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BMS 248 - Neural circuits > Stimulus recognition > Flashcards

Stimulus recognition Flashcards

1
Q

What projects to the lateral geniculate nucleus?

A

BOTH the parvocellular and magnocellular ganglion cells

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2
Q

How many layers are there in the LGN?

A

6

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3
Q

How many layers of the LGN receive input from the P-ganglion cells?

A

4

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4
Q

How many layers of the LGN receive input from the M-ganglion cells?

A

2

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5
Q

What is received at each layer of the LGN?

A

Input from a single eye at each layer

Alternates between input from contralateral and ipsilateral eye

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6
Q

Where does the right LGN receive input from?

What is this seen by?

A

From the left visual field

Seen by the nasal left retina and the temporal right retina

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7
Q

Where does the left LGN receive input from?

What is this seen by?

A

From the right visual field

Seen by the right nasal retina and temporal left retina

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8
Q

How are the layers kept in the LGN?

A

Remain SEGREGATED

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9
Q

How is the LGN organised?

A

Retinotopically

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10
Q

Why can we not used imaging to find out some of the functions of the LGN?

A

It is located deep within the brain

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11
Q

What is a new way of imaging the LGN?

A

Insert a tiny microscope into the brain

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12
Q

How do the ganglion cells make connections with the neurons in the LGN?

A

One to one connection

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13
Q

What are the receptive fields of the LGN neurons similar to?

A

The receptive fields of the ganglion cells

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14
Q

What are the non-retinal inputs to the LGN?

Why?

A
  • Neurons of the V1 cortex - to regulate the synaptic input to the LGN, for feedback
  • Local interneurons in the LGN - to shape the activity of other neurons
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15
Q

Describe the ventral pathway

A

P-ganglion cells - input to the P-cell layers of the LGN

Input to the V1 cortex
To the V2 and V4 cortical areas

To the inferior temporal cortex

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16
Q

Describe the dorsal pathway

A

M-ganglion cells - input to the M-cell layers of the LGN

To the V1 cortex
To the V2 and V3 cortical area

To the posterior parietal cortex

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17
Q

The further along the dorsal or ventral pathways, what happens to the neurons?

What does this allow?

A

They become more complex

Allows them to respond to more complex shapes

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18
Q

Do the ventral and dorsal pathways interact with each other?

A

Yes

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19
Q

What is the ‘Jennifer Aniston’ theory?

What is the alternative to this theory?

A

Jennifer Aniston theory:
A single neuron responds to a specific object

Alternative theory:
Large number of neurons which respond to MANY objects, but each object in a DIFFERENT way

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20
Q

If the ‘Jennifer Aniston’ theory is true, what does stimulating a specific neuron lead to?

A

Perception of the specific object that it responds to

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21
Q

What 2 things can the visual system do, as well as recognise objects that are different to each other?

A

1) Recognise objects in any orientation

2) Recognise objects independantly of their size

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22
Q

What does the hierarchical model of object recognition state?

A

Along the ventral stream, neurons respond to more and more complex shapes

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23
Q

What are the different stimulus complexity that can be responded to at different stages the ventral stream? (in regards to the hierarchical model of object)

A

Detection of EDGES

Detection of a combination of EDGES and CONTOURS

Detection of object PARTS (eg. face)

Detection of object from one point of VIEW

View-invariant object detection (eg. rabbit, car)

Categorisation (eg. human, animal, vehicle)

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24
Q

How can we test the hierarchical model of object recognition?

What do these tests show? Why?

A

Lesions in the inferior temporal cortex
- Show a decrease in the ability to recognise objects

Modelling and electrophysiology studies
- DON’T prove the model, as need to be able to image the neurons

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25
Q

As well as increasing in complexity, what else increases along the ventral stream?

A

Increase in receptive field size of neurons

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26
Q

How many layers are there in the cortex?

A

6

27
Q

What do different layers of the cortex contain?

What does this mean?

A

Some layers contain more cell bodies than other layers
Different layers contain different cells that perform different functions

Means that different layers of the cortex have different functions

28
Q

Where do cells in the LGN send their axons?

What does this allow

A

Different types of cells from the LGN (from the different LGN layers) send their projections to different layers of the cortex

To keep segregation of inputs (from the different parts of the retina) that are already segregated in the LGN

29
Q

What do interneurons in the cortex do?

A

Receive information from one layer and send projections to another layer

30
Q

As well as specific inputs to the different cortical areas, what else is specfic?

A

Specific output from each layer to different areas of the brain

31
Q

What are ‘columns’ in the cortex?

Where are they present?

A

Part of the brain which has very similar functions

Present in MANY cortical areas

32
Q

What are the 3 columns in the cortex?

