'Dark Matter' of Memory to Unlock Secrets to Learning, Brain Disorders, Study Says

It's common knowledge among learners and brain scientists that new memories such as names and faces are placed in the working memory. 

Neurons continue to function and gauge the importance of the new memory you have. If, say, the said memory is important, it's permanently encoded in the long-term memory. Interestingly, where does memory go in between? Scientists may have finally figured out the answer.

According to Science Magazine, a research team has shown that such memories can be resurrected from this "limbo"-like state. Their new study points toward a new form of working memory, which is called "prioritized long-term memory."

Their study suggests that this memory exists without elevated neural activity. This is consistent with other recent work, which indicates that this information can be somehow held among the synapses that connect neurons, even if the conventional working memory has already faded.

Geoffrey Woodman of the Vanderbilt University in Nashville said this find is like finding the "dark matter" of memory. Woodman, a neuroscientist that is not involved in a study, said while this was hard to measure, the prioritized long-term memory had to be there else everything else falls apart. 

According to Science Magazine, neuroscientists Nathan Rose and his colleagues at the University of Wisconsin had subjects watch a series showing faces, words, or dots moving in one direction. Using fMRI, they tracked the resulting neural activity and, with the help of machine learning, tried to associate brain activity with each item.

Then the subjects viewed them in combination but were cued to focus on just one of the two items. At first, brain signatures for both showed up, but activity for the "uncued" item dropped as if it were forgotten. Interestingly, people were still able to "recall" the uncued item a few seconds later. 

Rose and his colleagues now tried to use transcranial magnetic stimulation, a non-invasive method that uses rapidly changing magnetic fields to deliver a pulse to the brain. Subjects then performed the same tasks, but applied a short pulse after the signature of the uncued memory was "forgotten."

Interestingly, the appropriate activity for that item spiked, showing that it was "reactivated" into the consciousness.

While the study doesn't show (yet) how synapses or other neuronal features can hold this new discovery or how much information it could store. However, co-author neuroscientist Bradly Postle told Science Magazine that it's an important step on understanding how we "bring things to mind."