background Evidence from studies of memory and emotion point to the medial temporal lobe (mtl) as most relevant to the genesis of mood-congruent memory biases. Regulatory structures in the prefrontal cortex (pfc) are thought to be additionally involved in mediating these effects.
aim This study investigates the activity of these areas during encoding of affective words followed by subsequent free recall while undergoing positive and sad mood induction.
methods Functional imaging was twice performed in 18 healthy controls, counterbalanced between sad and happy mood. Contrasts were created to compare the activity during encoding of subsequently remembered and forgotten words, as well as mood-congruent and incongruent words.
results Behavioral results show a significant mood congruent memory bias for positive words during happy mood. fmri results show that the encoding of mood congruent versus incongruent words shows increased activation in left amygdala, while encoding of remembered versus forgotten words was characterised by increased medial-orbitofrontal activation. Mood-congruent subsequent memory effects appear to involve primarily increased activity in left hippocampus.
conclusions These results suggest that within the mtl, amygdala is primarily involved in detecting mood congruency, while hippocampus mediates mood-congruent memory effects. Medial pre-frontal areas also appear involved in successful memory formation, independent of mood-congruency, possibly by means of monitoring.