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BMS 248 - Neural circuits > Stimulus localisation and processing of motion > Flashcards

Stimulus localisation and processing of motion Flashcards

1
Q

How are processing of motion and stimulus localisation interlinked?

A

By identifying the direction of motion - can predict where the stimulus will be in the next moment of time

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2
Q

What are 4 examples of object localisation in the visual system? What are these?

A

1) Orienting reflex (Orientation of head so that the eyes can focus important stimulus on the fovea)
2) Smooth pursuit (Following a moving object)
3) Prediction of motion during prey capture (motion anticipation)
4) Saccadic movement of the eye (eyes flicker)

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3
Q

What does the orienting reflex happen independently of?

A

The stimulus

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4
Q

What happens when a stimulus appears in the visual field?

Why?

A

Orienting reflex:

Move head and eyes so this part of the visual field is focused on the fovea - highest visual acuity

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5
Q

When motion anticipation needed?

Why?

A

When something is moving fast:

  • Speed at which the brain processes information doesn’t allow to follow the stimulus at any moment in time
  • Phototransduction cascade takes time
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6
Q

Describe saccadic eye movements during object inspection?

A
  • They are not random

- Some parts are inspected more than others

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7
Q

What does ablation of the optic tectum/superior colliculus result in?

A

Disappearance of the orienting reflex

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8
Q

What is the optic tectum/superior colliculus?

A

Optic tectum is the lower vertebrate homologue of the superior colliculus (mammals)

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9
Q

What are the important areas in the brain involved in motion processing?

A
  • Retina - M-type ganglion cells
  • Dorsal stream in the visual cortex
  • Superior and inferior colliculus
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10
Q

Where does the superior colliculus receive inputs from?

What is the role of the superior colliculus?

A

ALL different sensory modalities (smell, taste, hear, see, touch)

Role: to INTEGRATE the information from different sensory modalities, in order to make decisions on where to move, issue motor commands

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11
Q

What is the MAIN function of the superior colliculus? (regulate…)

A

Regulates saccadic eye movements

Orienting reflex

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12
Q

What do lesions in the superior colliculus result in?

A

Disappearance of the orienting reflex

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13
Q

How are different brain areas organised?

Describe this organisation

A

Retinotopically:

- Neighbouring cells in the retina feed information to neighbouring places in the target structure

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14
Q

What changes the activity in the brain and why?

A

Position of the stimulus - activity of the brain is different
Firing in the TECTUM is not random

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15
Q

Where are retinotopic maps present in the brain?

A
  • Retina
  • Superior colliculus
  • LGN
  • Early visual cortex
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16
Q

What do ‘command’ neurons regulate?

A

Eye saccades

17
Q

What do command neurons do?

A

Spike before saccadic movements, in order to regulate them

18
Q

Where are command neurons present?

A

In the deeper layers of the superior colliculus

19
Q

How are the command neurons organised?

What is this similar to?

A

In maps

Similar to retinotopic maps

20
Q

Where do command neurons send their projections to?

What does this result in?

A

Different layers, to stimulate SPECIFIC neurons

Stimulation of a specific neuron leads to the eye shifting to a specific angle

21
Q

How can processing in the superior colliculus happen, where motor commands are issued?

Describe the processing

A

Retinotopic map (visual map) is aligned with a deeper motor map:

  • Stimulus in the visual field - stimulation of specific visual neurons in the superior colliculus
  • If the activation of this neuron is large enough - leads to activation of the lower neurons (in the motor map) which are responsible for moving the eye in that direction
  • This activation is via COMMAND NEURONS (send projections from visual map to motor map)
22
Q

Along the dorsal stream, what neurons become present?

A

Neurons that respond to moving objects (motion)

23
Q

Along the dorsal stream, what does movement of a stimulus in different directions cause?

A

Different responses of the specific neurons

24
Q

What is the direction of movement that causes the maximum response in a specific neuron?

A

Preferred direction

25
Q

What is the direction of movement that causes the minimum response in a specific neuron?

What is this opposite to?

A

Null direction

Opposite to the preferred direction (90 degree angle)

26
Q

Where is direction selectivity of neurons first apparent?

A

In the retina

27
Q

When do neurons in the retina start spiking/end spiking during a motion?

A

Start spiking when motion starts

Finish spiking when motion ends

28
Q

Describe the morphology of direction selective neurons

What can be determined from this morphology?

A

Highly asymmetric dendrites

Preferred direction of the neurons can be guessed from with direction the dendrites are in

29
Q

What inputs do retinal ganglion cells receive?

A

Both excitatory and inhibitory

30
Q

Where do the excitatory input to ganglion cells come from?

What mediates this?

A

From bipolar cells

Mediated by glutamate

31
Q

Where do the inhibitory input to ganglion cells come from?

What mediates this?

A

From amacrine cells

Mediated by GABA

32
Q

What inputs do direction selective ganglion cells receive?

A

Excitatory input from BIPOLAR cells

Inhibitory input from AMACRINE cells

33
Q

What happens to the activity in the ganglion cell in the stimulus is moving in the PREFERRED direction?

What does this cause?

A
  • Excitation is larger
  • Inhibition is smaller and delayed

Causes depolarisation of the membrane to THRESHOLD
Neuron spikes

34
Q

What happens to the activity in the ganglion cell in the stimulus is moving in the NULL direction?

What does this cause?

A
  • Excitation is smaller and delayed
  • Inhibition is larger

Still causes depolarisation but DOESN’T REACH threshold

35
Q

How are static stimuli and moving stimuli processed in the visual system?

A

Differently

36
Q

What cells in the retina predict the location of moving objects?

How?

How is this different for a static object?

A

Ganglion cells

They begin spiking BEFORE the object approaches the receptive field of the cell

Different for a static object - response is delayed

BMS 248 - Neural circuits (16 decks)

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