Biology subjects

Kim, H. F.

Publications and source records attributed to Kim, H. F..

8 recordsLinked to original sources

bioRxiv2026

Differential value processing in the rostral and causal subthalamic nucleus during flexible and habitual decision-making in primates: Implications for cognitive dysfunction in Parkinson's disease

The subthalamic nucleus (STN) is a major target region of deep brain stimulation (DBS) for Parkinson's disease (PD), effectively alleviating motor symptoms. However, STN-DBS can also induce cognitive impairments, suggesting that the STN contributes to cognitive functions beyond simple motor control. Furthermore, anatomical organization supports functional segregation of cognitive processes, as basal ganglia subregions encoding flexible and stable values topographically project to distinct STN subregions. Yet, whether the STN contributes to cognitive functions and, if so, how subregions of the STN differentially process cognitive flexibility and habitual stability remains unknown. Here, we reveal a rostral-caudal functional organization of the STN that differentially supports flexible value updating and long-term value memory, enabling adaptive and habitual decision-making, respectively. Neurons in the rostral STN (rSTN) preferentially encode flexibly updated values, whereas neurons in the caudal STN (cSTN) preferentially encode stable long-term value memories. Notably, inactivation of the STN along the rostral-caudal axis produced dissociable behavioral deficits: rSTN inactivation selectively impaired goal-directed behavior requiring flexible value updating, whereas cSTN inactivation selectively disrupted habitual behavior guided by long-term value memories. Together, these results reveal a rostral-caudal functional segregation of the STN, with the rSTN supporting goal-directed behavior and the cSTN supporting habitual behavior. These findings further provide a framework for understanding how STN dysfunction or STN-DBS in Parkinson's disease may differentially affect cognitive processes beyond motor control.

neuroscience↗

bioRxiv2026

A modular cranial window enabling maintainable widefield optical access in non-human primates

Longitudinal optical imaging of the primate cortex requires stable yet maintainable cortical access, but existing cranial window approaches remain limited by mechanical instability and tissue responses that progressively degrade optical clarity. These challenges are amplified in primates, where large craniotomies and physiological variability complicate chronic experiments. Moving beyond conventional fixed cranial windows, we present the PRIME cranial window (Primate Reconfigurable Interchangeable Modular Enclosure), a modular platform enabling maintainable, long-term, and widefield optical access in awake macaques. Built on a modular architecture, PRIME supports non-invasive adjustment, repeated cortical access, and on-demand maintenance, including tissue removal, without surgical re-entry, while a dual-ring sealing mechanism prevents cerebrospinal fluid leakage and contamination. Combined with optimized viral delivery, implantation, and maintenance strategies, PRIME preserves cortical integrity and optical clarity for long-term optical imaging. PRIME establishes a versatile, re-accessible experimental framework for chronic, large-area optical studies of the primate brain.

neuroscience↗

bioRxiv2026

Computational and causal dissociation in primate striatum during value-guided decision-making

How neural representations carrying similar information across brain regions are translated into behavioral control remains a fundamental question in neuroscience. In the primate striatum, whether subregions make overlapping or dissociable computational and causal contributions to value-guided decisions is unresolved. Here, we show that macaque striatal subregions make dissociable, modality-specific contributions: the putamen is required for tactile-value decisions, the caudate for visual-value decisions, and the ventral striatum for both. Despite broadly shared value encoding, causal necessity is predicted not by the strength of single-neuron value discrimination or population-level decoding, but by neural geometry-behavior coupling. These findings reveal a functional organization of the primate striatum and identify neural geometry-behavior coupling as a key determinant of behavioral control.

neuroscience↗

bioRxiv2026

Value and spatial preferences guide habitual reaching and manual object selection in primates

Habits are automatic actions shaped by prior experience, enabling efficient and fast responses in stable environments. While habitual gaze rapidly directs the eyes toward valuable objects, the mechanisms underlying habitual manual choice for reaching and grasping remain unclear. Here we show that macaque monkeys develop habitual manual choices toward previously rewarded objects through multi-day object-value learning, driven by learned value and spatial preferences. This reaching habit persisted without reward and showed shorter latencies than in value-deliberative tasks, consistent with automatic control. Regression analyses further revealed that manual choice was guided by learned object values, whereas visual salience had no effect, unlike gaze habits. Instead, intrinsic spatial preferences continued to bias reaching behavior even after long-term value learning. These findings demonstrate that habitual manual choice arises from the integration of spatial preferences and long-term value memory, defining a distinct mechanism of automatic behavior beyond habitual gaze.

