Cerebral Cortex Communications

Abstract Background: Long COVID frequently includes post-exertional malaise, neuromuscular fatigue, internal vibrations, tremor-like symptoms, orthostatic intolerance, sleep disturbance, cognitive dysfunction, and autonomic instability. Neuroimaging studies in Long COVID and post-infectious ME/CFS have identified abnormalities across limbic, thalamic, mesiotemporal, brainstem, cerebellar, and white-matter systems, but no single established circuit accounts for this clinical phenotype. We examined whether abnormalities cluster at the mammillary body-fornix-superior tuberal hypothalamic interface and within connected brainstem-cerebellar pathways. Methods: Structural MRI and diffusion tensor imaging were analysed in 88 participants with clinician-diagnosed Long COVID and 34 healthy controls (total N = 122). Thirty-three patients were classified as bedridden. Volumetric and diffusion analyses focused on the mammillary bodies, superior tuberal hypothalamic region, fornix, dorsal and median raphe, midbrain reticular formation, and cerebellar peduncles. Fractional anisotropy was used as an index of white-matter microstructural organisation. Exploratory clinical associations included motor impairment, proprioceptive dysfunction, autonomic symptoms, fatigue, internal vibrations, and tremor-like symptoms. Results: Three mammillary-body volume phenotypes were identified: reduced, enlarged, and control-range. Left and right mammillary-body volumes differed across groups, with large effect estimates. Segmentation showed narrowing or loss of a visible internal passage at the superior tuberal-mammillary interface, while the fornix showed altered diffusion measures and reduced tract coherence in the hypothesised gate region. Additional findings included lower superior cerebellar peduncle volume, lower middle cerebellar peduncle fractional anisotropy, and lower dorsal raphe and midbrain reticular formation volumes in Long COVID. Conclusions: The findings support an exploratory mammillary body-fornix gate model in which a vulnerable periventricular hypothalamic-limbic interface may contribute to network dysfunction in a subgroup of patients with severe Long COVID. The data do not establish direct viral invasion, a coronavirus entry route, axonal destruction, or a single causal pathway. Prospective replication with standardised acquisition, preregistered regions of interest, correction for multiple comparisons, objective movement and autonomic measures, and longitudinal follow-up is required. Keywords: Long COVID; post-COVID condition; ME/CFS; mammillary body; fornix; hypothalamus; diffusion tensor imaging; internal vibrations; tremor-like symptoms; neuromuscular fatigue; dysautonomia; brainstem

Primates rely on eye movements made 2-3 times every second to scan their visual environment. Each eye movement induces substantial retinal motion, yet observers readily suppress it to stitch together the percept of a stable world. Neurons in the middle temporal (MT) and medial superior temporal (MST) areas respond to motion, but also suppress that response during eye movements (Bremmer et al., 2009; Leopold & Logothetis, 1998; Thiele et al., 2002). This saccadic suppression could reflect the influence of corollary feedback from eye movement related brain structures (Berman et al., 2017). However, visual signals that detect wide-field motion characteristic of a saccade could also contribute to suppression, akin to visual masking (Idrees et al., 2020). We sought to disentangle the relative contributions of visual signals and corollary discharge in driving saccadic suppression in areas MT and MTC in marmoset monkeys. Marmosets freely viewed natural images, blank backgrounds, or externally moving images that simulated saccades, and also made saccades in complete darkness. We found a diversity of saccadic modulation across the population. Some neurons showed short latency excitatory responses to saccades while others showed suppression. Still others showed a bi-phasic response that began with suppression followed by an excitatory rebound. Neurons with early responses were frequently tuned for the direction of saccades on natural images and retained that same tuning for saccades on blank screens or in complete darkness, thus supporting a role for corollary feedback. However, these neurons also responded with similar directional tuning for retinal motion created by simulating saccades while the eyes were fixed, and thus also appear to integrate visual cues for saccadic motion. More so, these units were biased towards having narrow spike waveforms consistent with putative inhibitory cells, which drive suppression observed in the rest of the population. We also found a subset of neurons that responded robustly to simulated saccadic motion but had negligible response to motion from real saccades, such that they discounted saccade induced motion. Those neurons were biased to have broader spike waveforms, consistent with being putative excitatory projection neurons and could support our percept of stability during eye movements.

