Writing by hand involves a sequential component, characterized by the succession of strokes to form letters, and a motor adaptation component for controlling pen movements under spatial constraints. The topography of the brain network supporting handwriting is well established, but the functional properties of its components in the motor control of handwriting as a procedural skill remain poorly understood. To address this question, we recorded the brain activity of adult participants as they wrote in the MRI scanner. We manipulated the sequential component of handwriting, e.g., the succession of strokes, and the motor adaptation component, e.g., the visuo-spatial control of pen movements to manage spatial constraints. Analysis of the brain data revealed the recruitment of two distinct networks, depending on the component being manipulated. The motor adaptation component relies on the cortico-cerebellar loop. The sequential component of handwriting rather appears to be computed in both the cortico-striatal and cortico-cerebellar loops. Finally, our study specifies the functional contributions of several regions of the cortical motor system as a function of the sequential and spatial adaptation requirements of the writing movement.
Transcranial direct current stimulation (tDCS) is a promising tool for experimental and rehabilitation purposes, but its effects appear highly variable due to methodological and physiological factors. To overcome this issue, tDCS protocols combining computational modeling of electric fields and high-definition (HD)-tDCS are increasingly used to decrease the heterogeneity of tDCS effects in the motor as well as cognitive domains. However, the effects of HD-tDCS compared to conventional bipolar tDCS on behavioral variables and cortico-spinal excitability remain controversial. In this pre-registered study, we aimed to compare the differential effects of anodal conventional bipolar montage and anodal HD-tDCS montage, built upon an optimized computational model of electric field distribution, on cognitive performance in 48 participants. The Stop Signal Task (SST) was used to measure response inhibition, based on previous meta-analytic evidence showing a significant modulation of SST inhibitory performance when applying tDCS to the right inferior frontal gyrus (rIFG). Bayesian paired sample t-test comparing the effect of HD-versus sham tDCS on Stop Signal Reaction Times (SSRTs) showed moderate evidence in favor of the null hypothesis (i.e., no difference between conditions). Moreover, Bayesian analyses indicated that the data favored the null hypothesis when comparing SST performance between the HD-montage versus both conventional and sham montages, as well as between the conventional versus sham session. This study highlights the issue of the variability in the effects of tDCS, both for HD- and conventional montages, and further supports the need for replication studies even in the case of known effects in the literature.
The frontal eye field (FEF) and the inferior frontal junction (IFJ) are prefrontal regions that mediate top-down functions, with mounting neuroimaging evidence suggesting that they specialize in controlling spatial versus non-spatial processing, respectively. We hypothesized that their unique patterns of structural connectivity underlie these specialized roles. To infer the localization of FEF and IFJ in standard space, we performed an activation likelihood estimation meta-analysis of functional MRI paradigms that targeted these regions. Using surface-based probabilistic tractography methods at the individual subject level, we tracked streamlines ipsilaterally from the inferred FEF and IFJ activation peaks to the dorsal and ventral visual streams mapped on the native white matter surface of 56 subjects parcellated using the multimodal atlas by Glasser et al. (2016). By contrasting FEF and IFJ connectivity likelihoods, we found predominant structural connectivity from the FEF to regions of the dorsal visual stream compared to the IFJ (particularly in the left hemisphere), and conversely, predominant structural connectivity from the IFJ to regions of the ventral visual stream compared to the FEF bilaterally. Additionally, we analyzed the cortical terminations of the superior longitudinal fasciculus to the FEF and IFJ, implicating its first and third branches as segregated pathways mediating their communication to the posterior parietal cortex. The structural connectivity fingerprints of the FEF and IFJ support the view that the two visual stream architectures extend to the posterior lateral prefrontal cortex and provide converging anatomical evidence of their specialization in spatial versus non-spatial control.
