Biology subjects

Nazarian, B.

Publications and source records attributed to Nazarian, B..

8 recordsLinked to original sources

bioRxiv2024

From movements to words: action monitoring in the medial frontal cortex along a caudal to rostral prediction error gradient

Speech error monitoring recruits the medial frontal cortex (MFC) region in the human brain. Error monitoring-related activity in the MFC has been interpreted both in terms of conflict monitoring and feedback-driven control, but as similar regions of the MFC are implicated in various levels of behavioral control ranging from basic motor movement control to high-level cognitive control functions, a more comprehensive account is needed. Moreover, as speech errors and other actions that involve varying control demands engage a widespread yet partially overlapping set of regions of the MFC, such an account should ideally explain the anatomical distribution of error-related functional activations within the MFC. Here we wanted to assess the hypothesis that the MFC has a similar role in the evaluation of action outcomes for motor and mental actions, operating along a rostral-caudal gradient of higher-lower level control demands involving prediction errors from both sensory and epistemic sources. To this end, we conducted an individual-specific annotation of task-fMRI BOLD activation peaks related to speech errors versus correct productions (i.e. that involve the largest cognitive control demands, Study I and II), tongue movement monitoring (i.e. that involve an intermediate level of cognitive and motor control demands) and tongue movement (i.e. that involve only motor control demands, Study II) in the MFC region. Results revealed overlapping clusters across the three contrasts across the MFC, but importantly both the number of peaks and their relative position along the rostral caudal axis were consistent with a hierarchical rostral caudal processing gradient in the MFC. While tongue movement showed more caudal activation in the MFC, speech errors showed more rostral activation, and tongue movement monitoring patterned in between. Furthermore, the combined results of both studies suggested that activation peaks were located more dorsally for participants that had a paracingulate gyrus, replicating a previously documented effect for movement and further supporting a common functional role of the MFC across very distinct actions.

neuroscience↗

bioRxiv2024

Congruent brain signatures specific to speech sounds in fronto-temporal cortex during language production and understanding.

In this fMRI study we investigated whether language production and understanding recruit the same phoneme-specific networks. We did so by comparing the brains response to different phoneme categories in minimal pairs: Bilabial-initial words (e.g., monkey) were contrasted to alveolar-initial words (e.g., donkey) in 37 participants performing both language production and comprehension tasks. Region-of-Interest analyses showed that the same sensorimotor networks were activated across the language modalities. In motor regions, word production and comprehension elicited the same phoneme-specific topographical activity patterns, with stronger haemodynamic activations for alveolar-initial words in the tongue cortex and stronger activations for bilabial-initial words in the lip cortex. In the posterior and middle superior temporal cortex, production and comprehension likewise resulted in similar activity patterns, with enhanced activations to alveolar-compared to bilabial-initial words. These results disagree with the classical separation between language production and understanding in neurobiological models of language, and instead advocate for a cortical organization where the same phoneme-specific acoustic-and-articulatory representations carry production and comprehension.

neuroscience↗

bioRxiv2024

Revealing the co-existence of written and spoken language coding neural populations in the left-ventral occipitotemporal cortex

Reading relies on the ability to map written symbols with speech sounds. The left ventral occipitotemporal cortex (left-vOT) plays a crucial role in this process. Through the automatization of the mapping ability, this specific part of the ventral visual pathway (a.k.a., the Visual Word Form Area) progressively becomes specialized in written word recognition. Yet, despite its key role in reading, the area also responds to speech. This observation raises questions about the actual nature of neural representations encoded in the left-vOT and, therefore, the underlying mechanism of the cross-modal responses. Here, we addressed this issue by applying fine-grained analyses of within- and cross-modal repetition suppression effects (RSEs) and Multi-Voxel Pattern Analyses in fMRI and sEEG experiments. Convergent evidence across analysis methods and protocols showed significant RSEs and successful decoding in both within-modal visual and auditory conditions suggesting that subpopulations of neurons within the left-vOT distinctly encode written and spoken language inputs. This functional organization of neural populations enables the area to respond to speech input directly and indirectly, i.e., after speech sounds are converted to orthographic representations. The finding opens further discussions on how the human brain may be prepared and adapted for an acquisition of a complex ability such as reading. Significance StatementLearning to read generates new functional responses in neurons in the left ventral visual pathway. Soon after reading acquisition, these neurons become specialized in processing known scripts, thus leading to the functional designation of the "Visual Word Form Area" (VWFA). However, controversies remain regarding the nature of neural representations encoded in this "reading" region, as its activation to speech is also reported. We investigate the neural mechanism(s) underlying these bimodal responses using within and cross-modal repetition suppression and decoding protocols. fMRI and sEEG experiments provided converging evidence indicating that, despite its specialization in reading, VWFA also contained subpopulations of neurons that encode speech. This functional organization could reveal why neurons at this anatomical location are ideal for reading acquisition.

neuroscience↗

bioRxiv2023

Social Context and Drug Cues Modulate Inhibitory Control in Cocaine Addiction: involvement of the STN evidenced through Functional Magnetic Resonance Imaging

