1. Dorsal Lateral Geniculate Nucleus
&
Parallel Processing
GS Shrestha, M.Optom, FIACLE
Lecturer

2. Introduction
• The most significance
– Number of optic nerve fibres project to the
Lateral Geniculate Nucleus (LGN) in the
Thalamus
• Relay to the form vision
– From LGN, the visual pathway proceeds to
the primary visual cortex, V1
• Complex processing of visual signals
– Visual processing and object recognition is
enhanced by more than 30 extrastriate
cortical areas

3. Targets of the retinal projection
Retinal ganglion cell axons
Major Minor
•Several small
hypothalamic nuclei
•Suprachiasmatic , supra
optic, paraventricular
nuclei
•Accessory optic system
•Nucleus of optic tract
•Dorsal, medial and
terminal nuclei

4. dLGN
90% retinal ganglion cells project to
dLGN
Is Laminated and shows Retinotopic
Organization
Each layer receives input from a specific
eye and class of ganglion cell

5. Superior Colliculus
A midbrain structure conjunction with cortical frontal
eye fields and the brain stem reticular formation
 Is laminated and retinotopically organized nucleus.
 Visually guided saccadic eye movements
 Retinal projection segregates with alternating
columns of left and right eye terminals.
 10% of all retinal ganglion cells project to the SC
 Are small caliber originate from ganglion cells with
small dendritic fields and do not project to other
retinal targets

6. The Pretectum
A group of small midbrain nuceui is just rostral to the
SC
 Receives signals from a group of small diamter
retinal ganglion cells with large receptive fields
 Involve with the control of the pupillary light
reflex by means of a projection to the Edinger-
Westphal nucleus of oculomotor complex.
 Show consensual response

7. The Pulvinar nucleus
 Largest nucleus mass
 Receive projections from the small caliber fibres
from the optic nerve and the SC
 It projects to several visual cortical area
including V1 and extrastriate, parietal areas
 Represents second pathway that can bypass
the LGN to get the visual V1 and may plays a
role in processing from vision
 Code importance of visual stimuli-silence or
attention
◦ Eg, the eye hand co-ordination

8. Hypothalamic nucleus
Receives direct sparse retinal
projection that leave the dosal surface
of the optic chiasma and has been
implicated in the synchronization of
circadian rhythms

9. The paraventricular and supraoptic
nuclei
Involve with the regulation of the light
dark cycle for neuroendrocrine
functions

10. The Accessory optic systems
The lateral terminal nucleus
The medial terminal nucleus,
the dorsal terminal nucleus
NOT in the mid brain
Important role in optokinetic
nystagmus in viewing with prolong
large field motion

11. Overview of dLGN
Key gateway to visual signals
entering the cortex
Less agreement in role of vision
◦ Receptive field properties of dLGN cells=
retinal ganglion cell input
Regulate the flow and strength of
visual signals sent to cortex

12. Structural organization
Layers 2,3,5 receives input from Ipsilateral eye
Ipsi
Layers 1,4,6 receives input from Contralateral eye
Contra
Dorsal four layers-small neurons-P
layers
cells=Parvocellular layer (midget cells)
Ventral two layers-Large neurons M
cells=magnocellylar layers (parasol cells)
Between P and M cells=very small bistratified cells-
konio cells
Combination of all these layers=Parallel Processing

13. K6
K5
K4
Konio cells
K3
K2
K1
Coronal section of dorsolateral nucleus of the monkey

14. Structural Organizations
 Superior hemifield in retina=Lateral zone
 Inferior hemifield= medial zone
 Central (foveal)= posterior zone
 Peripheral-anterior zone
 Each layer receives monocular input
 contalateral input is received from contralateral eye only
(nasal fibres)
 Ipsilateral input receives input from ipsilateral eye only
(temporal fiblres)

15. Difference in M,P,K cells
Morphology of dendrites
Calcium binding protein content
Physiologic properties
Axonal projection within visual cortex

16. Difference in cell structures
P cells orients • M cells complex • K cells orients
perpendicular to radially branching parallel to the
the cell layers dendrites dLGN layers
 Maintain compact • Sample more • A few long
profile widely within M dendrites
 Small receptive layers • Larger receptive
field centres • Large receptive field
 Calcium binding field • Calcium binding
protein- • Calcium binding protein- calbindin
parvalbumin protein- D 28K
parvalbumin

