a, Visualization of striatal dopaminergic afferents by tyrosine hydroxylase (TH) staining in coronal slices. Scale bar, 1 mm. b, Loss of dopaminergic innervation in dorsomedial striatum one week after 6-OHDA injection. The arrow marks the injection site. c, ChR2–YFP expression in dorsomedial striatum of 6-OHDA-lesioned mice. d, Merged image shows overlap of ChR2 expression with the 6-OHDA lesion. e, Motor behaviour before (left, black bars) and after (right, red bars) 6-OHDA lesion in D1-ChR2 mice (n = 10). In 6-OHDA-lesioned mice, behaviour is shown before, during and after activation of the direct pathway. f–k, Effect of 6-OHDA lesion and direct pathway rescue on fine-movement velocity (f), initiation of ambulatory bouts (g), ambulation bout duration (h), ambulation velocity (i), frequency of freezing (j) and duration of freezing bouts (k). l, No change in gait was observed after 6-OHDA lesioning or direct-pathway activation. *P < 0.05; error bars, s.e.m.