporo-cerebellar connectivity with cerebellar dentate nuclei and crura I/II. These findings support the view that the encoding and modeling of rapidly modulated auditory spectro-temporal properties can rely on a temporo-cerebellar interface. We discuss these findings in view of the conjecture that proactive adaptation to a dynamic environment via internal models is a generalizable principle.

From letters to composed concepts: A magnetoencephalography study of reading

Language comprehension requires the recognition of individual words and the combination of their meanings to yield complex concepts or interpretations. This combinatory process often requires the insertion of unstated semantic material between words, based on thematic or feature knowledge. For example, the phrase horse barn is not interpreted as a blend of a horse and a barn, but specifically a barn where horses are kept. Previous neuroscientific evidence suggests that left posterior and anterior temporal cortex underpin thematic and feature‐based concept knowledge, respectively, but much remains unclear about how these areas contribute to combinatory language processing. Using magnetoencephalography, we contrasted source‐localized responses to modifier‐noun phrases involving thematic relations versus feature modifications, while also examining how lower‐level orthographic processing fed composition. Participants completed three procedures examining responses to letter‐strings, adjective‐noun phrases, and noun–noun combinations that varied the semantic relations between words. We found that sections of the left anterior temporal lobe, posterior temporal lobe, and cortex surrounding the angular gyrus were all engaged in the minimal composition of adjective‐noun phrases, a more distributed network than in most prior studies of minimal composition. Of these regions, only the left posterior temporal lobe was additionally sensitive to implicit thematic relations between composing words, suggesting that it houses a specialized relational processing component in a wider composition network. We additionally identified a left occipitotemporal progression from orthographic to lexical processing, feeding ventral anterior areas engaged in the combination of word meanings. Finally, by examining source signal leakage, we characterized the degree to which these responses could be distinguished from one another using source estimation.

Left posterior temporal cortex is sensitive to syntax within conceptually matched Arabic expressions

During language comprehension, the brain processes not only word meanings, but also the grammatical structure—the “syntax”—that strings words into phrases and sentences. Yet the neural basis of syntax remains contentious, partly due to the elusiveness of experimental designs that vary structure independently of meaning-related variables. Here, we exploit Arabic’s grammatical properties, which enable such a design. We collected magnetoencephalography (MEG) data while participants read the same noun-adjective expressions with zero, one, or two contiguously-written definite articles (e.g., ‘chair purple’; ‘the-chair purple’; ‘the-chair the-purple’), representing equivalent concepts, but with different levels of syntactic complexity (respectively, indefinite phrases: ‘a purple chair’; sentences: ‘The chair is purple.’; definite phrases: ‘the purple chair’). We expected regions processing syntax to respond differently to simple versus complex structures. Single-word controls (‘chair’/‘purple’) addressed definiteness-based accounts. In noun-adjective expressions, syntactic complexity only modulated activity in the left posterior temporal lobe (LPTL), ~ 300 ms after each word’s onset: indefinite phrases induced more MEG-measured positive activity. The effects disappeared in single-word tokens, ruling out non-syntactic interpretations. In contrast, left anterior temporal lobe (LATL) activation was driven by meaning. Overall, the results support models implicating the LPTL in structure building and the LATL in early stages of conceptual combination.

Lists with and without Syntax: A New Approach to Measuring the Neural Processing of Syntax.

In the neurobiology of syntax, a methodological challenge is to vary syntax while holding semantics constant. Changes in syntactic structure usually correlate with changes in meaning. We approached this challenge from a new angle. We deployed word lists—typically, the unstructured control in studies of syntax—as both test and control stimuli. Three-noun lists (“lamps, dolls, guitars”) were embedded in sentences (“The eccentric man hoarded lamps, dolls, guitars…”) and in longer lists (“forks, pen, toilet, rodeo, lamps, dolls, guitars…”). This allowed us to minimize contributions from lexical semantics and local phrasal combinatorics: the same words occurred in both conditions, and in neither case did the list items locally compose into phrases (e.g., “lamps” and “dolls” do not form a phrase). Crucially, the list partakes in a syntactic tree in one case but not the other. Lists-in-sentences increased source-localized MEG activity at ∼250–300 ms from each of the list item onsets in the left inferior frontal cortex, at ∼300–350 ms in the left anterior temporal lobe and, most reliably, at ∼330–400 ms in left posterior temporal cortex. In contrast, the main effects of semantic association strength, which we also varied, localized in the left temporoparietal cortex, with high associations increasing activity at ∼400 ms. This dissociation offers a novel characterization of the structure versus word meaning contrast in the brain: the frontotemporal network that is familiar from studies of sentence processing can be driven by the sheer presence of global sentence structure, while associative semantics has a more posterior neural signature.SIGNIFICANCE STATEMENT Human languages all have a syntax, which both enables the infinitude of linguistic creativity and determines what is grammatical in a language. The neurobiology of syntactic processing has, however, been challenging to characterize despite decades of study. One reason is pure manipulations of syntax are difficult to design. The approach here offers a novel control of two variables that are notoriously hard to keep constant when syntax is manipulated: word meaning and phrasal combinatorics. The same noun lists occurred inside longer lists and sentences, while semantic associations also varied. Our MEG results show that classic frontotemporal language regions can be driven by sentence structure even when local semantic contributions are absent. In contrast, the left temporoparietal junction tracks associative relationships.

Identification of subtypes for the behavioral variant of frontotemporal dementia based on the assessment of disinhibition and compulsion

AbstractBackgroundThe behavioral variant of frontotemporal dementia (bvFTD) is characterized by cognitive and behavioral decline due to the progressive brain damage of frontal and temporal regions. We aimed to: 1. identify bvFTD subtypes through the behavioral assessment of social disinhibition and perseveration/compulsion; 2. disentangle the underlying functional and anatomical correlates.MethodWe assessed occurrences of 19 behaviors (derived from current clinical criteria of bvFTD) linked to disinhibition and perseveration/compulsion in a quasi‐ecological setting in 17 bvFTD patients and 16 healthy controls (HC). Subjects also underwent neurocognitive tests and a structural MRI examination. Dimensions extracted through Principal Component Analysis from the behavior variables were compared between patients and HC. A clustering approach applied to behavioral scores allowed to isolate subgroups within the patients. Voxel based morphometry (VBM) was performed to identify specific grey matter atrophy patterns in each subgroup.ResultWe identified two principal behavioral dimensions significantly different between bvFTD and HC. Using scores on these two components (labelled as Compulsion and Disinhibition), we identified two different subgroups of bvFTD patients (bvFTD‐G1 and bvFTD‐G2). BvFTD‐G1, characterized by high Disinhibition, had a small pattern of atrophy, centered on left medial anterior and posterior temporal cortices. BvFTD‐G2, characterized by high Compulsion and cognitive impulsivity, presented a more diffuse and bilateral atrophy pattern largely involving frontotemporal and subcortical regions.ConclusionThe behavioral assessment of disinhibition and compulsion symptoms allowed the clinical stratification of bvFTD patients into more or less severe stages or forms, and the identification of specific brain circuits associated with disinhibition and compulsion.