Cerebral Cortex Communications

Moderate-to-severe traumatic brain injury (msTBI) is recognized as a chronic and evolving neurological condition characterized by progressive structural brain changes and persistent cognitive impairment. While prior studies have demonstrated widespread atrophy following msTBI, less is known regarding the longitudinal trajectory of gray matter (GM) changes during recovery and post-rehabilitation. The current study used longitudinal voxel-based morphometry (VBM) to characterize GM volume changes over a period of 9 months, in individuals with msTBI relative to healthy controls (HC). Associations between regional GM volume and neuropsychological functioning were examined. Twenty-eight participants (14 msTBI, 14 HC) completed MRI and neuropsychological assessments across three timepoints spanning outpatient rehabilitation and follow-up. Longitudinal VBM analyses revealed significant group and time interactions within subcortical and limbic regions. Relative to HC, individuals with msTBI showed lower GM volume in these regions at baseline, with trajectories that converged toward HC values (right hippocampus) or increased relative to HC over the rehabilitation period (bilateral pulvinar), whereas the right amygdala and inferior cerebellar vermis remained persistently reduced. Significant longitudinal improvements in memory and psychomotor speed during the rehabilitation period were demonstrated in msTBI. Greater (preserved) GM volume within the right hippocampus, thalamus, and bilateral pulvinar was associated with better performance across measures of verbal memory, processing speed, executive functioning, and cognitive flexibility. These findings suggest that msTBI is associated with dynamic structural brain changes involving subcortical, limbic, and cerebellar networks, and that the rehabilitation period was accompanied by relative volumetric stabilization in these regions and by meaningful cognitive improvement.

Verbal fluency is a behavioral task that requires the generation of words from a semantic category (category fluency) or words beginning with a specific letter (letter fluency). Although word production engages a frontal-temporal-parietal network, no studies have tested how lesions to temporal and parietal lobe areas that represent semantic and phonological knowledge dampen neural responses in the left pars triangularis and the left pars opercularis, two adjacent regions in the left inferior frontal gyrus implicated in word search and retrieval. Here, 52 patients with temporal lobe lesions underwent clinical functional MRI while performing the category and letter fluency tasks. We investigated where lesion presence was inversely related to the magnitude of task-specific neural responses in pars triangularis and pars opercularis using a technique referred to as voxel-based lesion activity mapping (VLAM). We found that lesions to the left anterior superior temporal gyrus, left temporal pole, left hippocampus, left insula, and underlying inferior fronto-occipital fasciculus were associated with reduced neural responses in the left pars triangularis during the category fluency task. Lesion damage to the right hippocampus was associated with reduced neural responses in the left pars opercularis during category fluency. By contrast, lesions to the left posterior superior temporal gyrus, left supramarginal gyrus, left parietal operculum, and the inferior fronto-occipital fasciculus and left arcuate fasciculus were associated with reduced neural responses in the left pars triangularis and the left pars opercularis during the letter fluency task. These results suggest that anatomically dissociable brain networks interact with the left inferior frontal gyrus when different search strategies constrain the retrieval of word representations.

Value-based decision-making is a dynamic and idiosyncratic process which requires appraising the value of options and comparing the values to select the best choice. An emerging view of orbitofrontal cortex (OFC) is that it achieves this by representing values serially during deliberation, alternating back-and-forth between transient states that encode the value of different options. While the time spent in each value state is known to reflect choice behavior, the source of the alternating dynamics remains unclear. One possibility is that fluctuations in value may be driven by attentional shifts between the choice options. Conversely, value dynamics in OFC may be generated locally, enabling OFC value signals to influence decision-making independently from attention. To test these hypotheses, we recorded from OFC and lateral prefrontal cortex (LPFC), a major attentional area in prefrontal cortex, to determine whether their population-level activity correlated in a manner consistent with crosstalk between neuronal systems involved in value and spatial attention. We found that OFC and LPFC selectively encoded option values and spatial locations, respectively, reflecting their specialized roles in cognition. Despite this functional dissociation, both OFC and LPFC dynamics were strongly affected by overt attention: which caused the value and spatial location of the fixated option to be represented at the same time. Additionally, fluctuations in the encoding strength of value in OFC and space in LPFC were temporally correlated above and beyond the effect of gaze, reflecting the effect of covert attention.