We report the case of a 58-year-old right-handed patient who presented with diagonistic dyspraxia of the left hand accompanied by various callosal disconnection symptoms, resulting from infarct lesions involving the right centrum semiovale as well as the corpus callosum. In addition to unintentionally performing actions opposite to those of the right hand, the left hand also exhibited movements identical to the right hand, movements unrelated to right-hand actions, and movements that preceded right-hand actions. Furthermore, the patient occasionally demonstrated symptoms not previously reported in classic diagonistic dyspraxia: the left hand involuntarily grasped objects despite the absence of pathological grasping, became unable to intentionally release grasped objects or, conversely, immediately released held objects. In linguistic tests conducted separately for each hand, errors such as the addition of actions were observed exclusively in the left hand, not only during the verbal command task but also when imitating the demonstrated actions included in the verbal commands, which did not require linguistic processing. The involuntary movements of the left hand observed in this patient suggest a dual disconnection mechanism: interhemispheric disconnection due to callosal lesions and intrahemispheric disconnection between the frontal and parietal lobes. The latter may contribute to impaired coordination between action inhibition and facilitation mechanisms as a result of disrupted association fibers caused by lesions in the right centrum semiovale.
Visual information plays a key role in guiding food-related decisions. While previous studies have shown that features such as calories and naturalness are encoded by the brain, upon simply seeing the stimuli, it remains unclear how this encoding is shaped by the observer's current state. In this study, we explore the effect of 1) hunger state, 2) task relevance, and 3) current individual preference on the processing of visual food information. Participants (N = 23) underwent two EEG sessions: one after fasting overnight and another after eating normally. During each session, participants did two separate tasks, one where the stimuli were task-relevant and one where attention was distracted away. We used multivariate analysis methods to assess the impact of hunger on the representation of food-related features, and to determine the time-course of information related to food flavour, personal appeal, and arousal, across both tasks. Results showed that information about edibility (food vs non-food object), food identity (e.g., hamburger vs pizza), flavour profile, or personal appeal and arousal was not influenced by the hunger manipulation. Flavour was represented regardless of attentive state, whereas personal appeal and arousal information emerged later and were only observed when the food was task-relevant. We found that food appeal and arousal encoding were more closely aligned with behavioural ratings within rather than between sessions, suggesting the nature of the encoding was driven by current state. The study provides insights into how personal preferences and physiological states influence the representation of food information in the brain.
Psychological distress is common among people living with neurodegenerative diseases of the motor system (NDMS) such as Parkinson's disease, motor neurone disease/amyotrophic lateral sclerosis, and Huntington's disease. Yet the way psychological difficulties are conceptualised in these populations is heavily shaped by medicalised language. Terms such as 'non-motor symptoms' and 'neuropsychiatric manifestations' were originally introduced to draw attention to difficulties beyond movement changes but they now risk positioning mood, anxiety, apathy, and related experiences solely as direct manifestations of neurological degeneration. This framing can obscure the rich psychosocial contexts in which distress arises, blur distinctions between emotional responses and disease processes, and reinforce deficit-based and disease-focused understandings that privilege biological explanations over person-centred ones. It may also influence clinical communication, treatment decisions, help-seeking behaviour, and access to psychological therapy and psychosocial interventions, contributing to inequities in care. This article argues that linguistic choices are not neutral: they construct the boundaries of what counts as legitimate knowledge, shape expectations about causality, and delimit the interventions considered appropriate. Without critical attention to these assumptions, individuals may experience distress as biologically inevitable and clinicians may overlook psychosocial contributors that are amenable to change. We propose that greater awareness of the power of language, coupled with empirical investigation into its effects, is essential for developing a linguistic reformulation of psychological distress in NDMS and more holistic, contextually grounded approaches to supporting psychological wellbeing.
Regularization has been extensively used in multivariate pattern classification (MVPA; decoding) of EEG data to mitigate the risk of overfitting. N-fold cross-validation is also used to mitigate this risk, and it is often combined with averaging across trials to improve the SNR. However, the impact of different regularization and cross-validation parameters on decoding performance remains unclear. This study aimed to evaluate the effects of variations in the support vector machine (SVM) regularization parameter (C) and the number of crossfolds (and the number of trials per average) on the performance of SVM-based decoding analyses. To achieve this, we examined the decoding performance in relatively simple binary classification tasks from seven commonly used event-related potential paradigms (N170, mismatch negativity, N2pc, P3b, N400, lateralized readiness potential, and error-related negativity). Additionally, we evaluated the decoding performance in more challenging multiclass tasks, including decoding face identity, facial expression, stimulus location, and stimulus orientation. The results revealed that both decoding accuracy and effect size were highest when the regularization strength was equal to or greater than 1. Furthermore, using between 3 and 5 folds with at least 10 trials per average yielded optimal decoding performance in most cases. Researchers applying SVM-based decoding to datasets similar to those examined here-in terms of population, recording systems, class numbers, and paradigms-might benefit from using the parameters that we found to be optimal here.
