Transcript DSGCbasics09opt

Cat Retinal Ganglion Cell Physiological Classes
Rabbit’s Visual Streak
Molecular Determination of Ganglion Cell Classes
Concentric G Cell Morpho Summary
Central Projections
Frog Retinal Ganglion Cell Classes
Amphibian RGCs directly mediate behavioral responses
Reporting direction of movement
On-Off DS GCs Have 4 Directional Subtypes
3-D Reconstruction of DS GC
No Overall Dendritic Asymmetry
DS Independent of Contrast
DS is
Independent
of Velocity
DS
Subunits
DS GCs
exhibit
directional
hyperauity
Anatomical Models
Starburst (Cholinergic) Amacrine Cells
One Hypothesis suggests asymmetric
cholinergic input to account for some DS
Borg-Graham & Grzywacz Asymmetric Ach Model
Spike Codes: Is rate all that matters?
Response
Variability
Control of Synchrony
The
Aperture
Problem:
What is
Missing in
the Output
of One
Cell
Correlated Firing Encodes Unified Motion in Visual Cortex
What is the Computational Importance of
Synchronous Firing to the Next Stage?
Hypothesis:
The Brain
Operates at
Multiple
Levels of
Coherence.
What Mechanisms Produce
Synchronous Firing in Visual Cortex?
Synchrony from Ganglion cells?
One Possible Solution:
Suppose Close-by Retinal
Ganglion Cells Supply a
Synchronous Signal for
Separated Cells in Higher
Centers?
Do Retinal Ganglion Cells Fire Synchronously?
Does Synchronous Firing Code Anything Interesting?
What Retinal Mechanisms Mediate Synchrony?
Ganglion cell Synchrony Questions
Multielectrode Recording: Flash vs Bar
Extended Bar
DS Ganglion Cell Responses to Extended Bars vs Flash (& Spot)
GABAergic Amacrine Cell Control of Synchrony
Spikes in Starburst Amacrine Cells
Patch-Clamp Recording
Multiple Spike Heights
Can
Hyperpolarizing
Somatic Current
Eliminate Spikes
Produced by
PreferredDirection
Motion?
Can
Depolarizing
Somatic
Current
Overcome
NullDirection
Motion
Inhibition?
Is Inability
to Generate
Spikes by
Current
During Null
Motion Due
to Fatigue
or Active
Adaptation?
Is Shunting at Soma the Problem?