Striatal circuit mechanisms of exploration/exploitation and vigor during naturalistic behavior

The NeuroSchool PhD Program of Aix-Marseille University (France) has launched its annual calls for PhD contracts for students with a master's degree in a non-French university. 

This project is one of the proposed projects. Not all proposed projects will be funded, check our website for details.

State of the art: During foraging, animals must balance the exploitation of current resources with the exploration of alternatives to optimize reward acquisition. Dopaminergic modulation of striatal projection neurons (SPNs) has been proposed to regulate this trade-off. The two principal SPN populations, D1- and D2-expressing neurons, exhibit opposing responses to dopamine and exert bidirectional influences on action selection, reward learning, and movement vigor. However, the respective contributions of D1- and D2-SPNs, as well as dopamine itself, to the decision-making and motor components of foraging have not been directly investigated. 

Objective : This project aims to determine whether and how D1/D2-SPNs and dopaminergic modulation in the dorsomedial striatum (DMS) regulate exploration/exploitation decisions and reward-oriented movement vigor during naturalistic foraging. We will (i) relate SPN and dopamine activity to exploration vs exploitation and movement kinematics, and (ii) establish the causal role of these populations of neurones in controlling exploitation duration and movement vigor 

Methods: Freely moving mice will perform the Towers Foraging Park, a novel patch-foraging task developed in our lab (Schaffahauser et al., 2025). This task allows us to easily quantify patch-leaving decisions and movement kinematics. We will use a protocol in which patches deplete at two different speeds, and the exploration cost is manipulated. We will record the activity of D1- or D2-SPNs and dopamine transients in the DMS using fiber photometry, and relate these signals to decision-making proxies (patchexploitation duration) and movement (kinematics of reward-oriented movement). To test causal roles, we will use closed-loop wireless optogenetic perturbations of D1- or D2-SPNs during specific behavioral events.  

Expected results:  We hypothesize that dopaminergic modulation of D1 and D2 SPNs exerts opponent control over the exploration/exploitation trade-off and the vigor of reward-oriented movements, with D1-SPNs favoring exploitation and D2-SPNs favoring exploration. 

Feasibility: The project builds on the validated TFP paradigm, which is routinely used in the host laboratory (APAFIS-46285). Fiber photometry is a standard technique in neuroscience, and wireless optogenetic perturbation approaches are currently being developed in the lab. The work is supported by ANR and AMIDEX grants, and additional funding applications are ongoing. 

Within Aix Marseille Université, NeuroMarseille brings together 8 research laboratories and NeuroSchool, a graduate school in neuroscience, to increase the attractiveness of the university, international collaborations, interdisciplinarity, links with the clinical and industrial worlds and the integration of students into professional life. 

Launched in July 2018, NeuroSchool unifies and harmonizes the training of the third year of the Bachelor of Life Sciences (Neuroscience track), the Master's and the PhD in Neuroscience. 

• Expected candidate profile : We are looking for candidates passionate about neuroscience and who enjoy working in a team. A good level of knowledge in neuroscience and a solid foundation in neural circuits are expected. Previous experience in imaging, optogenetics, stereotaxic injections, fiber photometry, or rodent behavior is an advantage but not required. An interest in animal behavior is essential. Analysis and task programming is done through Python scripts; no prior programming experience is required, but a willingness to learn is important.