Mental imagery and visual perception can both give rise to vivid visual experiences, yet the extent to which they can functionally influence each other remains an open question. Previous research has shown that imagining a stimulus before viewing a rivalrous display can bias perception towards the imagined content. However, this effect has been demonstrated primarily with simple, low-level stimuli such as oriented gratings. Here, we investigated whether imagery of more complex representations-people and buildings-can influence perception, using the binocular rivalry paradigm. Participants in our study imagined either a personally familiar person or personally familiar building before viewing a rivalrous face-house stimulus. We measured their perceptual dominance and imagery vividness on each trial. Their overall imagery ability was assessed using the Vividness of Visual Imagery Questionnaire (VVIQ). We found that participants were significantly more likely to perceive the imagined stimulus; however, this priming effect was driven by person imagery. Greater vividness of person imagery on each trial significantly increased dominance of the face stimulus, but this effect did not extend to building imagery and the house stimulus. Furthermore, the VVIQ did not predict individual differences in priming magnitude. These results extend previous work by showing that mental imagery can influence perception beyond simple stimuli, but that this functional link is shaped by stimulus-specific features. Our findings highlight the need for future research to examine the conditions under which imagining more complex representations affects seeing.
This review evaluates the diagnostic quality of the redundant target paradigm (RTP) as a tool for assessing residual visual capacities, like blindsight, in patients with visual field defects following brain injury. The RTP is based on the redundant target effect (RTE), whereby reaction times are slower to a single than to two redundant targets. In patients, the RTE indicates residual vision when the redundant target is presented within the blind field. By synthesizing data from the reviewed studies, we estimated measures of diagnostic quality. The specificity estimate was 89% [95%CI (69%, 97%)], indicating false-positive results were infrequent. Thus, a significant RTE suggests residual vision with high probability. However, sensitivity ranged from 42% [95%CI (19%, 68%)] to 77% [95%CI (57%, 90%)], showing that the RTP frequently fails to detect residual vision. The estimated reliability was low, with only 36% [95%CI (15%, 65%)] of cases demonstrating stable positive results. Therefore, absence of a significant RTE does not reliably indicate absence of residual vision. These findings limit the RTP's suitability to draw conclusions about specific neuronal structures or functions. Moreover, several patients exhibited blindsight in other paradigms but not in the RTP. Consequently, RTP-results cannot serve as a prerequisite for interpreting other blindsight tasks. The RTP's advantages, e.g., its ability to assess residual vision indirectly through a reaction-time effect, thereby avoiding biased response criteria, should encourage further research aimed at developing RTP-versions with improved diagnostic quality. However, low sensitivity and low reliability of current RTP-versions substantially limit its applicability for blindsight testing.
Narrative comprehension involves creating a mental representation of the events of the story: a "situation model". Maintaining a situation model is thought to be supported by the Default Mode Network (DMN), but recent work suggests that the semantic system, and specifically the ventrolateral anterior temporal lobe (ATL), may play a role in reflecting on and restructuring the situation model via internally-driven or endogenous semantic processing. The present study used fMRI to investigate how ATL and DMN brain regions respond under varying exogenous, or input-driven, and endogenous processing demands when reading social and non-social stories. We studied neural responses to three types of situation model manipulation: 1) add-incorporating new information into the situation model, 2) use-using the information in the situation model to support comprehension of narrative language input, and 3) reconfigure-restructuring the situation model. Relative to add, the use and reconfigure manipulations tended to elicit greater activation in regions of the DMN, including the dorsomedial prefrontal cortex, posterior cingulate cortex and precuneus, as well as the bilateral superior, middle and inferior ATL. Relative to non-social stories, add and use manipulations in social stories engaged the left anterior middle and superior temporal gyri and inferior parietal lobule (IPL), whereas reconfigure manipulations engaged the right superior, middle and inferior frontal gyri and IPL. The present results inform a developing framework for coordination between the ATL and DMN during narrative comprehension.