The ventral premotor cortex (PMv) has been implicated in both action selection and the perception of observed actions, but it remains unclear whether PMv activity during action observation reflects the observed action itself, or variables related to the observers own action when the observed action becomes behaviourally relevant. Here, we recorded neural activity in macaque PMv during a task that dissociated observed action, rule context, and the subsequently selected self-action. Population activity during observation was already biased toward the upcoming self-action and became increasingly aligned with it. At the level of single neurons, subsets showed modulation by rule and required self-action beyond the observed action. Task-related variables coexisted during observation, rather than being organized into distinct sequential stages. These findings indicate that PMv activity during action observation is not solely determined by the observed action, but instead reflects variables related to the selection of the agents own action, consistent with a transformation from observed action to self-action.

The consolidation of novel motor skills has traditionally been investigated over the timescale of hours-days following practice. However, a growing body of evidence has demonstrated that consolidation of skills occurs more rapidly across a scale of seconds - a process termed micro-consolidation. Micro-consolidation of explicitly cued motor sequences is supported by frontoparietal beta oscillations. Whether beta power modulation is a common mechanism supporting rapid consolidation of other forms of skill learning, such as implicit sequence learning, is yet to be elucidated. 72 healthy adults aged 18-35 (55% female) completed a serial reaction time task with concurrent electroencephalography recording. In line with our previous work, we show that the early fast learning on an implicit sequence task is primarily expressed as micro-offline gains during brief rest periods between periods of practice. Beta power was modulated as a function of active practice vs rest epochs (i.e., event-related synchronisation/desynchronisation), and here we demonstrate that micro-offline gains are associated with this modulation of beta power during the rest epochs. This relationship was specific to the beta frequency, and was not observed across either mu or gamma bands. Overall, in line with seminal work implicating beta in early explicit motor learning, our results indicate that beta is a shared neurophysiological signature of micro-consolidation of implicit sequences. Key points summary- Recent evidence demonstrates rapid consolidation of motor skills over seconds, termed micro-consolidation. - Seminal work has implicated beta oscillations in early explicit motor learning, though whether beta supports rapid consolidation of other forms of skill learning is unclear. - Using electroencephalography, we demonstrate that beta modulation is a neurophysiological signature of micro-consolidation of implicitly learnt motor sequences. - Lower beta at rest is associated with a higher degree of micro-consolidation. - Our findings shed critical new insight into the neurophysiological mechanisms mediating rapid consolidation of implicit motor skills during early fast learning.

The noradrenergic nucleus locus coeruleus (LC) is involved in numerous cognitive functions. Its activation often enhances sensory and motor performance and its activity correlates with arousal, which altogether suggest a general role in the mobilization of resources for cognition and action. We recently showed its strong and specific implication in physical effort and indirect evidence suggest that it might also be involved in cognitive effort. To address this question directly, we used a pharmacogenetic approach in rhesus macaques to selectively and reversibly inhibit LC neurons in a cognitively challenging task. Two monkeys were injected with viral vectors expressing inhibitory DREADDs (hM4Di) specifically in noradrenergic LC neurons, allowing reversible suppression of LC activity via systemic administration of deschloroclozapine (DCZ, 0.1 mg/kg). A third monkey served as a control and only received DCZ injections. Monkeys performed a simple hole-board task in which they searched for food rewards (raisins) hidden in a 5x5 grid of wells. In the transparent condition, rewards were visible, requiring minimal cognitive effort. In the opaque condition, rewards were hidden, such that monkey had to rely upon working memory to avoid revisiting empty wells. Thus, performance in opaque condition required more cognitive effort. Behavioral analysis showed that LC inhibition had no effect on performance in the transparent condition. However, in the opaque condition, it significantly impaired performance by increasing errors (revisits), without affecting the total number of rewards obtained, response times, or overall motivation. Monkeys compensated the decrease in success rate by performing more trials, indicating reduced efficiency rather than disengagement. These findings demonstrate that the LC plays a critical causal role in mobilizing cognitive resources for a demanding task. This is in line with the idea that the noradrenergic system contributes broadly to cognitive control and effort, extending previous findings on its involvement in physical effort. Overall, the study provides strong evidence linking LC activity to cognitive effort regulation, thereby complementing non-invasive studies in humans.

