Our memories connect us to who we are, the people we love, and the world around us. But not all of us are fortunate enough to have access to our full set of memories. Alzheimer's disease affects millions of people in the US, and many more suffer from memory impairments due to brain diseases, injuries, and age-related changes in the brain. Cognitive neuroscientist Joel Voss, PhD, wants to change that. “Solving memory is my ultimate goal,” he said.
Voss is a Professor of Neurology at the University of Chicago and Director of the new Center for Neurocognitive Outcomes Improvement Research (Center NOIR). He studies memory and memory disorders, primarily using non-invasive brain stimulation in human subjects.
Brain stimulation is accomplished by connecting a magnetic coil to the scalp that creates a magnetic field around the skull and induces an electrical current in the brain. That electrical current can then activate neurons in the part of the brain that is targeted.
Although brain stimulation technology has existed for decades, Voss’s work is innovative in applying them to study memory. His is among the first groups to use this to stimulate deep brain structures like the hippocampus, which are critical for memory, and by indirectly targeting them via their network of interconnected brain regions. Since around the middle of the 20th century, researchers have characterized the hippocampus as a key region of the brain for memory, particularly in memory formation. Individuals who suffer serious damage to the hippocampus have almost no ability to retain new information.
“They can meet you and have a conversation with you, but then if you walk out of the room and come back thirty seconds to a minute later, they'll have no idea who you are,” Voss said. “But they have mostly intact memories of events in their life that were formed before they had the damage that caused their amnesia. So, it seems to be a structure that's related to forming new memories and holding on to them.”
That formation process is the aspect of memory that Voss’s group focuses on, but their studies don’t target the hippocampus directly. Instead, they target other parts of the brain that form a network with the hippocampus. Networks are brain regions that work together but aren't necessarily right next to one another. Instead, they communicate via long-distance connections to create cognition.
“The hippocampus is an important area of the brain, but it doesn't do everything in isolation. It's part of a distributed network and participates with a lot of other areas,” Voss said. “We've developed what we call a ‘network targeting' approach of the hippocampus, where we use noninvasive stimulation to try to change the activity of the hippocampus indirectly by controlling its network.”
Stimulating neural networks
Voss began studying memory starting in his PhD at Northwestern University and continued through his postdoc at the University of Illinois at Urbana Champaign. But it wasn’t until he was a faculty member at Northwestern University Feinberg School of Medicine that he started using brain stimulation to improve memory in human subjects. He did this by targeting the hippocampus indirectly by stimulating its neural network with electromagnetic pulses. His team showed that they could make people better at memorizing things for days to weeks after they received stimulation by changing the level of connectivity of the hippocampus with the rest of its network partners.
Voss remembers being uncertain about this project at the time. “It was kind of a long-shot idea,” he said. “No one had ever shown that you could really change a deep brain target like the hippocampus by stimulating from outside the head on the cerebral cortex, so I was pretty skeptical that it would actually work.”
But the ‘long-shot’ idea paid off. “I remember pretty much jumping up and down when I saw the results,” Voss said.
Using electromagnetic stimulation, they targeted several different regions of the hippocampal network, which increase functional connectivity between those regions and improved memory performance in the subjects. The study opened a whole new area of research for his lab.
“From that point on, I was just hooked into doing that kind of research,” he said.
Ongoing research
Since they showed that memory can be improved by electromagnetic brain stimulation, Voss and his lab have been improving this method and testing whether it can be used to improve memory in people beyond young adults with no neurological issues. So far, they have had success using brain stimulation to improve the abilities of older adults with age-related memory problems to memorize information.
“With the stimulation parameters that we develop for use, we found that we could improve the memory of the older adults such that, for a period of time after receiving stimulation, you can no longer distinguish them from the group of younger adults performing the memory task,” he said.
Other groups in the field are currently conducting clinical trials using electromagnetic brain stimulation to treat Alzheimer's disease with promising results, and there is potential for treating other neurodegenerative disorders as well.
Voss also wants to understand the foundational question of how activity in the hippocampus is involved in short-term memory. His lab has found that the hippocampus plays a critical role in short-term memory when a task involves putting together pieces of information, and then holding onto that information. This research is done by analyzing recordings from electrodes implanted in subjects’ brains as treatments for other disorders. Those electrodes record what sort of activity is going on in the hippocampus and its associated neural network. The researchers can then look at those recordings to see what is happening in the brains of their subjects when they are given tasks requiring short-term memory.
“Humans use short-term memory to sample and pick up all the information in our environment and glue it together,” Voss said. “These short-term memory functions are very important, and we want to know how to affect them. We think that those kinds of short-term memory processes underlie long-term memory for life events.”
Voss believes that understanding more about how complex short-term memories are processed by the brain will inform future efforts to develop interventions to improve people’s memory abilities. As Director of the new Center NOIR, he looks forward to bringing together groups doing research in neuroscience, psychology, and other departments across the university and allowing them to connect with patients.
“The hope is to have a cutting-edge center for getting patients with neurological conditions involved in research, including interventional research, to test out whether we can do anything for the cognitive and memory problems that they’re experiencing,” he said.