Economic choices are believed to depend on the orbitofrontal cortex (OFC). Work in primates and rodents indicates that neurons in OFC participate in computing and comparing subjective values, suggesting that different groups of cells constitute the building blocks of a decision circuit. In a recent study (Livi et al., 2025), we examined the laminar organization of this circuit in mice. We found that different decision variables were differentially represented in layer 2/3 (L2/3) and layer 5 (L5). Furthermore, the temporal dynamics of decision signals indicated a combination of feed-forward and feed-back across layers, and pointed to L5 as the locus for winner-take-all value comparison. Importantly, these results were obtained under the constraint that each neuron encoded a single variable. Here, we tested whether our results on laminar organization depended on the categorical framework. We applied LASSO regression to identify a minimal set of variables explaining each neurons activity. Even with approximately half of all neurons representing two or more variables, the layer specificity of decision variables was preserved. In addition, Granger Causality Analysis and activity profiles reached similar conclusions as for analyses conducted under the single-variable constraint. We conclude that the decision circuit in OFC exhibits a laminar architecture, independently of whether the representation of decision variables in this area is categorical or mixed.

Models of predictive processing propose that the brain continuously generates predictions about incoming sensory input, updating an internal model of the environment through prediction errors when those predictions are violated. A foundational assumption of these models is that prediction error generation occurs automatically, independently of conscious awareness. Evidence from auditory oddball studies in unconscious patients appears to support this view, though findings are complicated by stimulus-specific adaptation confounds that make it difficult to isolate genuine predictive effects. To investigate whether expectation suppression or prediction-based attenuation extends to the motor system and whether it operates automatically, we developed a novel motor oddball paradigm using brain stimulation. Transcranial magnetic stimulation (TMS) delivered over the primary motor cortex elicit motor-evoked potentials (MEPs) in peripheral muscles, providing an index of corticospinal excitability. By varying stimulation intensity in an oddball-like manner using repeating and deviating sequences, we manipulated the predictability of TMS pulses and compared MEP amplitudes for expected versus unexpected intensity-matched stimulation. Incorporating experimental designs to control for adaptation and an instruction manipulation to test the role of awareness, expected TMS reliably produced smaller MEPs than unexpected TMS. Critically, this attenuation was observed only in participants with explicit knowledge of the sequence structure. These findings extend expectation suppression effects to the motor system and support the domain-generality of prediction-based neural attenuation while challenging the assumption that predictive processing operates entirely automatically.

Human long-term memory for visual scenes is remarkably robust, yet the neural mechanisms supporting memory encoding and retrieval remain poorly understood when both processes must operate at the same time. For instance, this might happen when we encounter a familiar place while simultaneously forming new memories of this encounter. We investigated electrophysiological correlates of visual recognition memory using a continuous recognition task (CRT), in which participants judged a continuous stream of scene photographs as previously seen or new, such that encoding and retrieval occurred in parallel on every trial. To make recognition particularly demanding, stimuli were drawn from only four scene categories. Thirty-one participants performed the task while EEG was recorded, and we analyzed canonical ERP markers of retrieval (mid-frontal FN400, 300-550 ms; late parietal effect, LPE, 550-800 ms) and encoding (subsequent memory effect, SME) as a function of stimulus repetition and lag between consecutive presentations. FN400 showed robust old/new effects for both repetitions, whereas LPE differences emerged only at the second repetition. While FN400 amplitude was insensitive to lag, LPE amplitude decreased systematically with increasing lag, mirroring the behavioral pattern of declining accuracy and slower responses. A significant SME emerged selectively for images subsequently recognized on both repetitions, indicating that the SME in continuous recognition is specific for the most robustly encoded items and reflects the strength of encoding. Together, these findings show that canonical ERP markers of recognition memory are preserved even when encoding and retrieval operate concurrently, but their expression depends on how often and how recently an item has previously been encoded - parameters that can be flexibly manipulated within the CRT. This demonstrates that the CRT is sensitive to fine-grained temporal dynamics of memory formation and retrieval that could be missed under standard single-repetition designs.

