Which brain regions are critically involved in the retrieval of old episodic memory?

Memory is two-sided like the head of Janus: it looks into the past (retrograde memory) and the future (anterograde memory). While current opinion assumes a strong anatomical interdigitation in the processing of either kind of memory, recent single case reports and results obtained with the positron emission tomographic subtraction method indicate the likely existence of a dissociation: regions of the limbic system are primarily engaged in the encoding of autobiographical and semantic information, while cortical areas in the orbitofrontal and anterolateral temporo-polar regions are principally engaged in information retrieval. Within this retrieval system the right hemisphere may subserve episodic memory retrieval, and the left retrieval from the knowledge system (semantic memory).