The
brain
extracts
behaviorally
relevant
sensory
input
to
produce
appropriate
motor
output.
On
the
one
hand,
our
constantly
changing
environment
requires
this
transformation
to
be
plastic.
On
the
other
hand,
plasticity
is
thought
to
be
balanced
by
mechanisms
ensuring
constancy
of
neuronal
representations
in
order
to
achieve
stable
behavioral
performance.
Yet,
prominent
changes
in
synaptic
strength
and
connectivity
also
occur
during
normal
sensory
experience,
indicating
a
certain
degree
of
constitutive
plasticity.
This
raises
the
question
of
how
stable
neuronal
representations
are
on
the
population
and
also
on
the
single
neuron
level.
Here
we
review
recent
data
from
longitudinal
electrophysiological
and
optical
recordings
of
single-­‐cell
activity
that
assess
the
long-­‐term
stability
of
neuronal
stimulus
selectivities
under
conditions
of
constant
sensory
experience,
during
learning,
and
after
reversible
modification
of
sensory
input.
The
emerging
picture
is
that
neuronal
representations
are
stabilized
by
behavioral
relevance
and
that
the
degree
of
long-­‐term
tuning
stability
and
perturbation
resistance
directly
relates
to
the
functional
role
of
the
respective
neurons,
cell-­‐types,
and
circuits.
Using
a
‘toy’
model
we
show
that
stable
baseline
representations
and
precise
recovery
from
perturbations
in
visual
cortex
could
arise
from
a
‘backbone’
of
strong
recurrent
connectivity
between
similarly
tuned
cells
together
with
a
small
number
of
‘anchor’
neurons
exempt
from
plastic
changes.