Human social perception relies on multiple visual signals, including object-directed actions and emotional facial expressions. It remains unclear whether responses to these signals converge within action-observation regions and whether apparent convergence depends on the spatial scale of analysis. We scanned 39 healthy human adults during two block-design fMRI tasks, hand action observations contrasted with paper-tube controls, and emotional expression observations contrasted with neutral faces. Using independently defined meta-analytic action observation network (AON) ROIs in the inferior frontal gyrus (IFG), inferior parietal lobule (IPL), and posterior superior temporal sulcus (pSTS), we analysed responses at whole-brain, ROI-average, and AON-constrained voxelwise scales. Whole-brain overlap between the two contrasts was localised primarily to the left lateral occipitotemporal extrastriate cortex, outside the AON. At the regional ROI-average scale, the IFG showed positive responses to both contrasts, whereas the IPL and pSTS showed opposing task preferences. Crucially, regional IFG co-engagement did not imply that the same voxels responded to both contrasts. Suprathreshold voxelwise overlap within the AON was virtually absent, and individual-level analysis revealed a small but reliable posterior displacement of hand action relative to emotional face within IFG. These findings show that spatial convergence between hand and emotion observation responses depends on the scale of analysis. The same IFG region can be engaged by both stimulus domains while retaining distinct local response topographies.

The dual mechanisms of control (DMC) framework distinguishes between proactive (anticipatory) and reactive (post-conflict) adaptive cognitive control mechanisms. Evidence for proactive deficits in Parkinsons disease (PD) is inconsistent, and the neurophysiological underpinnings remain poorly understood. We investigated adaptive control in 30 PD patients and 30 demographically similar healthy controls. Adaptive cognitive control was tested using a numerical Stroop test that included manipulations sensitive to proactive and reactive control. In both behavioral and EEG analyses, inducer items that trigger control adaptation were distinguished from diagnostic items, allowing adaptation to be assessed independently of learning effects. Event-related potentials (ERPs) derived from electroencephalography (EEG) captured signatures of proactive (N450) and reactive (Late Positive Complex, LPC) control. The HC group showed robust proactive control with faster responses compared to reaction times to reactive control condition, whereas PD revealed reduced proactive control, particularly for diagnostic items. ERP analysis indicated a clear N450 in the HC group, whereas the N450 was absent in the PD group. Both groups displayed LPC activity during reactive control, but PD also showed LPC activity in the adaptive proactive control condition, suggesting compensatory reliance on reactive mechanisms. Both, behavioural and ERP analyses provide insights into the dissociation of reactive and proactive control processes in PD. Our findings indicate selective impairments in proactive control, along with preserved reactive control, in patients with PD. Moreover, the presence of the LPC during proactive control trials suggests that the recruitment of reactive control mechanisms may compensate deficits in proactive control in PD.