A growing body of literature has characterized the extensive and widespread engagement of cortical resources during the execution of locomotor adaptations. However, evidence suggests that the extent of cortical regulation involved in such adaptations is modulated by the available time to respond. In this study, a treadmill-based virtual reality paradigm was used to examine the electrocortical oscillations associated with obstacle avoidance under short versus long available response times (ARTs). Electroencephalography data were recorded from healthy young adults as they stepped over virtual obstacles. These obstacles were presented in far space, allowing either a short (1.5 sec) or long (4 sec) ART between their presentation and clearance. Data were parsed with independent component analysis and clustered within the prefrontal, sensorimotor, parietal and occipital regions. Distinct spectral signatures were observed across all cortical regions, characterized by transient synchronizations shortly after obstacle presentation and immediately prior to clearance. Compared to the long ART condition, the short ART condition elicited stronger prefrontal theta, alpha, and beta synchronizations. During clearance, long ARTs were associated with a sensorimotor alpha desynchronization during obstacle clearance; however, such desynchronization was largely absent under short ART. Taken together, these findings suggest that tighter temporal constraints during obstacle avoidance enhance prefrontal involvement and decrease sensorimotor network activation. Such time-dependent cortical dynamics offer new insights into the neural mechanisms underlying locomotor adjustments that can inform our understanding of locomotor deficits in aging and neurological disorders.
Language neuroscience has historically relied on highly controlled experimental paradigms that differ markedly from the conditions of real-world communication. Although such approaches have yielded important insights, they often fail to capture the integrative processes required for discourse and connected language. Here, we treat discourse as language extending beyond a single simple clause and used for a specific purpose. Recent advances in computational modeling, natural language processing, and neurophysiological measurement now make it possible to study language in more naturalistic, temporally extended, and ecologically valid contexts. In this closing editorial for a special issue of Cortex, we synthesize contributions that collectively argue for a discourse-centered neuroscience: the view that the neural basis of language becomes most fully visible when language is studied in its connected, purposeful form. We organize the issue around four broad themes-cortical topography and continuous integration, structural connectivity, large-scale network dynamics, and clinical mapping of language, thought, and interaction-and show how each reveals aspects of language organization that remain difficult to detect in isolated word- and sentence-level paradigms. We conclude by considering the implications of this work for basic and clinical science and by outlining future directions for the neurocognitive study of discourse.
This review explored cognitive-communication disorders (CCD) in speakers of Berber languages residing in Morocco and abroad. It emphasized the unique interplay between neuropsychological, linguistic, and cultural factors relevant to Berber languages, which belonged to the Afroasiatic language family and included three main varieties in Morocco: Tachelhit, Tarifit, and Central Atlas Tamazight. A narrative review has been carried out of studies from MEDLINE, Web of Science, and Scopus, summarizing the demographic and clinical characteristics of the participants. The analysis of six remaining studies, comprising a combined sample size of over 923 participants, identified the diversity of Berber-speaking populations in Morocco and the Netherlands. These studies used cross-sectional designs and validation protocols for assessment tools. However, challenges included the significant scarcity of published articles, the suitability of standard tools for low-literacy or culturally diverse populations, limited sample sizes, and socio-cultural barriers. These studies provided a foundation for evidence-based practice using validated neuro-cognitive instruments in accordance with international standards. Therefore, clinicians should prioritize Amazigh cultural and linguistic awareness in diglossic contexts, as the growing prominence of these understudied languages underscored the need for fair, standardized cognitive-linguistic assessment tools.
