Efficient interaction with the visual world requires not only accurate object identification but also precise localization of objects in space. While spatial ("where") processing has traditionally been attributed to dorsal stream pathways, recent work has shown that object position can also be decoded from responses in ventral stream areas such as the inferior temporal (IT) cortex. However, because object position in these paradigms is tightly coupled to pixel-based location, it remains unclear whether ventral stream position signals reflect perceptually meaningful spatial representations or simply inherited retinotopic structure. To address this question, we used the motion aftereffect, a classic visual illusion that shifts perceived object position without changing retinal input. Combining large-scale intracortical recordings in macaque IT with matched human psychophysics, we found that motion adaptation induces systematic direction-opponent biases in IT population codes for object position that mirror human perceptual reports, despite identical pixel-level stimuli. These effects are accompanied by adaptation-driven changes in the geometry of IT population representations. We further tested whether artificial vision systems exhibit similar dynamics. Standard feedforward, recurrent, and state-of-the-art video-based neural networks accurately encode object position but fail to produce adaptation-induced position shifts. However, applying empirically derived transformations based on IT adaptation dynamics to model feature spaces is sufficient to generate similar biases. Together, these results indicate that IT represents object position in perceptually aligned coordinates and also highlight a gap between biological and artificial vision systems in capturing history-dependent spatial coding.

Transcranial ultrasound stimulation (TUS) is a promising noninvasive technique for modulating deep brain targets and circuits with high spatial precision. For its successful clinical translation, confirmation of target engagement, together with a deeper understanding of the effects of TUS, is essential. To advance these goals, we obtained direct measures of neural activity using electrodes implanted in the subthalamic nucleus (STN) in patients with Parkinson's disease (PD) during TUS of deep and superficial targets, guided by magnetic resonance imaging-based acoustic modeling and real-time neuronavigation. Seventeen patients were studied in the on-medication and off-deep brain stimulation states. Each patient received one active and one sham session in a randomized order, and 13 of 17 patients (76%) completed a third session, which was always active. Each active condition targeted a single site-either the primary motor cortex (M1), the globus pallidus internus (GPi), or the occipital cortex (control site)-with 10 patients per active target. TUS effects on the STN were found to be target specific. Stimulation of the M1 reduced STN beta oscillation activity compared with sham stimulation and was associated with improvements in motor signs. These effects were brain state specific, showing distinct modulation patterns at rest versus during movement. In contrast, TUS targeting the GPi increased beta activity relative to control conditions and did not improve motor signs. Our results provide mechanistic evidence that TUS can safely and selectively modulate pathological brain rhythms in the STN in PD, supporting its potential as a targeted, noninvasive therapeutic modality.

Ultrasound offers a powerful means of modulating human cognition by noninvasively targeting subcortical structures previously accessible only via invasive procedures. While decades of research have mapped cortical circuits of attention, deep hubs such as the basal ganglia and thalamus are increasingly recognized as key nodes in attention networks. We tested whether low-intensity transcranial ultrasound stimulation (TUS) of the globus pallidus internus (GPi) and pulvinar modulates visual search, an attention-dependent task, predicting site-specific effects that reflect distinct basal ganglia-thalamic circuit functions. Focal TUS reduced reaction times, suggesting a facilitation of attention-related task performance. A dissociation emerged across sites: stimulation of both GPi and pulvinar reduced reaction times, but pulvinar yielded more robust benefits for target-present trials at peripheral eccentricities, and improved search efficiency in the same trials. These results support distinct contributions of basal ganglia and thalamic nodes to attention-related behavior and show that TUS can be used to probe circuit-level mechanisms of cognition in humans.

The well-documented near-hand effect enhances visual processing when a hand is placed close to a stimulus, improving performance in tasks such as target detection, figure-ground discrimination, orientation processing, and working memory.1,2,3 These behavioral advantages are thought to facilitate efficient reaching and grasping4,5,6 in peripersonal space (PPS), the multisensory region surrounding the body. This effect has been attributed to enhanced attentional selection, potentially mediated by fronto-parietal bimodal neurons and feedback from grasping-related parietal areas (e.g., anterior intraparietal area [AIP] and V6A) to the early visual cortex.7,8,9,10,11 Notably, prior neurophysiological evidence in monkeys demonstrated that a visible hand near a stimulus increases firing rates and sharpens orientation tuning in V2 neurons,12 a modulation distinct from classic covert spatial attention, which typically affects response gain without altering tuning width.13,14 This study extends these findings by recording single-neuron activity in V2 of two rhesus monkeys during a fixation task, comparing three conditions: hand near and visible, hand near but occluded, and hand far away. Replicating earlier results, a visible hand near the stimulus enhanced firing rates and sharpened orientation selectivity.12 Critically, occluding the hand reversed this pattern, producing broader orientation tuning relative to the hand-away baseline, a novel indicator of visuo-proprioceptive mismatch. These rapid, population-coherent effects reveal two complementary feedback signals in V2: congruence-driven enhancement when visual and proprioceptive inputs align and mismatch-driven suppression when they conflict. Together, the findings show that V2 actively integrates multisensory cues to encode PPS and prioritize action-relevant visual processing.

