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From YouTube: The Neocortex
Description
An overview of the Neocortex, including the main lobes, regions and basic circuity, including a description of how each layer processes information, using the visual cortex as an example.
A
The
neocortex
is
too
wrinkled
outer
layer
with
the
brain.
The
word
cortex
comes
from
the
Latin
for
bark
as
the
cortex
wraps
around
the
brain
like
bark
wraps
around
the
trunk
of
the
tree
and
neo
means
new,
as
the
neocortex
is
the
part
of
the
brain
to
grow
and
develop
most
recently
in
evolution.
The
cortex
is
generally
divided
into
four
main
lobes
in
each
hemisphere.
A
The
frontal
lobe
at
the
front
they
occipital
lobe
at
the
back,
the
temporal
lobe
on
the
side
and
the
parietal
lobe
on
the
top
different
areas
of
the
neocortex
perform
different
functions.
A
few
of
the
main
areas
are
the
visual
cortex
at
the
base
of
the
occipital
lobe,
which
processes
visual
information,
the
auditory
cortex
at
the
top
of
the
temporal
lobe,
which
processes
sound.
A
The
somatosensory
cortex
at
the
front
of
the
parietal
lobe,
which
processes
information
about
touch
the
motor
cortex
at
the
back
of
the
frontal
lobe
responsible
for
organizing
and
performing
movements
and
the
prefrontal
cortex
at
the
front
of
the
frontal
lobe,
which
is
responsible
for
planning
and
decision-making.
However,
the
function
of
a
given
area
of
cortex
is
not
fixed
if
one
area
of
the
cortex
becomes
damaged,
other
areas
can
take
over
its
function
to
some
extent,
and
if
we
perform
a
task
repeatedly,
for
example,
practicing
a
musical
instrument.
A
The
ability
of
the
neocortex
to
adapt
to
a
new
function
and
its
rapid
growth
in
evolution
has
led
to
the
theory
that
there
is
a
common
general
cortical
circuit.
This
would
allow
one
cortical
area
to
easily
take
on
the
functions
of
another
and
would
allow
the
neocortex
to
evolve
quickly.
As
you
don't
have
to
evolve
a
whole
new
wiring
structure.
You
can
just
keep
on
expanding
the
same
circuit.
The
neocortex
is
composed
of
six
different
layers.
A
However,
layer
one
consists
primarily
of
the
dendrites
of
neurons
in
lower
layers
and
contains
few
actual
neurons
and
layers
2
&
3
are
often
considered
together,
partly
because
of
the
difficulty
in
distinguishing
them.
Experimentally,
but
also
because
they
have
similar
patterns
of
connectivity.
This
results
in
four
functional
layers
of
neurons
input
from
the
thalamus
arrives,
primarily
in
two
layer,
four
and
to
a
lesser
extent,
into
layer,
six
neurons
from
layer
four,
then
projects
primarily
into
layers
two
and
three
layers.
A
Two
and
three
then
project
down
into
layer,
five,
as
well
as
projecting
horizontally
to
other
areas
of
the
cortex
layer.
Five
then
projects
to
layer
six
as
well
as
projecting
to
the
basal,
ganglia
and
other
cortical
areas.
Finally,
layer:
six
projects
back
to
the
same
area
of
the
thalamus,
creating
a
feedback
loop
within
each
layer.
The
neurons
also
make
contact
with
each
other
and
with
inhibitory
interneurons.
We
can
now
look
in
detail
at
how
each
layer
of
the
cortex
processes
information
to
help
illustrate
this.
We
will
use
the
primary
visual
cortex
as
an
example.
A
The
primary
visual
cortex
is
a
region
of
the
occipital
lobe.
It
is
the
first
part
of
the
cortex
the
process,
visual
information.
It
receives
input
from
the
lateral
geniculate
nucleus
of
the
thalamus
neurons
in
the
lateral
geniculate
nucleus
receive
input
from
the
retina.
They
respond
to
points
of
light.
In
a
circular
area
of
the
visual
field,
known
as
their
receptive
field,
the
receptive
fields
of
many
lateral
geniculate
neurons
cover
the
whole
visual
field.
With
a
high
degree
of
overlap.
The
receptive
fields
have
a
center
surround
structure.
A
There
is
a
smaller
circle
in
the
centre
which,
if
stimulated,
will
cause
the
neuron
to
increase
its
firing
rate.
However,
if
an
area
in
the
surrounding
circle
is
stimulated,
the
cell
will
be
inhibited
if
a
bar
of
light
stimulates
the
whole
Center
and
only
part
of
the
surround.
The
result
is
a
net
increase
in
firing
rate,
this
makes
lateral
geniculate
neurons,
very
good
at
detecting
edges.
