Neurons at the extremes of the gradient have a near-exclusive expression of a few marker genes used to segregate them into a core (Spp1+) and shell (Ecel1+) TRN subpopulation with a differential propensity to generate intrinsic rebound bursting8 and consequently a differential contribution to network dynamics, as well as distinct roles in neuropsychiatric disorders like epilepsy and schizophrenia. The gene discussed is SPP1; the disease is schizophrenia.