Superior Colliculus

Question 1

Where are colliculi found?

Answer 1

dorsal surface of midbrain - 4 in total

Question 2

Where is main direct anantomical projection from? colliculi

Answer 2

retina

Question 3

Colliculi project to

Answer 3

LGN of thalamus then to visual cortex of occipital lobe

Question 4

2 layers of superior collciulus and functions

Answer 4

superficial - visual

deep - auditory + somatosensory

Question 5

SC superficial layers input

Answer 5

only visual

contralateral retina, LGN, visual cortex

Question 6

SC deep layers input

Answer 6

visual
somatosensory
auditory - inf colliculi
motor

Question 7

SC superficial layers output

Answer 7

visual centres - LGN

Question 8

SC deep layers output

Answer 8

ascending and descending fibres

commissural corssing over fibres

Question 9

3 functions of SC

Answer 9

trigger behavioural responses to novel stimuli
integrate sensory information
influence general behaviour state

Question 10

5 outcomes of SC following novel stimuli

Answer 10

pursue - crossed descending
defend - uncrossed descending
orient 
ANS changes 
EEG arousal

Question 11

Visual stimulus - SC

Answer 11

sensory stimulus activates contralateral SC

orient eyes, ears and head to stimulus

Question 12

SC ablation

Answer 12

unilateral SC ablation

contralateral sensory deficits - auditory, visual and somatosensory

Question 13

2 visual pathways in CNS

Answer 13

analysis of stimuli - geniculocortical system

visual attention/orientation = superior colliculus

Question 14

What is the sprague effect?

Answer 14

Lesion R visual cortex = contralateral neglect

Lesion left colliculus = orientation restored

Question 15

Explain sprague effect and its implications

Answer 15

Left and right SC inhibit eachother
substantia nigra feeds into left SC and right cortex into right SC
lesion right cortex, inhibtion from left SC predominates
get rid of this and restore balance
lesion studies misleading

Question 16

saccades

Answer 16

sudden movements of eyes when scan an image

Question 17

Brain areas involved in saccades

Answer 17

inhibit saccade = dorsolateral PFC

trigger saccade = frontal eye field

Question 18

explain experiment with SC and visual spatial attention with target and distractor

Answer 18

1 part of SC inactivated = hemi-neglect
cool down part dealing with distractor = improve target tracking efficiency
SC inactivated part dealing with target system = decrease efficiency

Question 19

Subconscious vision/blindsight

Answer 19

stroke patients damage to visual cortex - still some visual orientation

Question 20

SC role in consciusness

Answer 20

without knowing where you are/posture and sensory information would not be able to have conscious awareness

Question 21

Midbrain auditory maps - relevance

Answer 21

barn owl hunts at night

auditory map in deep SC crucial

Question 22

owl - 2 differences of auditory perception

Answer 22

interaural timing differences

interaural level differences

Question 23

Inter aural timing differences

Answer 23

noise closest to one ear arrives there first

time difference between arriving at 2nd ear

Question 24

Interaural level differences

Answer 24

1 ear slightly higher up

Question 25

SC in lower vertebrates

Answer 25

tectum

Question 26

Auditory orientation in barn owl

Answer 26

ITD, ILD and sound processed and project to inferior colliculi forebrain and inferior colliculi

Question 27

tonotopic maps

Answer 27

centre nucleus of Inferior colliculus | frequency specific channels

Question 28

topographic maps

Answer 28

space map - specific locations in colliculus respond to specific locations in periphery external nucleus IC and tectum

Question 29

how to do electrophysiological mapping in vivo

Answer 29

General anaesthetic, expose right SC - remove cortex anechoic chamber with 12 speakers and lights neuronal discharge analyse visual and spatial map

Question 30

anechoic chamber

Answer 30

12 speakers and 12 lights in front of animal

Question 31

analysing visual map - electrophysiology

Answer 31

topography on-off responses directional selectivity diameter of receptive fields

Question 32

analysing auditory map - electrophysiology

Answer 32

topography and on-off responses

Question 33

normalised polar plot

Answer 33

``` 0 degrees in front of animal 180 degrees is back probes fire - maximum cell response plot, speakers - how big is response from other location exclusively from side Q50 and Q75 RA = response area ```

Question 34

Tuned auditory responses

Answer 34

tuned topographic map tuned responses have clear preference to particular stimulus position RA, Q50 and Q75 small

Question 35

topographic organisation

Answer 35

plot position of SC used against position in space = linear relationship eg front of colliculus response to stimuli at front etc

Question 36

Formation of auditory map in deep SC

Answer 36

developmentally organised different age groups after birth - newborn not tuned day 32 = tuned responses

Question 37

white noise and SC

Answer 37

easier orientation to stimulus SC not frequency tuned mixed frequency activates SC better

Question 38

Sc and spatial attention

Answer 38

SC both implements motor consequences of attention crucial role in process of target selection that precedes movement shifts of covert attention - normal control of spatial attention

Question 39

Multisensory input Sc

Answer 39

deep layers visual/auditory/somatosensory do get individual senses too but most mixed

Question 40

Most frequent multisensory deep SC input in rodents and rattlesnakes

Answer 40

``` rodents = visual/somato snake = visual-infrared - locate prey! ```

Question 41

Integration in the SC - in vivo electrophysiology | response enhancement

Answer 41

bigger neuronal response when multimodal stimuli | amplify one another - even if no response alone can add together to make big response

Question 42

Integration in the SC - in vivo electrophysiology | response depression

Answer 42

less firing when combined | stimuli neither spatially or temporally related

Question 43

multisensory integration example

Answer 43

cat -bird in tree auditory alone = nothing visual alone = nothing both = auditory and visual input = orientation

Question 44

Multisensory integration - behavioural example - response enhancement

Answer 44

weak visual/auditory stimuli - correct approach rewarded combine both coincidentally effective enhancement of correct responses

Question 45

multisensroy - response depression example

Answer 45

strong visual stimuli combine visual and auditory 60 degrees apart depressed in comparison to just auditory