新托福考试阅读练习资料：Enzyme Can Strengthen Old Memories

本文是关于年龄的增长与记忆力的关系，下面就来一起看一看吧：

Precious memories need not fade if a report today bears fruit. Neuroscientists have successfully strengthened old memories in rats, according to research published today in Science.

A handful of substances can strengthen memories as they're being made. But a greater aim for neuroscientists is to learn how to enhance existing, older memories, such as where you live or your grandson's name -- memories often lost because of dementia or amnesia.

"Finding out what perpetuates long-term memory has been a real challenge," says Todd Sacktor, a neuroscientist at SUNY Downstate Medical Center in New York and an author on the paper. "What's special here is we've found a way to make old memories stronger without interfering with them as they're formed or recalled."

When a memory is made, new connections, or synapses, form between brain cells. To keep the memory, that synapse must endure. Scientists don't yet know exactly what strengthens these synapses to keep memories stable over time, but there are some clues. In 2007, Sacktor and his colleagues erased long-term memories that rats had formed weeks earlier using a drug that inhibited the enzyme protein kinase Mzeta (PKMzeta).

Doubts laid to rest

In the current study, the researchers alleviated some neuroscientists' concerns about the specificity of the PKMzeta-blocking drug by using genetic tools in rats to disrupt PKMzeta and also boost the enzyme in the neocortex, a presumed repository for long-term memory storage in the brain.

One week after rats fell ill from drinking sweet, lithium-laced water, they were given injections containing genetic elements that would either block or increase the activity of PKMzeta. Rats with abundant PKMzeta in their neocortices seemed to remember that sweet water caused illness. They hardly touched the sweet water when they were served it again a week after the injection -- far less so than untreated rats. Meanwhile, rats with reduced PKMzeta activity drank thirstily. The same thing happened with salty, lithium-laced water given a week before the treatment and again a week after.