BackgroundIn acute disorders of consciousness following severe brain injury, the heterogeneity and multiplicity of brain lesions make it difficult to infer a direct causal link between lesion patterns and impaired consciousness. As a result, neuroimaging analyses performed in intensive care settings can inform theories of consciousness mainly through correlational, rather than causal, evidence. The mesocircuit hypothesis proposes that interactions between the thalamus, basal ganglia, and cortex support the neural mechanisms underlying awareness. Among its key components, the intralaminar thalamic nuclei are thought to play a central role, yet their respective contributions to mesocircuit dynamics remain poorly understood. MethodsIn two macaque monkeys, we combined causal perturbations of three thalamic nuclei (the centromedian-parafascicular complex (CM/Pf), central lateral nucleus (CL), and mediodorsal nucleus (MD)) with a cue-guided behavioural task requiring the processing of multisensory information. Electrical microstimulation was first used to compare the behavioural consequences of perturbing each target. Reversible pharmacological inactivation using muscimol was subsequently performed in the CM/Pf and CL. Finally, the large-scale metabolic effects of CM/Pf inactivation (muscimol) and disinhibition (bicuculline) were assessed using [18F]FDG PET imaging. ResultsPerturbation of the intralaminar nuclei disrupted behavioural performance, with the strongest and most reproducible effects observed following CM/Pf manipulation. CM/Pf inactivation reduced correct responses and increased omissions and wrong responses, particularly under conditions requiring greater behavioural engagement. Importantly, these deficits occurred without evidence of major wakefulness impairment, as animals remained responsive throughout testing and showed no substantial increase in eye-closure probability. In contrast, CL perturbation produced weaker behavioural effects, suggesting distinct functional contributions of the two intralaminar nuclei. [18F]FDG PET imaging revealed that CM/Pf disinhibition increased glucose metabolism across thalamic, striatal, pallidal, and frontal cortical territories, whereas CM/Pf inactivation induced a broadly reciprocal pattern of metabolic pattern. These findings identify the CM/Pf as a major modulator of both thalamo-striatal and thalamo-cortical components of the mesocircuit. ConclusionsOur results show that a unilateral intralaminar nucleus perturbation is not sufficient to affect wakefulness, suggesting that this function is mediated by a bilateral network at the thalamus level within the mesocircuit. The CM/Pf emerged as the intralaminar nucleus exerting the strongest influence on goal directed behaviours requiring the mesocircuit dynamics. Our findings also support the existence of partially distinct intralaminar pathways contributing differentially to global state regulation of awareness-related functions, and identify the CM/Pf as a key thalamo-striatal hub within the mesocircuit.

Tourette Syndrome (TS) is a neurodevelopmental hyperkinetic disorder characterised by involuntary tics. These tics are thought to arise due to hyperexcitability of the motor cortex due to disinhibition within the cortico-striato-thalamo-cortical pathway. Given the involvement of motor circuits in this disorder, we explored whether there is a difference in the oscillatory dynamics of voluntary movements in people with tic disorders. We recorded optically pumped magnetometer magnetoencephalography during cued voluntary finger abductions in individuals with tic disorders and age- and sex-matched neurotypical controls. We analysed the data both using conventional time frequency analysis and using hidden Markov modelling to explore the difference in beta burst characteristics and dynamics. Whilst no differences were seen between groups during conventional analysis, we demonstrated an increase in beta burst duration during the post-movement beta rebound within the contralateral motor cortex in individuals with TS suggestive of increased inhibition following movement. We also show evidence of increased contralateral sensorimotor functional connectivity and reduced connectivity from and between frontal regions, as measured using coincident beta bursts. This is suggestive of disrupted functional connectivity within frontal control networks in individuals with TS.

Musical training produces behavioral gains that extend beyond the practiced context. Yet, it is unclear whether such generalization is accompanied by broadly transferable neural changes or whether training-induced plasticity remains tied to the specific features of the learned material. In this study, 80 musically naive adults completed four piano-training sessions and underwent functional MRI before and after training. Twenty untrained participants served as passive controls. Participants performed a passive listening task in which they listened to the trained melody (Fur Elise) and an untrained melody (Ode to Joy), each played on a trained musical instrument (piano) and an untrained musical instrument (saxophone). Following training, participants demonstrated improved accuracy and rhythmic performance when playing an unfamiliar melody, indicating behavioral generalization. Training-induced neural changes, however, were predominantly associated with the learned melodic content. Listening to Fur Elise elicited increased activity in the intraparietal and supplementary motor cortex and in the cerebellum, as well as decreased activity in the superior temporal cortex. Consistently, pre- and post-training scans were most accurately classified based on brain activity to Fur Elise played on piano or saxophone, rather than brain response to Ode to Joy, suggesting that neural reorganization was driven more strongly by the practiced melody than by the trained instrumental timbre. Training also enhanced the neural separability of both melodic and instrumental information. Critically, pre-training responses to Fur Elise played on the piano predicted subsequent playing accuracy, whereas pre-training sensitivity to instrumental timbre predicted rhythmic performance in a novel melodic context. Together, these findings suggest that while acquired musical skills behaviorally transfer to novel material, practice-induced functional plasticity remains predominantly melody-specific. We conclude that musical skill acquisition reflects complementary contributions of pre-existing neural characteristics and learning-induced plasticity, with baseline auditory representations potentially supporting successful behavioral transfer.

