The basal ganglia (BG) is a group of sub-cortical nuclei involved in motor control, learning and attention. The primary input nucleus of the BG is the striatum which receives cortical, thalamic and midbrain afferences on its two striatal projecting neurons’ (SPN) populations (the direct (d) and indirect (i) pathways) in a manner that remains elusive. Research on SPNs has mainly focused on characterizing its involvement in motor control rather than single neuron activity evolution during the process of action learning. This project aimed to dissect the relative contributions of both d- and i-SPNs during the learning process of a Fixed Ratio 1 (FR1) operant behavior.We used in vivo calcium imaging targeting the dorsal striatum on transgenic mice expressing GCaMP6s either on the d- or i-SPNs as an indicator of neuronal activity. Calcium recordings were paired with a FR1 task performed in an operant chamber, where mice need to press a lever to obtain a chocolate pellet as a reward.Our preliminary data shows that both SPNs populations present a time-dependent sequential activation along the task, from lever press to reward, that arises with learning. The percentage of neurons that are modulated during lever press and reward, and the conservation of same-neuron modulation across sessions is higher for dSPNs than for iSPNs.Preliminary results stay in line with previous literature showing that d-SPNs have a major role on the execution of sequences of actions while i-SPNs seem to have rather a modulatory role during the task.