Lecture 15- Visual Cortex 3

Question 1

How does Oregon Green (Ca2+ indicator dye) work?

Answer 1

It gets trapped in cells and fluoresces during Ca2+ influx - indicating cellular activity

Question 2

How are pinwheel centres ordered?

Answer 2

Pinwheel centres are highly ordered: neurons selective to different orientations are clearly segregated even in the very centre! Thus, pinwheel centres truly represent singularities in the cortical map. This highly ordered arrangement at the level of single cells suggests great precision in the development of cortical circuits underlying orientation selectivity

Question 3

Orientation pin-wheel centres (singularities) tend to fall over?

Answer 3

Centres of ocular dominance columns

Question 4

!Hypercolumns

Answer 4

A module of about 1 mm x 1 mm x 2 mm covers a pair of ocular dominance columns (one for each eye) and all the orientations. It acts as a small window on a small part of the visual world and processes the visual input in terms of elementary features

Question 5

Why do we have columnar systems?

Answer 5

1) Ensure all possible combination of stimulus features are represented within any given region of the visual field 2) To avoid the occurrence of functional blind spots for stimulus attributes across a sensory map Similar columnar systems have been demonstrated in other sensory systems - e.g. columns tuned to slowly or rapidly adapting mechanoreceptors from the same area of skin

Question 6

Where in the visual pathway the koniocellular pathway found?

Answer 6

In the early parts of the visual pathway: retina and LGN - not PVC

Question 7

There are two streams: Dorsal (Where) and Ventral (What) - which brain region does each go to after the LGN?

Answer 7

Dorsal - Thick stripes -> MT -> Posterior parietal cortex, input mainly from magno- cells Ventral - Blobs -> Thin stripes -> V4 ->IT input mainly from parvo-cells

Question 8

Classical view of properties of blobs and inter-blobs - but what did exp show

Answer 8

Blobs - colour selective, poor orientation selectivity Inter-blobs (between) - achromatic, good orientation selectivity Exp showed that orientation tuning is similar in cytochrome oxidase blobs and interblobs

Question 9

What do horizontal connections tell us about orientation selective cells?

Answer 9

Cells tuned to the same orientation are connected horizontally

Question 10

What is the relationship between different functional domains of the primary visual cortex?

Answer 10

In recordings of single cell responses in separate electrode penetrations, Hubel and Wiesel found that penetrations perpendicular to the cortical surface contained cells which contained similar orientation AND ocular dominance. Cytochromse oxidase blobs and orientation pin-wheel centres (singularities) , where orientation domains converge, tend to fall over centres of ocular dominance columns

Question 11

!Horizontal connections are formed primarily by

Answer 11

Axon collaterals of pyramidal neurons in layer 2/3 of the PVC. They extend for mm parallel to the cortical surface and form patch terminations