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(2) Tri A Visual Neuro > UMA’s summaries > Flashcards

UMA’s summaries Flashcards

1
Q

What is the retinal cellular pathways and the cells involved?

A

• VERTICAL PATHWAY (light to photoreceptor > bipolar cell > ganglion cell)
• HORIZONTAL (horizontal & amacrine cells)
• INTEGRATOR NEURONS: bipolar, horizontal, amacrine, ganglion

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2
Q

What are receptive fields and how do they present in the retina?

A

• Each neuron of retina covers an area in your field of vision.
• Receptive field = area in space where appropriate stimulus will modify activity of a neuron
• Towards the periphery - receptive fields larger & less specific
• Deeper layers of retina - more complex receptive field

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3
Q

How do photoreceptors activate and how do they converge?

A

• Photoreceptors are always hyperpolarised by light & depolarised by dark
• 130 million photoreceptors converge to RCG
• 1:1 at fovea, 500:1 periphery

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4
Q

What are rods? How do they work?

A

• Periphery
• Smaller than cones
• Scotopic conditions - no colour
• Hyperpolarise to DIM light - saturate quickly
• There are more rods than cones - more redundancy
• Spatial summation - photons don’t need to go to a specific rod to activate ganglion cell

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5
Q

Cone photoreceptors:

A

• Larger - 3 types: S, M L wavelength
• Fovea
• Hyperpolarise to brighter light (photopic)
• Less sensitive - saturate 2 log units slower
• Cones are only ‘on’ (hyperpolarising)
• Cones do not have centre surround organisation

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6
Q

What are the types of horizontal cells? What is their purpose ?

A

• Anatomical types: H1, H2, H3
• Receive input from R+C and make adjustments
• Provide surround information to bipolar cells
• Connect laterally
• INHIBITORY in nature, inhibit other cells selectively suppress signals (lateral inhibition)
• Purpose: only highest intensity output gets through which increases contrast and visual definition
• Communication in OPL, bodies in INL

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7
Q

What are Bipolar cells?

A

• Receive signals from photoreceptors
• Hyperpolarisation of photoreceptor = depolarisation of bipolar cell (inhibitory nature of synapse between them)
• Dendrites in OPL, axons IPL
• CONVERGENCE - signal neuron (bipolar or horizontal) collects info from more than one photoreceptor.

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8
Q

What are receptive fields?

A

• Circular
• Centre/surround, on/off

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9
Q

What are on centre cells?

A

• Light applied to centre = excitatory effect = depolarised (less negative)
• Light falls on surround = inhibitory effect = hyperpolarised (more negative)
• (cone in synapses with hyperpolarised, ON-centre bipolar cell depolarises)

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10
Q

What are off centre cells?

A

• Light applied to centre = inhibitory effect = hyperpolarisation
• Light falls on surround = excitatory effect = depolarisation
• Inhibited by light, excited by darkness

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11
Q

What are amacrine cells?

A

• Receive signals from bipolar cells & are involved in regulation/integration of bipolar and ganglion cells
• Functions of integrating ganglion cell output
• Excited by bipolar cells

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12
Q

What are ganglion cells?

A

• Do not absorb light - process neural information
• GC long axons = optic nerve
• End of intra-retinal processing, beginning of output to V1
• Small 1 million % contribute little/nothing to vision - neural information - circadian rhythms, pupils

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13
Q

ganglion receptive fields:

A

• Tightly fixed in space
• Mostly linear - wont response to light outside area of receptive field
• They do not have orientation selectivity

• Concentric
• ON/OFF centre - respond by increasing or decrease frequency of action potentials
(NOT by de/hyperpolarisation)
• DEPOLARISATION of bipolar cell = EXCITES ganglion cell = INCREASED firing rate of action potentials
• HYPERPOLARISATION of bipolar = INHIBITS ganglion cell = DECREASED firing rate

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14
Q

How are ganglion cells classified?

A

• Within the retina there are ganglion cells, which are classified based on their structural and anatomical physiological basis.

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15
Q

What are the two stream pathways?

