Neural Circuits of Stimulus Localisation Flashcards
What are examples of object localisation in the visual system? (4)
- Orienting reflex
- Smooth pursuit
- Prediction of motion during prey capture
- Saccadic movements during object inspection
What is the orienting reflex?
Orientation of the head and eyes to focus a stimulus on the fovea
What is smooth pursuit?
Following a moving object
What does ablation of the optic tectum/superior colliculus result in?
Loss of the orienting reflex
Is the orienting reflex present at birth?
No, develops as babies get a bit older
Why do we need motion anticipation?
Phototransduction takes a relatively long time (in terms of being hunted by predators)
Which areas of the brain are involved in stimulus localisation and motion processing? (3)
- Retina (orientation selective ganglion cells, Magnocellular cells)
- Dorsal stream in the cortex
- Superior and inferior colliculus
What are the inputs into the superior colliculus? (3)
- Ganglion cells
- (Auditory system)
- Somatosensory system
What is the function of the superior colliculus? (2)
- Integrates information from different sensory modalities
- Regulates saccadic movements
What is the structure of the superior colliculus? (4)
- Retinotopic map
- Organised into layers based on where the areas receive input from and where they send output to
- Superficial layers receive input from the retina
- Inputs from the cortex (V1, somatosensory) do processing
What is a retinotopic map?
Organisation whereby neighbouring cells in the retina feed information to neighbouring places in their target structures
Which areas of the brain have retinotopic maps? (3)
- Visual cortex
- LGN
- Superior colliculus
Which brain areas are involved in orientation during hunting in zebrafish? (5)
- Retina
- Optic tectum
- Pretectum
- Hindbrain
- Reticulospinal system signalling causes movement towards the stimulus
Which pathway is responsible for processing motion in mammals?
Dorsal stream
What is the dorsal stream pathway for processing motion? (7)
- Magnocellular ganglion cells
- LGN
- V1 cortex
- V2 cortex
- V3 cortex
- Medial temporal cortex
- Parietal cortex
What does a stroke in the medial temporal (MT) cortex cause? (2)
- Difficulty perceiving motion
- Objection recognition and colour perception intact (ventral stream)
Where does direction selectivity occur?
On-off direction selective (DS) cells in the retina only respond to movements in specific directions
How does the morphology of DS cells link to their function?
They have highly asymmetric dendritic trees so motion in the same direction as the dendritic tree will stimulate the cell
What inputs do retinal ganglion cells receive? (4)
- Excitatory input from the bipolar cells
- Inhibitory input from the amacrine cells
- Interaction occurs in the inner plexiform layer (IPL)
- Bipolar cells activate amacrine cells, amacrine cells inhibit bipolar cells
Where does direction selectivity arise in the retina?
Inner plexiform layer (IPL)
How does direction selectivity arise in the IPL? (4)
- Direction selective (DS) ganglion cells receive excitatory input from bipolar cells and inhibitory input from amacrine cells
- In the DS preferred direction excitation is large, inhibition is small and delayed
- In the null direction excitation is small and delayed, inhibition is large
- Summation causes greater depolarisation in the preferred direction and less in the null direction
