Download Cellular Neuroscience - How Your Brain Works

Seeing Things 2
Visual Processing in the Brain
How Your Brain Works - Week 4
Dr. Jan Schnupp
[email protected]
HowYourBrainWorks.net
Visually Guided Behaviour
• To catch a prey, your sensory system has to “represent” the target
to be caught in a manner that can “instruct” the appropriate motor
commands.
• In reptiles and amphibia, this representation most likely resides in
the optic lobe, also called the optic tectum, or (in mammals)
superior colliculus.
Motor Maps in the Superior Colliculus
Retinotopic Map
Motor Map
• Microstimulation studies have shown that the SC contains a
“motor map”, which is in register with the retinotopic sensory
map
There is more to vision than visual reflexes
• Often we have to balance the desire to catch one
object with the need to dodge another, or choose
which from a variety of objects is most worth
pursuing.
• Which objects need catching, and which need
dodging, may change over time. This creates a
need for quite abstract representations of objects
within a flexible, rapidly adaptable system. Is that
what sensory cortex is for?
Primary and
“Extrastriate” Visual
Cortex
Decoding Brain Activity
• Miawake et al. Neuron
2008
• Observed activity of ca
1500 voxels of (3mm)3.
• Reconstructed the image
shown from recorded
activity
Seeing Lines
Simple Cell Receptive Fields
LGN
- + - + -- +
-
Cortex
+ - + - + - +
Cortical Layers
• 1: “tufts” of apical dendrites receive
cortico-cortical connections.
• 2/3: gets input from layer 4. Many simple
cells. Outputs to other parts of cortex.
• 4: gets most input from LGN. Many LGNlike, non-oriented cells. Output to layers
2/3.
• 5/6: inputs from layers 2/3. Output to
subcortical targets
Cortical Columns as
“Computational Modules”
•
Surface
I •
•
II/III
Supragranula
r
IV
•
Granul
ar
•
•
InfraGranul
ar
•
•
White
matter
V
VI
From
Thalamus
Subcortical
Targets
Representing Shape and Position
Within an “Orientation Map”
• Pseudocolour “orientation tuning” map of ferret
primary visual cortex (revealed with intrinsic
optical imaging).
Binocular Vision
Binocular Fusion
• Try “shooting a hole” into
your hand by rolling up a
piece of paper into a tube,
holding it in front of one eye,
and holding your free hand
flat in front of the other eye,
as shown here.
• Your brain will try, as best it
can, to paint a single scene
out of the disparate images
seen by each eye.
Stereopsis (Stereo vision for depth)
B
A
+ -+ - +- -+ - +- -+ - +- +
A
B
B
A
Ocular dominance
Cytochrome Oxidase Blobs
Cortical
Hypercolumns
Break
Cortical
Hypercolumns
Distribution of orientation tuning in V1 of kittens
reared in a vertically...
Stripe
Rearing
... or horizontally striped environment.
What would the world look like to a stripe
reared kitten?
Three-eyed Frogs
means that if you want to predict the PSTH of
Strabismus
Amblyopia
• Inputs from each eye are
thought to “compete” for
cortical territory during early
development.
• If one eye is “weaker” (e.g.
due to an optical defect), it
may fail to get properly
connected to the visual
cortex.
• This in principle essentially
healthy eye can then
become functionally blind.
• To prevent amblyopia,
children at risk sometimes
have their stronger eye
temporarily deprived of
input.
Meltzoff & Moore 1977
• Neonates are said to
be able to mimic facial
or hand gestures after
14 to 21 days.
means
• Wilderbeast
runthat
withif you want to predict the PSTH of
the herd after just a
few hours.
• Experience dependent
maturation of the
visual system may
need to be rapid.
Enriching
Early
Experience
Parallel Pathways
colour
shape motion
Retina
LGN
V1
Extrastriate
cortex
M
Magnocellular
Layer IVCαβ
then IVB
P
Parvocellular
Layer IVCβ
interblob
V2
non-M
non-P
Koniocellular
blob
V4
V5 (MT)
Higher order Visual
Pathways
Shape processing
hierarchy
Face Cells
• Infero-temporal cortex
containsmeans
neurons
that
that
if you want to predict the PSTH of
appear to be selective for
visual objects, such as faces
or hands.
• Damage to these areas can
lead to “visual agnosia”, and
inability to recognize objects
by sight even though there
is no blindness.
+ - + - + - +
Motion
Sensitivity
+ - + - + - +
+ - + - + - +
Newsome’s Moving Random Dots
Neurometric Curves
•
•
•
•
•
Hatched Bars: responses to movement in preferred direction
Filled black bars: responses to movement in null direction
Open (white) circles: psychometric function (animal’s choices)
Filled (black) circles: neurometric function (neuron’s “choice”)
From Newsome, Britten, Movshon (1989) Nature 341:52
Microstimulation Biases Perceptual Choice
• From Salzman, Britten, Newsome (1989) Nature
346:174
The Motion
Aftereffect Illusion
http://www.michaelbach.de/ot/mot_adapt/index.html
Go
Hemineglect
Syndrome
• Drawing of a
clock by a
means that if you want to predict the PSTH of
patient with a
lesion in the
right posterior
parietal lobe.
Form from Motion
means that if you want to predict the PSTH of