Retinal targets Flashcards
(29 cards)
What retinal targets do we care about?
Superior Colliculus, Lateral Geniculate Nucleus, large thalamic nuclei called Pulvinar.
Hendry’s law of lamination
When you see layers, you know more than 1 thing is going on.
What are the layers of the SC?
SGS: superficial (above Opt)
SGI
SGP: profundum (deep)
What is the interesting property of neurons in different layers of the SC?
above Opt, neurons are only sensory(Visual)
Deeper, you get other senses (SGI)
Even deeper, you get neurons with motor field, they do saccades.
What does SC do when eyes move focus?
SC has circuitry to take other sensory inputs and recode them such as when the eyes move, the other sensory RFs move too.
How does the arrangement the retinal map translate to the tectum?
Nasal to temporal becomes Caudal to Rostral. Dorsal to Ventral becomes Medial to Lateral. -90degree turn.
What did Rodieck&Watanabe think about monkey cells that send axons to SC? What’s the truth?
They thought there existed a unique cell that sent axons to SC. Turns out it’s M ganglions.
Explain cortico-tectal innervation. What does this achieve?
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.
Explain sensory coherence in SC.
Keep head centered move eyes, as eyes move auditory and somatic RF move with them.
Explain arrangement of auditory and visual RFs in SC.
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.
What drives saccades and how do they work?
SC drives saccades. Stimulating it gives rapid nonsmooth eye movement. During acquisition, they move rapidly. Then they slow down, and correct.
What is the main function of the SC?
Drive reflexive eye movements based on visual + auditory responses.
How can you make a saccade map?
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.
When multiple cells are active in SC, how is eye movement calculated?
Linear sum.
What are two mutually compatible models of neural activity -> saccade?
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.
Does SC send any axons to anywhere in the direction of the retina?
It sends axons to two deepest K layers of LGN. These guide eye movement.
What are the two models of the visual thalamus?
Old model: two types of input, specific and nonspecific.
New model: first order input and higher order input.
Explain the old model for the visual thalamus.
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.
Explain the new model for the visual thalamus.
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.
Explain how layers in LGN send axons to V1 in macaque
Strictly segregated. Not only input but also output segregated.
What does the LGN do?
Not a lot. Spatially and chromatically nothing. LGN has inhibitory cells. It does some sort of filtering. Allows different responses to same retinal input.
Explain LGN relay.
1 spike into LGN-> %33 chance of seeing postsynaptic spike. 2 spikes into LGN-> change increases greatly (9/10). Burst mode increases effectiveness drastically.
What does the LGN synaptic circuit do?
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.
How does the LGN neuron switch between burst and relay?
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.
