Can neural activity during encoding under stress predict memory specificity over time?
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Issue Date
2016-09-01
Language
en
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Abstract
Events
under
stress
are
in
general
better
remembered,
but
the
effect
of
stress
specifically
on
detail
and
gist
information
of
the
events
is
still
inconsistent
among
studies.
What
could
explain
the
mixed
findings
together
may
be
that
the
quality
of
memories
changes
over
time.
Declarative
memory
depends
less
on
the
hippocampus
over
time,
and
this
region
is
regarded
essential
for
detailed
memory
suggested
by
multiple
studies
on
pattern
separation.
Taking
into
account
that
stress-‐
induced
noradrenaline
increase
can
enhance
synaptic
plasticity
in
the
hippocampus,
we
hypothesized
that
details
might
initially
be
better
remembered
if
encoded
under
stress,
and
a
stronger
gist
may
remain
over
time.
Correspondingly,
we
predicted
that
encoding
neural
activity
in
the
hippocampus
should
reflect
such
modulation,
specifically
be
able
to
better
predict
subsequent
detailed
memories
encoded
under
stress.
The
present
study
was
designed
to
test
the
hypotheses
in
humans
using
event-‐related
functional
Magnetic
Resonance
Imaging.
We
investigated
neural
activity
during
memory
formation
in
49
healthy
participants
in
an
incidental
encoding
task
containing
embedded
in
either
a
neutral
or
stressful
context.
Subsequent
recognition
test
containing
identical
targets,
similar
lures
and
novel
foils,
was
performed
after
24h
and
1
week
by
asking
participants
to
respond
‘new’,
‘similar’,
or
‘old’
per
stimulus.
Functional
MRI
and
heart
rate
were
acquired
throughout
procedures.
Blood
pressure
and
a
set
of
questionnaires
were
obtained
additionally
at
specific
times.
Our
data
show
that
heart
rate
frequency
and
the
negative-‐affect
scores
of
PANAS
were
higher
in
the
stress
group
compared
to
the
neutral
group,
but
we
did
not
find
group
differences
in
blood
pressure
and
heart
rate
variance.
These
together
indicated
a
moderate
effect
of
stress
induction.
We
used
recog
index
and
patsep
index,
calculated
from
response
proportions
in
the
recognition
test,
to
respectively
represent
gist
and
detailed
memory.
No
difference
of
two
indices
were
detected
between
the
neutral
and
stress
groups
at
both
delays.
As
for
the
encoding
neural
activity,
we
did
not
find
different
hippocampal
activation
in
target
trials
that
were
later
remembered
than
in
trials
later
forgotten,
a
contrast
for
gist
memory
subsequent
memory
effect
(SME).
Critically,
there
was
no
difference
of
hippocampal
activation
in
response
to
lures
that
were
later
responded
as
‘similar’
than
‘old’,
defined
as
an
SME
representing
pattern
separation
process.
Stress,
moreover,
showed
no
effects
on
both
SMEs
in
the
hippocampus.
To
conclude,
during-‐encoding
stress
in
this
study
did
not
show
improvement
for
gist
memory,
or
enhancing
effect
of
detailed
memory.
Hippocampal
activity
is
not
predictive
for
the
subsequent
pattern
separation,
and
is
not
further
influenced
by
stress
induction.
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