L17 - Visual Cortex- Cell types & Orientation selectivity (TV) Flashcards
Lower/upper visual field is represented in the lower/upper back half of the calcrine sulcus and vice versa
Upper, lower
Scotoma
Affects one small area of visual field
There are over __ different visual areas beyond V1 in the macaque brain - there is also reasonable degree of functional localisation among these areas
30
Human brain has over >___ visual areas in brain
180
How are visual areas distinguished from one another?
On the basis of cyto- and myelo- architectonics and physiological studies
How is striate cortex (V1) easily identified?
From prominent layer 4b - the stria of Gennari
What border represents vertical meridian?
V1/V2 Border
What border represents horizontal meridian?
A/B border - at the epicenter
Spiny stellate cells are excit/inhib
Spineless stellate cells are excit/inhib
Spiny excit (Glut) Spineless inhib (GABA)
P cells from LGN project to layers _ and _ with a sparse projection to layer _
4Cbeta, 4A, 6
M cells project to _ with a sparse projection to layer _
4Calpha, 4B, 6
K cells project to layers _ and _
1 and 3 (The supragranular layers - as layer 4 is the granular layer)
Hubel and Wiesel discovery?
Cells fire in response to edges
Simple cell - Describe receptive field? Best stimulus?
- Small highly elongated receptive field
- Best stimulus for this cell is to position a bar of light that covers the cell properly e.g. a bar - using restricted visual stimulus
Complex cell - describe receptive field?
- Large square receptive field
- Orientation is important but not position
!Which layer of PVC is the densest and darkest? Loosely packed?
Dense - 4C and 6
Loose - 1, 4B, 5
What does layer 1 contain?
Hardly any nerve cells but has abundant axons, dendrites and synapses
Which PVC layers are pyramidal cells founds in? Stellate cells?
Pyramidal - ALL but layer 1 and 4
Stellate - ALL
Input for simple cell comes from excitatory convergence of?
(LGN) Geniculate cells (not orientation selective) whose receptive fields are in a row in visual space
Input for complex cells is from excitatory convergence of?
Simple cells - all tuned to the same orientation
Input for hypercomplex cells come from?
Excitatory input from a complex cell in the centre and inhibitory inputs in the inhibitory end zones
The simple, complex, hypercomplex hiearchy scheme is partly true - why?
Complex cells often respond to stimuli that simple cells do not. Both complex and hypercomplex cells can be monosynaptically excited from LGN.
Hypercomplex cells are defined by the property of end-stopping - what is it?
It is a decrease in firing strength with increasingly larger stimuli. The sensitivity to stimulus length is accompanied by selectivity for the specific orientation, motion, and direction of stimuli.
Orientation selectivity may arise before the level of striate cortex - varying degrees of orientation selectivity are present subcortically in the retina
Orientation selectivity may arise before the level of striate cortex - varying degrees of orientation selectivity are present subcortically in the retina
Orientation selectivity is controversial - if the model is based on excitatory convergence, why is orientation selectivity reduced/abolished when inhibition is removed?
Orientation selectivity is controversial - if the model is based on excitatory convergence, why is orientation selectivity reduced/abolished when inhibition is removed?
