Proliferation of NTRK2-KO glioma cells was similar in wild-type mice and in mice lacking activity-regulated BDNF (Bdnf-TMKI) following optogenetic stimulation of cortical projection neuronal activity, indicating that the loss of activity-regulated BDNF does not exert effects that are independent of glioma TrkB signalling (Extended Data Fig. 1k). Here, BDNF is linked to central nervous system cancer.