Understanding how the brain represents meaning at different levels of specificity, from general categories (bird) through combined phrases (nocturnal bird) to specific exemplars (owl), is a central question in semantic cognition and its disorders. The anterior temporal lobes (ATL) have been implicated in both activating stored conceptual representations and combining them, yet whether these two routes to conceptual content engage the ATL in the same way remains an open question. We recorded concurrent MEG-EEG from 36 participants reading 100 conceptual triads varying parametrically in specificity: general words (bird), adjective-noun phrases (nocturnal bird), and specific words (owl). Source analyses revealed a non-linear pattern in bilateral ATL (400-520ms): high-specificity concepts elicited greater activity than both low-specificity words and mid-specificity phrases. Bilateral inferior frontal cortex showed this effect with similar timing (430-630ms). N400 amplitude and ATL source activity showed a functional dissociation in their sensitivity to word frequency, ruling out a purely frequency account of the ATL and IFC effects. Results imply that accessing high-specificity concepts requires individuating stored representations among competitors, whereas phrases construct meaning through a different route. These findings extend the unified semantic hub account by revealing that computational operations within the ATL vary depending on task and stimulus demands.

The cerebellum has long been considered a late-maturing structure subordinate to neocortical development, therefore its potential role as an early driver of cortical organization remains largely unexplored. Using two large longitudinal neuroimaging cohorts of developing children together with lesion experiments in mice, we show that early cerebellar morphology may drive neocortical maturation in a regionally specific manner. These cross-species findings implicate the cerebellum as a possible regulator of neocortical organization.

Introduction: Parkinson's Disease (PD) motor features typically begin unilaterally, but it remains unclear whether dominant versus non-dominant side motor symptoms differentially affect lateralized aspects of fine motor control. Methods: We recruited 16 right-handed participants with mild, asymmetric PD (8 primarily left-side affected, 8 primarily right-side affected) and 10 age-matched controls to complete a bimanual tablet task in which one hand draws a stylus to targets (leveraging trajectory control mechanisms) while the other hand simultaneously stabilizes a stylus over a stationary target (leveraging stabilizing control mechanisms). The styli are connected via a resistance band to mimic internal forces that arise during asymmetric, bimanual activities of daily living. Results: Both PD groups demonstrated preserved trajectory control in their dominant hand relative to controls (p > .072), but significantly impaired stabilizing control in their non-dominant hand (p < .022), with the largest deficits observed in the left-side PD group. Trajectory control performance significantly correlated with an overall measure of motor severity (r(14) = .69; p = .004), while stabilizing control did not (p = .56). Discussion: These findings suggest that left- and right-side motor symptoms in early PD produce distinct patterns of functional impairment (rather than simple contralateral analogs) that may be related to underlying lateralized motor control mechanisms. This work highlights a potential gap in standard clinical motor assessments, which may not adequately capture non-dominant side stabilizing deficits in early PD.

Background: Neuromelanin-MRI enables in vivo assessment of the substantia nigra (SN) and locus coeruleus (LC) in individuals with Parkinson's disease (PD), yet longitudinal studies rely on cross-sectional processing that may introduce measurement variability and confound estimates of change over time. Objectives: In this paper, a longitudinal neuromelanin-MRI processing framework is presented that is designed and validated to improve measurement stability and reduce processing-related variability across repeated scans. Methods: Imaging and clinical data from the Quebec Parkinson Network were analyzed in 268 participants (199 PD, 69 controls), including a longitudinal subset of 74 participants (49 PD, 25 controls) scanned approximately one year apart. Validation experiments evaluated slice-by-slice intensity normalization for slice dependent intensity variation, bias field correction for LC signal asymmetry, and the effects of longitudinal registration on measurement stability and PD-control discrimination. Results: Slice-by-slice intensity normalization significantly reduced brainstem intensity variability by 3.6%. A systematic leftward signal asymmetry was observed in the LC and persisted following N4 bias field correction, suggesting a scanner-related effect not captured by conventional bias field modeling. Longitudinal registration reduced annualized change variability by 25-36% for SN_CR and 27-34% for LC_CR metrics in controls, indicating improved within-subject measurement stability. Residual variability was also reduced for contrast-based metrics by up to 28%. Longitudinal registration generally produced larger PD-control effect sizes at baseline and follow-up, particularly for SN volume metrics. However, no significant method x group x time interactions were observed, indicating that estimated longitudinal trajectories did not differ significantly between longitudinal and conventional cross-sectional processing. Conclusions: Longitudinal registration reduced technical variability and improved the precision of NM-MRI measurements. Although it did not significantly enhance detection of longitudinal PD-control differences over the follow-up interval examined here, it provides a more robust framework for longitudinal NM-MRI studies and may improve sensitivity to subtler biological effects in future investigations.

