Alzheimer’s ‘lost’ memories may be recoverable

Sufferers of Alzheimer’s disease may not have “lost” their memories, but could simply have difficulty accessing them, researchers said as they unveiled a possible treatment that could one day offer a cure to the ravages of dementia.

Nobel Prize-winner Susumu Tonegawa said studies on mice showed that by stimulating specific areas of the brain with blue light, scientists could make the creatures recall thoughts that were otherwise unavailable to them. The results published on Wednesday offer some of the first evidence that Alzheimer’s disease does not destroy specific memories, but rather makes them inaccessible. “As humans and mice tend to have a common principle in terms of memory, our findings suggest that Alzheim-er’s disease patients, at least in their early stages, may also keep memories in their brains, which means there may be a possibility of a cure,” Tonegawa said. Tone-gawa’s team used mice that had been genetically modified to exhibit symptoms similar to those of humans suffering from Alzheimer’s disease. The animals were put in a box which had a low level electrical current passing through the floor — giving an unpleasant, but not dangerous, shock to their feet. An unaffected mouse that is returned to the same box 24 hours later freezes in fear, anticipating the same nasty sensation. Mice with Alzheimer’s do not, suggesting they have no recollection of the experience. But when researchers stimulated targeted areas of the animal’s brains — the “engram cells” associated with memory — using a blue light, they appeared to recall the shock. The same result was noted even when placing the creatures in a different box during stimulation, suggesting the memory had been retained and was being reactivated.

By examining the physical structure of the mice’s brains, researchers noted that those affected with Alzheimer’s-like conditions had fewer “spines” — conduits through which synaptic connections are formed. Via repeated light stimulation they were able to increase the number of spines to levels indistinguishable from those in normal mice, resulting in their exhibiting the freezing behaviour seen in the original box.

“The mice’s memories were retrieved through a natural cue,” Tonegawa said, referring to the box that initially triggered the freezing behaviour. “This means that symptoms of Alzheimer’s disease in mice were cured, at least in their early stages.”

The research, carried out by the RIKEN-MIT Centre for Neural Circuit Genetics, is among the first to prove that recall, rather than memory, is the problem, Japan-based RIKEN said.