For decades now, scientists have believed that working memory, a form of short term memory, can be accessed only through the sustained firing of neurons. Working memory is used constantly in our day to day lives — from remembering the name of someone you just met while carrying on a conversation, to mixing the right ingredients in a recipe – it allows us to access the bits of information needed to process and carry out simple tasks. Until recently, the scientific consensus has been that once our brain is no longer actively maintaining these memories, the information is irretrievably lost. A new technique called transcranial magnetic stimulation (TMS) uses focused electromagnetic fields in order to reactivate neurons and retrieve these memories.
The study, based out of the University of Notre Dame, gathered 66 participants and asked them to remember both a face and a word. MRI scans revealed that two distinct patterns emerged in separate groups of cells, suggesting that each region was uniquely responsible for keeping track of the face or the word. When they asked participants to focus only on the face, the brain activity associated with the word completely disappeared. Using TMS, the researchers found that they were able to reactivate the region where the word was stored.
Although these findings seem to challenge previously held beliefs about how working memory functions, there are a number of caveats to keep in mind. For instance, the processing of information from the retina to the brain is necessarily complex, and so it’s difficult to guarantee whether the firing of activity in the two groups of cells is actually representative of fluctuations in working memory or simply the processing of visual information. Furthermore, it’s likely that there is a time delay of at least a few minutes between the application of TMS and the subsequent MRI scan, raising the question of whether these are re-stimulated working memories or memories that have since passed to long-term memory.
Scientists still don’t understand exactly how the brain allocates information or decides which thoughts to pay attention to. Continued TMS experiments could hold the key to understanding these processes and other cognitive functions like mental illness and learning.
Acknowledgements: Many thanks to Harvard PhD students Leyla Tarhan, a student in the Psychology department, and Dana Boebinger, a student in Speech and Hearing Bioscience and Technology, for their extremely helpful knowledge and expertise on the subject.
Managing Correspondent: Tarraneh Eftekhari
Scientific Paper: Reactivation of latent working memories with transcranial magnetic stimulation – Science
Media Coverage: Magnets are being used to retrieve patients’ lost, short-term memories – Science Alert