Biology subjects

Ballard, I.

Publications and source records attributed to Ballard, I..

4 recordsLinked to original sources

bioRxiv2026

Altered Dopamine-Linked Striatal Hemodynamic Latency in Early Psychosis

Key Points Question: Is striatal hemodynamic latency, a novel indirect correlate of dopamine physiology, altered in individuals with early psychosis? Findings: In this cross-sectional study of 105 individuals with early psychosis and 55 healthy comparison participants, early psychosis was associated with significantly lower striatal hemodynamic latency. Differences were observed in the dorsal striatum (caudate and putamen), whereas ventral striatal (nucleus accumbens) latency did not significantly differ between groups. Meaning: These findings support further evaluation of striatal hemodynamic latency as a noninvasive, indirect marker of dopamine-linked physiology in early psychosis. Abstract Importance: Psychosis is strongly associated with striatal dopamine dysfunction, but noninvasive measures that capture variation in dopamine remain limited. Hemodynamic latency, which quantifies the timing of low-frequency blood oxygen level-dependent (BOLD) fluctuations, may provide a way to indirectly probe dopamine dysfunction in psychosis. Objective: To determine whether striatal hemodynamic latency differs between individuals with early psychosis (EP) and healthy control (HC) participants and whether latency is associated with positive or negative symptom severity. Design: Cross-sectional analysis of resting-state functional magnetic resonance imaging (fMRI) data from the Human Connectome Project (HCP)-EP dataset. Setting: Multisite study at 4 sites using 3T Siemens Prisma MRI scanners. Participants: 105 individuals with EP and 55 HC participants with usable resting-state fMRI and hemodynamic latency data. Exposure: EP status. Main Outcomes and Measures: Voxel-wise hemodynamic latency was estimated using RapidTide and summarized within 6 striatal regions: nucleus accumbens core and shell, anterior and posterior caudate and putamen. Group differences were evaluated using linear mixed-effects models accounting for region and subject-level random effects and controlling for age, sex, and mean framewise displacement. Positive symptoms were measured using the Positive and Negative Syndrome Scale positive subscale; negative symptoms using the Clinical Assessment Interview for Negative Symptoms. Associations with symptoms were assessed using nested linear regressions within the EP group. Results: Latency was significantly lower in the dorsal than ventral striatum in HC and EP, with a greater difference in EP (b=-119.46 ms, SE=52.16, p=.022). Follow-up six-subregion models found significant main effects of group F(1,156.55)=7.79, p=.006, and region F(5,2760)=187.99; p< .001, but no group-by-region interaction F(5,2760)=1.74; p=.121. Region-specific contrasts showed lower latency in EP in the anterior caudate (p=.014), posterior caudate (p<.001), anterior putamen (p=.007), and posterior putamen (p=.029), but not NAc core or shell. Striatal latency was not significantly associated with positive or negative symptom severity among participants with EP. Conclusions and Relevance: EP was associated with broadly reduced striatal hemodynamic latency, with the strongest differences in the caudate and putamen. Altered striatal latency in psychosis warrants further evaluation as a noninvasive indirect marker of striatal pathophysiology linked to dopamine.

neuroscience↗

bioRxiv2026

The Prefrontal Cortex Organizes Visual Evidence by Representational Abstraction

Perceptual decisions often depend on both lower-level visual features and higher-level object representations, yet natural images entangle these levels of abstraction. We used deep neural network features to dissociate lower- and higher-level visual similarity during a naturalistic image-similarity judgment task. Participants relied on both forms of evidence, with greater weighting of higher-level similarity. Across prefrontal cortex, visual evidence was systematically organized by representational level: lower- and higher-level similarity were expressed in distinct prefrontal regions during comparison and remained spatially differentiated as they were transformed into decision signals. This organization was behaviorally relevant, with prefrontal activation predicting which level of evidence guided choice when the two conflicted. Together, these findings identify representational level as an organizing principle of prefrontal cortex during visual decisions.

neuroscience↗

bioRxiv2025

Temporal fMRI Dynamics Map Dopamine Physiology

Spatial variations in dopamine function are linked to cognition and substance use disorders but are challenging to characterize with current methods. Because dopamine influences blood vessel dilation, we hypothesized that hemodynamic latency, which reflects BOLD signal timing, could serve as an indirect marker of dopamine physiology. Across four datasets, we found a topography of hemodynamic latencies that precisely distinguished the nucleus accumbens, a dopaminergic region implicated in motivation and substance abuse, from other striatal regions. Using PET, genetics, and pharmacology, we found that hemodynamic latencies are robustly related to dopamine function and dopamine-linked behavior. In individuals with cocaine use disorder, we observed a spatial gradient of altered hemodynamic latencies in the striatum. This pattern independently predicted nicotine use, revealing a conserved physiological profile associated with addictive substance use. Hemodynamic latencies map regional, individual, and pathological differences linked to dopamine, opening new avenues for indirectly assessing the role of dopamine in healthy cognition and disease.

neuroscience↗

bioRxiv2017

Beyond Reward Prediction Errors: Human Striatum Updates Rule Values During Learning

Humans naturally group the world into coherent categories defined by membership rules. Rules can be learned implicitly by building stimulus-response associations using reinforcement learning (RL) or by using explicit reasoning. We tested if the striatum, in which activation reliably scales with reward prediction error, would track prediction errors in a task that required explicit rule generation. Using functional magnetic resonance imaging during a categorization task, we show that striatal responses to feedback scale with a \"surprise\" signal derived from a Bayesian rule-learning model and are inconsistent with RL prediction error. We also find that striatum and caudal inferior frontal sulcus (cIFS) are involved in updating the likelihood of discriminative rules. We conclude that the striatum, in cooperation with the cIFS, is involved in updating the values assigned to categorization rules when people learn using explicit reasoning.

neuroscience↗