We investigated the dimensions of output zones affecting specific combinations of forelimb muscles in the precentral "motor" cortex of macaque monkeys. Single-pulse intracortical microstimulation (S-ICMS) was used to evoke subthreshold effects in multiple wrist and finger muscles. Results indicate that each motor cortex site represents a different combination of muscles. The effects evoked from cortical sites separated by several hundred microns invariably involved different profiles of muscle activity. The muscle fields of remote CM cells were rarely identical, while the fields of neighboring CM cells were often similar. Given the number of unrecorded muscles, we conclude that primate motor cortex is a mosaic of output sites representing forelimb muscles in different combinations.

The prefrontal cortex (PFC) plays a critical role in maintaining working memory (WM) representations while filtering irrelevant distractors. In macaques, PFC neurons exhibit persistent delay period activity that is robust to distractor interference. The common marmoset has emerged recently as a complementary primate model for investigating the neural basis of cognitive processes including WM, in part because the relatively lissencephalic cortex of this species enables laminar recordings which could provide substantial insight into the microcircuit basis of these functions. It remains unknown however, whether marmoset WM performance is robust to distractors presented during delay periods of WM tasks, and how such distractor filtering may be implemented in PFC circuits. Here, we addressed this gap by conducting wireless recordings of PFC in freely moving marmosets performing a touchscreen-based delayed-match-to-location (DML) task in which a salient visual distractor was presented during the delay period on a subset of trials. Marmosets maintained WM performance on distractor trials, showing a decrease in accuracy of only 5%. Consistent with prior observations in both the macaque and marmoset models, we found that many PFC neurons exhibited activity related to the stimulus sample, during the delay period, and around the time of the behavioural response. In a subset of neurons, we observed distractor-mediated modulations of persistent delay period activity which were associated with a greater incidence of performance errors on the DML task. These findings reveal that marmoset WM is robust to distractor interference, and that the PFC mechanisms instantiating WM and distractor filtering are conserved in this primate species. Taken together, they support the common marmoset as a complementary model for investigating the contribution of PFC circuits to mnemonic and attentional processes.

Background: Persistent neurological and cognitive symptoms following SARS-CoV-2 infection point to long-term alterations in brain structure and function. The thalamus, orbitofrontal cortex, and limbic networks are particularly susceptible to inflammatory and neurovascular stressors. However, the relationship between cortical, white-matter, and thalamocortical alterations in post-COVID syndrome remains unclear. Methods: 76 COVID-19 recovered participants (CRPs) and 51 healthy controls (HCs) underwent multimodal MRI comprising T1-weighted structural, diffusion, and resting-state functional acquisitions. Grey-matter morphology was assessed using voxel-based morphometry (VBM), white-matter microstructure using tract-based spatial statistics (TBSS), and thalamocortical functional connectivity (TC-FC) using seed-based analyses from major thalamic nuclei. Results were evaluated both across the groups (HC vs. CRP) and after stratifying CRPs by hospitalisation status (HC vs. Non-hospitalized patients (NHPs) vs. Hospitalized patients (HPs)). Results: No group-level grey-matter differences were observed between HCs and CRPs; however, HPs showed localized volume loss in the orbitofrontal and frontal-pole cortices (pFWE < 0.05). TBSS revealed widespread microstructural abnormalities, including reduced fractional anisotropy and mean diffusivity across association and commissural tracts (pcorr < 0.05), with regional increases in mode of anisotropy indicating selective loss of crossing fibres (pcorr < 0.05). Resting-state analyses revealed increased TC-FC from the mediodorsal thalamic nucleus to anterior cingulate, parietal, and occipital cortices (pcorr < 0.05), while differences in pulvinar and ventrolateral nuclei were not significant (pcorr > 0.05). Conclusions: Our findings indicate that COVID-19 recovery is associated with enduring alterations in fronto-limbic and thalamo-cortical circuits, most prominently in individuals with severe infection. Convergent structural and functional changes involving the orbitofrontal cortex and mediodorsal thalamus suggest network-specific reorganisation that may underpin persistent cognitive and affective symptoms of post-COVID syndrome.

