In cresyl violet sections, there was a positive correlation between VLM neuronal density and duration of epilepsy (P < 0.01) and a trend for higher TPH2 neuronal counts in epilepsy patients with epilepsy duration of >10 years compared to cases with epilepsy onset <2 years (P ≤ 0.05, Supplementary Fig. 3B). Here, TPH2 is linked to epilepsy.