How does the brain distinguish between old and new information?
Whether a word is freshly memorized or remembered does not change the frequency with which the neurons in the hippocampus fire. The crucial thing is their timing.
The nerve cells in the hippocampus have to archive what has just been experienced as well as retrieve memories. But how does the brain know, based only on the electrical signal, whether it is fresh stock for the thought store or long-known knowledge that is being retrieved? Neurologist Hye Bin Yoo and two colleagues at the University of Texas Southwestern Medical Center observed for the first time how the human thought organ makes this distinction.
The subjects were 27 epilepsy patients with implanted electrodes to record brain activity. The experiment was simple: first, the subjects were asked to learn a list of things. After a brief distraction, they had to recall the words. The nerve signals for memorizing and remembering one and the same concept were identical, only the timing differed. Experts refer to this as a "phase offset."
Could help in understanding schizophrenia
Neurons send their signals at a certain frequency, the firing rate. You can think of these like the hand of a clock, for example, which turns faster at a higher frequency. When a word is freshly memorized or remembered, it doesn't change the speed. But Yoo's team observed that - metaphorically speaking - the position of the hand where the neurons send their signals changes; so they fire at the same rhythm, but at a different time.
"This is some of the clearest evidence yet of how the human brain works when it comes to remembering something or forming new memories," says Bradley Lega, who was also involved in the study. It is possible that the findings will help in understanding schizophrenia in the future. After all, sufferers are often unable to distinguish their own memories from delusions, which could also be explained by a disturbed phase offset.
Spectrum of Science
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