Object representations in the human ventral occipitotemporal cortex (VOTC) are organized along multiple dimensions, including shape (rectilinear vs. curvilinear), real-world size (large vs. small), and mobility (stationary vs. mobile). However, these dimensions are strongly correlated in naturalistic vision, making their separate contributions to VOTC organization unclear. For example, large objects (e.g., a wardrobe, a house) are typically rectilinear and stationary, while small objects (e.g., a ball, a cup) are more curvilinear and mobile. Here, we used fMRI, together with a new stimulus set that orthogonally manipulates shape, size, and mobility, to investigate the separate influences of these dimensions on VOTC organization. Example stimuli include air balloon (large, curvilinear, mobile), radar dish (large, curvilinear, stationary), and mailbox (small, rectilinear, stationary). Contrasts revealed that large (vs. small), rectilinear (vs. curvilinear), and stationary (vs. mobile) dimensions all independently evoked strong and overlapping activity in medio-anterior VOTC. This overlapping activity was at the intersection of the parahippocampal place area (PPA) and the ventral place-memory area (VPMA). Similar results were found at the intersection of the scene-selective occipital place area and the lateral place-memory area (LPMA). Finally, large (vs. small), but not rectilinear (vs. curvilinear) or stationary (vs. mobile) activity, was found in additional posterior ventral scene-selective regions, as well as in early visual cortex. Overall, these results indicate that object shape, real-world size, and mobility dimensions all independently activate scene-selective PPA and OPA, showing joint selectivity for distinct low- and high-level object properties that are highly correlated in naturalistic vision.

Adaptive deep brain stimulation (aDBS) of the subthalamic nucleus (STN) ameliorates motor symptoms in advanced Parkinson's disease (PD) by modulating stimulation in real time using neural signals linked to motor symptoms. Whether these signals also reflect ongoing behavior in naturalistic settings remains unknown. We recorded bilateral STN local field potentials from eight PD patients undergoing aDBS during live-streamed sports viewing and show that low-frequency dynamics encode behavioral engagement across multiple timescales. Engaged viewing increased activity in the stimulation-targeted frequency band relative to control conditions. At a finer timescale, moment-to-moment engagement modulated rapid fluctuations in left STN activity with amplitude maxima and minima time-locked to salient in-match events. These findings reveal that STN activity dynamically reflects real-world behavioral states and establish a foundation for behaviorally informed neuromodulation strategies.

Prior studies in bilinguals have reported relationships between brain structure and the dimensions of (i) language proficiency or (ii) language balance (the discrepancy between a bilinguals two proficiencies), but rarely both, even though they are highly related. These studies were often conducted in late bilinguals and the analyses limited to regions of interest. Here, we tested for relationships between brain structure and these two dimensions in 46 early cultural Spanish-English bilinguals (mean age = 16.7 years) at the level of the whole brain for gray matter volume (GMV) and cortical thickness (CT). Results revealed a positive association between GMV and proficiency in the weaker language in the right angular gyrus (AG; BA 39) extending into the superior temporal gyrus (BA 22). More balanced bilingualism was also associated with more GMV in the AG (BA 39), in addition to less GMV in left postcentral gyrus (BA 1), right cerebellum lobule IX and right superior occipital gyrus (BA 18). However, these relationships between GMV and balance disappeared after controlling for language proficiency. No significant associations were observed for CT and these two dimensions of language. Our findings suggest that relationships between GMV and balance are driven by language proficiency, and that the relationship between GMV and language proficiency likely does not involve language-specific mechanisms, given the location of the association is in the right inferior parietal cortex. Together, this study separates the neuroanatomical bases of these two language dimensions and places them in brain regions outside those usually targeted in prior studies. HighlightsO_LINeuroanatomy was correlated with proficiencies in early Spanish-English bilinguals C_LIO_LIRight angular gyrus gray matter volume (GMV) was positively related to proficiency C_LIO_LIGMV was positively related to balance, but not after controlling for proficiency C_LIO_LIRelations with these language dimensions are located outside of language cortex C_LIO_LINo significant associations were observed for cortical thickness C_LI

