Impressive as this may sound this is not the first study of its kind. Studies since 2009 (mentioned in the abstract) in the amygdala have been able to direct and inactivate fear memories in a reversible manner via optogenetics again (see http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2844777/) . In these studies killing as much as 15% of the cells did not erase the memory, indicating that it's ensembles, not single neurons that encode fear memories.
To complicate the picture even more, each neuron is part of more than one memory engrams, and memories are stored in synaptic connections which are formed in the vast dendritic trees of neurons. So you have a very sparse and reduntant encoding of this associative memory.
Finally, note that both the amygdala and the hippocampus are very old structures so we don't know if the same processes take place in the neocortex (although it's likely so).
I don't mean to belittle the article, but it's mostly proof of concept if you have followed the relative literature. Tonegawa's lab had some even more fascinating papers published recently that probe the process of memory encoding to the level of single dendrites.
To complicate the picture even more, each neuron is part of more than one memory engrams, and memories are stored in synaptic connections which are formed in the vast dendritic trees of neurons. So you have a very sparse and reduntant encoding of this associative memory.
Finally, note that both the amygdala and the hippocampus are very old structures so we don't know if the same processes take place in the neocortex (although it's likely so).
I don't mean to belittle the article, but it's mostly proof of concept if you have followed the relative literature. Tonegawa's lab had some even more fascinating papers published recently that probe the process of memory encoding to the level of single dendrites.