Structural differences observed in collision-sport athletes may reflect repetitive head-impact exposure, broader effects of athletic training, or pre-existing individual variation, making inclusion of a non-collision athlete group important for interpretation of any differences seen. Here, structural T1-weighted MRI data from 17 collegiate American football players, 16 cross-country runners, and 9 non-athletes were analyzed using FSL voxel-based morphometry (VBM), FIRST subcortical volumetry and vertex-wise shape analysis, and FAST whole-brain tissue segmentation. Spatial inference used permutation testing with threshold-free cluster enhancement and family-wise error correction, while scalar analyses used multiplicity-corrected procedures. FAST-derived absolute tissue volumes were also examined in a sensitivity analysis adjusting for FreeSurfer estimated total intracranial volume (eTIV). VBM showed recurrent brainstem-centered differences, with non-athletes showing greater local gray matter measures than both athlete groups, whereas football players showed greater brainstem measures than runners. FIRST vertex-wise analysis identified corrected differences involving the brainstem and selected subcortical structures, while no total FIRST structure volume survived false discovery rate correction. Unadjusted FAST analysis identified a CSF group effect, F(2, 24.38) = 11.46, p < .001, q = .001. After eTIV adjustment, the CSF group effect remained, F(2, 38) = 14.30, q < .001, and a white matter group effect was also identified, F(2, 38) = 9.59, q < .001; gray matter and total segmented tissue did not show corrected adjusted effects. These findings indicate that structural variation depends on anatomical scale, comparison group, and head-size adjustment and cannot be attributed uniquely to collision-sport exposure.

When people watch the same political narrative, they often form different interpretations. Although prior research has shown that political ideology can shape shared neural responses to sociopolitical content, less is known about how individual differences in national identity ideology are associated with inter-individual similarity in neural dynamics during naturalistic viewing, particularly in sociopolitical contexts where national identity is highly salient in public discourse. We addressed this question across two studies in Taiwan by examining how Greater Chinese ideology relates to positive engagement and neural dynamics during naturalistic viewing of a pro-China video. In Study 1 (N = 52), higher Greater Chinese ideology was associated with greater positive engagement. In Study 2 (N = 60), participants underwent fMRI while viewing the same video. Intersubject representational similarity analysis showed that inter-individual similarity in Greater Chinese ideology was associated with inter-individual similarity in neural dynamics within the frontoparietal control network and default mode network. Notably, neural similarity was primarily observed among participants lower in Greater Chinese ideology, revealing an asymmetric pattern across the ideological continuum. These findings extend prior work on political ideology by demonstrating that national identity ideology is linked to both subjective experience and shared neural dynamics during political narrative processing in a non-Western context. HighlightsO_LINational identity ideology was linked to positive narrative engagement C_LIO_LIIdeology similarity mapped onto neural similarity in the FPN and DMN C_LIO_LIExperience and neural dynamics varied with national identity ideology C_LI

Parkinson disease (PD) is characterized by excessive neural synchronization in the 13 to 30 Hz beta band within basal ganglia circuits. Conventional therapies, including dopaminergic medication and deep brain stimulation (DBS), reduce beta synchrony while enhancing lower-frequency theta activity. As an adjunct to these treatments, music and auditory rhythms improve motor function in PD, but the neural mechanisms remain unclear. Here, we recorded local field potentials in the subthalamic nucleus (STN) of patients with PD in the medication off state to test how structured musical elements shape subcortical synchrony. Spectral and neural state-space analyses showed that rhythmic and harmonic components of music produced effects comparable to dopaminergic therapy, suppressing beta-band oscillations while enhancing theta band activity. These effects were strong in the dorsal sensorimotor STN, whereas the ventral limbic STN showed minor modulation. Directional connectivity analysis further revealed that music-induced beta and theta changes were accompanied by increased cortex to STN drive, consistent with top down recruitment of the cortical subthalamic hyperdirect pathway. Notably, harmonic consonance produced network-level modulation comparable to, and in some cases greater than, rhythmic entrainment, extending beyond the established framework of beat based basal ganglia engagement. Together, these findings identify frequency selective, region specific, and stimulus-locked mechanisms by which music reshapes pathological basal ganglia activity in PD, providing direct electrophysiological evidence that auditory stimulation can transiently shift subcortical dynamics toward a medication like state.

