1. The LGN

2. Retina overview
--The image of that apple is formed on your retina --Light from this image is going to excite and inhibit the rods & cones. --This induces a chemical reaction, which turns light into an electrical signal. This signal either excites or inhibits the retinal ganglion cells (RGC).

3. The RGC send these signals along the optic nerve
The RGC send these signals along the optic nerve. Some of these signals go to the Superior Colliculus to control eye movements, but the majority goes to the Lateral Geniculate Nucleus of the Thalamus.

4. What’s the thalamus, you ask?
Major relay of info to the cerebral cortex while also processing signals from the cortex.
Divided into separate nuclei that process information from the periphery & also other parts of the brain.

5. The LGN is a bean shaped nucleus.
anterior nuclei
internal medullary lamina
intralaminar nuclei
other medial nuclei
midline (medial) nuclei
interthalamic adhesion
pulvinar
medial geniculate
nucleus
lateral geniculate MD LD LP
VPL
VPM CM VA VL VI
Thalamic nuclei
CM centromedian
LD lateral dorsal
LP lateral posterior
MD medial dorsal
VA ventral anterior
VI ventral intermedial
VL ventral lateral
VPL ventral posterolateral
VPM ventral posteromedial
thalamic reticular nucleus
(pulled away)
lateral
geniculate
visual
cortex
retina
anterior nuclei
internal medullary lamina
intralaminar nuclei
other medial nuclei
midline (medial) nuclei
interthalamic adhesion
pulvinar
medial geniculate
nucleus
lateral geniculate MD LD LP
VPL
VPM CM VA VL VI
Thalamic nuclei
CM centromedian
LD lateral dorsal
LP lateral posterior
MD medial dorsal
VA ventral anterior
VI ventral intermedial
VL ventral lateral
VPL ventral posterolateral
VPM ventral posteromedial
thalamic reticular nucleus
(pulled away)

6. The LGN does not ONLY relay information from the retina to the cortex!!!!!!!!
It regulates neural information from the retina & other parts of the brain as it flows to & from the cortex

7. Visual Cortex TRN Input to be Relayed Retina PBR Thalamic LGN Relay
layer 4
layer 4
Visual
Cortex
layer 6
Glu
Glu
GABA
GABA
interneurons
TRN
ACh
ACh
PBR
mid-
brain
excitatory
excitatory
inhibitory
inhibitory
relay
relay
cells
cells
Input to
be Relayed
Thalamic
Relay
Retina
LGN

8. The LGN’s function is not only dependent on information sent from the retina, but also:
Other neurons in the LGN
Neurons from the cortex
Neurons in the brain stem
**Signals that come down from the visual cortex to the LGN actually outnumber the signals that travel from the retina to the LGN.

9. Most impressive aspect of the LGN is how it organizes the information that flows into it.
For instance, signals from the retina are routed to different layers of the LGN based on the eye that the signals come from & the type of RGC are propagating that signal.
C [on/off] Parvo
Konio
I [off/on] Parvo
C [on/off] Parvo
I [off/on] Parvo
I [on/off] Magno
C [off/on] Magno

10. The LGN is comprised of multiple layers.
Each layer receives input from only one eye.
Some get Ipsilateral input (from the eye on the same side of the LGN) to LGN layers 2,3 & 5.
Others get Contralateral input (from the eye on the opposite side of the LGN) into LGN layers 1,4 & 6.

11. Inputs to the LGN from the retina will be from “similar” cells.
In other words, retinal ganglion cells that have red-on/green-off center surround receptive fields will project onto LGN cells that also have red-on/green-off center surround receptive fields.

12. There are 4 types of Retinal Ganglion cells.
1)Parasol cells, aka M-cells synapse onto layers 1& 2 of the LGN. These layers are called the magnocellular layers.
2) midget cells, aka P-cells, synapse onto layers 3-6 of the LGN. These layers are called the parvocellular layers.
3) S-cells synapse onto the interlaminar layers of the LGN.
The cells that populate these layers are called koniocellular cells.

13. The Primate Lateral Geniculate Nucleus
Konio-cells
Very large receptive fields
Snail-like conduction velocity
low spatial resolution
slow temporal resolution
project to brain regions responsible for motion perception & the primary visual cortex…
Excited by blue/yellow stimuli
Magno-cells
large receptive fields
high conduction velocity
low spatial resolution
fast temporal resolution
project to brain regions responsible for motion perception
Excited by contrast luminant stimuli
Parvo-cells
small receptive fields
medium conduction velocity
high spatial resolution
slow temporal resolution
project to brain regions responsible for color and form perception
Excited by red/green stimuli

14. Two types of neurons exist in the dLGN: relay cells and interneurons.
The relay cells' axons go the visual cortex.
Interneurons' axons do not leave the dLGN

15. Interneurons have small cell bodies (somas)
represent about % of the total cell population
have a complex branching pattern of the dendrites
have center-surround receptive fields
receive feedback excitation from visual cortex
interneurons act inhibitorily (on cells within dLGN) using the neurotransmitter GABA

16. Relay cells have center-surround receptive fields
Relay cells emit the neurotransmitter glutamate (and are thus glutamatergic).
Glutamate generally acts in an excitatory fashion on the receiving cell.

17. 1st Order Nuclei
The LGN is a nucleus of the Thalamus that is considered a 1st order nucleus.
it relays subcortical (i.e., retinal) information to cortex for the first time.

18. Higher Order Nuclei
pulvinar complex, seems largely to be a higher-order relay, since much of it seems to relay information from one cortical area to another

19. Area “A” (FO) Area “B” (HO) FO HO CORTEX layer 5 layer 6 TRN THALAMUS
glomerulus
(e.g., LGN)
(e.g., Pulvinar)

20. Why should Higher Order Nuclei concern us?
Much more cortico-cortical processing may involve these "re-entry" routes than previously thought.
If so, the thalamus sits at indispensable position for cortical processing.

21. Cortico-cortical Information Flow is Relayed through Thalamus?
Cortical area 1 (FO)
Cortical area 2 (HO)
“higher order” thalamic relay
(Pul, MGNmagno, POm, etc.)
Cortical area 3 (HO)
1-3
modulator? 4 5 6
driver
modulator
“first order” thalamic relay
(LGN, MGNv, VP, etc.)
from
brainstem

22. 2 pathways of information flow
Driving pathway: Drives principal information into a thalamic nucleus
Modulating pathway: Modulates the way the information is processed.
It turns out that these pathways differ both morphologically and functionally.

23. On the way to V1
The center/surround receptive fields of 3 geniculate cells are aligned so that when output axons of these cells converge onto a cortical cell in layer 4, the receptive field of the cortical cell has an elongated shape with orientation selectivity