Primary Visual Cortex
(V1, area 17, striate cortex)
1. Organization of early visual pathway
2. Circuitry of primary visual cortex
a. layering, inputs, outputs
b. cell types
3. RF properties of V1 neurons
a. orientation selectivity
b. simple cell and complex cell
4. Circuitry basis of the RFs
5. Columnar Organization
a. orientation columns
b. ocular dominance columns
c. hypercolumn
6. Horizontal connections
Visual pathway from retina to V1
LGN
eye
V1
A top-down view diagram
fixation point
left visual field
nasal
half
right visual field
left
right
nasal
half
temporal half
temporal half
optic
chiasm
lateral
geniculate
nucleus
LGN
(LGN)
V1
V1
axons from nasal retina cross  contralateral LGN
axons from temporal retina stay  ipsilateral LGN
left visual field  right LGN  right V1
right visual field  left LGN  left V1
Circuitry -- inputs, outputs and layering
1
2/3
4A
4B
4
4C
4C
5
6
M P
(LGN)
Input
LGN  layer 4, layer 6
Layer 4  layer 2/3  layer 5  layer 6
Output
Layer 2/3, Layer 4B  other visual cortical areas
Layer 5  superior colliculus
Layer 6  LGN
two basic morphological types of cells
Pyramidal
cell
Axons
Stellate
cell
Pyramidal cells
• large, pyramid shaped cell bodies
• project to other areas, also connect to other local neurons
• excitatory (glutamate)
Non-pyramidal cells
• small and stellate shape (spiny stellate or smooth stellate)
• local interneurons (smooth)
• either excitatory (spiny, with many dendritic spines, glutamate)
or inhibitory (smooth, few spines, GABA)
Hetergeneity in the interneuron types
Morphology
Physiology (spiking properties)
Biochemistry (neuropeptide contents),
Connectivity (dendrite-domain specific
innervation of pyramidal cells).
David Hubel (left) and Torsten Wiesel
V1 cells have orientation selectivity
orientation response
Response (spikes/sec)
Orientation tuning curve
120
80
40
0
0
30
60
90 120 150
Orientation (o)
Two cell types based on response property
simple cell -- separated ON and OFF regions
ON ---- increase its response to light on (bright stimulus)
OFF ---- increase its response to light off (dark stimulus)
complex cell -- overlapping ON and OFF regions
 
  
 
 
 



simple cell
complex cell
position sensitivity
position insensitive
length summation
length summation
width summation
no width summation
orientation sensitive
orientation sensitive
Simple cell and complex cell
simple cell
position
sensitive
(yes)
increase response
decrease response
length
summation
strong response
 
  
 
(no)
 
  
 
increase
response
(yes)
 
   little response
 
 
  
 
strong response
(no)
(yes)
Little or no
response
orientation
selectivity
 
  
 
(yes)
little response
width
summation
complex cell
 
  
 
little or no
response
(yes)
(yes)
strong response
 
   strong response
 
weak response
 
   weak response
 
Little or no response
 
  
 
Little or no response
Circuitry basis of V1 RFs (simple cell)
circuitry
+
+
+
cortical
simple cell
LGN cells
receptive field
Hubel & Wiesel, 1962
LGN cells
cortical
simple cell
1. Simple cell is built up from many LGN cells
2. These LGN cells have the same center/surround
structure
3. The centers of these LGN cells are distributed along a
line
* you can also add a set of OFF-centered LGN cells,
with their centers along the OFF subregion
Circuitry basis of V1 RFs (complex cell)
circuitry
receptive field
+
+
+
complex cell
complex cell
simple cells
simple cells
1. Complex cell is built up from many simple
cells
2. These simple cells have the same preferred
orientation
3. These simple cells have overlapping RFs
4. These simple cells have different
arrangement of subregions
Columnar Organization--Cells in the
same column have similar properties (RF
position, orientation preference, ocular
dominance)
(1) Orientation columns
Oblique penetration in V1
--preferred orientation gradually shifts
Vertical penetration in V1
--same preferred orientation
Afferent pathways from the two eyes
right eye
nasal
temporal
left V1
left eye
LGN
6
5
C
4
3
2
1
I
C
I
I
C
Layer 4
R
L
2. Ocular dominance (OD) columns in V1
left eye
layer 4
.
right eye
left eye
R
L
R
L
Rl
Lr
Rl
Lr
R
L
R
L
Rl
Lr
Rl
Lr
right eye
~ 0.5mm
Oblique penetration: cells responding to
left and right eyes alternately
Vertical penetration: cells responding to
one eye exclusively or more strongly
Definition of Ocular Dominance Groups
Eyes
Cortical
cells
1
contra-
2
3
4
equal
5
6
7
ipsi-
groups
OD distribution in normal adult V1 (monkey)
Number of cells
Normal V1
Equal
contralateral
ipsilateral
OD groups
Normal adult V1 –
Binocular cells are common above &
below layer 4), with each eye represented
to different degrees
Hypercolumn—An ensemble of
orientation and ocular dominance (OD)
columns in V1, including one set of L and
R eye OD columns and a set of
orientation columns for lines of all
orientations. All cells within the
hypercolumn have RFs that cover a
similar area in the visual field.
Optical imaging of intrinsic light scattering
signals reveals pinwheel pattern of
orientiation columns
Blobs in Layer 2/3
--- Columns (blobs) revealed by
cytochrome oxidase staining that are color
sensitive
--- Cells between the blobs (interblobs) are
color insensitive, orientation sensitive
Horizontal Connections
Cells with similar response properties in
different columns (orientation, color) are
linked by long-range horizontal
connections made by axons of Layer 2/3
C. Gilbert