BackgroundAddictions often develop in a social context, although the influence of social factors did not receive much attention in the neuroscience of addiction. Recent animal studies suggest that peer presence can reduce cocaine intake, an influence potentially mediated, among others, by the subthalamic nucleus (STN). However, there is to date no such neurobiological study in humans. MethodsThis study investigated the impact of social context and drug cues on brain correlates of inhibitory control in individuals with and without cocaine use disorder (CUD) using functional Magnetic Resonance Imaging (fMRI). Seventeen CUD participants and 17 healthy controls (HC) performed a novel fMRI Stop-Signal task in the presence and absence of an observer while being exposed to cocaine-related and neutral pictures as cues. ResultsThe results showed that CUD participants, while slower at stopping with neutral cues, recovered control level stopping abilities with cocaine cues, while HC did not show any difference. Neuroimaging revealed the involvement of frontal cortical regions and of the subthalamic nucleus (STN) in inhibitory control, which was modulated by both social context and drug cues in CUD participants but not in HC. ConclusionsThese findings highlight the impact of social context and drug cues on inhibitory control in CUD and suggest potential targets for intervention such as the STN, also emphasizing the importance of considering the social context in addiction research and treatment.

neuroscience↗

bioRxiv2022

Graph theoretical analysis reveals the adaptive role of the left ventral occipito-temporal cortex in the brain networks during speech processing

The left ventral occipito-temporal cortex (left-vOT) plays a key role in reading. Several studies have also reported its activation during speech processing, suggesting that it may play a role beyond written word recognition. Here, we adopt a graph theoretical analysis to investigate the functional role of this area in the whole-brain network while participants processed spoken sentences in different tasks. We find that its role and interactions with other areas changes in an adaptive manner. In a low-level speech perception task, the left-vOT is part of the visual network and acts as a connector that supports the communication with other cognitive systems. When speech comprehension is required, the area becomes a connector within the sensorimotor-auditory network typically recruited during speech processing. However, when comprehension is compromised due to degradation of speech input, the area disengages from the sensorimotor-auditory network. It becomes part of the visual network again and turns from connector into a simple peripheral node. These varying connectivity patterns are coherent with the Interactive Account considering the left-vOT as a convergent zone with multiple functions and interaction patterns that depend on task demands and the nature of sensory input.

neuroscience↗

bioRxiv2021

On the Gestural Origin of Language Lateralisation: Manual Communication reflects Broca's Asymmetry in Monkeys

Manual gestures and speech recruit a common neural network, involving Brocas area in the left hemisphere. Such speech-gesture integration gave rise to theories on the critical role of manual gesturing in the origin of language. Within this evolutionary framework, research on gestural communication in our closer primate relatives has received renewed attention for investigating its potential language-like features. Here, using in-vivo anatomical MRI in 50 baboons, we found that communicative gesturing is related to Broca homologues marker in monkeys, namely the ventral portion of the Inferior Arcuate sulcus (IA sulcus). In fact, both direction and degree of gestural communications handedness - but not handedness for object manipulation - are associated and correlated with contralateral depth asymmetry at this exact IA sulcus portion. In other words, baboons that prefer to communicate with their right hand have a deeper left-than-right IA sulcus, than those preferring to communicate with their left hand and vice versa. Interestingly, in contrast to handedness for object manipulation, gestural communications lateralisation is not associated to the Central sulcus depth asymmetry, suggesting a double dissociation of handedness types between manipulative action and gestural communication. It is thus not excluded that this specific gestural lateralisation signature within the baboons frontal cortex might reflect a phylogenetical continuity with language-related Broca lateralisation in humans.

neuroscience↗

bioRxiv2020

Action Observation Network activity related to object-directed and socially directed actions in Adolescents

The Action Observation Network (AON) encompasses brain areas consistently engaged when we observe others actions. Although the core nodes of the AON are present from childhood, it is not known to what extent they are sensitive to different action features during development. As social cognitive abilities continue to mature during adolescence, the AON response to socially-oriented actions, but not to object-related actions, may differ in adolescents and adults. To test this hypothesis, we scanned with functional magnetic resonance imaging (fMRI) 28 typically-developing teenagers and 25 adults while they passively watched videos of hand actions varying along two dimensions: sociality (i.e. directed towards another person or not) and transitivity (i.e. involving an object or not). We found that observing actions recruited the same fronto-parietal and occipito-temporal regions in adults and adolescents. The modulation of voxelwise activity by the social or transitive nature of the action was similar in both groups of participants. Multivariate pattern analysis, however, revealed that the accuracy in decoding the social dimension from the brain activity patterns, increased with age in lateral occipital and parietal regions, known to be involved in semantic representations of actions, as well as in posterior superior temporal sulcus, a region commonly associated with perception of high level features necessary for social perception. Change in decoding the transitive dimension was observed only in the latter region. These findings indicate that the representation of others actions, and in particular their social dimensions, in the adolescent AON is still not as robust as in adults. Significance statementThe activity of the action observation network in the human brain is modulated according to the purpose of the observed action, in particular the extent to which it involves interaction with an object or another person. How this conceptual representation of actions is implemented during development is largely unknown. Here, using multivoxel pattern analysis of fMRI data, we discovered that, while the action observation network is in place in adolescence, the fine-grain organization of its posterior regions is less robust than in adults to decode the social or transitive dimensions of an action. This finding highlights the late maturation of social processing in the human brain.

neuroscience↗

bioRxiv2020

The cerebellum is involved in internal and external speech error monitoring

An fMRI study examined how speakers inspect their own speech for errors. In a word production task, we observed enhanced involvement of the right posterior cerebellum for trials that were correct, but on which participants were more likely to make a word-as compared to a non-word error. Furthermore, comparing errors to correctly produced utterances, we observed increased activation of the same cerebellar region, in addition to temporal and medial frontal regions. Within the framework associating the cerebellum to forward modelling of upcoming actions, this indicates that forward models of verbal actions contain information about word representations used for error monitoring even before articulation (internal monitoring). Additional resources relying on speech perception and conflict monitoring are deployed during articulation to detect overt errors (external monitoring). In summary, speech monitoring seems to recruit a network of brain regions serving domain general purposes, even for abstract levels of processing.

neuroscience↗