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Neural Circuits > Stimulus Localisation and Recognition > Flashcards

Stimulus Localisation and Recognition Flashcards

1
Q

What is Echolocation?

A

a physiological process for locating distant or invisible objects by means of sound waves reflected back to the emitter by the objects

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2
Q

How does a bat use echolocation with water surface?

A

Water surface is smooth so the bat can sense sounds in all directions but the only one that will come back is from behind because every other wave reflected goes elsewhere

This allows bats to survey water surface by using echolocation

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3
Q

How does an electric fish use echolocation?

A
  • create an electric field around them and have sensors to detect
  • If object in close proximity there will be changes in the electric field
  • If object is big they can decide to swim away or if its small they can bite it
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4
Q

What is scale invariance?

A

recognising an object at a different size

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5
Q

What is a centre question in understanding object recognition?

A

what features do we identify to specific objects e.g. stick men and women

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6
Q

What is the hierarchy of object recognition?

A
  1. Detection of edges
  2. Detection of combination of edges and contours
  3. Detection of object parts i.e.face
  4. Detection of objects from one point of view
  5. View-invariant object detection
  6. Categorisation (human, animal etc.)
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7
Q

What increases as object recognition hierarchy increases?

A
  1. Complexity
  2. The receptive field size of neurons along the ventral stream
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8
Q

What are present at the top of the visual pathway?

A

Neurons that respond to more complex features e.g. the presentation of certain objects

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9
Q

Describe the structure of the Lateral Geniculate Nucleus (LGN)

A
  • Contains 6 layers
  • All layers receive input from the ganglion cells but two of them receive information from magnocellular cells and 4 of the layers receive information from parvocellular cells
  • Layers alternate with visual input from left/right eye
  • Ganglion cell axons make 1:1 connections with LGN projection neurons
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10
Q

What is the difference between parvocellular and magnocellular cells?

A

Parvocellular = object recognition
Magnocellular = stimulus recognition and speed etc.

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11
Q

Where does most of the input to the LGN come from?

A

V1 cortex, 60% of input comes from the V1 cortex rather than the retina

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12
Q

Where does information go once its been in the LGN?

A

V1 cortex where it can go into the Dorsal root ‘where’ pathway or the ventral root ‘what’ pathway

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13
Q

Describe the cortical layers

A
  • 6 of them too with ocular dominance columns and orientation columns
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14
Q

How are ocular dominance columns found?

A
  • injecting radioactive substances into one of the eyes you see alternate layering
  • radioactive part showing receives input from one eye and the other receives input from the other eye
  • can also inject radioactive glucose in the cortex and stimulate one eye with light
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15
Q

What is a Blob?

A
  • Stained by cytochrome oxidase
  • Process information about colour
  • Receive input from Parvocellular cells of the LGN
  • Not orientation-selective
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16
Q

What are Columnar orientation columns?

A

Different neurons respond to different orientations
- Within each orientation column, neurons have similar orientation preferences, meaning they respond most strongly to visual stimuli with specific orientations
- Neurons within orientation columns detect specific visual features (edges or lines) aligned with their preferred orientation.

17
Q

Where are the columnar orientation columns and how can you experimentally test them?

A
  • In v1 cortex
  • Stimulating visual system using recording electrode when exposed to certain stimulus
  • Turning the orientation leads to less AP fired in certain parts of the brain
  • The cells that fire AP are called ‘simple cells’ located in layers 4 and 6
18
Q

What are simple cells?

A

located along orientation columns which all respond to the same of the orientation which changes depending on the column

(e..g one column responds to a horizontal bar)

19
Q

What is the difference between the receptive field in the cortex and the receptive field in the retina?

A

Retina = Small and round
Cortex = Longer

20
Q

What is a hypercomplex cell?

A
  • When bar turns in to something more complex, hypercomplex cell activates
  • If the bar goes out of the receptive field the cells stop responding as the bar starts to activate inhibitory surroundings
20
Q

What is a complex cell?

A
  • RESPOND TO BARS PRESENTED IN ANY PART OF THE RECEPTIVE FIELD , more based on orientation
  • Layers 3,4 and 5
  • Input is the simple cells , complex cells receive input from many simple cells with similar orientation
  • Bigger receptive field
21
Q

What is the pattern of what happens in the receptive fields further and further downstream of V1?

A
  • Increase in complexity
  • Receptive fields increase in size
22
Q

Where are face sensitive neurons and how do we know they are face sensitive?

A
  • Temporal lobe
    The temporal lobe responds less when you remove specific facial features
23
Q

How do we use electrodes to study brain stimulation?

A
  • Use electrode in patients that already need them on their brain anyway e.g. epileptic patients
24
Q

What is the Jeniffer Aniston neuron?

A
  • Concept that certain neurons respond to specific faces e.g. there is a specific neuron that recognises Jennifer Aniston’s face in several patients
25
Q

What do the studies regarding face-specific neurons not take into account?

A
  • Feedbacks from higher cortical areas (top-down regulation)
  • Pre AND post synaptic responses , difficult as it means lots of electrodes
26
Q

What are saccadic movements?

A

moving our eyes around an object to recognise the whole thing

27
Q

What is the orienting reflex?

A

Turning eyes/head to get a holistic view of the stimulus and so the source of the sound is projected on to the fovea

28
Q

Why do we need motion anticipation?

A

The process of a photoreceptor being activated takes 60ms so when we see an object it was the object 60ms ago
Involves:
1. Retina (specifically RGCs)
2. Areas of cortex dorsal stream
3. Superior and inferior colliculus for the orienting reflex

29
Q

What is the role of the superior colliculus?

A

-Received input from ganglion cells, the auditory system and the somatosensory system
- Regulation of saccadic movements (moving eyes towards stimulus)

30
Q

What is the experimental evidence for the role of the superior colliculus?

A
  • If a cat sees a stimulus it orients itself towards the stimulus
  • If you ablate the SC in a cat, the cat is not able to perform this task
31
Q

What is the structure of the Superior colliculus?

A

Retinotopic organisation = neighbouring cells in the retina feed info to neighbouring places in the SC
- Diff. layers receive input from different brain areas: retina, somatosensory cortex, visual cortex etc

32
Q

What is the structure similar to the Superior colliculus referred to in fish and what does it do?

A

Optic tectum
- Neurons from different parts of the tectum send projections to motor neurons which tell them which degree to turn

33
Q

What is the dorsal stream responsible for?

A

The perception of motion

34
Q

How does motion detection and direction selectivity happen?

A

ON/OFF cells asymmetric morphologies where dendrites only extend in one direction
- Receive excitatory input from bipolar cells and inhibitory from amacrine
- In preferred direction excitation>inhibition

So light in preferred direction = excitatory input to Direction sensitive ganglion cells from bipolar and photoreceptors, the DSGCs which are not in the rpeferred direction are inhibited
movement in the preferred direction results in a more synchronized and robust excitatory signal along the dendrites of the DSGCs.
Like the DSGCs dendrities are towards the direction they are preferrential to

Neural Circuits (9 decks)

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