A
In
the
case
of
the
primary
visual
cortex
neurons
in
layer,
4
unknown
as
simple
cells,
they
receive
input
from
a
number
of
lateral
geniculate
neurons,
whose
receptive
fields
are
arranged
in
a
line.
This
means
they
will
respond
to
a
line
of
a
particular
orientation
in
a
particular
region
of
space
layer.
Four
excitatory
neurons
preferentially
connect
to
other
neurons,
which
respond
to
lines
orientated
at
the
same
angle,
however,
neurons
responding
to
all
orientations
connect
to
inhibitory
neurons,
which
in
turn
inhibit
nearby
neurons,
regardless
of
orientation
preference.
A
This
means
that
when
a
line
is
presented,
it
will
excite
simple
cells
responding
to
that
orientation
in
that
region
of
the
visual
field.
These
will
excite
inhibitory
interneurons,
which
will
inhibit
neurons
responding
to
lines
of
different
orientations,
as
well
as
the
original,
simple
cell.
However,
they
will
also
excite
other
simple
cells
with
the
same
orientation
preference
who
will
in
turn
provide
recurrent
excitation
back
to
the
original
cell.
This
excitation
allows
them
to
overcome
the
general
inhibition.
It
means
a
sub
network
of
simple
cells.
A
Responding
to
that
orientation
is
active,
whilst
the
others
are
inhibited
neurons
in
layer
4,
then,
project
delay
is
2.
&Amp;
3
neurons
in
layers,
2
&
3
wire
in
a
similar
way
to
layout
for
neurons
in
the
primary
visual
cortex
layers.
2
&
3
contain
neurons
known
as
complex
cells.
These
receive
input
from
multiple
simple
cells,
responding
to
lines
with
the
same
orientation,
but
from
different
regions
of
space.
This
means
complex
cells,
respond
to
a
line
of
a
certain
orientation
anywhere
in
a
much
larger
region
of
space.
A
Again
in
layers,
two
and
three
neurons
preferentially
connect
to
and
formed
strong
synapses
with
other
neurons,
responding
to
lines
with
the
same
orientation,
whereas
inhibitory
interneurons,
innovate
surrounding
neurons,
regardless
of
orientation
tuning
and
receive
input,
regardless
of
orientation
tuning.
This
results
in
a
dense
blanket
of
inhibition.
That
means
when
a
line
is
presented,
a
sparse,
sub
Network
of
complex
cells
tuned
to
that
orientation
will
recurrently
excite
each
other,
whilst
neurons
tune
to
different
orientations,
will
not
be
able
to
overcome
this.
A
Inhibition
neurons
in
layer
5
receive
input
through
different
sub
networks
in
layers,
2
&
3,
and
they
also
form
sub
networks
connecting
preferentially
to
other
layer.
5
neurons
with
the
same
inputs.
Layer,
5
neurons,
also
form
sub
networks
based
on
their
long-range
connections,
with
neurons
that
project
the
same
part
of
the
brain
preferentially
connecting
to
each
other
layer.
A
Five
contains
two
main
types
of
excitation
neurons,
quantico
cortical
neurons,
which
predict
two
other
areas
within
the
cortex
and
Quantico
subcortical
neurons,
which
project
to
other
subcortical
structures,
including
the
thalamus,
both
types
of
layer,
v,
neurons
project
to
the
basal,
ganglia,
inhibitory,
interneurons
in
layer,
5
connect
in
a
similar
manner
to
the
previous
layers
and
inhibit
the
surrounding
layer.
V
neurons
nonspecifically,
providing
a
blanket
of
inhibition
layer
v
neurons
also
have
tall
tufted,
apical
dendrites,
which
form
synapses
with
the
axons
in
layer
1.
These
axons
in
layer
1
originate
from
other
cortical
areas.
A
They
also
receive
input
directly
from
the
thalamus
and
from
layer
4
kwatak,
o'the,
animate
neurons,
rarely
connect
to
other
excitatory
neurons
within
layer
6,
but
frequently
connect
to
inhibitory,
interneurons
and
inhibitory
interneurons
inhibit
both
types
of
excitation,
neuron
layer,
6,
chord
acocella
make
cells
are
able
to
provide
feedback
to
the
thalamus,
which
has
a
number
of
complicated
effects,
including
controlling
the
gain
depth.
Anomic
neurons,
making
them
respond
more
or
less
to
incoming
stimuli,
switching
dynamic,
neuron
firing
mode
between
bursting
and
tonic
and
synchronizing
the
firing
of
dynamic
neurons.
