Summary: Researchers have revealed how the thalamus, specifically the paraventricular nucleus (PVT), translates hunger into motivated behavior. Using innovative experiments in mice, the team identified two distinct PVT neuronal populations that exert opposite influences on goal-directed actions such as foraging. These findings clarify how internal states like hunger shape pursuit and termination of actions and point to potential targets for treating motivational disorders.
This study shows that dopamine D2 receptor–expressing PVT neurons (PVTD2(+)) amplify motivation and action vigor during goal pursuit, while PVTD2(–) neurons are more active during action termination. By demonstrating parallel thalamo-striatal pathways from the PVT to the nucleus accumbens (NAc), the work reframes the PVT’s role from a passive relay to an active regulator of motivational signals.
Key Facts:
- Distinct neuronal roles: PVTD2(+) neurons increase activity during reward approach and correlate with motivation measures, whereas PVTD2(–) neurons increase activity at the end of a goal-directed action.
- PVT as a processor of motivation: Rather than serving only as a relay, the PVT integrates hypothalamic state signals and relays motivation-related dynamics to the nucleus accumbens.
- Therapeutic implications: Identifying separable PVT circuits that drive approach versus termination opens avenues for interventions targeting motivational deficits in conditions such as depression, substance abuse, and binge eating.
Source: University of Alabama at Birmingham
Hunger and motivated behavior
Hunger creates an internal drive that motivates animals to forage and obtain food. To investigate how the brain converts this internal state into goal-directed actions, researchers from the University of Alabama at Birmingham and the National Institute of Mental Health studied mice performing a foraging-like task while recording neural activity in the paraventricular nucleus of the thalamus (PVT).
Mice were trained in a long corridor with a trigger zone at one end and a reward zone at the other (over four feet apart). After waiting in the trigger zone until a cue, mice traversed the corridor at their own pace to reach the reward zone and received a small sip of strawberry-flavored Ensure. To complete a trial, animals left the reward zone and returned to the trigger site to wait for the next cue. Mice learned quickly and performed many trials, providing rich behavioral data for neural analysis.
Recording neural dynamics with fiber photometry
To measure population activity, the team used fiber photometry with the calcium indicator GCaMP. Optical fibers were implanted above the PVT to track calcium transients as proxies for neuronal firing while mice performed approach and termination phases of the task. The researchers focused on two genetically defined PVT cell types distinguished by the presence or absence of dopamine D2 receptors: PVTD2(+) and PVTD2(–). Dopamine D2 receptor expression served as a marker to separate functional subpopulations within the PVT.
Results showed clear, opposite dynamics: PVTD2(+) neurons ramped up activity during the approach to the reward and declined during trial termination, whereas PVTD2(–) neurons showed the reverse pattern. Crucially, these signals were task-specific — PVTD2(+) activity increased during engaged, goal-directed approaches but not during casual roaming in the enclosure.
Parallel projections to the nucleus accumbens
The PVT projects to the nucleus accumbens (NAc), a key node in the brain’s reward and motivation circuitry. By recording at PVT axon terminals in the NAc, researchers confirmed that activity patterns observed in PVT cell bodies were relayed to downstream targets: PVTD2(+)-NAc terminals signaled approach-related dynamics, and PVTD2(–)-NAc terminals signaled termination-related dynamics. These parallel thalamo-striatal pathways provide a mechanism by which internal states are converted into coordinated initiation and cessation of motivated actions.
Advanced analytic approach
High-resolution photometry generated large datasets (8–10 samples per second per session) and introduced potential sources of variability. The research team applied a functional linear mixed modeling framework tailored to these recordings. This approach accounted for trial-by-trial variability and allowed detailed correlations between neural signals and behavioral covariates such as latency, velocity, and hunger state.
For example, trials were categorized as “fast” (2–3 seconds to reach the reward) or “slow” (9–11 seconds). PVTD2(+) neurons exhibited larger calcium ramps during fast trials, linking their activity to vigor and motivational drive. In contrast, PVTD2(–) neurons correlated with termination but showed weaker relationships to motivational measures.
Implications for psychiatric conditions
Motivational deficits underlie many psychiatric disorders, including depression, substance use disorders, and disordered eating. By delineating distinct PVT circuits that separately govern approach and termination, this research identifies specific pathways that could be targeted to restore healthy motivational balance. Understanding how the PVT encodes hunger-driven motivation offers a more nuanced blueprint for future therapeutic strategies.
Co-authors include Isbah Khan, Claire Gao, Gabriel Loewinger, Emma Macdonald, Alison Bashford, Shakira Rodriguez-Gonzalez, Francisco Pereira and Mario Penzo from the NIMH. Sofia Beas, Ph.D., is the senior author and corresponding investigator on the study.
Funding: Research support came from NIH award K99/R00 MH126429, a NARSAD Young Investigator Award from the Brain & Behavior Research Foundation, and NIMH Intramural Research Program award 1ZIAMH002950.
Abstract
Dissociable encoding of motivated behavior by parallel thalamo-striatal projections
Highlights
- PVTD2(+)-NAc pathway encodes execution and vigor of goal-directed actions.
- PVTD2(−)-NAc pathway encodes termination of goal-directed actions.
- PVTD2(+) neuronal activity tracks motivation parameters such as latency and velocity.
- PVTD2(−) neurons are also sensitive to motivation but to a lesser extent.
Summary
Successful goal pursuit requires both initiation and timely termination of actions, processes guided by internal drives like hunger and modulated by neural circuits that translate interoceptive signals into behavior. The paraventricular nucleus of the thalamus (PVT) integrates hypothalamic state information and communicates with the nucleus accumbens to shape motivated behaviors. Using in vivo fiber photometry in a foraging-like task, this study identifies two genetically distinct PVT populations that differentially encode the execution and termination of goal-directed actions and demonstrates that these dynamics are transmitted to the nucleus accumbens via parallel thalamo-striatal projections.