Superior Colliculus Flashcards
Where is the superior colliculus
Forms roof of the midbrain - 2 of them superior and inferior colliculus
What sense is directly connected to the superior colliculus
Eyes - retinal fibres into superior colliculus in the midbrain.
What makes up the superior colliculus
Made up of layers of alternating grey and white matter
What info goes into the superior colliculus
Superficial - eyes (visual input only)
Deep - visual and somatosensory and auditory inputs and motor (substantia nigra)
What info leaves the superior colliculus
Superficial - eyes and attention for decision making
Deep - thalamic and midbrain (Ascending bundles), Brainstem nuclei
on both sides (descending bundles) and commissural connection between left and right
What are the overall 3 functions of the superior colliculus?
React to normal sensory stimuli - visual and auditory
Integrates sensory info from ears and eyes
Influence general behavioural state e.g. posture, eyes, ears, stimuli decision making
Why does the contralateral superior colliculus get activated during visual stimuli
Becomes the visual fibres cross over
What happens when you remove/lesion the superior colliculus
Stimulus neglect -
Right SC removal - anything that appears on left-hand side be neglected
Left SC removal - anything that appears on left hand side is neglected
What is the difference between the geniculocortical system and the SC
Geniculo-cortical system analyses the size shape and colour of stimuli, voluntary brain response
SC is very primal as triggers initial attention to stimuli
What is the link between the geniculo-cortical system and the SC
SC triggers initial attention to stimuli, the GC system analyses the size, shape and colour.
They both interact to give functional and anatomical interactions
What is the sprague effect
The Sprague effect is the phenomenon where homonymous hemianopia, caused by damage to the visual cortex, gets slightly better when the contralesional superior colliculus is destroyed.
Essentially the right cortex caused initation of right SC but the left SC caused inhibition of it. When the right cortex was removed this caused purely inhibition of right SC by the left SC.
When the left SC was removed the right SC lost this inhibition so regulated itself, making the HH a bit better.
What does the superior colliculus affect selecting and tracking of visual targets
Target attention towards eyes and mouth in a process called saccades.
What can inhibit the saccades
The dorsal lateral prefrontal cortex
What did Krauzlis et al find out regarding the deactivation of one SC and saccades in mice in 2013
When deactivated one side - contralateral visual field had decreased saccade efficiency due to SC cross over.
Drops from 66% to 15% efficiency
What is blindsight
When people go blind from damage to primary visual cortex, they cant seen anything however there is a subconscious visual system that can visualise the world around them subconsciously.
What is found in the deep layers of the SC
Auditory centres that process somatosensory and other stimuli to coordinate a motor output
What is the interaural timing difference
Difference in timing between a sound reaching the left and right ear.
What is different about nocturnal hunters regarding ear level
One is higher up than the other - intraural level distance
Why do nocturnal hunters have a difference in ear level
Causes a slight delay in one ear over other for stimulation
This can help the animal determine the direction of the stimulus
What are the three parts of the brain that interpret auditory stimuli
Central nucleus of inferior colliculus
External nucleus of inferior colliculus
Optic tectum
What does the central nucleus of the inferior colliculus do
Auditory cues to specific frequencies
What does the external nucleus of the inferior colliculus do?
Auditory space map
What does the optic tectum do
Multimodal space map
What are topographic maps
When specific locations in the brain respond to specific types of stimuli
Why does white noise stimulate the SC better than IC
SC is not frequency specific so can pick up on all white noise frequencies
IC is frequency specific
What is target selection
Zoning out other noises to pay attention to one
Why is the SC needed in spatial awareness
SC is needed to change attention to sounds around you so you can adjust during judgements of movement.
What are most of the neurons in the superior colliculus
Most are multimodal - visual, auditory and somatosensory
Some are unimodal
Why are bimodal neurons important
Was shown that both auditory and visual stimuli caused a synergistic effect compared to just 1 stimuli present
What happens if the sensory stimuli are not spatially related.
Multisensory neurons show response depression via inhibitory network - because its contradictory then not a massive response is produced, need to analyse further.
