June 23, 2011

A First Step Toward a Prosthesis for Memory

A neural implant helps rats with short-term recall.

(June 23, 2011)  Researchers have developed the first memory prosthetic device—a neural implant that, in rats, restored lost brain function and improved short-term memory retention. While human testing is still a distant goal, the implant provides evidence that the brain’s complex neural code can be interpreted and reproduced to enhance cognitive function.

The device, which consists of a tiny chip and a set of 32 electrodes, marries math and neuroscience. At its heart is an algorithm that deciphers and replicates the neural code that one layer of the brain sends to another. The function restored by the implant is limited—rats were able to remember which of two levers they had pressed. But its creators believe that a device on the same principle could one day be used to improve recall in people suffering from stroke, dementia, or other brain damage.

Wake Forest University neurophysiologist Samuel Deadwyler first trained the rats to press two different levers in succession. The animals learned to press one lever as it was presented to them and then, after a delay, remember which they’d pressed and choose the other one the second time around. While the rats performed the task, two sets of minute electrodes recorded the activity of individual neurons on the right and left sides of the hippocampus, an area of the brain that consolidates short-term memory by processing information as it passes through multiple layers. A set of 16 electrodes—eight on the right, eight on the left—monitored signals being sent from neurons in an area of the hippocampus called the CA3 layer, and another 16 monitored the processed signals received by neurons in the CA1 layer.

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