17. Cell Classes
Two principal cell classes
• Relay cells: send axon
cells • Interneurons whose
to visual cortex axons remais with in
• Glutamic acid -neuro the dLGN
trasmitter • γ-aminobutyric acid-
• 4:1 neurotransmitter
• 1:4

18. X cells and y cells
First evidence of parallel processing
in the mammalian retina (Enroth-
Cugell and Robson, 1966)-cat
ganglion cells to spatial stimuli
specifically sine wave gratings

20. X- and Y-cells
X- cells linear cells
◦ For an X-cell a spatial gratings can be
positioned within the cell’s receptive field such
that no response is elicited.
◦ Excitation and inhibition are linearly summed
and cancel each other. The excitation is equal to
the inhibition.
Y-cells nonlinear cells
◦ Y- cells doesn’t sum spatial information in a
linear fashion.

21. Afferent axons
80% input from midget ganglion cells
7-9% input from parasol ganglion cells
Retinal input for K cells?

22. Efferent axons
 In primates- efferent out put from LGN terminates
within the primary visual cortex and the visual
sector of the thalamic reticular nucleus
 A minor efferent projection from LGN terminate in
several extrastriate ares-originates from K LGN
cells
◦ Implicates as residual vision in Blind Sight (loss of
primary visual cortex)
 Inconclusion, most K cells and all P and M cells
send axons to primary visual cortex

24. Efferent Axons
P cells send efferent axons to 4Cß of
Primary Visual Cortex
M cells send efferent axons to 4Cά
more sparesly to layer 6
K cels send their axons to cortical layer
3B where they terminate in patches of
cells and some k cells also send axons
to cortical layer to 1

25. Receptive field properties
On and OFF centre with opposing
surrounds
K relay cells appear to have
nonstandard visual receptive field

26. Wave length based
discrimination of P cells

28. Response Time
Parvo
◦ Sustained response when presented with a long duration
stimulus
◦ Sustained neurons respond to a stimuli for a
longer period of time they are better suited to
code Low Temporal Frequency Stimuli
Magno
◦ Transient response to the same stimulus with only
 Brief burst at stimulus onset and offset (transient
amacrine cells)
◦ Transient respond to rapid illumination changes
give M-neurons the capability to resolve high
temporal frequency stimuli

29. Receptive Fields
Parvo
◦ Smaller Receptive Fields
◦ Higher Spatial Frequency Resolution
◦ Parvo cells make up the great majority of
retinal ganglion cells, both foveal and
nonfoveal.
Magno
◦ Larger Receptive Fields

30. Conduction Velocity
Parvo
◦ Slower
Magno
◦ Faster
◦ Larger Diameter Axons transmit
information (action potentials) faster

31. Retinal Concentration
Parvo
◦ Represents 90% of Foveal Ganglion Cells
Magno
◦ Concentration is constant outside the
fovea
◦ Represents 10% of non-Foveal Ganglion
Cells

32. Functions of the Pathways
Magno System
◦ “Where” System
◦ Alerts us that a visual event has occurred
◦ Detects movement with rapid transmission
◦ Dorsal cortical processing stream
Parvo System
◦ “What” System
◦ Details of the event are analyzed
◦ Ventral cortical processing stream

33. Characteristics of Parvo and Magno neurons
Characteristics P Cell M Cell K cell
Some size Medium large small
Receptive field Centre Centre variable
organization surround surround
Dendrite field size Small Medium large
Contrast sensitivity Low/ weak High but Intermediat
saturated e
Cortical projection 4Cß 4Cά 3b and 1
Color coding Color Non color Some blue
opponent opponent on
Speed of transmission Slow Fast

34. Characteristics of Parvo and Magno neurons
Characteristics P Cell M Cell K cell
TMTFs low high variable
Preferred spatial High Low Low
frequency
Speed of transmission medium (4 Fast (2msec) Low (5msec)
msec)
Spatial linearity Linear Linear or -
nonlinear
Color vision and contrast Poor at high Poor low
sensitivity spatial frequency
frequency contrast
Temporal Sustained Transient Both type
responsiveness

35. Thank you