X-Message-Number: 16333
From: "Jan Coetzee" <>
Subject: Memories are not electrical (Nature) New!
Date: Fri, 25 May 2001 01:33:05 -0400

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lifelines: Mushrooms aid total recall 

      Drosophila: offers clues to how we keep memories in mind.

Learning to love putrid pongs must take some nerve. But flies can learn smells 
even when critical nerve connections in their brains are blocked, researchers 
have found - although recalling the scents needs cells that are fully switched 
on1. The findings offer clues on how the mind keeps track of its memories. 

Flies like dung because of a brain nodule called the mushroom body. This knot of
nerves is involved in learning and remembering smells - but whether it makes 
the memories, stores them or recalls them was unknown. 

By silencing synapses, the connections between nerve cells, Josh Dubnau and his 
colleagues at Cold Spring Harbor Laboratory in New York found that the 
fruitflies' ability to memorize smells is not affected when the mushroom body is
switched off. "I was very surprised that electrical activity is not required 
for learning," says Dubnau. 

The team used a heat-sensitive switch to silence the nerves. Putting the flies 
in a hot room overheated dynamin, the synapse protein found in the cells of the 
mushroom body. For a few minutes at a time, these hot nerve cells could receive 
but not send signals. Meanwhile the flies learnt to choose between two smells: 
liquorice and sweaty tennis shoes.

Memories formed by the flies when they were hot could still be recalled when the
insects were cooled down. But if the flies were heated up while remembering, 
they could not recall a thing. 

The findings challenge a long-standing idea that memories are formed by 
persistent electrical signals echoing around the brain, says Randolf Menzel, who
works on bee learning at Freie Universit t Berlin. "If such a circulating 
activity does exist, it does not involve the part of the network responsible for
reading out the information," he says.

      The mushroom body: may be responsible for learning smells.  

Instead, Dubnau's team speculates that electrical activity entering nerve cells 
in the mushroom body stops there, creating biochemical changes that store the 
memory. "The cells can learn this information without communicating with other 
neurons," says Dubnau.

But Scott Waddell of the Massachusetts Institute of Technology, Cambridge, who 
also works on fly memory, thinks that other brain areas may also have been 
affected by the synaptic knockout. "I don't think you can pin it down to the 
mushroom body," he says.

Nevertheless, he notes that "understanding information processing and storage in
any animal relates to others". The mushroom body is a simple neural network, 
and the way it works relates to other networks, such as our own hippocampus and 



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