The central panel depicts the thalamo-cortico-striatal projections and their neurotransmitter systems. Curved arrows show neural pathways; dashed arrows indicate data obtained in a specific condition or from the specific brain area. a,b | The thalamus projects to cortical areas that are involved in the processing of numerosity: the frontal cortex (a) and parietal cortex (b). Panel a shows the representation of numerosity in the frontal cortex of primates; spike rate varies with number of items. Panel b shows the neural representation of the second and fifth items in a motor sequence in the primate parietal cortex. c | Cortical areas send glutamatergic connections to the caudate–putamen, the neural activation of which peaks at the criterion duration in interval-timing procedures. d | Degeneration of the dopaminergic nigrostriatal projection (as seen in Parkinsons disease) results in abnormal processing of temporal information. Deep brain stimulation (DBS) of the indirect subthalamic projection eliminates the retrieval deficit but not the encoding distortion. GABA, γ-aminobutyric acid; GPe, external segment of globus pallidus; GPi, internal segment of globus pallidus; NB, nucleus basalis; PFC, prefrontal cortex; PPC, posterior parietal cortex; SMA, supplementary motor area; SNc, substantia nigra pars compacta; SNr, substantia nigra pars reticulata; STn, subthalamic nucleus; X, denotes degeneration of nigrostriatal projection in Parkinsons disease.