L17 - Visual Cortex- Cell types & Orientation selectivity (TV)

Question 1

Lower/upper visual field is represented in the lower/upper back half of the calcrine sulcus and vice versa

Answer 1

Upper, lower

Question 2

Scotoma

Answer 2

Affects one small area of visual field

Question 3

There are over __ different visual areas beyond V1 in the macaque brain - there is also reasonable degree of functional localisation among these areas

Answer 3

30

Question 4

Human brain has over >___ visual areas in brain

Answer 4

180

Question 5

How are visual areas distinguished from one another?

Answer 5

On the basis of cyto- and myelo- architectonics and physiological studies

Question 6

How is striate cortex (V1) easily identified?

Answer 6

From prominent layer 4b - the stria of Gennari

Question 7

What border represents vertical meridian?

Answer 7

V1/V2 Border

Question 8

What border represents horizontal meridian?

Answer 8

A/B border - at the epicenter

Question 9

Spiny stellate cells are excit/inhib

Spineless stellate cells are excit/inhib

Answer 9

Spiny excit (Glut)
Spineless inhib (GABA)

Question 10

P cells from LGN project to layers _ and _ with a sparse projection to layer _

Answer 10

4Cbeta, 4A, 6

Question 11

M cells project to _ with a sparse projection to layer _

Answer 11

4Calpha, 4B, 6

Question 12

K cells project to layers _ and _

Answer 12

1 and 3 (The supragranular layers - as layer 4 is the granular layer)

Question 13

Hubel and Wiesel discovery?

Answer 13

Cells fire in response to edges

Question 14

Simple cell - Describe receptive field? Best stimulus?

Answer 14

• 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

Question 15

Complex cell - describe receptive field?

Answer 15

• Large square receptive field

- Orientation is important but not position

Question 16

!Which layer of PVC is the densest and darkest? Loosely packed?

Answer 16

Dense - 4C and 6

Loose - 1, 4B, 5

Question 17

What does layer 1 contain?

Answer 17

Hardly any nerve cells but has abundant axons, dendrites and synapses

Question 18

Which PVC layers are pyramidal cells founds in? Stellate cells?

Answer 18

Pyramidal - ALL but layer 1 and 4

Stellate - ALL

Question 19

Input for simple cell comes from excitatory convergence of?

Answer 19

(LGN) Geniculate cells (not orientation selective) whose receptive fields are in a row in visual space

Question 20

Input for complex cells is from excitatory convergence of?

Answer 20

Simple cells - all tuned to the same orientation

Question 21

Input for hypercomplex cells come from?

Answer 21

Excitatory input from a complex cell in the centre and inhibitory inputs in the inhibitory end zones

Question 22

The simple, complex, hypercomplex hiearchy scheme is partly true - why?

Answer 22

Complex cells often respond to stimuli that simple cells do not. Both complex and hypercomplex cells can be monosynaptically excited from LGN.

Question 23

Hypercomplex cells are defined by the property of end-stopping - what is it?

Answer 23

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.

Question 24

Orientation selectivity may arise before the level of striate cortex - varying degrees of orientation selectivity are present subcortically in the retina

Answer 24

Orientation selectivity may arise before the level of striate cortex - varying degrees of orientation selectivity are present subcortically in the retina

Question 25

Orientation selectivity is controversial - if the model is based on excitatory convergence, why is orientation selectivity reduced/abolished when inhibition is removed?

Answer 25

Orientation selectivity is controversial - if the model is based on excitatory convergence, why is orientation selectivity reduced/abolished when inhibition is removed?