Impaired reading, i.e., alexia, is common after left hemisphere stroke. The most common deficit in alexia is a difficulty reading aloud pronounceable novel words, also called pseudowords. While semantic and phonological processes both subserve reading real words, pseudoword reading deficits in alexia are typically ascribed to phonological deficits alone. Some theories, however, suggest that pseudoword reading relies in part on lexical-semantic knowledge, such that semantic deficits could also contribute to poor pseudoword reading in alexia. Leveraging a large sample of left-hemisphere stroke survivors, we examine the cognitive and neural substrates of pseudoword reading accuracy and two error types: lexicalization errors, where a pseudoword is incorrectly read as a real word, and nonword errors, where a pseudoword is read as an incorrect nonword. 76 left-hemisphere stroke survivors read 60 pseudowords aloud, and performed two pseudoword repetition tasks to assess phonological processing and two picture naming tasks to assess mappings between lexical semantics and phonology. Regression models assessed how pseudoword repetition and naming related to overall accuracy and rates of lexicalization and nonword errors in pseudoword reading. Voxel-based and connectome lesion-symptom mapping localized the neural territory responsible for these errors. Both pseudoword repetition and naming independently related to pseudoword reading accuracy. Pseudoword repetition but not naming deficits predicted higher rates of lexicalization errors, while naming but not pseudoword repetition deficits predicted higher rates of nonword errors. Greater nonword error rate also predicted smaller imageability effects in real word reading (t(71)=-3.2, p=0.002). Lexicalization errors were associated with lesions to and disconnections of the left putamen and basal ganglia. Nonword errors were associated with lesions to the superior and middle temporal gyri, as well as broad temporo-parietal disconnections, overlapping with previous lesion-mapping results implicating these regions in semantic contributions to word reading. These results suggest that lexicalization errors result from impaired planning and execution of novel motor plans, causing a reliance on the well-learned motor plans associated with lexical items. In contrast, greater rates of nonword errors, relative to lexicalization errors, occur when semantic contributions to reading are impaired. Overall, these findings demonstrate that semantic processes are involved in reading pseudowords, at least in stroke alexia. These findings support connectionist accounts of reading in which damage in the direct orthography to phonology route for reading leads to reliance on semantic representations, even for pseudowords, suggesting a reinterpretation of pseudoword reading as a pure measure of phonological reading deficits.

Episodic memory involves reconstruction of past events through integration of multiple types of information, including perceptual details, narrative content, and emotional tone. The default mode network (DMN) is a set of regions thought to support episodic retrieval, yet it remains unclear how distinct subnetworks contribute to recall of these different memory features. Here, we examined how DMN subnetworks support and represent memory for naturalistic emotional events. Male and female human participants encoded short news videos that varied in emotional valence and recalled them in response to neutral cues during functional MRI scanning. Videos were again recalled one day later and memories were scored for perceptual and narrative details. Activity in the dorsomedial subnetwork was related to the emotional valence of the memory, while activity in the medial temporal subnetwork was associated with the number of perceptual details recalled. Multivariate pattern analyses further revealed that the medial temporal subnetwork exhibited greater pattern stability across recalls when recalling more perceptual details, while stability in the dorsomedial and core subnetworks was tied to emotional remembering. Our findings suggest that the dorsomedial subnetwork provides an affective frame for a memory, while the medial temporal subnetwork contributes perceptual specificity. These results demonstrate that the contents of memory retrieval shape network engagement during emotional recall, providing insight into how the brain reconstructs complex real-world experiences. Significance StatementHow do we remember the emotional tone of an event versus its visual details? This study examines how distinct subnetworks within the brains default mode network (DMN) contribute to remembering different features of memory. While the medial temporal subnetwork is connected to retrieving the perceptual details of past events, the dorsomedial subnetwork supports recall of the emotional tone. Furthermore, patterns of activity in the medial temporal subnetwork are more stable when recalling more perceptually rich memories, while stability in the dorsomedial subnetwork is tied to emotional remembering. These findings suggest that the default mode network flexibly responds to different kinds of memory features, supporting the reconstruction of rich emotional memories from complex real-world experiences.