How does the human brain decode facial expressions? Addressing this question requires models that tightly link neural representations to behavior. Here, we first establish rhesus macaques as an animal model of human facial expression discrimination, showing strong behavioral correspondence across six expressions. To probe underlying neural mechanisms, we leverage artificial neural network (ANN) models of the ventral stream as explicit computational hypotheses explaining macaque behavior. Despite action unit-based stimulus generation and high classification accuracies of face-optimized models, broadly-trained ANNs best match macaque image-level behavior. Interestingly, ANNs showing the strongest behavioral alignment are those whose internal representations best resemble macaque inferior temporal (IT) representational geometry. Neural recordings further reveal that early IT responses best predict our measured expression judgments and exhibit a heterogeneous coding architecture in which identity and expression information coexist along partially overlapping dimensions. Together, these findings constrain mechanistic accounts of facial expression discrimination in high-level visual cortex.

A major goal of computational neuroscience has been to explain how the primate ventral visual stream (VVS) transforms visual input into temporally evolving neural representations that support robust visual perception. Historically, most modeling efforts have assumed static conditions: monkeys fixate a dot, images are briefly flashed, and neural responses are analyzed through time-averaged metrics. Feedforward deep networks trained on static object recognition tasks outperform prior work in approximating these static snapshot-driven VVS responses. However, mounting neurophysiological evidence demonstrates that VVS responses are rich dynamical signals shaped not only by the retinal input but also by intrinsic circuit dynamics, recurrent interactions, and widespread top-down modulation. Moreover, real-world vision is inherently dynamic: objects move, the observer moves, and the eyes actively sample the environment. Here, we review recent progress in modeling dynamic responses in the macaque ventral stream across three domains: (1) intrinsic dynamics elicited by static images, (2) dynamics evoked by dynamic visual stimuli, and (3) dynamics generated by active sensing during eye movements. We argue that accurately modeling VVS dynamics will require representational, circuit-level, and behavioral perspectives, including multi-area recurrence, structured E/I interactions, and temporal objectives that better reflect natural behavior. We outline some key missing ingredients and propose a roadmap toward dynamic, multi-timescale models of the primate VVS.

Understanding how the human brain decodes facial expressions remains a fundamental challenge, requiring computational models that tightly connect neural responses to behavior. Here, we demonstrate that rhesus macaques provide a unique and powerful animal model to uncover the neural computations behind human facial expression discrimination, bridging critical gaps between behavior, neural activity, and computational theory. Despite the challenges of establishing reliable behavioral paradigms in macaques, we developed a robust discrimination task spanning six emotional categories, yielding strong, image-by-image behavioral correspondence between macaques and humans. By systematically comparing artificial neural networks (ANNs) to macaque behavior and IT neural data, we found that traditional action unit–based models fail to capture image-level behavioral structure, while ANNs with IT-like internal representations outperform all others. Neural recordings showed that the specific IT population responses (70–100 ms) carried the strongest predictive power for facial expression discrimination, underscoring the primacy of feedforward codes in guiding behavior. Expression coding in IT was significantly shaped by face-selective neurons that also encoded identity. This convergence points to a shared functional subspace in IT, where stable (identity) and dynamic (expression) information coexist along overlapping dimensions. Such an architecture moves beyond the classical view of segregated pathways, revealing a general coding principle by which IT flexibly supports multiple socially relevant functions within a common representational geometry. ### Competing Interest Statement The authors have declared no competing interest. Simons Foundation, https://ror.org/01cmst727, SFARI, 967073 Brain Canada Foundation, https://ror.org/01bcmwk98, 2023-0259 Canada First Research Excellence Fund, https://ror.org/01ktx4s83, VISTA Program, Connected Minds National Sciences and Engineering Research Council of Canada, RGPIN-2024-06223 Canada Research Chairs Program, CRC-2021-00326 Deutsche Forschungsgemeinschaft, 414985841 Canadian Institute of Health Research (CIHR) Postdoctoral Fellowship Alfons and Gertrud Kassel-Stiftung

