Retinal targets

Question 1

What retinal targets do we care about?

Answer 1

Superior Colliculus, Lateral Geniculate Nucleus, large thalamic nuclei called Pulvinar.

Question 2

Hendry’s law of lamination

Answer 2

When you see layers, you know more than 1 thing is going on.

Question 3

What are the layers of the SC?

Answer 3

SGS: superficial (above Opt)
SGI
SGP: profundum (deep)

Question 4

What is the interesting property of neurons in different layers of the SC?

Answer 4

above Opt, neurons are only sensory(Visual)
Deeper, you get other senses (SGI)
Even deeper, you get neurons with motor field, they do saccades.

Question 5

What does SC do when eyes move focus?

Answer 5

SC has circuitry to take other sensory inputs and recode them such as when the eyes move, the other sensory RFs move too.

Question 6

How does the arrangement the retinal map translate to the tectum?

Answer 6

Nasal to temporal becomes Caudal to Rostral. Dorsal to Ventral becomes Medial to Lateral. -90degree turn.

Question 7

What did Rodieck&Watanabe think about monkey cells that send axons to SC? What’s the truth?

Answer 7

They thought there existed a unique cell that sent axons to SC. Turns out it’s M ganglions.

Question 8

Explain cortico-tectal innervation. What does this achieve?

Answer 8

SC is also innervated by cerebral cortex. Inner layers get from V2,3, extrastriate. Auditory belt, SII (second somatic sensor, also some SI). These have a broader grained RF than retina. This allows coherent sensory input.

Question 9

Explain sensory coherence in SC.

Answer 9

Keep head centered move eyes, as eyes move auditory and somatic RF move with them.

Question 10

Explain arrangement of auditory and visual RFs in SC.

Answer 10

The same area in the real world overlap verticall in SC. Visual map is small and on superficial layer. Auditory map is below that and larger.

Question 11

What drives saccades and how do they work?

Answer 11

SC drives saccades. Stimulating it gives rapid nonsmooth eye movement. During acquisition, they move rapidly. Then they slow down, and correct.

Question 12

What is the main function of the SC?

Answer 12

Drive reflexive eye movements based on visual + auditory responses.

Question 13

How can you make a saccade map?

Answer 13

Stimulation of deep layers in SC produces saccades of particular direction and amplitude. Small saccades near center of vision require small amplitude, large saccades at peripheral require srs eye contraction.

Question 14

When multiple cells are active in SC, how is eye movement calculated?

Answer 14

Linear sum.

Question 15

What are two mutually compatible models of neural activity -> saccade?

Answer 15

A: Uniform activity across SC leads to a movement vector
B: Concentric circles of activity leads to mvoement vector. This one says spike rate matters.

Question 16

Does SC send any axons to anywhere in the direction of the retina?

Answer 16

It sends axons to two deepest K layers of LGN. These guide eye movement.

Question 17

What are the two models of the visual thalamus?

Answer 17

Old model: two types of input, specific and nonspecific.

New model: first order input and higher order input.

Question 18

Explain the old model for the visual thalamus.

Answer 18

LGN is the specific input, SC is the nonspecific. V1 driven by LGN, pulvinar by SC. V1 sends to V2, which sends to 2,3,4,5 and a little bit of V1.

Question 19

Explain the new model for the visual thalamus.

Answer 19

First order input: LGN>V1
Higher order: V1>HO1>V2>HO2>V4/MT (later 5 neurons in V1/2). V1 return path to LGN from L6. L5 stuff is critical because it provides HO areas with precise info.

Question 20

Explain how layers in LGN send axons to V1 in macaque

Answer 20

Strictly segregated. Not only input but also output segregated.

Question 21

What does the LGN do?

Answer 21

Not a lot. Spatially and chromatically nothing. LGN has inhibitory cells. It does some sort of filtering. Allows different responses to same retinal input.

Question 22

Explain LGN relay.

Answer 22

1 spike into LGN-> %33 chance of seeing postsynaptic spike. 2 spikes into LGN-> change increases greatly (9/10). Burst mode increases effectiveness drastically.

Question 23

What does the LGN synaptic circuit do?

Answer 23

LGN neuron membrane depolarized to -55mv is relay mode. Action potential in, best case: action potential out. WHen you hyperpolarize, input comes in: you get bursts. Action potential in: 7-8 action potentials out.

Question 24

How does the LGN neuron switch between burst and relay?

Answer 24

There is a voltage dependent Ca2+ channel. Has activation and inactivation gate. Hyperpolarizing membrane>inactivation gate open>Ca enters(current).>Action potential. This can respond to small input.
Ca provides trigger to enable burst. happens until longterm membrane potential depolarizes, shuts Ca, opens K. Tonic hyperpolarization+excitatory input=burst.

Question 25

What does the pulvinar do and where is it innervated from?

Answer 25

Takes visual stim and boosts output to cortical cells. Inferior pulvinar by SC and extrastriate. Tactile and cortical. Lateral pulvinar by extrastriate. Cortical.

Question 26

Where does pulvinar provide input to?

Answer 26

Both dorsal and ventral stream. V1/2>axons>V4 (ventral).
V1/2>axons>MT (guidance of mvmt)
V1/2>inferior pulvinar>MT
V1/2>lateral pulvinar>V4

Question 27

Explain pulvino-cortical anatomy.

Answer 27

Lateral pulvinar>ventral. Inferior pulvinar>dorsal.

Pulvinar chooses which pieces of V1 and MT talk to each other.

Question 28

What happens when you remove the V1 of a person? Why?

Answer 28

They are blind but can still avoid obstacles. They can guess between dark and bright. MT still remains.

Question 29

What happens when you remove the SC of a person?

Answer 29

They lose all sight and navigational capabilities.