ABSTRACT
It is generally accepted that there are different types of memories, involving distinct neural circuits, sometimes working in parallel (Cohen & Eichenbaum, 1993; Gaffan, 1994; Squire & Zola, 1996). For example, explicit declarative memory formation appears to rely chiefly on the hippocampal formation, rhinal cortex, and associated cortical regions (Eichenbaum, 1999; Gaffan, 1994), whereas some forms of implicit procedural memories, such as skill learning, mainly depend on the striatum (Graybiel, 1995). Emotional memories, particularly those associated with painful or otherwise unpleasant experiences are stored in the amygdala and related brain regions (Davis, 1992; Fanselow, 1994; LeDoux, 2000). This system mediates the emotional reactions that are elicited when these stimuli are re-encountered. It can operate at an implicit or unconscious level (LeDoux, 1996; Öhman, Flykt, & Lundqvist, 2000). However, we usually have explicit or conscious memories about emotional situations as well. These, like other explicit memories, are mediated by the medial temporal lobe memory system mentioned above. The implicit memories of emotional events have been called “emotional memories”, and the explicit memories have been termed “memories about emotions” (LeDoux, 1996). Implicit emotional memories are elicited automatically in the presence of trigger stimuli and do not require conscious retrieval or recall, whereas explicit memories of emotion are retrieved consciously. In humans, damage to the amygdala interferes with implicit emotional memories but not
explicit memories about emotions, whereas damage to the medial temporal lobe memory system interferes with explicit memories about emotions but not with implicit emotional memories (Bechara et al., 1995; LaBar, LeDoux, Spencer, & Phelps, 1995).