Background Deep brain ultrasound offers a novel means of modulating human cognition by noninvasively targeting subcortical structures that were previously accessible only through invasive procedures. While decades of research have mapped cortical circuits of attention, the causal roles of deep hubs such as the basal ganglia and thalamus remain poorly understood in the healthy human brain. Objectives/Hypothesis To test whether low intensity transcranial ultrasound stimulation (TUS) of two nodes in the basal ganglia-thalamic network, the globus pallidus internus (GPi) and the pulvinar, causally alters visual attention. We hypothesized that TUS-induced modulations in attentional performance would be site specific, reflecting distinct circuit functions. Results Across sessions, focal TUS accelerated reaction time in a visual search task, indicating augmented attention. Reaction time improvements were observed after stimulation relative to baseline. A dissociation emerged across sites: both GPi and pulvinar enhanced reaction times, but pulvinar yielded more robust benefits for target present trials at peripheral eccentricities, and improved search efficiency in the same trials. Conclusions These findings provide causal evidence that human attentional control can be steered at deep subcortical sites. TUS offers a practical approach for dissecting circuit level contributions to cognition and a potential noninvasive avenue for enhancing attention and other cognitive or affective functions. ### Competing Interest Statement The authors have declared no competing interest. Canadian Institutes of Health Research, FDN 154292, PJT 198046 Natural Science and Engineering Research Council, RGPIN-2020-04176

Bringing the hand near a visual stimulus enhances visual processing. This effect is linked to peripersonal space (PPS), the body-centered region where visual and proprioceptive information interact. Despite extensive behavioral evidence, the neural basis of this interaction in early visual cortex remains unclear. In this study, we investigated how hand proximity modulates orientation selectivity in area V2 by recording single-neuron responses from two rhesus monkeys. The monkeys performed a fixation task while their hand was positioned near a visual stimulus while either being visible or occluded, and compared with when the hand was away from the stimulus. When the near hand was visible, neural firing rates in V2 were significantly higher, accompanied by sharper orientation tuning. In contrast, occluding the hand broadened orientation tuning compared to when the hand was away. These effects emerged rapidly after stimulus onset and were coherent across the population, demonstrating that PPS is actively prioritized during visual processing. Together, the findings reveal two complementary (feedback) signals in V2: a congruence-driven enhancement when visual and proprioceptive inputs align, and a mismatch-driven suppression when they conflict, indicating that V2 integrates multisensory cues to encode PPS and support action-relevant visual processing. ### Competing Interest Statement The authors have declared no competing interest. Canadian Institutes of Health Research, https://ror.org/01gavpb45

Transcranial ultrasound stimulation (TUS) offers precise, non-invasive neuromodulation, though its impact on human deep brain structures remains underexplored. Here we examined TUS-induced changes in the basal ganglia of 10 individuals with movement disorders (Parkinson’s disease and dystonia) and 15 healthy participants. Local field potentials were recorded using deep brain stimulation (DBS) leads in the globus pallidus internus (GPi). Compared to sham, theta burst TUS (tbTUS) increased theta power during stimulation, while 10 Hz TUS enhanced beta power, with effects lasting up to 40 min. In healthy participants, a stop-signal task assessed tbTUS effects on the GPi, with pulvinar stimulation serving as an active sham. GPi TUS prolonged stop-signal reaction times, indicating impaired response inhibition, whereas pulvinar TUS had no effect. These findings provide direct electrophysiological evidence of TUS target engagement and specificity in deep brain structures, suggesting its potential as a noninvasive DBS strategy for neurological and psychiatric disorders. Transcranial ultrasound stimulation (TUS) is a non-invasive method to modulate deep brain activity. Using direct recordings from implanted electrodes, we showed that TUS engages the human globus pallidus internus, with effects on neural oscillations and behavior.

