In the latest issue of Science Magazine, a group of Israeli scientists recorded neurons of the hippocampus in humans with microelectrodes as part of an epilepsy surgery. As the single neurons were recorded, the patients were played videos from various pop culture sources. After the movies were played, the subjects were then asked to recall what they saw. As you can see in the movie below, the sample neuron fires whenever Tom Cruise is shown, and, later, when the patient freely recalls what he saw on the TV, notice the neuron fires again approximately 1-2 seconds before the patient says "Tom Cruise."
The video is amazing for its sheer pop art meets neuroscience combination. I thought it could be in a museum as an experimental modern art piece. But that aside, the big science ramification is that, perhaps, this neuron is where "the memory" of Tom Cruise resides. It also probably encodes more than Tom Cruise (as you can see in its sporadic response to other images), and whether it is truly where the memory trace exists can only be shown by either deactivating that neuron with GABA agonists / cooling, which is only done in animal models, or by stimulating that neuron and then asking if the patient immediately thinks of Tom Cruise. Even then, the neuron may still only be the "librarian" of the memory, and not the actual storage. Perhaps the brain doesn't make such distinctions in its storage mechanisms.
These are tough problems to solve, but ultimately the most fascinating. I consider it even more interesting than the "C-word" problem. Oh brain oh brain, how ever do you store declarative memory?
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