A Million Dollar Question: Does LTP = Memory?

The auditory thalamus sends information about sounds directly to the amygdala (other thalamic nuclei also proHere’s a million dollars. You have to bet it on whether ject directly), and cortical areas, especially the hippothe following statement will finally turn out to be true campus, inform the amygdala about theanimal’s current or false: “Long-term potentiation (LTP) and long-term situation. A neutral stimulus like a tone would, before depression (LTD) are cellular mechanisms underlying fear conditioning, normallyprovoke only weak discharge some forms of memory.” in the amygdala, but after the animal learns to fear the I have been taking an opinion poll of neuroscientists tone, its presentation will cause a much larger neuronal at Learning and Memory meetings for the past halfresponse. The hypothesis is, then, that the normally weak dozen years, to see if they think LTP and LTD form auditory synapses in the amygdala become strengtha basis for memory, and have used a two-alternative, ened by LTP during the training that attaches “fear” to forced-choice design like the question above. Two interthe tone. The memory of the tone as a fear-producing esting facts have emerged. First, 5 or 6 years ago, less stimulus resides, according to this hypothesis, in the than half of those polled used to bet on “true,” but strength of the synapses from the auditory thalamus. now about 60% go for “true.” Second, most people are How could this idea be tested? It should be that (1) profoundly reluctant to bet (which is why you have to blocking LTP prevents fear learning; (2) the sensory give only two alternatives and force a choice)—a reflecpathways from the thalamus and cortex to the amygdala tion, I believe, of the general belief that we are still not are capable of LTP; (3) auditory fear conditioning invery close to really knowing the answer. A few are pascreases the amygdala’s postsynaptic response to the