Researchers from the University of Pennsylvania have done a study confirming a long held belief by most neuroscientists that during memory recall the brain “time travels” back to the state it was in when the memory was formed. As reporterd by LiveScience.com today, the scientists have found that by recording the brain activity of people while they are forming memories, they can later predict ahead of time what memory a person is trying to recall by analyzing their brain activity during the memory retrieval process.
Sean Polyn, a postdoctoral researcher, led the study during which test subjects were shown images on a computer screen while having their brains scanned. The images fell into one of three categories: celebrities, geographical places, and everyday objects.
After the subjects had viewed the photos, and the researchers had recorded the corresponding neural activity associated with the creation of the memories of the images, the researchers then asked the subjects to remember as many of the pictures as possible while they continued to scan their brains.
The scientists discovered that when a subject remembered an image, the pattern of neural activity in the subject’s brain matched the pattern recorded when the image was first seen. There was a distinct lag, however, between when the neural pattern matching a specific image fired and when the subject consciously, or more specifically, verbally identified what they were remembering. This delay averaged about 5.5 seconds allowing the scientists to know what the subjects were going to remember well before the subjects themselves!
Memory in this case works by a process known as contextual reinstatement during which memories are recalled through a series of refinements starting with broad classification and ending up at the specific memory itself. In other words, as a subject was trying to recall a celebrity, areas of the cortex that store faces would begin to activate, and as additional details were remembered, the neural activation pattern would refine itself to finally match the initial pattern recorded when the memory was formed.
The researchers liken the memory storage process to a search engine spidering the web and compare contextual reinstatement to using that same search engine to then search for a memory while constantly tweaking the keyphrase, or search parameters, to narrow in on the desired result.
The other implication of contextual reinstatement is that not only could the scientists tell ahead of time what the subject was trying to recall, but even before that they knew what category (celebrity, place, or object) the subject was thinking of based on the area of the cortex showing activity.
The study was published in the December 23rd issue of Science.
Visit Sean Polyn’s homepage.