Process-specific prefrontal contributions to episodic encoding and retrieval of tastes: a functional NIRS study.

The neural basis of memory subprocesses, encoding and retrieval, have been extensively examined in functional neuroimaging studies. However, the cortical substrates of taste memory, which form an important part of our episodic memory, have rarely been explored in humans. Previously, we have used functional near-infrared spectroscopy (fNIRS) and found activation of the lateral prefrontal cortex (LPFC) related to taste encoding. The method used in the current study allowed brain monitoring while participants tasted liquid taste-stimuli in upright positions. Here, using the same system, we examined the LPFC activity of 28 healthy volunteers during both the encoding and the retrieval of taste memory. The contrast between the retrieval and eyes-closed-resting conditions revealed activation in the bilateral LPFC. This activation was significantly larger than that for encoding in the bilateral frontopolar and right dorso-LPFC regions, particularly in the right hemisphere (N=28, P<0.05, FDR corrected), exhibiting right hemispheric dominance. Our findings are in line with the hemispheric encoding/retrieval asymmetry (HERA) model, which proposes a process-specific prefrontal contribution to memory function.