Obsessive-compulsive disorder (OCD) and schizophrenia are associated with disturbances in episodic memory, especially strategic processes such as the ability to mentally regroup related words together during verbal learning (semantic organization). Previous studies in neurologic lesion patients link this process to prefrontal cortex (PFC). However, PFC is functionally heterogeneous and different territories likely subserve different aspects of semantic organization. Distinct regions of PFC are also implicated in OCD and schizophrenia: OCD is linked to orbitofrontal cortex (OFC), and schizophrenia to lateral PFC. We have previously conducted a positron emission tomography study of semantic organization in normal subjects (SFN Abst '99). There were two primary encoding conditions: 1) Spontaneous: words were related in four semantic categories, and subjects were not instructed beforehand; 2) Directed: same as (1) but subjects were explicitly instructed to notice relationships and use them to improve memory. R...