Upper panel: time schedule for the manganese (Mn)-enhanced magnetic resonance imaging (MRI) analysis. MRI signals were obtained at 4 h after the Y-maze test (at 6 h after intraperitoneal injection of MnCl2). Lower panel: the intensity of the Mn-enhanced MRI signal in the medial prefrontal cortexes (mPFC) and the nucleus accumbens (NAc) shell of an AA( ? )/DHA( ? ) mouse was substantially greater than that of an AA(+)/DHA(+) mouse.