Scientists at the University of Southern California and the University of Illinois say they have confirmed the theory that the mind stores memories by "hard wiring" new connections between brain cells.
The findings were to be released this week at a meeting of the Society for Neuroscience in Phoenix, the Los Angeles Times reported.Psychobiologists Richard F. Thompson of USC and William Greenough of Illinois worked jointly to prove that the brain circuitry - the network of links between cells - goes through actual physical changes when a task is learned.
The so-called "hard wiring" memory theory is used to explain why some learned activities, such as riding a bicycle, are never forgotten.
Thompson and Greenough based their findings on a study of 15 rabbits that were conditioned to behave in certain ways. Thompson rang a bell and blew a small puff of air into one eye of each rabbit, causing the animals to blink. Soon, the rabbits would blink every time the bell sounded, without the puff of air.
Thompson discovered through electrodes planted in the rabbits' brains that there was increased activity in a group of cells called Purkinje cells, located in the cerebellum.
Greenough then studied the rabbits and discovered a greater number of intercellular connections in the side of the cerebellum that had learned the blinking than in the side that had not.
In the 15 rabbits studied over a two-year period, "the differences were statistically reliable and clearly visible," Greenough said. "We really have isolated a case where, in brain cells that are clearly involved in the performance of a task, we have crystal-clear structural change that indicates a change in anatomical circuitry."
The discovery "is not surprising, in that it fits theory, but there has been no particular evidence to support the theory before," Thompson said. "We were convinced there would be something like this because memories are never forgotten."
The scientists also did similar experiments with 19 rats, which were trained to walk up an elevated pathway. The rats also showed increased "hard wiring" after the learning the task, but in a different part of the brain.