Different types of memory require activity in various parts of the brain. When you recall a fact, for instance, you most likely use only the left side of your brain. When you recall events, which requires putting episodes in the context of place and time, you probably draw on both sides of your brain.

In the October issue of Neuropsychology, Stephen Christman and Ruth Propper, of the University of Toledo, Ohio present further evidence for the theory that recall of events, or “episodic memory,” involves coordinated processing on both sides of the brain.

In one experiment, the researchers tested 180 right-handed Air Force recruits on various aspects of verbal memory. Recruits with at least one left-handed family member were better at recalling words they had seen previously -- a measure of episodic memory. The researchers theorize that people from “lefty” families performed better because they are more likely to have inherited a large corpus callosum, a bundle of nerve fibers that fosters communication between the two sides of the brain. The corpus callosum is known to be larger in people who are left-handed.

To further test their theory, the researchers stimulated activity in one side of the brain or the other by restricting the visual fields of 84 right-handed undergraduates viewing a series of words. The researchers presented some words only to the right visual field (which activates the left side of the brain) and others only to the left visual field (which activates the right side of the brain). They also presented some words first to the left and then to the right visual fields, to stimulate both parts of the brain at separate times. Participants performed best on word recognition tests - another measure of episodic memory - when both sides of their brains were stimulated.

 

 

 

The researchers therefore conclude that communication between the two sides of the brain, or “inter-hemispheric processing,” is necessary for recalling events. The apparent importance of the corpus callosum in this process may also explain why young children are unable to remember events accurately. That part of the brain does not fully mature until age four.