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Monday, March 22, 1999 Published at 22:10 GMT


The chemistry of forgetting

A crucial chemical reaction that "writes" long-term memory into the brain has been revealed

The chemical key to forgetfulness may have been uncovered, believe scientists in the US.

They have revealed the biochemical changes that happen when an event is "written" into the brain's long-term memory. Their new understanding could lead to treatments for amnesia, they suggest.

Stephen Taubenfeld explains how memory can fail
"One day we could restore the biochemical cascade in the brain that is necessary for long-term memory," Stephen Taubenfeld, of Brown University, told BBC News Online.

Short-term memories, such as what you had for breakfast, are stored for a relatively short time. If an event, like a special romantic meal, is to be stored for a longer time, it needs to be built into your brain by rearranging the neurons.

This happens after a cascade of biochemical reactions. First, a protein called Creb enters the nucleus of brain cells and switches on certain genes, a process known as transcription.

[ image: The altered Creb protein, which creates memories, is brown in this brain slice]
The altered Creb protein, which creates memories, is brown in this brain slice
The structural proteins these genes produce then "hard-wire" the memory into the brain. This happens because the structural proteins change and strengthen synapses in the brain and move neurons in and out of contact to one another.

The new research makes the connection between forgetful behaviour, chemical changes to the Creb protein and damage to a part of the brain that is already known to result in amnesia in human patients.

The team, lead by Dr Cristina Alberini of Brown University, took two sets of rats. One set had their fornix cut - this is a part of the brain which connects to the memory-storing hippocampus - the other did not.

[ image: This rat brain shows no altered Creb protein and could not form memories]
This rat brain shows no altered Creb protein and could not form memories
The rats were then given a choice between a light and dark chamber. Entering the dark chamber resulted in a two-second electric shock to the feet.

The normal rats remembered this lesson for up to a month, but those with a damaged fornix, forgot the danger after only six hours.

Examination of their brains showed that the Creb protein had only changed chemically (adding a phosphate group) in the rats which could remember to avoid the dark rooms.

This research breakthrough shows how the chain of events that make up remembering is broken chemically if a part of the brain is injured. The next step, says Taubenfeld, is to identify the specific genes on which Creb acts.

The research is published in Nature Neuroscience.

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