A

• Y CELLS = Midget cells (P-CELLS) = > Parvocellular layer of LGN = > Ventral stream = Detail
• X-CELLS = Parasol (M-CELLS) = > Magnocellular layer of LGN = > Dorsal stream = Where

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16
Q

Y/P cells:

A

• Central retina - fovea
• Linear summation
• 80%
• Slow, sustained response (slow for detail)
• Small receptive fields (midget = small)
• Colour opponency, image detail

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17
Q

Best way to remember Parvocellular pathway

A

• Midget = small receptive fields for small detail
• P-cells = parvo = pardon = what stream, v in parvo = ventral
• Need more of these small cells so we can see lots of detail - detailed work in fovea
• Parvocellular pathway caries info from small RCGs > LGN (layers 3,4,5,6) > V1

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18
Q

What are X-cells/M-Cells?

A

• More peripheral retina
• Non-linear summation
• 10%
• Fast, transient response
• Parasol = large dendritic fields, complex
• Movement, achromatic

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19
Q

Tips to remember magnocellular pathway

A

• Parasol cells = large receptive field like a parasol
• M-cells = magna = motion = dorsal MD makes u move about so motion)
• Large receptive fields as motion over large area in periphery
• Magnocellular pathway carries info from large RCGs > LGN (layers 1&2) > V1

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20
Q

What are K cells/W cells?

A

• Don’t fit into X/Y categories
• Non-concentric receptive fields
• More common in lower animals

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21
Q

What experiment was done to map out ON-OFF regions of RF ganglion cells?

A

• Anaesthetised animal set up with viewing screen, where small lights can he flashed
• Extracellular single unit electrode inserted into animals optic nerve, which records action potentials
• Electrode connected to amplifier, which feeds amplified signals an oscilloscope, for viewing the signal, an audio amplifier for listening and recording action potentials

• Small spots of light were flashed at various locations and their direct effect on cells spontaneous firing rate was assessed
• If firing rate increased when light is flashed, that location is considered ON part of receptive field
• It firing rate decreased, considered OFF part of receptive field

From recording these locations, one can construct a receptive field

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22
Q

Why is retinal processing needed?

A

RETINAL PROCESSING is needed to adjust the gain of the retina (make pupil bigger), and code information for efficient transmission to the brain.

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23
Q

What are the 6 steps in post retinal processing?

A
  1. GANGLION CELLS leave retina at OD
  2. ON crosses at chiasm (nasal cross to opposite sides, temporal remain uncrossed)
  3. Axons are now part of the OPTIC TRACT
  4. Most axons from optic tract terminate in LGN (visual part of thalamus)
    - Axons can also project to SUPERIOR COLLICULUS in midbrain (rapid eye movement), SUPERCHIASMATIC NUCLEUS of the hypothalamus for circadian rhythms.
  5. Most axons from LGN > OPTIC RADIATIONS
  6. OPTIC RADIATIONS > PRIMARY VISUAL CORTEX (cerebral cortex)
    a. Axons with info about superior VF = occipital lobe via Meyers loop
    b. Axons with info about inferior VF = parietal cortex
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24
Q

Describe the LGN

A

LGN (LATERAL GENICULATE NUCLEUS)
• Located in the posterior end of the thalamus

• Gets info from optic tract
• Sends input to V1

• LGN is a relay station for all sensory signals on their way to the cerebral cortex
• Introduces coding efficiencies by cancelling out redundant info from the retina
• Helps visual system focus on most important info & can direct us to points in space

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25
Q

What are the layers of the LGN and the differentiations?

A

• 6 layers (laminae) - each layer contains a retinotopic map of half the VF
- Layers 1,4,6 = contralateral eye (opposite eye - nasal input)
- Layers 2,3,5 = ipsilateral eye (same eye - temporal input)

• M CELL bodies in layer 1+2 = large (magnocellular bodies, parasol) bottom = where
• P CELL bodies layers 3,4,5,6 = small (parvocellular bodies, midget) top = detail

• More dorsal (top) LGN = controls how much of the signal gets to V1 - has inhibitory circuits

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26
Q

Tips for remembering which layers of LGN are magno and same eye input:

A

• Magno = first 2 layers which are at the bottom
• Input from same side (uncrossed) = 2+3 = 5 which is right so its not crossed (ipsilateral)

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27
Q

What is the receptive field of the LGN??

A

• Large, concentric ON/OFF
• Stronger surround inhibition = cells amplify differences in luminance

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28
Q

midbrain’s structures important for visual processing:

A

• SUPERIOR COLLICULUS = orientation movements of eye towards objects, inter/motor sensory eye movements of head/eyes - no pattern analysis. Contains the retinotopic map.
- Receptive field= simple, ill-defined, centre surround, surround is strictly inhibitory
• Red nucleus, basal ganglia, cerebellum = coordinate movement

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29
Q

What, and where is the striate cortex?

