Individual differences in indirect speech act processing found outside the language network

Face-to-face communication requires skills that go beyond core language abilities. In dialog, we routinely make inferences beyond the literal meaning of utterances and distinguish between different speech acts based on e.g. contextual cues. It is however not known whether such communicative skills potentially overlap with core language skills or other capacities, such as Theory of Mind (ToM). In this fMRI study we investigate these questions by capitalizing on individual variation in pragmatic skills in the general population. Based on behavioral data from 201 participants, we selected participants with higher vs lower pragmatic skills for the fMRI-study (N = 57). In the scanner, participants listened to dialogs including a direct or an indirect target utterance. The paradigm allowed participants at the whole group level to (passively) distinguish indirect from direct speech acts, as evidenced by a robust activity difference between these speech acts in an extended language network including ToM areas. Individual differences in pragmatic skills modulated activation in two additional regions outside the core language regions (one cluster in the left lateral parietal cortex and intraparietal sulcus and one in the precuneus). The behavioral results indicate segregation of pragmatic skill from core language and ToM. In conclusion, contextualized and multimodal communication requires a set of inter-related pragmatic processes that are neurocognitively segregated: (1) from core language and (2) partly from ToM.

Similarity of Computations Across Domains Does Not Imply Shared Implementation: The Case of Language Comprehension

Understanding language requires applying cognitive operations (e.g., memory retrieval, prediction, structure building) that are relevant across many cognitive domains to specialized knowledge structures (e.g., a particular language’s lexicon and syntax). Are these computations carried out by domain-general circuits or by circuits that store domain-specific representations? Recent work has characterized the roles in language comprehension of the language network, which is selective for high-level language processing, and the multiple-demand (MD) network, which has been implicated in executive functions and linked to fluid intelligence and thus is a prime candidate for implementing computations that support information processing across domains. The language network responds robustly to diverse aspects of comprehension, but the MD network shows no sensitivity to linguistic variables. We therefore argue that the MD network does not play a core role in language comprehension and that past findings suggesting the contrary are likely due to methodological artifacts. Although future studies may reveal some aspects of language comprehension that require the MD network, evidence to date suggests that those will not be related to core linguistic processes such as lexical access or composition. The finding that the circuits that store linguistic knowledge carry out computations on those representations aligns with general arguments against the separation of memory and computation in the mind and brain.

Domain-specific and domain-general neural network engagement during human-robot interactions

To what extent do domain-general and domain-specific neural networks generalise across interactions with human and artificial agents? In this exploratory study, we analysed a publicly available fMRI dataset (n = 22; Rauchbauer, et al., 2019) to probe the similarities and dissimilarities in neural architecture while participants conversed with another person or a robot. Incorporating trial-by-trial dynamics of the interactions, listening and speaking, we used whole-brain, region-of-interest, and functional connectivity analyses to test response profiles within and across social or non-social, domain-specific and domain-general networks, i.e., the person perception, theory-of-mind, object-specific, language, multiple-demand networks. Listening to a robot compared to a human resulted in higher activation in the language network, especially in areas associated with listening comprehension, and in the person perception network. No differences in activity of the theory-of-mind network were found. Results from the functional connectivity analysis showed no difference between interactions with a human or robot in within- and between-network connectivity. Together, these results suggest that while similar regions are activated during communication regardless of the type of conversational agent, activity profiles during listening point to a dissociation at a lower-level or perceptual level, but not higher-order cognitive level.

