Transcript Lecture 4 - TeachLine

‫ניורוביולוגיה ומדעי המח‬
‫ – מערכת הראייה‬2 ‫חלק‬
Introduction to Neurobiology
Part 2 – The Visual System
Shaul Hochstein
‫ניורוביולוגיה ומדעי המח‬
Introduction to Neurobiology
Introduction to Sensory Systems
Retina & Lateral Geniculate Nucleus (LGN)
“From Neuron to Brain” Chapters 19 & 20:
pages 379-405 & 407-425
Transduction and signaling in the retina &
Signaling in the LGN & primary visual cortex
Introduction to Sensory Systems- The retina
1- Structure of the eye - ✔
2- Muscles of the eye – fixation; convergence; accommodation - ✔
3- Structure of the retina - ✔
4- The fovea: Comparing central and peripheral vision - ✔
5-The blind spot - ✔
Rods and Cones - ✔ -6
- ✔ 7- Structure-Function relationships
8- Color vision: Young & Helmholtz - ✔
- ✔ 9- Visual Pigments
- ✔ 10- Photoreceptor sensitivity and signal amplification
- ✔ Light & dark adaptation -11
- ✔ 12- lateral inhibition
- ✔ 13- Ribbon synapses
14- Action potentials versus passively conducted graded potentials - ✔
15- Horizontal cells and gain control - ✔
16- The Receptive Field and synaptic organization - ✔
17- Bipolar cells; center-surround antagonism; On- & Off-center cells - ✔
18- Retinal Ganglion Cells; X & Y in cat; M & P in primate
‫ניורוביולוגיה ומדעי המח‬
Introduction to Neurobiology
Introduction to Sensory Systems
layers of neurons & connections in the retina.
The Retina and its layers
Cell bodies
connections
Cell bodies
connections
Cell bodies
‫ניורוביולוגיה ומדעי המח‬
Introduction to Neurobiology
Introduction to Sensory Systems
Hyperpolarizing receptor potential signal
Depolarizing and Hyperpolarizing bipolar cells
Depolarizing Amacrine & Retinal Ganglion Cell
generator potentials
Retinal Ganglion Cell action potentials
‫ניורוביולוגיה ומדעי המח‬
Introduction to Neurobiology
Introduction to Sensory Systems
Transduction = the use of signal (optic)
energy to trigger a neuronal response
The absorption of light by photoreceptor cell
Rhodopsin molecules is such a trigger,
leading to a physiological response = an
ion-specific change in cell conductance.
‫ניורוביולוגיה ומדעי המח‬
Introduction to Neurobiology
Introduction to Sensory Systems
Adaptation:
reduction in sensitivity of visual system in
presence of high levels of ambient light.
1- in transduction process
2- Rhodopsin available to absorb light
3- Calcium level in cell
4- neural interactions
120
Adaptation
Response - transient and steady state
100
80
60
40
20
0
0
5
10
15
Light Intensity (arbitrary units)
20
25
‫ניורוביולוגיה ומדעי המח‬
Introduction to Sensory Systems
Adaptation:
1- enable response over extremely large
range of ambient light levels.
2- emphasize response to temporal
change in light rather than steady state.
3- maintain same relative response
irrespective of light (and response) level.
4- maintain constant appearance for
same relative change in intensity.
Lateral Inhibition: 4 levels of analysis:
1- receptive field measurement
– center/surround
2- physiological mechanism
– lateral inhibition
3- computational equivalent
– smooth and take second derivative
4- psychophysical phenomenon
– Mach bands
5- perceptual advantage
– edge enhancement
250.00
200.00
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100.00
Center-surround
receptive field
in shape of a
Mexican hat:
looks like the
difference of two Gaussians: DOG (green):
one central, narrow and high, with a positive
excitatory impact (in ON center cells), and
the other broad and low with a negative
inhibitory impact (in OFF surround cells).
surround
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center
DOG
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1
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5
7
9 11 13 15 17 19 21 23 25 27 29 31
Lateral Inhibition
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Intensity and Response
Smoothing with a
“boxcar” square-wave
function or with a
Gaussian function
(to emphasize center
of smoothing curve).
In each case, smooth by taking the average of
the multiples of each point of the smoothing
curve and the parallel point on the stimulus
curve. This gives the response of the cell at
the center of the smoothing curve.
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stimulus
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receptive field
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2 4 6 8 10 12 14 16 18 20 22 24
position in visual field
Lateral Inhibition
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Intensity and Response
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100.00
intensity
50.00
Use of the DOG
Center-surround
Receptive Field
“smoothing curve”
results in a smooth response of the layer of
retinal ganglion cells with an emphasis of the
corners where there is a transition from dark
to light, as seen in Mach bands.
receptive field
0.00
2 4 6 8 10 12 14 16 18 20 22 24
-50.00
-100.00
position in visual field
250.00
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100.00
surround
50.00
center
DOG
0.00
1
3
5
7
9 11 13 15 17 19 21 23 25 27 29 31
-50.00
-100.00
-150.00
Thus, the DOG receptive field smoothes over
a noisy signal, but still emphasizes the major
transitions between dark and light areas.
