09/08/2025
Scientists Discover the Brain’s “Reset Button”
That Separates Your Memories
A brainstem region helps punctuate memories.
Stress may block its ability to mark new
experiences.
Although life unfolds in a continuous flow,
our memories don’t capture it that way. We
don’t recall the past as one seamless timeline
but rather as a sequence of distinct,
meaningful moments—much like how sentences are
broken up with grammar and punctuation. This
mental structure gives our experiences clarity
and helps us understand both what happened and
when it occurred.
The brain must devote a lot of space to this
herculean task, right?
Wrong! It turns out that a tiny but mighty
region pulls far more than its weight.
In a study published in Neuron, psychologists
from UCLA and Columbia University used brain
imaging and pupil measurements to reveal that
a tiny group of neurons in the brainstem,
called the locus coeruleus, functions like a
“memory reset button” when meaningful changes
occur.
“Our key question was: as an experience
unfolds, how does the brain ‘know’ when one
meaningful memory has ended and the next
should begin?” said UCLA psychology professor
and first author David Clewett. “Research has
shown that remaining in a stable context, such
as the same room, binds sequential experiences
together in memory. By contrast, experiencing
a shift in context, or event boundary, drives
memories apart to represent distinct events.
In this way, context acts as the grammar of
human memory. What we found is that the locus
coeruleus is most active at event boundaries
when memories become separated. Thus, this
small region at the core of the brain’s
arousal system may serve to punctuate our
thoughts and memories.”
Auditory cues shape context and memory
Clewett, along with co-authors Ringo Huang
from UCLA and Lila Davachi from Columbia,
conducted an experiment with 32 participants
who viewed images of neutral objects while
undergoing MRI scanning. To simulate changes
in context, the researchers played simple
tones in either the left or right ear. When
eight identical tones were played repeatedly
in the same ear, it created the feeling of a
continuous event. A shift in tone pitch, and
ear location signaled a change, creating the
perception of an event boundary. This
alternating pattern continued, generating the
impression of four distinct auditory events.
Next, the team evaluated how these context
shifts affected memory. They hypothesized that
the ability to recall the correct order of
events would reflect whether the experiences
had been stored as a single episode or
separated into distinct memories. When events
are encoded together, sequence recall should
be easier; when they are stored apart, it
becomes more difficult.
As expected, increased activity in the locus
coeruleus during event boundaries was linked
to poorer recall of the order of item pairs
that crossed those boundaries, suggesting the
memories had been stored separately. To
validate this, the researchers compared their
fMRI readings of locus coeruleus activity with
measurements of pupil dilation taken at the
same time, since pupil size tends to increase
during new events and locus coeruleus
activation. The consistency between these data
confirmed that the fMRI signals were
accurately capturing activity in this small
brain region. Functional magnetic resonance
imaging, or fMRI, monitors brain activity by
measuring changes in blood flow while
participants are inside the scanner.
How hippocampus responds to boundary signals
The impact of this neural “reset” signal
extended well beyond initial memory
segmentation. Higher levels of locus coeruleus
activity at event boundaries were linked to
more pronounced shifts in activation within
the hippocampus—a brain region crucial for
encoding new memories and tracking contextual
information such as location and timing.
“Part of the job of the hippocampus is to map
the structure of our experiences, so it has an
index of the beginning, middle, and ends of
events. We found that the locus coeruleus may
provide the critical ‘start’ signal to the
hippocampus, as if saying, ‘Hey, we’re in a
new event now,’” said Davachi. “Prior work had
shown that bursts of locus coeruleus activity
help reconfigure brain networks to direct
attention to new and important experiences.
Our findings suggest that this updating signal
is even more widespread, also reaching
memory-related regions that carry
representations of ongoing events.”
The researchers also examined how brief bursts
of locus coeruleus activation are influenced
by background levels of locus coeruleus
activity. This matters because locus coeruleus
neurons operate in two distinct modes: a
burst-like mode that flags significant events
and forms new memories, and a background mode
that regulates general alertness and stress.
“The locus coeruleus is like the brain’s
internal alarm system,” Clewett said. “But
under chronic stress, this system becomes
overactive. The result is like living with a
fire alarm that never stops ringing, making it
difficult to notice when a real fire breaks
out.”
Although the dynamic interplay between these
firing patterns has been studied in the
context of decision-making, perception, and
learning, its relevance for how we perceive
and remember events has, thus far, been
unclear. So, the authors set out to test
whether bursts of locus coeruleus activation
at event boundaries, the neural signals that
segment memories, might be weakened or lost
under conditions of chronic stress. This
question posed a challenge, as fMRI alone
cannot measure absolute levels of stress or
locus coeruleus activation. To address this,
they used an imaging method that indirectly
measures neuromelanin, a pigmented
neurochemical that accumulates in the locus
coeruleus with repeated activation over time.
Stress weakens the brain’s event detection
signals
As predicted, participants with a higher
neuromelanin-related signal, thought to
indicate chronic stress, showed weaker pupil
dilation responses to event boundaries.
Stronger low-frequency fluctuations in locus
coeruleus activation, a proxy for background
levels of activity, also predicted weaker
spikes in locus coeruleus activation and pupil
responses to boundaries during the task.
Together, these findings suggest that chronic
hyperarousal may blunt one’s sensitivity to
change, disrupting the cues that anchor and
organize new episodes in memory.
Identification of the locus coeruleus as the
gateway or conductor for memory formation may
lead to better ways to treat PTSD and other
memory-related disorders, such as Alzheimer’s
disease, where the locus coeruleus is
unusually hyperactive. There are potential
ways to quiet an overactive locus coeruleus,
whether pharmacologically or through slow-
paced breathing or even hand-squeezed stress
balls. But good long-term solutions require
further research and will take time to
discover and bring to market. Perceiving
events in the “right” way is directly linked
to better memory, suggesting that improving
locus coeruleus function is an effective
target for either protecting or recovering
memory function.
Clewett said that the sophisticated tools
necessary to look into the brain require the
kind of funding that only the federal
government can provide. Clewett said that
several NIH grants that funded this research
paid for the scanning and facilities they used
to do the experiments, for example.
“Conducting basic science and clinical
research is critical for opening new doors for
treating debilitating disorders,” Clewett
said. “Recent legislative actions threaten
this future, not only for scientific research
but for breakthroughs that can improve the
lives of patients and their families. It is
perhaps ironic that at a time when legislation
promises ‘big and beautiful change,’ it turns
out one of the brain’s smallest players may
have the biggest impact on how we understand
and remember our lives.”
