April 18th, 2023
Written by: Catrina Hacker
Who would you be without your memories? Our memories heavily influence the actions and reactions that define our personalities. Our relationships, interests, and careers are built from memories of past experiences and interactions. When it comes down to it, we are our memories. Beyond forming the foundation upon which we define ourselves, memory is essential to many seemingly simple actions we take each day, like finding a parked car or cooking ourselves dinner. This is why brain disorders and diseases that cause memory loss can be so devastating. Treatments capable of restoring memory function could give millions of people their lives back.
What causes memory loss?
Memory loss is often associated with aging, and while it’s normal for aging to cause some mild forgetfulness, there are many causes of memory loss that affect people in all age groups to even greater degrees1. One prominent cause of memory loss is forms of dementia, like Alzheimer’s Disease, that are most common in older populations. Other medical conditions that also impact younger adults, like brain tumors, stroke, or poorly controlled epilepsy, can also lead to memory loss. In other cases, memory loss is a symptom of another neurological disease like Parkinson’s Disease, multiple sclerosis, or Huntington’s Disease. Environmental factors like the use/abuse of drugs and alcohol, and mental health disorders like bipolar disorder, depression, and experiencing trauma can also lead to memory loss. Finally, physically banging your head can lead to a concussion or traumatic brain injury which both can also lead to memory loss. All of this is to show that memory loss can impact almost anyone in a variety of ways.
How do neuroscientists try to treat memory loss?
There is currently no treatment or cure for memory loss. Most attempts have aimed to prevent the memory loss in the first place. For example, for memory loss that is caused by chronic diseases like Alzheimer’s Disease or Parkinson’s Disease, neuroscientists have tried to prevent it by identifying the cause of the disease and developing drugs that prevent it from progressing. Unfortunately, this approach hasn’t been very successful. For the causes of memory loss that are more sudden (e.g., head injury, stroke, or trauma), this approach of preventing memory loss in the first place will not work, because we can’t predict when these events might occur.
Given our failure so far to treat memory loss, neuroscientists are starting to consider alternative approaches. One possibility is to use a piece of technology called a Brain Computer Interface (BCI) to stimulate the brain at particular moments so that patients will remember them. BCIs allow neurosurgeons to record signals inside the brain, use computer programs to interpret them, and even activate the brain themselves2. Recently, neuroscientists have made several breakthroughs in using BCIs to help patients with brain disorders. BCIs have been used to help blind patients see and allow patients with ALS to speak through a robotic voice. This summer, a group of neuroscientists were able to use a similar kind of technology to stimulate a memory center in the brain to improve memory in patients suffering from memory loss3.
How does the memory stimulator work?
The goal of the study was to improve the memory of patients suffering from memory loss as a consequence of a traumatic brain injury (TBI) by stimulating a memory center in their brains. To do so, the research team recruited epilepsy patients who had electrodes implanted in their brains as part of a procedure to identify where in the brain their seizures are coming from. While these patients are in the hospital, some of them are generous enough to volunteer to participate in other experiments to help neuroscientists learn more about how the human brain works. Luckily, these electrodes are often implanted in or near a brain region that is important for memory, called the hippocampus. The neuroscientists were able to recruit some of these patients who also had a history of a TBI and memory deficits to participate in their study.
The patients performed a memory task while the neuroscientists recorded their brain activity. They then used the brain activity from the memory task to train a computer model about the memory signals in each person’s brain. After the model was trained, the neuroscientists asked the patients to do the memory task again. As the patients completed the memory task for the second time, the researchers used their model to stimulate the brain in a way that the model thought would improve their memory. Afterwards, they compared how much the patients remembered during the first task without stimulation to how much the patients remembered during the second task with the brain stimulation.
Overall, the stimulation was successful. On average, all patients did better on the memory task when their brains were being stimulated than without the stimulation, including the patients who had experienced a TBI. The study also showed that the patients who reported mild-to-moderate difficulty with memory before the study were the patients whose memory improved the most. The fact that the stimulation helped improve memory is exciting because it shows that even when the brain has already been injured, as is the case following a TBI, stimulation can still improve memory. In other words, doctors may not need to prevent memory loss if they can simply overcome it through brain stimulation.
What’s next?
There is still a lot to learn before we consider this a cure for all memory disorders. Importantly, while a memory stimulator might help patients form new memories for short periods of time, it probably can’t recover old memories that have already been lost. In addition, testing the stimulator during a controlled memory task is an important first step, but memory is much more complicated in the real world. The kinds of computer models that worked for this task probably would not work in real-world situations. Finally, memory loss following TBI makes up only a small subset of all cases of memory loss. It’s possible that the same kind of stimulation might not work as well for patients with conditions like Alzheimer’s Disease. All that being said, this is still one exciting step toward a future where we may be able to stimulate brains to restore memory.
References
1. Memory Loss – Symptoms and Causes. https://www.pennmedicine.org/for-patients-and-visitors/patient-information/conditions-treated-a-to-z/memory-loss.
2. Nicolas-Alonso, L. F. & Gomez-Gil, J. Brain Computer Interfaces, a Review. Sensors 12, 1211–1279 (2012).
3. Roeder, B. M. et al. Patterned Hippocampal Stimulation Facilitates Memory in Patients With a History of Head Impact and/or Brain Injury. Front. Hum. Neurosci. 16, 933401 (2022).
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