animal behavior and cognition↗

bioRxiv2024

Neural geometry efficiently representing abstract form of value and modality in the primate basal ganglia

Basal ganglia process diverse values from various modalities using limited resources, necessitating efficient processing. This involves converging tactile and visual information within bimodal value-coding neurons, ensuring efficient processing with limited number of neurons. However, convergence at the single neuron level may compromise modality-specific information, raising the question: Does efficient processing inevitably degrade information quality? We investigated the representational geometry in the putamen of macaque monkeys trained to learn values from tactile and visual inputs. Here, we demonstrated that the population representation of bimodal value-coding neurons in the putamen preserved both value and modality information, and these representations were shared to efficiently maintain quality. Notably, these representations were generalized across identical modalities and values, resulting in an efficient low-dimensional representation. Furthermore, a faster transformation to a generalized value representation within neural geometry reflected greater confidence in value-guided choice behavior--this correlation not observed in conventional decoding. Our results suggest that bimodal value-coding neurons play a key role in balancing efficiency and information fidelity, facilitating cognitive states required for confident decision-making.

neuroscience↗

bioRxiv2024

Distinct representation of cognitive flexibility and habitual stability in the primate putamen, caudate, and ventral striatum

Recent primate studies have demonstrated a functional distinction along the rostral--caudal axis of the striatum, which has challenged the conventional view that flexible adaptation and habitual action differ in processing along the medial--lateral axis. We found that neurons in the rostral putamen, caudate, and ventral striatum encode values flexibly updated for adaptive choices, rather than values stably sustained for visual habit. In the reversal value learning, rostral striatal neurons dynamically updated their value discrimination responses after value reversals, whereas, in the stable value retrieval, most did not encode the value. Notably, caudate neurons were faster to update values after reversal trials than ventral striatum neurons. Slow-learning neurons were identified selectively in the ventral striatum. In each trial, their learning speeds were similar during initial learning, suggesting a parallel value update in each striatal region. Our findings thus indicate that the rostral striatum prioritizes cognitive flexibility over habitual stability.

neuroscience↗

bioRxiv2024

Efficient value encoding through convergence of tactile and visual value information in the primate putamen

The processing of diverse sensory values by a limited number of basal ganglia neurons raises the question of whether each value is processed independently or combined as the number of neurons decreases from the cortex to downstream structures. Here, we discovered that tactile and visual values were partially converged in the primate putamen, enhancing its efficiency in encoding values while preserving modality information. Humans and monkeys performed tactile and visual value discrimination tasks. Notably, the human putamen selectively represented both tactile and visual values in fMRI scans. Single-unit electrophysiology further revealed that half of the individual neurons in the macaque putamen encoded both tactile and visual values, and the other half encoded each value separately. The bimodal value neurons enable more efficient value encoding using fewer neurons than the modality-selective value neurons. Our data suggest that the basal ganglia system uses modality convergence to efficiently encode values with limited resources.

neuroscience↗

bioRxiv2022

Identifying brain areas for tactile perception through natural finger touch with MR-compatible tactile stimulus delivery system

Primates actively touch objects with their hands to collect information. In investigations of the tactile information processes, participants should experience tactile stimuli through active touch while brain activities are monitored. Here, we developed a pneumatic tactile stimulus delivery system (pTDS) that delivers various tactile stimuli on a programmed schedule and allows tactile perception through voluntary finger touches during MRI scanning. A pneumatic actuator moved tactile blocks and placed one in a finger hole. The time when an index finger touched a tactile stimulus was detected with a photosensor, allowing analysis of the touch-elicited brain responses. The brain responses were examined while the participants actively touched braille objects presented by the pTDS. BOLD responses during tactile perception were significantly stronger in a finger touch area of the contralateral somatosensory cortex compared with that of visual perception. This pTDS enables MR study of brain mechanisms for tactile processes through natural finger touch.

neuroscience↗