Extinction of operant conditioning as described by Pavlov and elaborated on by Skinner refers to the discontinuation of the conditioned response in a subject. Extinction occurs at some point after the positive reinforcement or rewarding is ceased. In other words the subject no longer exhibits the conditioned response. These notions do not apply with conditioning created by negative feedback reinforcement.
The time it takes for the conditioned subject to experience extinction is directly dependant on reinforcement modality; more specifically, reinforcement interval. Upon cessation of regular reinforcement intervals extinction occurs relatively quickly, with random reinforcement intervals or partial reinforcement, as it is also called, a much longer period is needed after cessation of reinforcement for conditioning extinction to occur.
Neurologists have observed differences in brain responses using PET Scans between normal individuals and those with addictive or obsessive compulsive personalities that correlate with conditioning extinction. Extinction may not occur in the latter groups with specific conditioned responses such as gambling, such that the subject will continue with a conditioned behaviour thoughout their life with minimal reinforcement.