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intercal - advanced molecules, membranes and cells > Superior Colliculus > Flashcards

Superior Colliculus Flashcards

1
Q

Where is the superior colliculus

A

Forms roof of the midbrain - 2 of them superior and inferior colliculus

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2
Q

What sense is directly connected to the superior colliculus

A

Eyes - retinal fibres into superior colliculus in the midbrain.

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3
Q

What makes up the superior colliculus

A

Made up of layers of alternating grey and white matter

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4
Q

What info goes into the superior colliculus

A

Superficial - eyes (visual input only)
Deep - visual and somatosensory and auditory inputs and motor (substantia nigra)

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5
Q

What info leaves the superior colliculus

A

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

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6
Q

What are the overall 3 functions of the superior colliculus?

A

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

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7
Q

Why does the contralateral superior colliculus get activated during visual stimuli

A

Becomes the visual fibres cross over

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8
Q

What happens when you remove/lesion the superior colliculus

A

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

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9
Q

What is the difference between the geniculocortical system and the SC

A

Geniculo-cortical system analyses the size shape and colour of stimuli, voluntary brain response
SC is very primal as triggers initial attention to stimuli

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10
Q

What is the link between the geniculo-cortical system and the SC

A

SC triggers initial attention to stimuli, the GC system analyses the size, shape and colour.
They both interact to give functional and anatomical interactions

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11
Q

What is the sprague effect

A

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.

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12
Q

What does the superior colliculus affect selecting and tracking of visual targets

A

Target attention towards eyes and mouth in a process called saccades.

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13
Q

What can inhibit the saccades

A

The dorsal lateral prefrontal cortex

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14
Q

What did Krauzlis et al find out regarding the deactivation of one SC and saccades in mice in 2013

A

When deactivated one side - contralateral visual field had decreased saccade efficiency due to SC cross over.
Drops from 66% to 15% efficiency

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15
Q

What is blindsight

A

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.

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16
Q

What is found in the deep layers of the SC

A

Auditory centres that process somatosensory and other stimuli to coordinate a motor output

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17
Q

What is the interaural timing difference

A

Difference in timing between a sound reaching the left and right ear.

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18
Q

What is different about nocturnal hunters regarding ear level

A

One is higher up than the other - intraural level distance

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19
Q

Why do nocturnal hunters have a difference in ear level

A

Causes a slight delay in one ear over other for stimulation
This can help the animal determine the direction of the stimulus

20
Q

What are the three parts of the brain that interpret auditory stimuli

A

Central nucleus of inferior colliculus
External nucleus of inferior colliculus
Optic tectum

21
Q

What does the central nucleus of the inferior colliculus do

A

Auditory cues to specific frequencies

22
Q

What does the external nucleus of the inferior colliculus do?

A

Auditory space map

23
Q

What does the optic tectum do

A

Multimodal space map

24
Q

What are topographic maps

A

When specific locations in the brain respond to specific types of stimuli

25
Q

Why does white noise stimulate the SC better than IC

A

SC is not frequency specific so can pick up on all white noise frequencies
IC is frequency specific

26
Q

What is target selection

A

Zoning out other noises to pay attention to one

27
Q

Why is the SC needed in spatial awareness

A

SC is needed to change attention to sounds around you so you can adjust during judgements of movement.

28
Q

What are most of the neurons in the superior colliculus

A

Most are multimodal - visual, auditory and somatosensory
Some are unimodal

29
Q

Why are bimodal neurons important

A

Was shown that both auditory and visual stimuli caused a synergistic effect compared to just 1 stimuli present

30
Q

What happens if the sensory stimuli are not spatially related.

A

Multisensory neurons show response depression via inhibitory network - because its contradictory then not a massive response is produced, need to analyse further.

31
Q

Do different neurons cause response enhancement and depression

A

No the same neurons can do both if there is spatial inconsistencies of the stimulus

32
Q

What pathway causes the animal to pursue a stimuli

A

Crossed descending pathway

33
Q

What pathway causes the animal to defend (freeze/flee) a stimuli

A

Uncrossed descending pathway

34
Q

What neurotransmitters are said to be important for long term potentiation

wider reading - Platt et al 1998

A

GABA

35
Q

What does lesions in the SC do to distractibility

WIDER READING - Gaymard et al 2003

A

in humans, removing the inhibitory control on the SC from the pre-frontal cortex, therefore increasing activity in the area, also increases distractibility

36
Q

What role does the SC have in ADHD

WIDER READING - Goodale 1978

A

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)

37
Q

How do amphetamines work in ADHD on the sc in hyperresponsive rats

WIDER READING - Clements 2014

A

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.

38
Q

What is the role og glycine in the SC

WIDER READING - Platt 1998

A

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.

39
Q

What role does melanin have in the SC

WIDER READING - White and Platt 2000

A

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)

40
Q

What happens to GABA signalling post-birth in the SC

WIDER READING - Clark, Garret and Plat 2001

A

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.

41
Q

What is affective blindsight

WIDER READING - anders et al 2004

A

the uncanny ability of such patients to respond correctly, or above chance level, to emotionally salient visual stimuli presented to their blind fields

42
Q

What was found regarding facial expressions and the amygdala with regards to blindsight

WIDER READING - Whalen et al 2004

A

. 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

43
Q

When does blindsight fail

WIDER READING - Rossion et al 2000

A

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)

44
Q

What is the beleived pathyway for blindsight

WIDER READING - de gelder et al 2011

A

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.

45
Q

Why was the pulvinar nucleus believed to be involved in blindsight

WIDER READING - Maior et al 2010

A

monkey pulvinar neurons display differential activity to specific emotional expressions

46
Q

Why is the SC and no cortex needed for blindsight

WIDER READING - Celeghin et al 2015

A

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;

intercal - advanced molecules, membranes and cells (31 decks)

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