prefrontal cortex
The Brain Ripples Before We Remember
Posted on by Dr. Francis Collins
Throw a stone into a quiet pond, and you’ll see ripples expand across the water from the point where it went in. Now, neuroscientists have discovered that a different sort of ripple—an electrical ripple—spreads across the human brain when it strives to recall memories.
In memory games involving 14 very special volunteers, an NIH-funded team found that the split second before a person nailed the right answer, tiny ripples of electrical activity appeared in two specific areas of the brain [1]. If the volunteer recalled an answer incorrectly or didn’t answer at all, the ripples were much less likely to appear. While many questions remain, the findings suggest that the short, high-frequency electrical waves seen in these brain ripples may play an unexpectedly important role in our ability to remember.
The new study, published in Science, builds on brain recording data compiled over the last several years by neurosurgeon and researcher Kareem Zaghloul at NIH’s National Institute of Neurological Disorders and Stroke (NINDS). Zaghloul’s surgical team often temporarily places 10-to-20 arrays of tiny electrodes into the brains of a people with drug-resistant epilepsy. As I’ve highlighted recently, the brain mapping procedure aims to pinpoint the source of a patient’s epileptic seizures. But, with a patient’s permission, the procedure also presents an opportunity to learn more about how the brain works, with exceptional access to its circuits.
One such opportunity is to explore how the brain stores and recalls memories. To do this, the researchers show their patient volunteers hundreds of pairs of otherwise unrelated words, such as “pencil and bishop” or “orange and navy.” Later, they show them one of the words and test their memory to recall the right match. All the while, electrodes record the brain’s electrical activity.
Previously published studies by Zaghloul’s lab [2, 3] and many others have shown that memory involves the activation of a number of brain regions. That includes the medial temporal lobe, which is involved in forming and retrieving memories, and the prefrontal cortex, which helps in organizing memories in addition to its roles in “executive functions,” such as planning and setting goals. Those studies also have highlighted a role for the temporal association cortex, another portion of the temporal lobe involved in processing experiences and words.
In their data collected in patients with epilepsy, Zaghloul’s team’s earlier studies had uncovered some telltale patterns. For instance, when a person correctly recalled a word pair, the brain showed patterns of activity that looked quite similar to those present when he or she first learned to make a word association.
Alex Vaz, one of Zaghloul’s doctoral students, thought there might be more to the story. There was emerging evidence in rodents that brain ripples—short bursts of high frequency electrical activity—are involved in learning. There was also some evidence in people that such ripples might be important for solidifying memories during sleep. Vaz wondered whether they might find evidence of ripples as well in data gathered from people who were awake.
Vaz’s hunch was correct. The reanalysis revealed ripples of electricity in the medial temporal lobe and the temporal association cortex. When a person correctly recalled a word pair, those two brain areas rippled at the same time.
Further analysis showed that the ripples appeared in those two areas a few milliseconds before a volunteer remembered a word and gave a correct answer. Your brain is working on finding an answer before you are fully aware of it! Those ripples also appear to trigger brain waves that look similar to those observed in the association cortex when a person first learned a word pair.
The finding suggests that ripples in this part of the brain precede and may help to prompt the larger brain waves associated with replaying and calling to mind a particular memory. For example, hearing the words, “The Fab Four” may ripple into a full memory of a favorite Beatles album (yes! Sgt. Pepper’s Lonely Hearts Club Band) or, if you were lucky enough, a memorable concert back in the day (I never had that chance).
Zaghloul’s lab continues to study the details of these ripples to learn even more about how they may influence other neural signals and features involved in memory. So, the next time you throw a stone into a quiet pond and watch the ripples, perhaps it will trigger an electrical ripple in your brain to remember this blog and ruminate about this fascinating new discovery in neuroscience.
References:
[1] Coupled ripple oscillations between the medial temporal lobe and neocortex retrieve human memory. Vaz AP, Inati SK, Brunel N, Zaghloul KA. Science. 2019 Mar 1;363(6430):975-978.
[2] Cued Memory Retrieval Exhibits Reinstatement of High Gamma Power on a Faster Timescale in the Left Temporal Lobe and Prefrontal Cortex. Yaffe RB, Shaikhouni A, Arai J, Inati SK, Zaghloul KA. J Neurosci. 2017 Apr 26;37(17):4472-4480.