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surround
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center
DOG
0.00
1
3
5
7
9 11 13 15 17 19 21 23 25 27 29 31
-50.00
-100.00
-150.00
According to David Marr, (father of the field of
Artificial Intelligence), use of a DOG receptive
field is the equivalent to smoothing and taking
the second derivative of the illumination profile
(because the DOG looks like the second
derivative of a Gaussian smoothing curve).
250.00
200.00
150.00
100.00
surround
Remember:
each retinal ganglion
cell applies the DOG
function at a different
point in the visual field
and therefore responds according to the light
profile around that point. Only the combined
responses of many retinal ganglion cells
reflects the full illumination profile.
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center
DOG
0.00
1
-50.00
-100.00
-150.00
3
5
7
9 11 13 15 17 19 21 23 25 27 29 31
4 principles of physiological research
Study of receptive fields is equivalent •
to study of computation; (from
input/output can deduce computation).
Study of receptive fields is equivalent •
to study of computation; (from
input/output can deduce computation).
Study of RF linearity/nonlinearity •
essential for deriving mechanisms.
Study of receptive fields is equivalent •
to study of computation; (from
input/output can deduce computation).
Study of RF linearity/nonlinearity •
essential for deriving mechanisms.
Division into neuron classes basic for •
visual system, differentiating processing
pathways, using one, the other, or a
combination of streams.
Study of receptive fields is equivalent •
to study of computation; (from
input/output can deduce computation).
Study of RF linearity/nonlinearity •
essential for deriving mechanisms.
Division into neuron classes basic for •
visual system, differentiating processing
pathways, using one, the other, or a
combination of streams.
Analysis of response types may aid in •
understanding neuron role/function.
‫ניורוביולוגיה ומדעי המח‬
Introduction to Neurobiology
Introduction to Sensory Systems
Linear and Nonlinear spatial summation
What do neurons convey to each other?
How do neurons sum their inputs?
Introduction to Sensory Systems
Linear and Nonlinear spatial summation
What do neurons convey to each other?
How do neurons sum their inputs?
We have already seen that the visual
system emphasizes changes over space
and time: lateral inhibition and adaptation.
How can it sum over space and still notice
local changes?
Does it want to?
StimulusStimulus spatial phase (degrees) contrast: 55% temporal frequency 4 Hz
spatial
-180 -150 -120 -90 -60 -30 0
30 60 90 120 150 180
frequency
StimulusStimulus spatial phase (degrees) contrast: 55% temporal frequency 4 Hz
spatial
-180 -150 -120 -90 -60 -30 0
30 60 90 120 150 180
frequency
X cell
StimulusStimulus spatial phase (degrees) contrast: 55% temporal frequency 4 Hz
spatial
-180 -150 -120 -90 -60 -30 0
30 60 90 120 150 180
frequency
X cell
X cell
Time of response
Stimulus
Receptive
Field
Position of Stimulus
and Receptive field
Y cell
Time of response
Stimulus
Receptive
Field
Position of Stimulus
and Receptive field
StimulusStimulus spatial phase (degrees) contrast: 55% temporal frequency 4 Hz
spatial
-180 -150 -120 -90 -60 -30 0
30 60 90 120 150 180
frequency
0.14
X cell
1.40
0.35
Y cell
00.7
Cat X and Y cells (Hochstein & Shapley, 1976a)
Contrast sensitivity of Fourier components to alternating grating as function of spatial phase.
Contrast sensitivity determined by amplitude of harmonic.
X cell. 1st harmonic (x) and negligible 2nd harmonic (D). (A)
Y cell. 1st harmonic: SF 0.14 & 0.7 c/deg (x , ☐); 2nd harmonic 0.14 & 0.47 c/deg ( , )(B)
Note Y cell 2nd Harmonic presence with spatial-phase and
relative (to Fundamental) SF insensitivity.
ON-center X cell. SF 0.7 c/deg.
ON-center Y cell.
Linear center
Nonlinear subunits
Linear surround
Spatial model for the Y cell receptive field.
Spatial extent of elements of a Y-type RGC,
linear center and large linear surround, as well as,
overlapping nonlinear surround sub-units, each
smaller than the center.
Cone pedicle diagram (from DeVries et al., 2006).
Diagram of invagination and surrounding region
showing ribbon (Rb), horizontal cells (HCs), central
invaginating contact (IC), and basal contacts
(BCs).
Ribbon synapse may be source of linear
Monkey P & M cells are not the
primate analogy of cat X and Y cells.
X
M
P
Contrast-response functions of cat and monkey RGCs.

P cell (
); X-type M cell ( ); cat X cell (). All
data from RGC S-potentials recorded at LGN.
‫ניורוביולוגיה ומדעי המח‬
Introduction to Neurobiology
Introduction to Sensory Systems
To where are retinal signals transmitted?