Where the brain stores emotional memories

The brain mechanisms involved in forming fear memories associated with smells, sounds, and visual images are fairly well understood, but where these old fear memories are stored in the brain has not been as clear. Sacco and Sacchetti now show that these fear memories are stored in secondary, but not primary, sensory cortices - depending on whether the conditioned stimulus was visual, auditory, or olfactory. Only "old," not new, memories are stored in this way, and lesions of secondary cortices, while disrupting the old memories, do not prevent the acquisition of new memories. Here is their abstract:

Visual, acoustic, and olfactory stimuli associated with a highly charged emotional situation take on the affective qualities of that situation. Where the emotional meaning of a given sensory experience is stored is a matter of debate. We found that excitotoxic lesions of auditory, visual, or olfactory secondary sensory cortices impaired remote, but not recent, fear memories in rats. Amnesia was modality-specific and not due to an interference with sensory or emotional processes. In these sites, memory persistence was dependent on ongoing protein kinase M activity and was associated with an increased activity of layers II–IV, thus suggesting a synaptic strengthening of corticocortical connections. Lesions of the same areas left intact the memory of sensory stimuli not associated with any emotional charge. We propose that secondary sensory cortices support memory storage and retrieval of sensory stimuli that have acquired a behavioral salience with the experience.