superior colliculus Flashcards
properties and functional anatomy, role in innate and defensive behaviour
What are sensory motor systems critical for?
Survival
Sensory motor systems integrate physiological aspects necessary for survival.
What is an example of a reflexive response in crayfish?
Jackknife reflex
This reflex allows crayfish to escape from predators.
What does the superior colliculus integrate?
Sensory and motor processes
It plays a critical role in sensory motor processing.
What is the evolutionary significance of the superior colliculus?
It is conserved across mammals and vertebrates
what is the superior colliculus otherwise referred to as
optic tectum
What does the term ‘superior colliculus’ translate to?
Little hill
This description relates to its position in the brain.
Where is the superior colliculus located in mammals?
On top of the midbrain, below the cerebral cortex in mammals
Its position reflects its function in sensory processing.
How does the size of the superior colliculus change with brain complexity?
It gets relatively smaller as the forebrain becomes larger
This reflects the increasing complexity of decision-making processes in larger brains.
What is the structure of the superior colliculus?
Multi-layered
- It consists of alternating layers of cell bodies and neural fibers.
What are the three broad layers of the superior colliculus?
Superficial, intermediate, and deep layers
what are the superficial layers thought of as?
primarily sensory
primarily visual brain region
what are the deeper layers thought of as ?
more motor-oriented
What type of input does the superficial layer of the superior colliculus primarily receive?
Sensory input from the visual system directly from retina
What percentage of retinal ganglion cells project to the superior colliculus in mice?
90%
This highlights the significance of visual processing in this area.
What is the retinotopic order in the superior colliculus?
Cells responding to specific visual regions are clustered together
This creates a map of the visual world in the brain.
What types of sensory information are represented in the deeper layers of the superior colliculus?
visual, auditory and somatosensory information
and recent experience (FEF, M2), target value, saccade control
These layers integrate multiple sensory modalities.
map alignment in SC
different layers of neurons in SC contain mutually aligned maps of space for each sensory modality
what does map alignment in the SC allow for ?
- multisensory facilitation; important for detecting biologically relevant events
- transformation from sensory cues to motor commands
What is multisensory facilitation?
Enhanced response to simultaneous inputs from different sensory systems
This leads to nonlinear responses to combined stimuli.
What is the benefit of the spatial organization in the superior colliculus?
Facilitates multisensory interactions and transformation from sensory to motor commands
This organization allows efficient processing of sensory information.
what do diverse inputs and outputs sllow the SC to do?
- recieve, process and integrate sensory information
- register information spatially
- diect appropriate behaviour
What behavioral outputs are driven by the activation of the superior colliculus?
Orienting movements and locomotion
This includes head movements and running.
What broad movements does the superior colliculus output?
Orienting and defensive movements (motor)
These movements can be classified based on the type of response.
What is the role of the superior colliculus in eye movement control?
It drives activity in brainstem regions for ocular motor responses
Neurons in the superficial layers are influenced by visual inputs.
What are neurons in the superficial layers of the SC driven by?
visual inputs
What enhances the response of neurons in the superficial layers of the SC when a stimulus appears?
if an animal is going to make a Saccadic eye movement to that location
what do distinct movement-related cells in the intermediate and deep SC fire in response to ?
fire just prior to saccades of specific size and direction
what are movement fields ?
movement-related neurons fire when they move to particular regions of visual space
in lower SC layers
what are actual eye movements encoded by ?
by a population code, as individual movement cells have large overlapping movement fields so need to be encoded together
where is the fixation zone
most rostral portion of SC
What is the fixation zone in the SC important for?
Maintaining fixation
What happens if the fixation zone is lesioned?
Reduced ability to maintain fixation
e.g. more likely to be distracted by other visuals stimuli
What brain region primarily drives saccadic movements?
Frontal eye fields
FEF provide direct excitatory projections
how does FEF drive indirect excitatory activity in SC?
- FEF drive activity in parietal cortex: lateral intraparietal area (LIP)
What is the role of the caudate nucleus in relation to the SC?
when excited by FEF it Inhibits the substantia nigra, reducing inhibition of the SC
What type of responses do the SC coordinate?
Orienting and defensive responses
- recieve process and integrate sensory information
- register it spatially
- direct appropriate behaviour (Orienting and defensive)
What technique can be used to silence specific neurons in the SC?
Tetanus neurotoxin - TeNT
What was observed when the activity of wide field neurons in the SC was silenced by TeNT?
- increased time taken to attack
- increased time taken to capture prey
SC involved
What modern technique allows for reversible manipulation of neuron activity?