[3] Human Cortical Neurons in the Anterior Temporal Lobe Reinstate Spiking Activity during Verbal Memory Retrieval. Jang AI, Wittig JH Jr, Inati SK, Zaghloul KA. Curr Biol. 2017 Jun 5;27(11):1700-1705.e5.
Links:
Epilepsy Information Page (National Institute of Neurological Disorders and Stroke/NIH)
Brain Basics (NINDS)
Zaghloul Lab (NINDS)
NIH Support: National Institute of Neurological Disorders and Stroke; National Institute of General Medical Sciences
A New Piece of the Alzheimer’s Puzzle
Posted on by Dr. Francis Collins
Credit: National Institute on Aging, NIH
For the past few decades, researchers have been busy uncovering genetic variants associated with an increased risk of Alzheimer’s disease (AD) [1]. But there’s still a lot to learn about the many biological mechanisms that underlie this devastating neurological condition that affects as many as 5 million Americans [2].
As an example, an NIH-funded research team recently found that AD susceptibility may hinge not only upon which gene variants are present in a person’s DNA, but also how RNA messages encoded by the affected genes are altered to produce proteins [3]. After studying brain tissue from more than 450 deceased older people, the researchers found that samples from those with AD contained many more unusual RNA messages than those without AD.
Cool Videos: Flashes of Neuronal Brilliance
Posted on by Dr. Francis Collins
When you have a bright idea or suddenly understand something, you might say that a light bulb just went on in your head. But, as the flashing lights of this very cool video show, the brain’s signaling cells, called neurons, continually switch on and off in response to a wide range of factors, simple or sublime.
The technology used to produce this video—a recent winner in the Federation of American Societies for Experimental Biology’s BioArt contest—takes advantage of the fact that whenever a neuron is activated, levels of calcium increase inside the cell. To capture that activity, graduate student Caitlin Vander Weele in Kay M. Tye’s lab at the Picower Institute for Learning and Memory, Massachusetts Institute of Technology (MIT), Cambridge, MA, engineered neurons in a mouse’s brain to produce a bright fluorescent signal whenever calcium increases. Consequently, each time a neuron was activated, the fluorescent indicator lit up and the changes were detected with a miniature microscope. The brighter the flash, the greater the activity!
Creative Minds: Helping More Kids Beat Anxiety Disorders
Posted on by Dr. Francis Collins
Dylan Gee
While earning her Ph.D. in clinical psychology, Dylan Gee often encountered children and adolescents battling phobias, panic attacks, and other anxiety disorders. Most overcame them with the help of psychotherapy. But not all of the kids did, and Gee spent many an hour brainstorming about how to help her tougher cases, often to find that nothing worked.
What Gee noticed was that so many of the interventions she pondered were based on studies in adults. Little was actually known about the dramatic changes that a child’s developing brain undergoes and their implications for coping under stress. Gee, an assistant professor at Yale University, New Haven, CT, decided to dedicate her research career to bridging the gap between basic neuroscience and clinical interventions to treat children and adolescents with persistent anxiety and stress-related disorders.
Creative Minds: REST-ling with Alzheimer’s Disease
Posted on by Dr. Francis Collins
Caption: The REST protein (green) is dormant in young people but switches on in the nucleus of normal aging human neurons (top), apparently providing protection against age-related stresses, including abnormal proteins associated with neurodegenerative diseases. REST is lost in neuron nuclei in critical brain regions in the early stages of Alzheimer’s disease (bottom). Neurons are labeled with red.
Credit: Yankner Lab, Harvard Medical School
Why do some people remain mentally sharp over their entire lifetimes, while others develop devastating neurodegenerative diseases that destroy their minds and rob them of their memories? What factors protect the human brain as it ages? And can what we learn about those factors enable us to find ways of helping the millions of people at risk for Alzheimer’s disease and other forms of senile dementia?
Those are just a few of the tough questions that Bruce Yankner, a 2010 recipient of the NIH Director’s Pioneer Award, has set out to answer by monitoring how gene activity in the brain’s prefrontal cortex (PFC) changes as we age. The PFC is the region of the brain involved in decision-making, abstract thinking, working memory, and many other higher cognitive functions; it is also among the regions hardest hit by Alzheimer’s disease.
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