Does frontal lobe activation during retrieval reflect complexity of retrieved information?

Neuroimaging studies of memory have consistently shown that episodic retrie val is associated with right frontal activation, whereas semantic retrieval is associated with left frontal activation. Various hypotheses have been p roposed to account for this lateralization in terms of underlying psycholog ical processes. Alternatively, this lateralization may reflect the complexi ty of information retrieved: retrieval of complex, contextual information a ccompanying episodic retrieval invokes right-lateralized processes preferen tially. We tested this hypothesis by manipulating the type and complexity o f information retrieved. Initial increase in complexity of both episodic an d semantic information was associated with right inferior frontal activatio n; further increase in complexity was associated with left dorsolateral act ivation. We conclude that frontal activation during retrieval is a non-line ar function of the complexity of retrieved information. NeuroReport 11:557- 561 (C) 2000 Lippincott Williams & Wilkins.