Superior Colliculus Flashcards
Where are colliculi found?
dorsal surface of midbrain - 4 in total
Where is main direct anantomical projection from? colliculi
retina
Colliculi project to
LGN of thalamus then to visual cortex of occipital lobe
2 layers of superior collciulus and functions
superficial - visual
deep - auditory + somatosensory
SC superficial layers input
only visual
contralateral retina, LGN, visual cortex
SC deep layers input
visual
somatosensory
auditory - inf colliculi
motor
SC superficial layers output
visual centres - LGN
SC deep layers output
ascending and descending fibres
commissural corssing over fibres
3 functions of SC
trigger behavioural responses to novel stimuli
integrate sensory information
influence general behaviour state
5 outcomes of SC following novel stimuli
pursue - crossed descending defend - uncrossed descending orient ANS changes EEG arousal
Visual stimulus - SC
sensory stimulus activates contralateral SC
orient eyes, ears and head to stimulus
SC ablation
unilateral SC ablation
contralateral sensory deficits - auditory, visual and somatosensory
2 visual pathways in CNS
analysis of stimuli - geniculocortical system
visual attention/orientation = superior colliculus
What is the sprague effect?
Lesion R visual cortex = contralateral neglect
Lesion left colliculus = orientation restored
Explain sprague effect and its implications
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
saccades
sudden movements of eyes when scan an image
Brain areas involved in saccades
inhibit saccade = dorsolateral PFC
trigger saccade = frontal eye field
explain experiment with SC and visual spatial attention with target and distractor
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
Subconscious vision/blindsight
stroke patients damage to visual cortex - still some visual orientation
SC role in consciusness
without knowing where you are/posture and sensory information would not be able to have conscious awareness
Midbrain auditory maps - relevance
barn owl hunts at night
auditory map in deep SC crucial
owl - 2 differences of auditory perception
interaural timing differences
interaural level differences
Inter aural timing differences
noise closest to one ear arrives there first
time difference between arriving at 2nd ear
Interaural level differences
1 ear slightly higher up
SC in lower vertebrates
tectum
Auditory orientation in barn owl
ITD, ILD and sound processed and project to inferior colliculi
forebrain and inferior colliculi
tonotopic maps
centre nucleus of Inferior colliculus
frequency specific channels
topographic maps
space map - specific locations in colliculus respond to specific locations in periphery
external nucleus IC and tectum
how to do electrophysiological mapping in vivo
General anaesthetic, expose right SC - remove cortex
anechoic chamber with 12 speakers and lights
neuronal discharge
analyse visual and spatial map
anechoic chamber
12 speakers and 12 lights in front of animal
analysing visual map - electrophysiology
topography
on-off responses
directional selectivity
diameter of receptive fields
analysing auditory map - electrophysiology
topography and on-off responses
normalised polar plot
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
Tuned auditory responses
tuned topographic map
tuned responses have clear preference to particular stimulus position
RA, Q50 and Q75 small
topographic organisation
plot position of SC used against position in space = linear relationship
eg front of colliculus response to stimuli at front etc
Formation of auditory map in deep SC
developmentally organised
different age groups after birth - newborn not tuned
day 32 = tuned responses
white noise and SC
easier orientation to stimulus
SC not frequency tuned
mixed frequency activates SC better
Sc and spatial attention
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
Multisensory input Sc
deep layers
visual/auditory/somatosensory
do get individual senses too but most mixed
Most frequent multisensory deep SC input in rodents and rattlesnakes
rodents = visual/somato snake = visual-infrared - locate prey!
Integration in the SC - in vivo electrophysiology
response enhancement
bigger neuronal response when multimodal stimuli
amplify one another - even if no response alone can add together to make big response
Integration in the SC - in vivo electrophysiology
response depression
less firing when combined
stimuli neither spatially or temporally related
multisensory integration example
cat -bird in tree
auditory alone = nothing
visual alone = nothing
both = auditory and visual input = orientation
Multisensory integration - behavioural example - response enhancement
weak visual/auditory stimuli - correct approach rewarded
combine both coincidentally
effective enhancement of correct responses
multisensroy - response depression example
strong visual stimuli
combine visual and auditory 60 degrees apart
depressed in comparison to just auditory