Ketamine is a widely used clinical drug that has several functional and clinical applications, including its use as an anaesthetic, analgesic, anti-depressive, anti-suicidal agent, among others. Among its diverse behavioral effects, it influences short-term memory and induces psychedelic effects. At the neural level across different brain areas, it modulates neural firing rates, neural tuning, brain oscillations, and modularity, while promoting hypersynchrony and random connectivity between neurons. In our recent studies we demonstrated that topical application of ketamine on the visual cortex alters neural tuning and promotes vigorous connectivity between neurons by decreasing their firing variability. Here, we begin with a brief review of the literature, followed by results from our lab, where we synthesize a dendritic model of neural tuning and network changes following ketamine application. This model has potential implications for focused modulation of cortical networks in clinical settings. Finally, we identify current gaps in research and suggest directions for future studies, particularly emphasizing the need for more animal experiments to establish a platform for effective translation and synergistic therapies combining ketamine with other protocols such as training and adaptation. In summary, investigating ketamine’s broader systemic effects, not only provides deeper insight into cognitive functions and consciousness but also paves the way to advance therapies for neuropsychiatric disorders.

The sudden appearance of a visual distractor shortly before saccade initiation can capture spatial attention and modulate the saccade trajectory in spite of the ongoing execution of the initial plan to shift gaze straight to the saccade target. To elucidate the neural correlates underlying these curved saccades, we recorded from single neurons in the frontal eye field of two male rhesus monkeys shifting gaze to a target while a distractor with the same eccentricity appeared either left or right of the target at various delays after target presentation. We found that the population level of presaccadic activity of neurons representing the distractor location encoded the direction of the saccade trajectory. Stronger activity occurred when saccades curved toward the distractor, and weaker when saccades curved away. This relationship held whether the distractor was ipsilateral or contralateral to the recorded neurons. Meanwhile, visually responsive neurons showed asymmetrical patterns of excitatory responses that varied with the location of the distractor and the duration of distractor processing relating to attentional capture and distractor inhibition. During earlier distractor processing, neurons encoded curvature toward the distractor. During later distractor processing, neurons encoded curvature away from the distractor. This was observed when saccades curved away from distractors contralateral to the recording site and when saccades curved toward distractors ipsilateral to the recording site. These findings indicate that saccadic motor planning involves dynamic push-pull hemispheric interactions producing attraction or repulsion for potential but unselected saccade targets.

The gaze-following patch (GFP) is located in the posterior temporal cortex and has been described as a cortical module dedicated to processing other people's gaze-direction in a domain-specific manner. Thus, it appears to be the neural correlate of Baron-Cohen's eye direction detector (EDD) which is one of the core modules in his mindreading system-a neurocognitive model for the theory of mind concept. Inspired by Jerry Fodor's ideas on the modularity of the mind, Baron-Cohen proposed that, among other things, the individual modules are domain specific. In the case of the EDD, this means that it exclusively processes eye-like stimuli to extract gaze-direction and that other stimuli, which may carry directional information as well, are processed elsewhere. If the GFP is indeed EDD's neural correlate, it must meet this expectation. To test this, we compared the GFP's BOLD activity during gaze-direction following with the activity during arrow-direction following in the present human fMRI study. Contrary to the expectation based on the assumption of domain specificity, we did not find a differentiation between gaze- and arrow-direction following. In fact, we were not able to reproduce the GFP as presented in the previous studies. A possible explanation is that in the present study-unlike the previous work-the gaze stimuli did not contain an obvious change of direction that represented a visual motion. Hence, the critical stimulus component responsible for the identification of the GFP in the previous experiments might have been visual motion.

Effective interaction with moving objects and the ability to infer and predict their motion (a core component of “intuitive physics”) is essential for survival in the dynamic world. How does the primate visual system process such stimuli, enabling predictive capabilities for dynamic stimuli statistics like motion velocity and expected trajectories? In this study, we probed brain areas in the ventral visual pathway of rhesus macaques implicated in object recognition (areas V4 and inferior temporal, IT, cortex) to evaluate how they represent object motion speed and direction. We assessed the relationship between the distributed population activity in the ventral stream and two distinct object motion-based behaviors—one reliant on information directly available in videos (speed discrimination) and the other predicated on predictive motion estimates from videos (future event predictions). Further, employing microstimulation strategies, we confirm the causal, functional role of the IT cortex in these behaviors. Our results underscore the need to re-examine the traditional functional segregation of the primate visual cortices into “what” and “where” pathways and provide empirical constraints to model their interaction for a better circuit-level understanding of visual motion and intuitive physics.### Competing Interest StatementThe authors have declared no competing interest.