A
So,
to
sum
up
layer,
four
neurons
receive
input
from
the
thalamus
in
a
specific
pattern,
and
by
connecting
two
neurons
which
respond
to
similar
stimuli,
they
are
able
to
amplify
these
patterns,
neurons
in
layers,
2
&
3,
combine
inputs
from
layer,
4
and
form
sub
networks,
where
neurons
with
similar
properties,
recurrently
excite
each
other
again,
a
background
of
general
inhibition
layer.
Five
neurons
integrate
this
information
and
form
sub
networks
based
upon
what
they
encode
and
where
they
send
this
information
to
layer.
A
Six
can
use
this
information
to
provide
feedback
to
the
thalamus
forming
a
loop
whereby
an
area
of
cortex
is
able
to
modulate
its
own
input.
We
can
see
that
in
almost
all
layers,
cortical
neurons
connect
to
each
other
following
some
general
rules,
neurons
combine
inputs
in
a
specific
pattern
to
allow
them
to
extract
information,
such
as
the
orientation
of
a
line
neurons
connect
preferentially
to
other
neurons,
with
similar
responses,
neurons,
which
project
to
other
brain
areas
also
connect
preferentially
to
cortical
neurons,
which
project
to
the
same
area.
A
Inhibitory
interneurons,
connect
generally,
two
excitatory
neurons,
regardless
of
their
response
properties
resulting
in
a
general
field
of
inhibition.
These
specific
sub
networks
of
neurons,
responding
to
the
same
stimuli,
can
be
thought
of
as
the
basic
information
encoding
unit
of
the
cortex.
These
functional
sub
networks
are
formed
through
synaptic
plasticity,
for
example
in
the
primary
visual
cortex
when
an
animal
experiences,
natural
visual
stimuli
lines
of
a
particular
orientation
tend
to
extend
across
a
large
portion
of
the
visual
field
and
often
appear
in
parallel.
A
This
means
that
neurons,
responding
to
similar
stimuli
are
often
activated
together
and
due
to
the
synaptic
plasticity
we've
seen
in
previous
videos,
the
connections
between
them
are
strengthened.
In
contrast,
the
connections
between
neurons
active
at
different
times
are
weakened
over
time.
This
leads
to
the
formation
of
specific
sub
networks
of
neurons,
responding
to
similar
stimuli.
The
connections
in
and
between
these
sub
networks
continue
to
be
modified
through
synaptic
plasticity
throughout
our
lives.
This
means
that
if
the
input
to
an
area
of
cortex
is
significantly
changed,
different
combinations
of
neurons
will
be
active.
A
At
the
same
time,
this
will
lead
to
the
formation
of
new
sub
networks,
and
this
area
of
the
cortex
will
begin
to
extract
and
process
information
differently.
It
is
this
plasticity
which
allows
one
area
of
the
cortex
to
change
its
function
in
response
to
a
change
in
its
input,
we
have
seen
how
the
primary
visual,
cortex
or
v1
is
able
to
use
input
from
the
thalamus
to
detect
lines
of
specific
orientation,
as
well
as
input
from
the
thalamus
cause.
Equal
areas
also
receive
input
from
other
cortical
areas.
A
A
So
we
concede
that
subsequent
areas
of
the
cortex
can
combine
the
information
encoded
in
preceding
areas
to
build
increasingly
complex
representations.
In
conclusion,
the
neocortex
is
the
outer
layer
of
the
brain,
different
regions
of
the
neocortex
process,
different
information
to
perform
different
functions.
It
is
hypothesized
that
the
neocortex
is
made
of
repeating
units
of
the
same
basic
circuit
in
this
basic
circuit
layer,
four
receives
input
from
the
thalamus
layer.
A
Four
then
sends
this
information
fillets
two
and
three
layers:
two
and
three
projector
other
areas
of
the
cortex
and
to
layer,
five
layer,
five
projects
to
other
cortical
areas
and
other
subcortical
areas,
as
well
as
to
layer,
six
and
layer
sinks
projects
back
to
the
thalamus,
completing
a
feedback
loop
in
most
layers
of
the
neocortex
neurons
encoding.
The
same
features
connect
preferentially
to
each
other
forming
sub
networks,
whilst
inhibitory
neurons
provide
general
inhibition
to
the
surrounding
neurons.
A
These
sub
networks
are
formed
through
synaptic
plasticity,
with
the
connections
between
neurons
active
at
the
same
time
strengthened,
and
the
connections
between
neurons
active
at
different
times
weakened.
If
the
input
to
an
area
of
cortex
changes,
different
combinations
of
neurons
will
be
active
at
the
same
time
and
synaptic
plasticity
will
result
in
the
formation
of
new
sub
networks.
This
allows
an
area
of
cortex
to
change
that
processes,
information
and
therefore
what
function
it
performs.