New York: Scientists have developed a new brain implant that can boost memory function in laboratory rats; a breakthrough which they say could lead to the development of neuroprosthetic devices that can help tackle dementia, stroke and repair brain injuries in humans.
       
Though it's yet to be tested in humans, the scientists at Wake Forest University and the University of Southern California said their implant demonstrated for the first time that a cognitive function can be improved with a device that mimics the firing patterns of neurons.
       
In recent years scientists have devised implants that allow paralyzed people to move prosthetic limbs or a computer cursor, using their thoughts to activate the machines.
       
But in the latest work, the researchers used some of the same techniques to read neural activity, but translated those signals internally to improve brain function rather than to activate outside appendages, reported daily.
      
In a series of experiments, the scientists trained the rats to remember which of two identical levers to press to receive water.
       
The animals first saw one of the two levers appears and then (after being distracted) had to remember to press the other lever to be rewarded.
       
Repeated training on this task teaches rats the general rule, but in each trial the animal has to remember which lever appeared first, to inform the later choice.

The rats were implanted with a tiny array of electrodes, which threaded from the top of the head down into two neighboring pieces of the hippocampus, a structure that is crucial for forming these new memories, in rats as in humans.
   
The two slivers of tissue, called CA1 and CA3, communicate with each other as the brain learns and stores new information. The device transmits the exchanges to a computer.
       
To test the effect of the implant, the team used a drug to shut down the activity of CA1. Without CA1, the rats could not remember which lever to push to get water.
       
They remembered the rule -- push the opposite lever of the one that first appeared -- but not which they had seen first.
       
The researchers, having recorded the appropriate signal from CA1, 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," said Theodore Berger, who led the study, which is published in the journal of Neuro engineering and Rehabilitation.
       
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.
       
The authors said that with wireless technology and computer chips, the system could be easily fitted for human use, but there are a number of technical and theoretical obstacles.
       
For one, the implant must first record a memory trace before playing it back or amplifying it; in patients with significant memory problems, those signals may be too weak.
       
In addition, human memory is a rich, diverse neural process that involves many other brain areas, not just CA3 and CA1; implants in this area will be limited.

(Agencies)