X-Message-Number: 16322
From: Brent Thomas <>
Subject: memory usage and formation
Date: Thu, 24 May 2001 09:41:35 -0400

from http://www.sciencedaily.com/releases/2001/05/010524061819.htm

very interesting practical research revealing some secrets of how the mind
No direct implication for cryonics but its a very relevant field.

       Scientists Switch Memory
       Recall On And Off In Fruit

       Cold Spring Harbor, NY -- Scientists at Cold
       Spring Harbor Laboratory have used a genetic
       strategy in fruit flies to switch electrical activity in
       the insect brain on and off at will. In doing so,
       they have made the surprising discovery that
       switching off electrical activity in the brain blocks
       memory recall, but not initial formation of

       "The brain of the fly works very much like the
       brain of other animals, including humans. Flies are
       capable of learning just like Pavlov's dogs," says
       Dr. Tim Tully, one of the authors of the study,
       which appears in this week's issue of Nature.
       [May 24]. 

       After ringing the dinner bell and presenting his
       dogs with food several times over a few days, the
       Russian physiologist Ivan Pavlov found that
       eventually, his dogs would display dinnertime
       behavior (drooling, excitement) on just the sound
       of the bell. 

       Today, all dog and cat owners are familiar with
       this form of "associative learning." They see it in
       action each time the sound of the can opener
       sends their furry friends running to the kitchen in
       anticipation of their supper. 

       What pet owners are actually seeing, however, is
       the retrieval of the "can opener:food" memory
       that has already been acquired and stored in the
       animal's brain. Now, the Cold Spring Harbor
       Laboratory researchers have found that memories
       based on associative learning can be formed in the
       absence of electrical activity in the fruit fly brain,
       but cannot be recalled. 

       Memory has three components: acquisition
       (learning), storage, and retrieval (recall). By
       training flies to avoid an odor-and by switching
       off electrical activity in the brain at different
       times during or after training-the researchers
       could test whether electrical activity in the insect
       brain is necessary for the acquisition, storage, or
       retrieval phases of memory. 

       The scientists used a new genetic strategy to
       answer an age-old question in neurobiology: Is
       persistent electrical activity necessary for memory
       formation? "The surprising answer is no!" says

       "A simple form of memory can be acquired and
       stored normally in the absence of electrical
       activity, but recall is blocked. This suggests that
       these memories are happening as a chemical
       process and that electrical activity is necessary
       only to recall these memories." 

       The key to the study was expressing a mutant
       form of a gene called Shibire ("sha-beer-ee") in
       the flies' brain. Normally, the gene is involved in
       neurotransmitter release. However, the mutant
       form of the gene encodes a protein that works at
       low temperature (20 C) but which blocks
       neurotransmitter release at high temperature
       (30 C). This property allowed the scientists to
       switch Shibire activity in the brain on and off at
       will by shifting the flies from high to low or low to
       high temperature. 

       "When this gene does not function, neurons run
       out of neurotransmitter and this paralyzes that
       part of the brain," says Dr. Josh Dubnau, the lead
       author of the study. "By raising the temperature
       of the animal slightly we shut off a part of the
       brain involved in learning this simple task. When
       we shift the temperature back down, normal
       electrical function is restored." 

       Dubnau, Tully and their colleagues trained flies to
       avoid an odor and later tested the flies' recall by
       exposing them to the same odor and measuring
       their avoidance response. The scientists
       discovered that the flies' ability to recall memories
       could be switched on, off, and back on again by
       simply shifting the animals to different

       "In most other studies, scientists have typically
       had to cause permanent structural damage to
       study brain function. In this study, the flies can
       develop and learn normally and then brain activity
       can be shut down in a reversible way to test
       memory. It is a very elegant approach," says
       Steven de Belle, a neuroscientist at the University
       of Nevada, Las Vegas. 

       When the researchers switched electrical function
       off in part of the brain during or just after training
       flies, the flies avoided the odor upon subsequent
       testing. In contrast, when the scientists switched
       electrical function off in part of the brain during
       the recall period, the flies did not avoid the odor.
       "These findings mean that different parts of the
       brain do not have to communicate with each other
       to store memory, but they do need to
       communicate to recall memory," says Dubnau. 

       When it comes to learning and memory, "The
       brain must function electrically to recall what is
       stored chemically," says Tully. 

Brent Thomas

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