+ Memory Implant Improves Memory in Rats

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In a study reported on by Benedict Carey in the NY Times, scientists have designed a brain implant that restored lost memory function in laboratory rats.  It also strengthened recall of new information.

The research marks a crucial first step in the development of neuroprosthetic devices which might repair deficits in patients suffering from dementia, stroke or brain injury.

Be aware, however, that use of the implant in humans is still a long way off.

The implant research was led by Sam A. Deadwyler, a scientist at Wake forest.  In a series of experiments, the researchers trained rats to remember which of two identical levers to press to receive water.  First, the animals saw one of the two levers appear and then were distracted.  They then had to remember to press the other lever to be rewarded.

Repeated training on this task taught the rats the general rule, but in each trial, the animal had to remember which lever appeared first and use that information to inform the subsequent choice. 

The rats were implanted with a tiny array of electrodes in two neighboring pieces of the hippocampus, the brain structure which is crucial for forming new memories in both rats and humans.

The two slivers of tissue are called CA1 and CA3.  They communicate with each other as the brain learns, and stores, information.  The device transmitted these exchanges to a computer.

To test the effect of the implant, researchers used a drug to shut down the activity of CA1.  Without CA1 online, rats could not remember which lever to push in order to get their water.

They remembered their rule — push the opposite lever from the one that first appeared — but they couldn’t remember which they had seen first.

So researchers, who had recorded the appropriate CA1 signal, simply replayed it (like a melody on a player piano) and the animals remembered.

The implant acted as if it were CA1, at least for this one task. 

“Turn the switch on, the animal has the memory; turn it off and they don’t: that’s exactly how it worked,” says the lead author of the study, Theodore W. Berger, professor of engineering at USC.

It is being published by The Journal of Neural Engineering.  Co-authors were Robert E. Hampson and Anushka Goonawardena, along with Dr. Deadwyler of Wake Forest , Dong Song and and Vasilis Z. Marmarelis of USC.

In rats that did not receive the drug, new memories faded by about 40 percent after a long distraction period.  But if the researchers amplified the corresponding CA1 signals using the implant, the memories eroded only about 10 percent in that time.

With wireless technology and computer chips, say the authors, the system could easily be fitted for human use.  But there are a number of technical and theoretical obstacles.

One problem is that the implant must first record a memory trace before playing it back or amplifying it.  But in patients with significant memory problems, those signals may be too weak.

Another is that human memory, a rich, diverse neural process, involves many other brain areas, not just CA3 and CA1.  Implants in those areas will be limited.

Nevertheless, some restored memories such as “Where is the bathroom? Where are the pots and pans stored? — could make a big difference in the lives of a dementia patient.

Says Dr. Berger, “If you’re caring for someone in the house, for example, it might be enough to keep the person out of the nursing home.”

For the article, the sole source for this post, visit http://www.nytimes.com/2011/06/17/science/17memory.html?scp=3&sq=Benedict%20Carey&st=cse

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