Drawing upon a database of over 1,400 medieval holy persons and in-depth studies of individual saints, this illuminating study examines the relationship between medieval mystical experiences, the religious practices of mortification; laceration of the flesh, sleep deprivation and extreme starvation, and how these actions produced altered states of consciousness and brain function in the heroic ascetics. Examining and disputing much contemporary writing about the political and gender motivations in the medieval quest for a closeness with God, this is essential reading for anyone with an interest in medieval religion or the effects of self-injurious behaviour on the mind.