Functional Connectivity as a Potential Mechanism for Language Plasticity

Background and Objectives:Task-fMRI is a clinical tool for language lateralization, but has limitations, and cannot provide information about network-level plasticity. Additional methods are needed to improve the precision of presurgical language mapping. We investigate language resting-state functional connectivity(RS fMRI;FC) in typically developing children and children with epilepsy. Our objectives were to: 1)Understand how FC components differ between typically developing (TD) children and those with epilepsy. 2)Elucidate how the location of disease (frontal/temporal epilepsy foci) effects FC. 3)Investigate the relationship between age and FC.Methods:Sample includes 55 TD children (mean age 12 years, range 7-18, and 31 patients with focal epilepsy (mean age 13) with same range. All subjects underwent RS fMRI. Using a bilateral canonical language map as target, vertex wise intra-hemispheric FC map and inter-hemispheric FC map for each subject were computed and thresholded at top 10% to compute an FC laterality index (FCLI;((L-R)/(L+R)) of the frontal and temporal regions for both integration (intra-hemispheric FC; FCLIi) and segregation (Inter-hemispheric FC; FCLIs) maps.Results:We found FC differences in the developing language network based on disease, seizure foci location, and age. Frontal and Temporal FCLIi was different between groups (t(84)=2.82, p<.01; t(84)=4.68, p<.01, respectively). Frontal epilepsy foci had the largest differences from TD (Cohen’s D Frontal FCLIi=0.84, FCLIs=0.51; Temporal FCLIi=1.29). Development and disease have opposing influences on the laterality of FC based on groups. In the frontal foci group, FCLIi decreased with age (r=-0.42), whereas in the temporal foci group FCLIi increased with age (r=0.40). Within the epilepsy group, increases in right frontal integration FCLI relates to increased right frontal task activation in our mostly left language dominant group (r=.52, p<.01). Language network connectivity is associated with higher verbal intelligence in children with epilepsy (r=.45, p<.05).Discussion:These findings lend preliminary evidence that FC reflects network plasticity in the form of adaptation and compensation, or the ability to recruit support and reallocate resources within and outside of the traditional network to compensate for disease. FC expands on task-based fMRI and provides complementary and potentially useful information about the language network that is not captured using task-based fMRI alone.

Asymmetry of cortical functional hierarchy in humans and macaques suggests phylogenetic conservation and adaptation

The human cerebral cortex is symmetrically organized along large-scale axes but also presents inter-hemispheric differences in structure and function. The quantified contralateral homologous difference, i.e., asymmetry, is a key feature of the human brain left-right axis supporting functional processes, such as language. Here, we assessed whether the asymmetry of cortical functional organization is heritable and phylogenetically conserved between humans and macaques. Our findings indicate asymmetric organization along an axis describing a hierarchical functional trajectory from perceptual/action to abstract cognition. Whereas language network showed leftward asymmetric organization, frontoparietal network showed rightward asymmetric organization. These asymmetries were heritable and comparable between humans and macaques, suggesting (phylo)genetic conservation. However, both language and frontoparietal networks showed a qualitatively larger asymmetry in humans relative to macaques and variable heritability in humans. This may reflect an evolutionary adaptation allowing for experience-dependent specialization, linked to higher-order cognitive functions uniquely developed in humans.

CNTM-05. Left hemisphere gliomas induce a plastic bi-hemispheric language network further characterized by lobe specific glioma data

Primary brain tumors are among the most burdensome diagnoses patients can receive as they often carry with them externally obvious and significant detriments to motor and speech. The stroke model is severely limited by the inherent nature of the insult to the brain: binary, relatively instantaneous and defined by vascular boundaries. We instead have chosen to study glioma-induced neuroplasticity in patients with gliomas as presentation is over a significantly longer time course with a gradient of insult to language activation areas instead of immediate ablation. Chart review was conducted on 545 patients who completed fMRI imaging from 2013–2019 while completing 1+ of the following language tasks: antonyms, reading comprehension, rhyming, word generation and picture naming. A total of 117 patients’ fMRI scans were included in the final analysis which entailed both a cluster-based analysis in FSL and a 34 gyral, mask-based analysis using FEATquery. Right hemisphere gliomas (RHG) were first established as a reliable control group by averaging anatomically significant voxels across all five language tasks (LT) yielding a core conserved network. Left hemisphere gliomas (LHG) were then directly compared to the RHG language tasks. We found LHG induced global reorganization of the conserved language network with little evidence for direct homologous recruitment of functional structures. Instead, a generalized right hemisphere recruitment is observed with 87% of non-zero masks shifting their laterality index to the right hemisphere. Furthermore, in each of the five LT, the LHG activates fewer total suprathreshold voxels in both the mask and cluster based analyses while having a higher peak intensity within the activated clusters. A preliminary analysis of frontal LHG compared to temporal LHG reveals increased contralateral recruitment in the frontal subgroup with more direct homologous recruitment. This nuanced understanding of existing mechanisms for neuroplasticity can aid in our future intentional manipulation for therapeutic benefit.