Most people don’t give much thought to the function of memory or how it works. However, memories are an essential part of everything we do. If we didn’t have the capability to form them, we wouldn’t remember how to eat with a fork and knife, have a conversation with a friend, or do our jobs. For the most part, people take this gift for granted, but it can become very obvious how large a role memory plays in our everyday lives when neurodegenerative conditions begin to affect it.
Understanding Short-Term and Long-Term Memory
The human brain is hardwired to save some memories and let go of others. For example, you don’t need to remember what you had for breakfast three weeks ago, but you do need to remember how to drive a car or how you met your spouse. The hippocampus, a region of the brain, can store five to nine short-term memories at a time, and the average length it holds these for is about 30 seconds. Meanwhile, the neocortex can hold any amount of information for an indefinite amount of time.
The Process of Storing and Retrieving Memories
Everything you do gets turned into a memory. However, your brain stores some and forgets others. A memory begins formation in the hippocampus (the home of short-term memory) when a group of neurons connects through synapses. When it’s time for you to use this information, your brain goes through the retrieval process by activating this specific group of neurons.
Retrieving a memory also has the power to strengthen the memory and shift it into a long-term one. A study on students learning Swahili vocabulary words examined different retrieval methods to see which would work best. A week after students learned these words, they were tested to see which they remembered best. Words that students saw only once and were not asked to recall during the session had the lowest retrieval rate. In the middle were words that students were asked to retrieve once and words that students were asked to retrieve multiple times back to back. The words with the highest retention were the ones that students had to recall repeatedly over varying amounts of time during the session.
Sharp Wave-Ripples and Their Impact on Memory
While actively trying to recall memories can help consolidate memories in the neocortex, so can resting. Baylor St. Luke’s Medical Center neurosurgeon Dr. Sameer Sheth collaborated on research that found there was “a modest yet significant increase in ripple properties (rate, duration, and amplitude) during resting task states,” including sleep. Sharp wave-ripples (SWRs) are high-frequency oscillatory bursts originating from the hippocampus that promote interactions with the neocortex and aid in memory consolidation. Essentially, one part of your brain sends out waves to activate the groups of neurons that store memories in another part of the brain to make them more durable. This research highlights the importance of giving your brain a break and resting.
Alzheimer’s Disease, Memory Loss, and Potential Therapies
Alzheimer’s disease and dementia are both characterized by memory loss and changes in sleep patterns. Researchers are looking into whether the lower-quality sleep accounts for partial memory loss due to a reduced amount of SWRs. If a correlation is discovered, scientists may one day find a way to stimulate the brain into creating artificial SWRs that can mediate this in adults with Alzheimer’s disease and dementia.
“I hope that this research not only reveals the amazing capacity of the human brain, but also leads to treatments for the great number of patients without other options.”
- Sameer Sheth, MD
Our neurology and neurosurgery team is proud to participate in research that can change how we view the brain and find ways to turn this data into revolutionary therapies. Discover how our team can help you. Schedule an appointment with a St. Luke’s Health neurologist today.
Psychology Today | Spaced Repetition
NCBI | Is There a Link Between Sleep Changes and Memory in Alzheimer's Disease?
Harvard University | How Memory Works
bioRXiv | Stability of Ripple Events During Task Engagement in Human Hippocampus
Nature | The Hippocampal Sharp Wave–Ripple in Memory Retrieval for Immediate Use and Consolidation
The University of Queensland | Where Are Memories Stored in the Brain?
Scientific American | Where Does the Brain Store Long-Ago Memories?
NCBI | The Stuff of Memories: Sharp Wave Ripple Memory Consolidation in Epilepsy
NCBI | Memory Loss in Alzheimer's Disease