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1 What are memories made of?
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WHAT ARE MEMORIES MADE OF?
MEMORIES are the basic stuff of thought. We access our stores of knowledge every time we perform a task, communicate through speech or formulate the simplest concepts. Yet the physical form of memory has long been mysterious. What changes occur in the brain when a new memory is encoded? One thing we do know is that memory formation involves the strengthening of synaptic connections between nerve cells. Using sea slugs, which have a relatively simple nervous system, a team led by Kelsey Martin at the University of California, Los Angeles, last year became the first to watch memories being made, in the form of new proteins appearing at the synapses (Science, vol 324, p 1536). Where, though, is knowledge stored in the complex brains of mammals? Short-term memories, such as a telephone number about to be used, seem to be stored in two small curled-up structures called the hippocampi, buried deep in the brain’s two hemispheres. In 2008 Courtney Miller and David Sweatt at the University of Alabama in Tuscaloosa showed in mice that during the first hour after a memorable event there were chemical changes to the DNA of neurons in this area, altering the proteins produced. Over the subsequent week, there were similar changes to the genes of neurons in the cortex. These changes seemed to be permanent, indicating that long-term memories are stored there (Neuron, volume 53, p 857). The pair think they watched shortterm memories form in the hippocampus, which then became long-term memories in the cortex. The brain pays extra attention to things that frighten us, as remembering them could mean the difference between life and death. A structure next to the hippocampus called the amygdala is known to play a role in stamping this indelible mark. Last year, a team led by Sheena Josselyn at the Hospital for Sick Children in Toronto, Canada, found that in mice they could erase a frightening memory of a noise by killing amygdala neurons whose synapses had recently been strengthened after exposure to the noise (Science, vol 323, p 1492). It was the first time a specific memory had been traced to the nerve cells that encoded it. It’s still a far cry from seeing a memory in a human being, though. Emma Young
28 | NewScientist | 3 April 2010
The nervous system has 10,000 different types of neuron
WHAT IS THE FUNCTION OF MIRROR NEURONS?
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WHAT ARE MEMORIES MADE OF?
MEMORIES are the basic stuff of thought. We access our stores of knowledge every time we perform a task, communicate through speech or formulate the simplest concepts. Yet the physical form of memory has long been mysterious. What changes occur in the brain when a new memory is encoded? One thing we do know is that memory formation involves the strengthening of synaptic connections between nerve cells. Using sea slugs, which have a relatively simple nervous system, a team led by Kelsey Martin at the University of California, Los Angeles, last year became the first to watch memories being made, in the form of new proteins appearing at the synapses (Science, vol 324, p 1536). Where, though, is knowledge stored in the complex brains of mammals? Short-term memories, such as a telephone number about to be used, seem to be stored in two small curled-up structures called the hippocampi, buried deep in the brain’s two hemispheres. In 2008 Courtney Miller and David Sweatt at the University of Alabama in Tuscaloosa showed in mice that during the first hour after a memorable event there were chemical changes to the DNA of neurons in this area, altering the proteins produced. Over the subsequent week, there were similar changes to the genes of neurons in the cortex. These changes seemed to be permanent, indicating that long-term memories are stored there (Neuron, volume 53, p 857). The pair think they watched shortterm memories form in the hippocampus, which then became long-term memories in the cortex. The brain pays extra attention to things that frighten us, as remembering them could mean the difference between life and death. A structure next to the hippocampus called the amygdala is known to play a role in stamping this indelible mark. Last year, a team led by Sheena Josselyn at the Hospital for Sick Children in Toronto, Canada, found that in mice they could erase a frightening memory of a noise by killing amygdala neurons whose synapses had recently been strengthened after exposure to the noise (Science, vol 323, p 1492). It was the first time a specific memory had been traced to the nerve cells that encoded it. It’s still a far cry from seeing a memory in a human being, though. Emma Young
28 | NewScientist | 3 April 2010
The nervous system has 10,000 different types of neuron
WHAT IS THE FUNCTION OF MIRROR NEURONS?
3