The contralateral delay activity (CDA) is a widely used electrophysiological marker of visual working memory (VWM), yet recent work has questioned whether typical sample sizes in CDA studies are sufficient to robustly detect set size effects and brain-behavior correlations. As part of the #EEGManyLabs initiative, the present multi-site replication study aimed to rigorously test replicability of the key findings of Vogel and Machizawa (2004)using a large sample of 304 participants across 10 laboratories and a preregistered analysis plan. We replicated the expected contralateral-ipsilateral asymmetry and observed increases in CDA amplitude from set size 2 to 4 and from set size 2 to 6. In contrast, the hypothesized positive correlation between the CDA increase from set size 2 to 4 and individual VWM capacity was not replicated in the preregistered meta-analytic correlation. Across different pipelines and statistical analyses, the meta-analytic correlation estimate was small (r = .15) and substantially attenuated relative to the original effect size in Vogel and Machizawa (2004)study (r = .78). To contextualize these findings, we applied a funnel-plot diagnostic combining published effects with the #EEGManyLabs data, indicating small-study inflation and publication bias. Taken together, our results indicate that reports of strong correlations between CDA amplitude and VWM capacity may have been overestimated, in part because statistically significant findings were selectively reported. Our results highlight the importance of open science practices, including well-powered, preregistered studies with transparent data and analysis pipelines, in order to characterize the magnitude and robustness of individual-difference associations in psychophysiology.
Tool use and physical reasoning are often assumed to rely on shared cognitive and neural mechanisms. At some level, this correspondence is expected: using an object typically requires understanding its physical properties. However, both capacities are complex and multicomponential, so the relationship between them may vary across levels of representation and task demands. Here, we asked whether third-person physical reasoning about object dynamics can dissociate from tool use (i.e., performing a tool's typical action) in individuals with left-hemisphere stroke. We tested 11 patients, five of whom showed impairments in tool use. Physical reasoning was assessed using a novel collection of tasks probing judgments about mass, velocity, and timing across static and dynamic scenes. Tool use was evaluated using a classic gesture-to-sight task, a pantomime-based measure in which participants are shown pictures of familiar tools and asked to demonstrate how each would be used. We identified an individual-level dissociation: patient I.A.∗ showed impairment in gesturing the use of objects despite preserved physical reasoning, often outperforming neurotypical controls. This pattern was complemented by patient N.P., who showed the reverse profile, with intact tool use gestures but difficulties in some physical reasoning tasks. These findings suggest that the ability to reason about the physical world and tool use can dissociate behaviorally and be independently disrupted by brain damage. This challenges the view that physical reasoning and tool use draw on the same underlying cognitive and neural mechanisms and suggests that at least some of their components are distinct. ∗ Both initials I.A. and N.P. are pseudonyms used to protect participant identities.
The Sense of Agency (SoA), the subjective experience that 'I am in control of my actions', has been proposed to involve both early implicit sensorimotor processes (feeling of agency) and later explicit higher-level processes (judgment of agency). Even though SoA is fundamental to our interactions with the external world and to our construct of the self, its underlying neural mechanism remains elusive. In this pre-registered EEG study, we used time-frequency analysis and Multivariate Pattern Analysis (MVPA) to investigate the neural characteristics of sensorimotor conflicts within an agency paradigm. Using an established embodied virtual reality paradigm, we modulated visual feedback to examine neural responses to conflicts between predicted and perceived sensory feedback. Participants moved their finger while viewing a virtual hand that either mimicked their movement, differed anatomically (identical movement, different finger), or spatially (identical finger, angular shift), and then rated their SoA while brain activity was recorded. In accordance with our pre-registered hypothesis, visuomotor conflicts, which were associated with robust decreases in self-attribution, were linked to increased alpha-band power, and exploratory analyses further revealed increased theta-band power. We show that trials containing a sensorimotor alteration could be reliably decoded from unaltered trials with up to 68% accuracy starting around 200 msec after movement onset. Cross-decoding further revealed shared neural patterns across anatomical and spatial manipulations, emerging around 500 msec post-movement. Together, our results indicate a temporal progression from early, condition-specific sensorimotor responses to a later domain-general component, consistent with the two-step model of agency.