Do different neurons cause response enhancement and depression
No the same neurons can do both if there is spatial inconsistencies of the stimulus
What pathway causes the animal to pursue a stimuli
Crossed descending pathway
What pathway causes the animal to defend (freeze/flee) a stimuli
Uncrossed descending pathway
What neurotransmitters are said to be important for long term potentiation
wider reading - Platt et al 1998
GABA
What does lesions in the SC do to distractibility
WIDER READING - Gaymard et al 2003
in humans, removing the inhibitory control on the SC from the pre-frontal cortex, therefore increasing activity in the area, also increases distractibility
What role does the SC have in ADHD
WIDER READING - Goodale 1978
one such locus is the superior colliculus (SC), a sensory structure intimately linked with distractibility and the production of eye and head movements. It is proposed that in ADHD, the colliculus is hyper-responsive, leading to the core symptom of increased distractibility.
This can be backed up by -
ADHD patients show increased distractibility in tasks which are sensitive to collicular function
ADHD patients have a general problem inhibiting saccades, the generation of which involves the SC;
Covert shifts in attention (which also have been argued to involve the SC) are also impaired in ADHD
Reading disorders are frequently co-morbid with ADHD; dyslexia (which is associated with eye movement problems)
How do amphetamines work in ADHD on the sc in hyperresponsive rats
WIDER READING - Clements 2014
Suppresses activty in the colliculus in healthy animals - shown via extracellular activty (multi unit and local field porential) in the superficial layers of SC in ADHD rat models.
Showed that ADHD rat models SC responded significantly more that controls to flashing lights.
This was significantly dampened down by D-amphetamine.
What is the role og glycine in the SC
WIDER READING - Platt 1998
Causes long term potentiation (long term changes in synpatic efficacy) of evoked excitatory postsynaptic potentials recorded in the superficial layers.
The strength of potentiation was found to be concentration-dependent and partially independent from synaptic stimulation - confirmed by NDMA inhibitors having no effect.
What role does melanin have in the SC
WIDER READING - White and Platt 2000
Was shown that when comparing albino rats and pigmented rats that - albino rats showing less enhancement of the strength of synaptic transmission in the SC compared to pigmented rats. Suggesting that melanin may play an important role in maturation of the superficial SC (visual section)
What happens to GABA signalling post-birth in the SC
WIDER READING - Clark, Garret and Plat 2001
all three GABA receptor types were found to be present in the superior colliculus from birth, and all show some form of postnatal modification, with GABA(A) receptors demonstrating the most dramatic drop. However, GABA(B) and GABA(C) receptors are modified significantly around the onset of input-specific activity e.i eye opening in these rats.
What is affective blindsight
WIDER READING - anders et al 2004
the uncanny ability of such patients to respond correctly, or above chance level, to emotionally salient visual stimuli presented to their blind fields
What was found regarding facial expressions and the amygdala with regards to blindsight
WIDER READING - Whalen et al 2004
. Neuroimaging studies on healthy subjects in whom visual awareness was prevented by backward masking have shown that the amygdala responds to the eye whites, which are particularly informative in conveying fear
Suggests our emotional systems are tuned to understand face configuration
When does blindsight fail
WIDER READING - Rossion et al 2000
When facial expressions are not present - For example, patients with blindsight fail to guess non-emotional facial attributes correctly, such as personal identity or gender
Even complex facial expressions fail - guilt arrogance and emotions (celeghin et al)
What is the beleived pathyway for blindsight
WIDER READING - de gelder et al 2011
evidence was converging on the existence of a subcortical route from the superior colliculus to the amygdala via the pulvinar nucleus of the thalamus
Pulvinar nucleus important for attention and vision.
Why was the pulvinar nucleus believed to be involved in blindsight
WIDER READING - Maior et al 2010
monkey pulvinar neurons display differential activity to specific emotional expressions
Why is the SC and no cortex needed for blindsight
WIDER READING - Celeghin et al 2015
In such patients, the entire cortical mantel of one hemisphere has been removed for clinical purposes, including the amygdala and large portions of the pulvinar, and leaving only the superior colliculus entirely intact. Using indirect methods we have been able to show nonconscious processing of unseen emotional stimuli in such patients. These initial findings would suggest not only that the superior colliculus is involved in affective blindsight, but also, and more conclusively, that the cortex is not strictly necessary for affective blindsight to occur;