Chemogenetics
can choose what type of GPCR into cell to selectively silence neurons
how do chemogenetics work?
- Gi couple GPCR input
- activated by synthetic drug CNO
- cAMP decreased
- Intracellular calcium decreased
-K+ efflux increased - decreased neuronal firing
What happens to behavior of mice when WF neurons are silenced?
- detection impaired: distrupted prey detection and approach inititation
- but orienting in tact
what happened to behaviour of mice when NF neurons were silence?
- no impact on distant approach
- impaired orienting and interception
i.e. noticed cricket but didn’t catch it
what does an overhead looming stimulus do ?
drives motor responses
e.g. mimics owl swooping - defense behaviour initiated
what did an experiment with the looming stimulus show ?
Lee et al . 2020
- SC encodes looming stimuli in a layer-specific way
- superficial layer respond robustly to looming stimulus/ visual imput
- dorsal layers (deep)had more role in driving motor response
Fill in the blank: The SC uses a _______ code to perform computations.
Population
True or False: The SC directly receives input from the frontal eye fields.
True
What happens to the firing of neurons in the SC with repeated presentations of a stimulus?
Habituation occurs
respond less with time as SC encodes looming stimulus
optogenetic inhibition in silence dmSC (dorsal medial)?
- firing rate inhibited dramatically with iChloC (inhibit chlorine channels)
- in medial superior colliculus
what does inhibition of glutamatergic neurons via iChloC do to mice behaviour ?
- escape behaviour reduce
what is the dPAG ?
dorsal periaqueductal grey
- primary output of SC
how do inhibiting neurons in dPAG affect mice behaviour ?
- no response to looming stimulus
- no escape response
- mice froze
what did inhibiting the dPAG reveale about the SC?
- threat is still detected, indicating that PAG initiates escape behaviour
- compared to when only dmSC inhibited the link between sensory input and response is comprimised so no escape behaviour
what is the LPTN?
- lateral posterior thalamic nucleus
what is the PBGN?
parabigeminal nucleus
why does the freeze behaviour happen ?
- PBGN drive responses in the PAG
- when we inhibit PAG pathway, animals switch to engage pathway driven by LPTN (include PBGN)
what did optigentic activation of PV neurons show ?
did specifcally for neurons recieving input from SC /no visual stimuli p
PV parvalbumin neurons
- when neurons from SC to PBG activated we see escape behaviour
- from SC to LPTN they displayed freezing behaviour
both pathways involved in driving behavioural outputs to stimuli
What are the two types of neurons identified in the SC that have different roles in prey detection?
Wide field neurons and narrow field neurons
What role does the dorsal periaqueductal gray region play in motor response?
It drives changes in output behavior, affecting how animals respond to stimuli.
Inhibiting this region led to different behaviors, such as freezing instead of normal responses.
What was observed in animals when the superior colliculus was inhibited?
There was no motor output; the animals did not freeze or run, continuing their behavior as normal.
This indicates a compromise in the sensory-motor input link.
What behavior did animals exhibit when the output region, the PAG, was inhibited?
The animals detected the stimulus but showed a change in behavior, such as freezing.
The superior colliculus remained active but did not lead to the usual motor responses.
What hypothesis was proposed regarding the engagement of different pathways when the PAG pathway was inhibited?
The animals may engage the pathway driven by the LPTN as an alternative response.
This suggests redundancy or flexibility in behavioral responses.
What technique was used to activate neurons in the study?
Optogenetics was used to activate neurons by shining light on them.
This allows researchers to drive neuronal spikes without external stimuli.
What was the behavior of animals when neurons receiving input from the SC to the PBGN were activated?
The animals exhibited a motor response similar to fleeing.
This aligns with the PBGN’s role in driving outputs to the PAG.
What happened when neurons in the LPTN were activated?
The animals stopped all movement and exhibited freezing behavior.
This indicates that the LPTN is involved in inhibiting movement.
What do the findings suggest about the relationship between the PBGN and LPTN pathways?
There is likely a push-pull dynamic between these two systems depending on context and behavioral state.
This reflects the complexity of sensory-motor integration.
What is the primary function of the superficial regions in the superior colliculus?
They allow the SC to receive, process, and integrate sensory information and direct appropriate behaviors.
This includes registering sensory input in space.
How does the superior colliculus integrate sensory inputs?
It combines sensory inputs with higher-order influences, such as eye movements and defensive behaviors.
This integration is crucial for orienting responses.
True or False: The superior colliculus is solely responsible for motor output.
False.
It integrates sensory information with various motor outputs, involving multiple circuits.
