NEURO-SCI: Lefty Memory

From: J. R. Molloy (
Date: Fri Oct 19 2001 - 07:51:07 MDT

Findings also help explain why children don't remember events until about age
4, when the fibers connecting the halves fully develop

WASHINGTON - Does coming from a family full of "lefties" tend to make a person
better at remembering events? The data from two recent experiments answer in
the affirmative. What's more, psychologists may finally be able to explain why
kids don't remember events until they are about four years old. This recent
research is reported in the October issue of Neuropsychology, published by the
American Psychological Association (APA).

Stephen D. Christman, Ph.D., and Ruth E. Propper, Ph.D., of the University of
Toledo in Ohio, studied memory as a function of family handedness.
Interestingly, people don't have to be personally left-handed to share a
trait: There is evidence that the two brain hemispheres of even right-handers
with left-handed relatives share functions more equally, interact more and are
connected by a larger corpus callosum (the bundle of mediating fibers) than
hemispheres of people with right-handed relatives. Although it is not well
understood, there is a hereditary component to handedness.

Christman and Propper studied two types of memory -- episodic (the recall and
recognition of events) and non-episodic (factual memory and implicit memory,
the latter of which concerns things people "just know"). Strength or weakness
in either, says Christman, "may not have much effect in educational settings,
as we can recall things we have learned by 'remembering' them (episodic
or by 'knowing' them (implicit memory). The main difference is that people who
'remember' can also recall details about the time and place at which they
learned this fact."

In the first experiment, which studied 180 right-handed Air Force recruits at
Lackland Air Force Base in San Antonio, Christman and Propper found that for
different types of word-memory tasks, participants with left-handed relatives
had superior episodic memory and inferior implicit memory, at a rate greater
than chance. The researchers therefore speculate that a higher level of
inter-hemispheric interaction facilitates episodic memory.

In the second experiment, the authors studied episodic and semantic (factual)
memory in 84 right-handed undergraduates, studying what happened when they
presented words and letter strings to either one part of the brain or to both.
When Christman and Propper presented stimuli to one part of the brain,
participants remembered facts better. When the researchers presented stimuli
both halves of the brain, participants remembered events better -- again
supporting the role of inter-hemispheric processing in episodic memory.

Christman and Propper conclude that because our brains' two halves work
together to help us remember events, people whose brains' halves work together
more actively (people with left-handedness in their families) remember events
better than they remember facts. As a result, the authors say that memory
studies should factor in the familial and probably personal handedness of
participants (having a weak versus strong hand preference may also matter).
Further research may help explain why episodic memory benefits from the two
halves working together, whereas factual/implicit memory is better processed
one half alone.

The researchers stress that memory performance has nothing to do with
"brain dominance." "While the notion of people being right-brained or
left-brained is common in the popular press," says Christman, "it has received
very little support in the scientific literature. Both hemispheres of all
people are going to be involved in virtually all tasks."

Finally, the findings shed light on why children have no episodic memories
until about age 4. The onset of episodic memory roughly coincides with the
corpus callosum's maturation and myelinization, the growth of fatty protective
sheaths around nerve fibers. In light of the findings, it would mean that a
functional corpus callosum is critical in the formation of event memories and
therefore explain why its maturation in early childhood is at least partly
responsible for the emergence of episodic memory.

Article: "Superior Episodic Memory is Associated with Interhemispheric
Processing," Stephen D. Christman, Ph.D., and Ruth E. Propper, Ph.D., both
with the University of Toledo, Toledo, Ohio; Neuropsychology, Vol. 15, No 4.
Ruth E. Propper is now at the Department of Psychology, Merrimack College.

Stephen D. Christman can be reached by e-mail at
by phone at (419) 530-4684.

Full text of the article is available from the APA Public Affairs Office and
after November 10 at

The American Psychological Association (APA), in Washington, DC, is the
scientific and professional organization representing psychology in the United
States and is the world's largest association of psychologists. APA's
membership includes more than 155,000 researchers, educators, clinicians,
consultants and students. Through its divisions in 53 divisions of psychology
and affiliations with 60 state, territorial and Canadian provincial
associations, APA works to advance psychology as a science, as a profession
as a means of promoting human welfare.

--- --- --- --- ---

Useless hypotheses, etc.:
 consciousness, phlogiston, philosophy, vitalism, mind, free will, qualia,
analog computing, cultural relativism, GAC, Cyc, Eliza, cryonics, individual
uniqueness, ego, human values, scientific relinquishment

We move into a better future in proportion as science displaces superstition.

This archive was generated by hypermail 2b30 : Sat May 11 2002 - 17:44:14 MDT