Summary
Decisions in complex environments rely on flexibly utilizing past experience as required by context and instructions. This process depends on medial frontal cortex (MFC) and the medial temporal lobe (MTL), but it remains unknown how these structures interact during memory retrieval. We recorded single neurons in MFC and MTL while human subjects switched between making memory and categorization-based decisions. Here we show that MFC rapidly implements changing task demands by utilizing different subspaces of neural activity during different types of decisions. Choices requiring memory retrieval selectively engaged phase-locking between theta-frequency band oscillations in MTL and MFC neurons. Choice neurons signaled decisions independent of output modality. In contrast, no effect of task demands was seen locally in the MTL. This work reveals a mechanism for selectively engaging memory retrieval and shows that unlike perceptual decision-making, memory-related information is only represented in frontal cortex when choices require it.
