Fibrillar deposits of tau protein (neurofibrillary tangles) are thought to cause neuronal death in patients with Alzheimer's disease, and tau-related frontotemporal dementia. Here, however, the opposite has been found: the activation of executioner caspase enzymes occurs first, preceding tangle formation by hours to days. Tangle-bearing neurons seem to be long-lived, indicating that tangles might be 'off pathway' to acute neuronal death