Alzheimer’s disease robs those afflicted by it of their memories, but how it does exactly, isn’t fully understood. To borrow from an entirely inaccurate computer analogy, a problem with your hard disk can stem from the hard disk’s ability to write data (“create” new memories), store data (hold the memories that do get written), or retrieve data successfully written and stored (the memories are there alright; they’re just tantalizingly out of reach).
This distinction is important; figuring out where the problem is allows us to fix it – unless we plan on completely replacing the hard disk- not exactly the recommended route when referring to humans.
Research with mice appears to show that memory retrieval is the source of an early Alzheimer patient’s troubles. If the right neurons gets stimulated, the process can even be reversed.
When memories take root in our minds, they leave trails known as “engrams.” Researchers searched for neurons that retain engrams and found a set (called DG neurons) that respond to fear. When mice are trapped in a container and undergo an “aversive experience,” they do the only thing they can – they freeze out of fright.
Mice remember this experience and freeze when placed in the box again the next day. However, mice that were afflicted with the early symptoms of Alzheimer’s, did not react in this way.
Next, the researchers manipulated the DG neurons in the Alzheimer’s mice, so that they can be stimulated by blue light. When the mice were returned to their Box of Horror and had their neurons stimulated with blue light, the mice froze with fright; they could remember again.
In a further set of experiments, mice that had their DG neurons completely removed with diphtheria toxin, were similarly unable to recall their “shocking” inside-of-box experience. Furthermore, even memories that do not correspond to intense fear and shock, could be brought back when the DG cells were stimulated – mice could also be made to remember objects they had seen the day before.
The researchers do add a disclaimer: the sort of artificial memory failure they had manipulated in their mice might not be the same as the sort experienced by Alzheimer patients. In later stages of the disease, other bits of hardware might also be affected.
Sources: Ars Technica, AOL
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