Where is Memory?

If there is a holy grail of neurobiology and behavior, it is the engram—the internal record of a remembered event. The basic principle underlying long-term memory is that synapses are “plastic”; their responses to the synapses of neighboring cells can change, and that this change becomes the record of a remembered event. The big question is where in the vertebrate brain does this occur. The most likely locations are the neocortex, the amygdala, and the hippocampus. Substantial debate, over the last forty years, has failed to completely resolve this question [eg, Rosenkranz and Grace 2002 argue for the amygdala, but Pare (2002) does not agree]. We must also consider that not all memory is formed in the same way. Human memory is thought to be divisible into episodic, working, conditioning, and skill memory; it is entirely possible that different pathways and storage locales are invoked for each type of memory.

In insects, long-term memory resides in the Kenyon cells of the mushroom bodies, which exhibit the same sort of synaptic plasticity that has been postulated for the parts of the vertebrate brain which are involved in memory.

Bliss TVP 2003 A journey from neocortex to hippocampus PHILOS T ROY SOC B 358 (1432): 621-623
Zhang W, Linden DJ 2003 The other side of the engram: Experience-driven changes in neuronal intrinsic excitability NATURE REVIEWS NEUROSCIENCE 4 (11): 885-900
Menzel R, Muller U 1996 Learning and memory in honeybees: From behavior to neural substrates. ANNU REV NEUROSCI 19: 379-404
Milner, B., Squire, L.R., and Kandel, E.R.1998. Cognitive neuroscience and the study of memory. Neuron 20:445-468
Pare D 2002 Mechanisms of Pavlovian fear conditioning: has the engram been located? TRENDS NEUROSCI 25 (9): 436-437
Rosenkranz JA, Grace AA 2002 Dopamine-mediated modulation of odour-evoked amygdala potentials during pavlovian conditioning NATURE 417 (6886): 282-287