Scientists find that directly stimulating the amygdala can improve memory the next day, marking the first time ever that electrical stimulation has boosted memory for more than a few minutes.
Being able to boost one's long-term memory sounds like science fiction. It still is, but a team of researchers from Emory University Hospital in Atlanta, GA, has brought us one step closer.
They investigated how direct brain stimulation might influence performance in a memory task.
This line of investigation aims to, eventually, improve the lives of millions of people living with conditions that impact memory function, such as neurodegenerative diseases and traumatic brain injuries.
Direct stimulation of the amygdala
The study was conducted on 14 people with epilepsy who underwent intracranial monitoring, which involves introducing electrodes directly into the brain to find the origin of seizure activity. It offers a unique opportunity to experiment; the subjects must remain fully awake while the neurosurgeons do their work.
Specifically, the researchers targeted the amygdala. The amygdala is associated with both memory and emotion, making it a prime candidate for memory enhancement; situations that are emotive are easier to remember.
First study author Joseph Manns, Ph.D., talks about why they picked the amygdala:
"We chose the amygdala because of decades of research in rodents, showing that it interacts with several other memory structures in a modulatory role. We wanted to stimulate its endogenous function, which we think is to signal salience — something standing out — so that specific experiences are remembered in the future."
In other words, the amygdala signposts objects in the world around us. We are constantly barraged with sights and sounds, yet our brains only pay attention to the things that count. The amygdala helps us to do this.
These findings were recently published in the journal PNAS.
Long-term memory testing
The study participants were all shown 160 neutral objects and asked to decide whether each object belonged indoors or outdoors. For half of the images, the participants received brain stimulation for 1 second following their presentation.
Importantly, during stimulation, participants did not show an emotional response, elevated heart rate, or any other signs of arousal. They "reported that they did not notice the stimulation at any point."
Straight away, participants were "quizzed on half the stimulated and half the unstimulated images." Then, the next day, they were tested on the remaining images, alongside 40 "decoy" images.
The test that was conducted on the day of the stimulation showed little improvement. However, the results from the test on the following day yielded fascinating results: 79 percent of them performed significantly better on the stimulated images the next day (while the remaining 21 percent showed neither improvement nor impairment).
According to Mann, "This makes sense because the amygdala is thought to be important for memory consolidation — making sure important events stick over time."
Some people involved had existing memory impairments from epilepsy. Those with the most severe memory issues benefited the most from the stimulation. For example, one individual remembered none of the unstimulated images but performed well for the stimulated ones.
How long could the enhancement last?
Medical News Today caught up with senior study author Dr. Jon T. Willie, an assistant professor of neurosurgery and neurology. We asked whether this effect might last longer than 1 day.
"We don't know until we test it," he replied, "but it is encouraging that we have enhanced what is technically long-term memory, not short-term or working memory. Our study is unique in that we enhanced memory at a long-term time point (the next day)."
"Most other studies," he added, "have tested the ability to examine memory within minutes only. Ultimately, we are designing experiments that will allow us to test longer time points such as days to weeks."
MNT also spoke with study co-author Cory Inman, Ph.D., a postdoctoral fellow in the Department of Neurosurgery. He answered the same question.
"I believe the memory enhancement effect would have still been evident after a few days," he said, "perhaps even more clear given that memory for the non-stimulated images would likely be forgotten more quickly than the memories for stimulated images."
"Although we have not yet had the opportunity to test that hypothesis, we plan to test it as soon as we have optimized the stimulation parameters that produce the memory enhancement effect."
Despite the fact that these findings will not be useful therapeutically for some time, neurosurgeons such as Dr. Willie already use implants that provide deep brain stimulation for individuals with conditions such as Parkinson's disease.
When MNT asked about Dr. Willie's research plans, he said, "The long-term goal of research such as this is to understand the basic pathways and 'rules of engagement' for circuits involved in memory so that their function can be improved, especially in disorders that impair cognitive function such as dementia, traumatic brain injury, and epilepsy."
"The near and long-term goals of this research are to develop appropriate implantable devices, evaluate different brain targets, and work out the ideal stimulation parameters and timing to enhance memory and provide safe, effective therapy."
This recent study will become a framework for what comes next. Dr. Willie explained to MNT what steps might be taken next: "There are many directions to go from here. Our immediate continuing studies are testing how specific the amygdala target is for memory enhancement."
He added, "We are directly stimulating other brain sites to examine advantages and disadvantages of different approaches. We are also applying what we have learned to determine the feasibility of novel approaches to treating post-traumatic stress disorder, which is a disorder associated with abnormal amygdala function."
Inman explained, "We are doing our best to balance asking interesting scientific questions, while also aiming to optimize the amygdala-mediated memory enhancement effect."
"We are currently running [follow-up] experiments manipulating various stimulation parameters to determine whether they provide an additional boost to the memory enhancement effect," he concluded.
The current study is the first of its kind. No doubt there are fascinating insights to come.