Alzheimer’s disease now affects approximately 5.5 million Americans, and it is estimated that 16 million people will be living with the disease by the year 2050. To put this in perspective, while deaths from heart disease have decreased by 14 percent since 2000, deaths from Alzheimer’s disease have increased by 89%.
It is interesting to note that 35 percent of caregivers (family and friends) of Alzheimer’s or other dementia patients report that their own health has declined compared to 19 percent of caregivers of older people with no dementia. This illness can cause intense suffering not only for those with the disease, but for those who love and care for them as well.
Thankfully, there is a lot of promising research underway that will hopefully benefit those with Alzheimer’s disease. In a study published on May 10, 2018, in the journal Current Biology, neuroscientists at Indiana University (IU) reported the first evidence that non-human animals can mentally replay past events from memory. This discovery could potentially help advance the development of new drugs to treat Alzheimer’s disease.
The study was led by IU professor Jonathon Crystal who says:
“The reason we’re interested in animal memory isn’t only to understand animals, but rather to develop new models of memory that match up with the types of memory impaired in human diseases such as Alzheimer’s disease.”
Dr. Crystal goes on to explain that most preclinical studies on potential new Alzheimer’s drugs examine how these compounds affect spatial memory, one of the easiest types of memory to assess in animals. But the loss of spatial memory is not the most debilitating effect of Alzheimer’s disease. It’s the loss of episodic memory, which is the ability to remember specific events.
A good example of episodic memory is when we misplace our car keys and then we try to retrace our steps (the “episode”) to find them. This ability to replay these events in order is known as “episodic memory replay.” Unfortunately, this type of memory declines in Alzheimer’s disease, as well as in aging generally.
Back to the experiment. Scientists in Dr. Crystal’s lab spent almost a year working with 13 rats, training them to memorize a list of up to 12 different odors. The rats were placed inside an “arena” with different odors and rewarded when they identified the second-to-last odor or fourth-to-last odor in the list.
The team altered the number of odors in the list before each test to confirm the odors were identified based upon their position in the list, not by scent alone, proving the animals were relying on their ability to recall the whole list in order. Arenas with different patterns were used to communicate to the rats which of the two options was sought.
Crystal said that after the training the animals successfully completed their task about 87 percent of the time across all trials. The results are strong evidence the animals were employing episodic memory replay.
Additional experiments were conducted that confirmed the rats’ memories were long-lasting and resistant to “interference” from other memories, both hallmarks of episodic memory. The researchers also conducted experiments that temporarily suppressed activity in the hippocampus — the site of episodic memory — to confirm the rats were using this part of their brain to perform their tasks.
“We’re really trying push the boundaries of animal models of memory to something that’s increasingly similar to how these memories work in people,” Dr. Crystal said. “If we want to eliminate Alzheimer’s disease, we really need to make sure we’re trying to protect the right type of memory.”
I am hopeful that this exciting breakthrough will lead to better treatment for Alzheimer’s disease, so that fewer people will have to deal with the debilitating and often heartbreaking effects of episodic memory loss.