Prolonged access to cafeteria food causes persistent elevations in threshold for BSR: comparison with drugs of abuse. (a) BSR threshold during daily intake of cafeteria food or drugs. (b) BSR threshold after loss of access to cafeteria food or drugs. Data were redrawn from Johnson and Kenny² and refs. 3–7. In these studies, rats performed an operant response to obtain rewarding electrical brain stimulation into the median forebrain bundle at the level of the lateral hypothalamus. BSR threshold is defined as the minimum intensity of electrical stimulation that maintains operant responding. Increased BSR threshold is hypothesized to reflect decreased sensitivity of the brain reward system. Extended access to cafeteria food causes progressive disruption of the brain reward system that persists for long periods after loss of access to the food. In contrast, although extended access to abused drugs also causes progressive disruption of the brain reward system, this disruption dissipates in the first few days after withdrawal from the drugs.