Sleep supports episodic memory consolidation, yet it remains unclear how naturalistic post-encoding sleep quality relates to the neural reinstatement of episodic representations across adulthood. The present study examined whether sleep discontinuity during the retention interval predicted delayed context memory and encoding-retrieval similarity (ERS) of EEG in younger and older adults. Participants completed an object-scene context memory task with immediate and delayed retrieval, while EEG was recorded during encoding and retrieval. Actigraphy was used to measure sleep across the post-encoding retention period, and principal component analysis identified sleep discontinuity and sleep time components. Behavioral results showed that greater post-encoding sleep discontinuity, but not sleep time, was associated with poorer delayed memory accuracy for mismatching object-context pairs across age. ERS analyses further showed that greater sleep discontinuity was associated with reduced ERS for correctly rejected mismatching pairs across frontal and posterior spatiotemporal clusters. Age moderated sleep-ERS associations: greater sleep discontinuity was generally related to lower ERS in younger adults, whereas some spatiotemporal clusters showed positive associations in older adults, potentially reflecting compensatory or effortful retrieval-related processing in poorer sleepers. Together, these findings suggest that sleep continuity during the post-encoding retention interval is important for preserving high-fidelity episodic representations needed for later context discrimination. More broadly, the results demonstrate that naturalistic sleep fragmentation is linked to both behavioral memory outcomes and neural reinstatement across adults.

Heschls gyrus (HG), which contains the primary auditory cortex, shows marked individual variability in its folding pattern, ranging from a single gyrus to partial or complete duplication. Greater HG duplication has been reported in expert musicians, often interpreted as evidence that auditory experience can shape cortical morphology. However, these structural differences might alternatively indicate a bias for musical careers in individuals whose anatomical predispositions facilitate expertise. Here, we examined HG morphology in blind individuals--a population with extensive auditory experience but without selection based on auditory ability. T1-weighted MRI data from 100 human participants (48 females, 42 males, 10 unknown) across blind and sighted groups were analyzed. HG was manually defined in each hemisphere, and folding was measured using both categorical morphology classification and continuous surface-based metrics. Across all analyses, blindness did not increase HG folding. These results suggest that the morphology of HG is largely predetermined. Significance statementIncreased anatomical folding in the auditory cortex has been reported in professional musicians. Is this structural variability due to experience-dependent plasticity, or is it that individuals with increased anatomical folding are more likely to become musicians? We examined Heschls gyrus (HG), which contains the primary auditory cortex, in blind individuals who rely heavily on auditory input. Despite extensive auditory experience, blindness did not alter HG folding. This finding suggests that the morphology of HG is not strongly influenced by auditory experience.

Memory formation relies on the hippocampus and unfolds over time across experience, such as during the visual exploration of complex, naturalistic scenes. Eye movements evoke hippocampal activity, including fixation-locked field potentials and phase resets of theta oscillations. This suggests that hippocampal encoding is temporally structured by the sequence of visual fixations. Because eye-movement sequences sample semantically meaningful portions of scenes, they provide temporal structure to semantic content in memory. However, it remains unclear how the semantic content and temporal order of fixations jointly shape medial temporal lobe activity. We therefore tested whether intracranial EEG recordings from human hippocampus and amygdala reflect the semantic content and temporal order of individual fixations during encoding of naturalistic scenes. Relative to other semantic content, fixations on people were particularly relevant for memory, with the first fixation on a person predicting subsequent scene recognition. Fixation-locked hippocampal responses were enhanced for fixations to people relative to other semantic content, expressed in both larger fixation-evoked potentials and stronger theta phase locking. These effects were strongest for the first fixation relative to subsequent fixations. Theta phase locking was also enhanced in both hippocampus and amygdala for first fixations on people relative to later fixations and to other semantic content. These findings indicate that medial temporal lobe activity is structured by discrete fixation-level events during scene encoding, suggesting that theta-paced sampling contributes to the transformation of semantic and temporal components of visual experiences into memory. Significance StatementThis study shows that the semantic content and order of eye fixations jointly influence human hippocampal activity during memory encoding. Combining intracranial recordings, eye-movement tracking, and deconvolutional modeling, we show that the first glance at a person within naturalistic scenes is a privileged event, associated with increased hippocampal activity, theta-phase resetting in hippocampus and amygdala, and subsequent memory success. These findings recast eye movements not as mere motor acts, but as an important process that helps medial-temporal structures prioritize and integrate behaviorally relevant information into episodic memory.

