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.”
Source: https://myfusimotors.com/2020/03/08/scientists-monitor-brains-replaying-memories-in-real-time/
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