Left prefrontal function and semantic organization during encoding and retrieval in healthy and psychiatric populations

Memory makes learning and cognition possible as it bridges temporal gaps between behavior and outcome. Given the fundamental importance of this function it is not surprising that it is subject to prefrontal control. To facilitate its study, memory has been subdivided into different categories and stages of processing. The chapter will begin with a review of this taxonomy to illustrate how lesion models evolved from a primary focus on the hippocampus to a growing appreciation of the prefrontal cortex. Presentation of more recent neuropsychological and imaging data will describe the role of the left and right prefrontal cortex in word encoding and retrieval. These data will show how the left inferior prefrontal cortex mediates semantic organizational processing and contributes to efficient encoding and retrieval. A discussion of schizophrenia will illustrate how psychiatric disorders that disrupt prefrontal function also compromise strategic memory processes and impair episodic memory performance. The chapter will close with preliminary data demonstrating how providing patients with organizational strategies may help to reengage their prefrontal cortex and improve task performance. A discussion of cognitive remediation implications will end the chapter. <bold>Memory systems and effects of focal lesions</bold> As the “father” of psychology, William James was probably the first to realize the importance of developing operational definitions of different memory functions to facilitate scientific study. He made an initial distinction between short-term memory and long-term memory that remains relevant today.