The Neurobiology of Drug Addiction

The development of tolerance to the analgesic effects of morphine involves different areas of the brain separate from those in the reward pathway. Point to the two areas involved here, the thalamus, and the spinal cord (green dots). Both of these areas are important in sending pain messages and are responsible for the analgesic effects of morphine. The parts of the reward pathway involved in heroin or morphine addiction are shown for comparison.