Individuals with borderline personality disorder (BPD) show alterations in empathic abilities, potentially involving automatic simulation processes supported by mirror-like mechanisms in the somatosensory domain. Within the tactile mirror system (TaMS), observing touch on another person's body activates cortical regions involved in tactile perception, including the primary somatosensory cortex (S1). Although mirror-like alterations have been suggested in BPD, the underlying mechanisms of plasticity remain underexplored. Here, we used a cross-modal paired associative stimulation (cm-PAS) protocol to investigate the plasticity mechanisms of TaMS functioning in BPD. Twenty-four individuals with BPD and 24 healthy controls (HCs) were included. Empathic abilities were assessed using self-report questionnaires. Participants performed tactile acuity and visuo-tactile spatial congruity (VTSC) tasks before and after a cm-PAS protocol. During cm-PAS, images of a hand being touched were paired with transcranial magnetic stimulation over the S1. The effects of cm-PAS were assessed on tactile acuity, as an index of S1 activity, and VTSC performance, as an index of TaMS functioning. Preregistered analyses revealed that patients with BPD tended to have lower cognitive empathy than HCs, with no significant cm-PAS effects on tactile acuity or VTSC performance in HCs, precluding between-group comparisons of plasticity effects. Exploratory analyses were conducted to further investigate potential sources of variability in the effects of cm-PAS, as well as the relationship between cognitive empathy and visuo-tactile processing as measure of TaMS functioning.
Visual symmetry activates the extrastriate visual cortex and generates an Event Related Potential (ERP) called the Sustained Posterior Negativity (SPN). SPN amplitude is often reduced when stimuli are presented in perspective. We call this reduction SPN perspective cost. Previous research has shown that SPN perspective cost is flexible. We examined flexibility in SPN perspective cost by comparing three experimental conditions in three separate blocks. In the frontoparallel block, the stimuli were seen face on. In the real perspective block, the physical monitor was rotated with respect to the participant's line of sight, so the stimuli were viewed from an unconventional angle. In the drawn perspective block, the physical monitor was not rotated, but the stimuli were drawn as if viewed from the same unconventional angle. The same group of 72 participants completed all three blocks. As predicted, the SPN was selectively reduced in the drawn perspective block. We conclude that when sufficient visual depth cues are available, the brain can construct a view invariant representation. This is an important step forward in the wider research project to determine when different forms of perceptual organization happen.
Human perception relies on bottom-up sensory input and top-down prior knowledge, and object recognition is known to be modulated by the semantic relationship between objects and their surrounding context. However, the dynamic processing mechanism during object recognition and the resulting interaction between top-down and bottom-up factors remains unclear. The present study investigated how stimulus contrast modulates the effect of scene-object semantic congruency. Participants performed an object-recognition task in which target objects of high or low contrast appeared within semantically congruent or in congruent natural scenes. In Experiment 1, behavioral results (N= 73) on recognition accuracy revealed a congruency benefit for high-contrast objects and an incongruency benefit for low-contrast objects, indicating a contrast-dependent shift in how scene context influences recognition. Experiment 2 (N= 19) employed event-related potentials (ERPs) to examine the neural activity of these effects. For high-contrast targets, congruency effects emerged in the N300 and N400 over central-parietal regions, and in the P600 over frontal sites. For low-contrast targets, effects were observed in the late component. These findings provide novel evidence that low-level visual contrast determines whether prior knowledge facilitates or interferes with object recognition, offering critical insights into the mechanisms underlying the dynamic interaction between bottom-up and top-down processes in visual perception.
Body perception and movement control are altered in most neurological, neurodegenerative, and psychiatric diseases. The homuncular organization of the sensorimotor cortex, referring to the regular organization of neurons responsive to body movement and body touch, is therefore of fundamental relevance for brain health. Developmental changes of homuncular readouts, such as during aging and neurodegeneration, relate to mechanisms of resilience against cognitive, emotional, and behavioural decline. Recent advances in ultra-high field MRI allow the in-vivo parcellation of cortical areas. Based on mesoscale profiles, this method has been used to evidence the existence of distinct cortical fields within the homuncular map, each representing a major body part and, and borders between these fields. This topographic "split" defines new units of homuncular network organization and questions the idea that mechanisms of neurodegeneration or plasticity detected in one area of the sensorimotor cortex transfer to other areas within the topographic map. In-vivo brain parcellation that allows the definition of these units in individual patients provides a novel and unique perspective on brain health that support an individualized investigation of affected circuits.