The neuronal population of the striatum is primarily composed of medium spiny projecting neurons (MSNs), with only a small percentage (around 5% in mice) being locally projecting neurons or interneurons. Despite their low numbers, interneurons play a crucial role in regulating the flow of information within the striatum and to other brain nuclei, thereby having significant implications for motor control and cognition.We recently identified one of the most abundant populations of GABAergic interneurons in the striatum that express Pthlh and varying levels of Pvalb, which correlates with intrinsic electrophysiological properties, regional distribution within the striatum (Muñoz-Manchado et al., Cell Reports, 2018), and different input areas (Bengtsson et al., Scientific Reports, 2020). Remarkably, we have also discovered that this interneuron population is among the most abundant in the human caudate and putamen (Garma et al., Research Square, 2023, preprint).To gain insight into the function of this novel interneuron population in the basal ganglia circuit, we developed the Pthlhcre::R26R-tdTomato mouse line. Through fluorescence in situ hybridization (FISH) and electrophysiological recordings we have characterized the labelled cells in the dorsal striatum of this mouse line confirming its value as a tool for examining the role of the Pthlh population in the striatal circuit.Subsequently, we aimed to explore the function of the Pthlh population by performing chemogenetic inhibition in our transgenic mouse line. This activity manipulation showed that the Pthlh population mainly affects learning and memory and may also influence exploratory behavior and motor learning.