Aphasia is characterized by impaired word retrieval, yet most cognitive models of word production assume that underlying conceptual-semantic representations are largely preserved. This study investigated whether concept-level semantic structure remains decodable from BOLD signals in chronic post-stroke aphasia and which semantic models best explain neural representational geometry during covert semantic feature generation. Eight healthy adults and six individuals with chronic aphasia completed a dense-sampling fMRI protocol in which they viewed 57 pictured nouns while silently generating semantic features. Representational similarity analysis showed that an experiential model (Exp48) best matched neural geometry in both people with aphasia and controls, outperforming taxonomic (WordNet) and distributional (Word2Vec, GloVe) models. Using representational similarity decoding, concept identity was recovered well above chance in both groups. No relationship was found between decoding accuracy and language measures from individuals with aphasia. These findings suggest that experiential semantic structure remains robustly represented and decodable in chronic aphasia despite lesion-related language impairments, highlighting preserved conceptual representations alongside altered anatomy.

Unveiling the plastic mechanisms of the primary visual cortex (V1) is crucial for understanding how visual processing can change and adapt, ultimately informing interventions to promote functional recovery following visual system damage. Paired associative stimulation (PAS) protocols can induce associative plasticity within the human V1. However, previous paradigms used full-field visual stimulation, engaging both hemispheres simultaneously, leaving unclear whether plasticity can be selectively targeted to a single visual pathway and whether it can modulate the non-stimulated hemisphere. Across three experiments in healthy participants, we investigated the neurophysiological, behavioural, and interhemispheric outcomes of a novel lateralized visual PAS protocol (vPAS). Pattern-reversal checkerboards were presented in a single visual hemifield and time-locked to transcranial magnetic stimulation (TMS) pulses delivered over the contralateral V1. Experiment 1 assessed neurophysiological effects by recording hemifield-lateralized visual-evoked potentials (VEPs) and testing three inter-stimulus intervals (ISIs: 75, 100, and 125 ms) between vPAS-paired stimuli. Experiment 2 evaluated perceptual changes in contrast detection, while Experiment 3 examined vPAS hemispheric specificity and aftereffects on interhemispheric visuomotor transfer. Only the 75-ms ISI consistently modulated visual processing in the non-conditioned hemisphere, reducing N75 amplitude and improving contrast detection for visual stimuli presented contralateral to the TMS side. Longer ISIs were not effective. Furthermore, this protocol altered interhemispheric transfer exclusively when the left, but not the right, V1 was targeted during vPAS. In conclusion, lateralized vPAS induces timing-dependent changes beyond the stimulated cortex, suggesting that associative plasticity can engage contralateral visual circuits and modulate visual processing.

Propofol-induced general anesthesia and natural sleep are both associated with GABA-A-ergic inhibition and slow-wave activity. Whereas sleep actively supports memory consolidation, consolidation may be disrupted during anesthesia. Here, we compared EEG and memory data from 19 participants undergoing surgery under propofol-induced anesthesia with data from 17 participants taking a nap. In both groups, participants completed a hippocampus-dependent spatial memory task (Virtual Water Maze) and a procedural memory task (Mirror Tracing) before (pre) and after (post) an interval filled with either anesthesia or sleep. Performance declined from pre to post in the propofol group for both tasks, whereas it remained stable in the sleep group. Slow oscillations (SO) occurred during both non-REM sleep and propofol-induced anesthesia. However, only during non-REM sleep did SOs show increased spindle activity during the SO upstate. Together, these findings suggest that propofol anesthesia disrupts memory consolidation, most likely because SOs under anesthesia lack the spindle coupling that mediates the hippocampal-neocortical information transfer underlying systems memory consolidation.