Scientists monitor brains replaying memories in real time

Brain abstract illustration (stock image).

In a study of epilepsy patients, researchers at the National Institutes of Health monitored the electrical activity of thousands of individual brain cells, called neurons, as patients took memory tests. They found that the firing patterns of the cells that occurred when patients learned a word pair were replayed fractions of a second before they successfully remembered the pair. The study was part of an NIH Clinical Center trial for patients with drug-resistant epilepsy whose seizures cannot be controlled with drugs.

"Memory plays a crucial role in our lives. Just as musical notes are recorded as grooves on a record, it appears that our brains store memories in neural firing patterns that can be replayed over and over again," said Kareem Zaghloul, M.D., Ph.D., a neurosurgeon-researcher at the NIH's National Institute of Neurological Disorders and Stroke (NINDS) and senior author of the study published in Science.

Dr. Zaghloul's team has been recording electrical currents of drug-resistant epilepsy patients temporarily living with surgically implanted electrodes designed to monitor brain activity in the hopes of identifying the source of a patient's seizures. This period also provides an opportunity to study neural activity during memory. In this study, his team examined the activity used to store memories of our past experiences, which scientists call episodic memories.

In 1957, the case of an epilepsy patient H.M. provided a breakthrough in memory research. H.M could not remember new experiences after part of his brain was surgically removed to stop his seizures. Since then, research has pointed to the idea that episodic memories are stored, or encoded, as neural activity patterns that our brains replay when triggered by such things as the whiff of a familiar scent or the riff of a catchy tune. But exactly how this happens was unknown.

Over the past two decades, rodent studies have suggested that the brain may store memories in unique neuronal firing sequences. After joining Dr. Zaghloul's lab, Alex P. Vaz, B.S., an M.D., Ph.D. student at Duke University, Durham, North Carolina, and the leader of this study decided to test this idea in humans.

"We thought that if we looked carefully at the data we had been collecting from patients we might be able to find a link between memory and neuronal firing patterns in humans that is similar to that seen in rodents," said Vaz, a bioengineer who specializes in deciphering the meaning of electrical signals generated by the body.

To do this they analyzed the firing patterns of individual neurons located in the anterior temporal lobe, a brain language center. Currents were recorded as patients sat in front of a screen and were asked to learn word pairs such as "cake" and "fox." The researchers discovered that unique firing patterns of individual neurons were associated with learning each new word pattern. Later, when a patient was shown one of the words, such as "cake," a very similar firing pattern was replayed just milliseconds before the patient correctly recalled the paired word "fox."

"These results suggest that our brains may use distinct sequences of neural spiking activity to store memories and then replay them when we remember a past experience," said Dr. Zaghloul.

Last year, his team showed that electrical waves, called ripples, may emerge in the brain just split seconds before we remember something correctly. In this study, the team discovered a link between the ripples recorded in the anterior temporal lobe and the spiking patterns seen during learning and memory. They also showed that ripples recorded in another area called the medial temporal lobe slightly preceded the replay of firing patterns seen in the anterior temporal lobe during learning.

"Our results support the idea that memories involve coordinated replay of neuronal firing patterns throughout the brain," said Dr. Zaghloul. "Studying how we form and retrieve memories may not only help us understand ourselves but also how neuronal circuits break down in memory disorders."

This study was supported by the NINDS Intramural Research Program and NIH training grants (NS113400, GM007171).

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Materials provided by NIH/National Institute of Neurological Disorders and Stroke. Note: Content may be edited for style and length.

Beauty sleep could be real, say body clock biologists

Woman waking up from bed (stock image).

Biologists from The University of Manchester have explained for the first time why having a good night's sleep really could prepare us for the rigours of the day ahead.

The study in mice and published in Nature Cell Biology, shows how the body clock mechanism boosts our ability to maintain our bodies when we are most active.

And because we know the body clock is less precise as we age, the discovery, argues lead author Professor Karl Kadler, may one day help unlock some of the mysteries of aging.

The discovery throws fascinating light on the body's extracellular matrix -which provides structural and biochemical support to cells in the form of connective tissue such as bone, skin, tendon and cartilage.

Over half our body weight is matrix, and half of this is collagen -- and scientists have long understood it is fully formed by the time we reach the age of 17.

But now the researchers have discovered there are two types of fibrils -- the rope-like structures of collagen that are woven by the cells to form tissues.

Thicker fibrils measuring about 200 nanometres in diameter -- a million million times smaller than a pinhead -- are permanent and stay with us throughout our lives, unchanged from the age of 17.

But thinner fibrils measuring 50 nanometres, they find, are sacrificial, breaking as we subject the body to the rigours of the day but replenishing when we rest at night.

The collagen was observed by mass spectrometry and the mouse fibrils were observed using state of the art volumetric electron microscopy -- funded by the Wellcome Trust -- every 4 hours over 2 days.

When the body clock genes where knocked out in mice, the thin and thick fibrils were amalgamated randomly.

"Collagen provides the body with structure and is our most abundant protein, ensuring the integrity, elasticity and strength of the body's connective tissue," said Professor Kadler

"It's intuitive to think our matrix should be worn down by wear and tear, but it isn't and now we know why: our body clock makes an element which is sacrificial and can be replenished, protecting the permanent parts of the matrix.

He added: "So if you imagine the bricks in the walls of a room as the permanent part, the paint on the walls could be seen as the sacrificial part which needs to be replenished every so often.

"And just like you need to oil a car and keep its radiator topped up with water, these thin fibrils help maintain the body's matrix."

"Knowing this could have implications on understanding our biology at its most fundamental level. It might, for example, give us some deeper insight into how wounds heal, or how we age.

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Materials provided by University of Manchester. Note: Content may be edited for style and length.