A

1) Ocular dominance column
2) Orientation column
3) Blobs

33
Q

What do ocular dominance columns receive input from?

A

Only one eye (either the contralateral or ipsilateral eye)

34
Q

Using proline, how were ocular dominance columns visualised?

A
  • Inject radioactive proline into one eye
  • Proline follows the pathway of information flow (from ganglion cells, to LGN, to V1 cortex)
  • Optical methods show that the proline formed stripes in the V1 cortex - representing inputs from the eye where the proline was injected
35
Q

Using radioactive glucose, how were ocular dominance visualised?

A
  • Inject into the cortex
  • Stimulate one eye with light
  • As glucose is needed in neurons to produce energy, glucose will go into the active neurons
  • See stripes of input, depending if input from ipsilateral or contralateral eye
36
Q

What are orientation columns?

A

Neighbouring parts of the brain which respond to different orientations of bars of light/different orientation in motion

37
Q

How are orientation columns different to each other?

A

They have different neurons with different properties

38
Q

Where are orientation columns observed in the brain?

A

In many areas, including the LGN

39
Q

What do blobs in the brain process?

A

Information about colour

40
Q

What are hypercolumns?

A

Columns in some parts of the brain that have all 3 columns:

  • Blobs
  • Ocular dominance
  • Orientation

And can process ANY type of information

41
Q

What did Hubel and Wiesel do?

What did they discover?

A

Worked on the V1 cortex in cats

Discovered different orientations of light produces different responses in different neurons

42
Q

Where do ocular dominance columns extend through?

A

The entire thickness of the cortex

43
Q

For a particular neuron, when if the weakest response, when changing the orientation of the bars of light?

What graph does this produce

A

Weakest response when the orientation is PERPENDICULAR to optimum

Produces a bell shaped curve - where the most activity occurs when the bar of light is in the optimum orientation

44
Q

What do simple cells of the cortex respond to?

A

Orientation but ONLY when the stimulus is in the CENTRE of the receptive field

45
Q

Where are simple cells found in the V1 cortex?

A

In layers 4 and 6

46
Q

How is the receptive field of the cortical simple cells different to the receptive field of the ganglion cells and LGN neurons?

A

Elongated vertically

Whereas in the ganglion cells and LGN - it is round

47
Q

Why does the receptive field of the simple cells change from round shaped?

A

Several neurons in the LGN orientated in ONE LINE feed to the SAME neuron (simple cell) in the visual cortex

Receptive field of the neurons synapsing onto the simple cell are located in one line - simple cell then has an elongated receptive field

48
Q

What layer of the cortex are orientation columns not present?

A

Layer I

49
Q

What do complex cells of the cortex respond to?

A

Orientation presented ANYWHERE in the visual field

50
Q

Where are complex cells found in the V1 cortex?

A

Found in layers 2,3,5

51
Q

Where do complex cells in the V1 cortex receive input from?

A

MANY simple cells with SIMILAR orientation of receptive field

BUT in different POSITIONS in the receptive field

52
Q

What is a ‘hypercomplex’

A

An END-STOPPED complex cell

53
Q

What do hypercomplex cells respond to?

A

CHANGES in orientation that are produced by a right angle of stimulus (with combination of edges)

54
Q

What are the inputs to the V1 cortex?

A

From M-cell and P-cell layers of the LGN

55
Q

Where do outputs from the V1 cortex go to?

A
  • Other cortical areas

- LGN and deep structures

56
Q

What happens to the receptive fields downstream of V1?

A

Increase in size

Increase in complexity

57
Q

Where are face sensitive neurons present?

A

In the inferior temporal cortex

58
Q

What happens to face sensitive neurons when you start to remove features from a face?

A

Face sensitive neurons spike less

59
Q

What do face sensitive neurons respond to?

A

Shapes that resemble faces

60
Q

What happens to the face sensitive neurons when they are repeatedly shown the same ‘face’ or the ‘face’ stimulus is prolonged?

A

They undergo adaptation

61
Q

What is present at the top of the heirarchical model?

What are these called?

A

Neurons which respond to VERY specific objects

Called the ‘grandmother cell’ or the ‘Jenifer Aniston’ neuron

62
Q

What does particular Jenifer Aniston neurons respond to?

Why is it called this?

A

Responds specifically to presentation of PARTICULAR IMAGES

Found that a particular neuron responds to imges of JS but not of other people

63
Q

What are the problems with the heirarchical model?

A
  • It is a feedforward model and doesn’t take into account feedback from higher cortical areas
  • Poor in scale and orientation invariance
64
Q

What is top-down regulation?

A

Feedback from higher cortical areas

BMS 248 - Neural circuits (16 decks)

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