Claims about shared neural processing between object and action words have mainly been based on spatial overlap. Spatial overlap alone, however, provides an incomplete understanding of neural (dis)similarity. Here, we compared object and action word retrieval within participants utilising temporal, spectral, and spatial information in the electroencephalogram (EEG) recorded during context-driven object and action picture naming. Constrained sentence contexts elicited pre-picture lexical-semantic word planning for object and action words, indexed by power decreases in the alpha-beta frequency range (8 - 30 Hz). Using a novel approach based on mutual information and source-reconstructed EEG signal, we computed joint temporo-spectro-spatial (dis)similarity indices across object and action naming in the constrained condition where information retrieval occurred. Spatially, dissimilarities were found in bilateral frontal, anterior superior temporal, and right anterior-to-middle temporal areas. Similarity, by contrast, was linked to the precunei and right temporo-parietal areas, regions associated with lexical-semantic processing and word retrieval. Crucially, similarity in the precunei compared to the temporo-parietal regions was characterised by differential patterns of the alpha-beta activity, implying processing and, potentially, functional differences between the areas. This finding highlights how conclusions about shared neural processes depend on the degree of abstraction (e.g., spatial, spatial-spectral) chosen to define the compared neural mechanisms. We tentatively interpret the contribution of the right hemisphere and left frontal areas to (dis)similarity as coarser, less fine-grained lexical-semantic computations.

Neural activity in frontal-striatal circuits underlies reinforcement learning. Traditional theories suggest that reinforcement signals, which drive learning, strengthen connections within the basal ganglia. This strengthening is believed to shift information processing from cortical regions to subcortical regions as learning becomes established over time. To examine this hypothesis, we trained macaques to associate multiple sets of images with their values. Selecting different images led to either an increase (+2, +1) or a decrease (-1, -2) in the number of tokens, which subsequently determined the amount of juice reward the macaques received. We simultaneously recorded neuronal activity from orbitofrontal cortex, ventral striatum, amygdala, and dorsomedial thalamic nucleus, analyzing the dynamic changes in these brain regions during both the initial learning and overlearned stages. The results indicated that as learning progressed from the initial stage to the overlearned stage, information processing shifted from the ventral striatum to the orbitofrontal cortex, corresponding to the abstraction from stimulus value to state value. This finding challenges traditional theories and provides a new perspective on the neural circuit mechanisms of learning.

Parkinsons disease (PD) is marked by impairments in voluntary movement, including prolonged movement preparation and execution, yet how parkinsonism alters neural processing to produce these deficits remains unresolved. Prior work examining M1 spiking activity in parkinsonian states has largely characterized firing-rate changes and motor representations at the level of individual neurons, with inconsistent results and limited insight into population-level organization. Here we investigated how parkinsonism reshapes the population-level organization of neural activity in M1 during movement. We simultaneously recorded large populations of neurons from M1 in two nonhuman primates performing reaching tasks before and after induction of parkinsonism with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In the parkinsonian state, both preparation and reach durations were significantly prolonged. Population-level analyses revealed that parkinsonism increased the dimensionality of M1 activity during both preparation and movement and reduced the orthogonality between preparatory and movement-related subspaces. Moreover, trial-by-trial variability in reach duration was explained by the alignment of the preparatory and reach subspaces, indicating the functional role of subspace orthogonality. Together, these findings suggest that parkinsonism disrupts the population-level organization of cortical dynamics across computations, providing a population-level framework linking altered cortical dynamics to the movement-related dysfunction observed in PD.