Brain ‘ripples’ appear just before you remember something | Science News for Students

Brain ‘ripples’ appear just before you remember something

New data show neurons in a key memory center fire in sync during the recall process
Sep 24, 2019 — 6:45 am EST
a series of blue brain scans

One or two seconds before people recall an image they had previous seen, cells in a key memory center in the brain fire together, creating a “ripple” of activity.

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Seconds before a memory pops up, certain nerve cells jolt into action in sync. This new finding sheds light on how the brain stores and recalls information.

Studying brain cells in action inside the human head is tricky. Putting electrodes in someone’s brain requires surgery. It’s not something researchers do without a good reason. The new study involved people who already had electrodes put in their brains for some medical purpose. These participants all had epilepsy. That brain disorder causes storm-like surges of electrical activity in the brain, known as seizures. Doctors put the electrodes in the patients' brains so they could pinpoint those surges.

In the new study, Yitzhak Norman of the Weizmann Institute of Science in Rehovot, Israel, and his colleagues tuned into signals from cells in the brain’s hippocampus. That’s a key memory center.

First, patients were shown images of people and places they already knew. For example, they might see a picture of former President Barack Obama. Or they might view an image of the Eiffel Tower in Paris, France. As each picture appeared, electrodes picked up bursts of activity. These so-called sharp-wave ripples happen when many nerve cells fire together.

Earlier studies suggested that these ripples in the hippocampus were important for forming memories. But it wasn’t clear if the ripples also had a role in recalling memories.

To test that, Norman’s group blindfolded the patients. Then they asked each to recall the pictures they’d seen. A second or two before the participants began describing each picture, researchers noticed an uptick in sharp-wave ripples. Those ripples echoed the ones seen earlier.

Norman’s team shared its new discovery August 16 in Science. The authors say their data suggest those ripples help people make and recall memories.

an image of a brain scan
Using implanted electrodes (shown in yellow), researchers spied on brain activity as people formed and recalled memories. The team found that just before a person remembered a face or object they’d seen earlier, the hippocampus underwent “ripples” of activity (colored areas). 
Weizmann Institute of Science

Power Words

(more about Power Words)

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells.

colleague     Someone who works with another; a co-worker or team member.

data     Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.

disorder     (in medicine) A condition where the body does not work appropriately, leading to what might be viewed as an illness. This term can sometimes be used interchangeably with disease.

electrode     A device that conducts electricity and is used to make contact with non-metal part of an electrical circuit, or that contacts something through which an electrical signal moves. r) that either releases or collects electrons or holes, or that can control their movement.

epilepsy     (adj. epileptic) A neurological disorder characterized by seizures.

hippocampus     (pl. hippocampi) A seahorse-shaped region of the brain. It is thought to be the center of emotion, memory and the involuntary nervous system.

nerve     A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

recall     (in cognition) To remember. (in commerce and regulation) A procedure whereby companies remove particular products from the market (i.e. store shelves) because the products were defective, dangerous or might pose some newfound risk of harm. Or a product that had already been purchased (such as a car or lawn mower) might be recalled so that a manufacturer could fix a problem in it or give people their money back.

seizure     A sudden storm-like surge of electrical activity within the brain. Seizures are often a symptom of epilepsy and may cause dramatic spasming of muscles.

wave     A disturbance or variation that travels through space and matter in a regular, oscillating fashion.


Journal: Y. Norman et al. Hippocampal sharp-wave ripples linked to visual episodic recollection in humans. Science. Vol. 365, August 16, 2019, p. 65. doi: 10.1126/science.aax1030.