A

• Striate cortex = part of the cerebral cortex which is responsible for processing visual information
• Location = calcarine fissure in occipital lobe
• The whole visual cortex takes up all of occipital lobe, inferior temporal lobe, parts of the parietal and frontal lobes (divided into ~ 30 interconnected regions after V1)

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30
Q

Where does the striate cortex receive inputs, and what does it analyse?

A

• Input to V1 - receives input directly from LGN
• Analyses = lines, spatial frequencies, direction, orientation (yet we perceive complex 3D images)

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31
Q

How is the retinotopic map represented in v1?

A

• V1 contains a retinotopic map
• Retinotopic organisation fovea represented at back of brain - overrepresented
• peripheral VF = more anterior location
• upper VF = more ventral

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32
Q

Columnar architecture in V1

A

• Orientation, directional selectively etc - eventually all this information goes to the extra striate cortex where images are formed from information which is integrated in the primary visual cortex.
• Electrode moves vertically, more neurons have same selectivity

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33
Q

Ocular dominance columns

A

• Cells from LGN layer will project to target cells in layer 4 (monocular) of V1
• Groups of cells form alternating stripes in layer 4
• Above & below layer 4 = most cells are driven binocularly
• Move electrode across the cortex, cells respond to left eye inputs, then binocular, then right eye, then binocular, then left eye etc

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34
Q

Orientation columns - V1

A

• Moving electrode in oblique direction, find cells selective for vertical, then diagonal, then horizontal etc
• In V1
- Electrode vertically = same selectivity.
- Electrode horizontally = cells respond best to RE, LE, binoc
- Electrode in oblique direction = orientation selectivity

35
Q

Hypercolumn - V1

A

• Chunk of cortex about 1mm square by 3mm thick that contains neurons, all with approximately the same receptive field location, but with different selectivity’s (direction, orientation, eye). These make of the structure of V1.

36
Q

Cells and units in V1

A

• Parvo and magno pathways are segregated into 3 independent units:

• Blobs - inputs from parvocellular layers of LGN, process colour
• Interblobs - input from parvocellular layers of LGN, process fine patterns
• Layer 4b - input from magnocellular layers of LGN, motion and very low contrast

• V1 = 6 layers - V4 thickest
• Three types of cells in V1 - some cells are directionally selective
- Simple cells
- Complex cells
- Hypercomplex cells

37
Q

Simple Cells

A

• Respond best to bars of light
• Respond to moving stimuli and flicker
• Orientation selective

• ON/OFF
• Monocular or binocular
• Length summation - greater response with increases bar length, at which point response plateaus

38
Q

Complex Cells

A

• Respond best to line orientation
• No ON/OFF subregions, spatially homogenous
• Mostly binocular
• Length summation
• Highly non-linear
• Can fire in response to stimuli in a comparatively wider region

39
Q

Hypercomplex cells

A

• Like complex, but inhibitory flanks at end of receptive field
• Responses increases with bar length, but then as bar is made longer, inhibited, END STOPPING

40
Q

What and where is parallel processing?

A

Parallel processing - simultaneous processing of visual information with different attributes in separate modules. V1 subcontracts information to extra striate areas. These areas process information regarding/relating to form, colour, motion and depth.

41
Q

What is the ventral stream?

A

VENTRAL STREAM = WHAT PATHWAY

X/P/MIDGET RCGs > PARVOCELLULAR LAYER OF LGN > VENTRAL STREAM for DETAIL

42
Q

What is the route of the ventral stream?

A

ROUTE OF THE VENTRAL STREAM:
• Striate cortex (V1) > ventrally > posterior temporal cortex
• Passes through areas V2 (thin) & V4, and sub regions of the inferior temporal cortex.

43
Q

What is the purpose of the ventral stream? Lesions?

A

PURPOSE
• Analysis of physical properties of an object (size, colour, texture, shape)
• Known as the “what” pathway since the responses of neurons more closely reflect the attributes of the visual stimuli (rather than its location & direction)

• Lesions in the inferior temporal cortex = failure to recognise previously represented previously present objects/faces
• Lesions in posterior temporal cortex = loss of pattern discrimination

44
Q

Summarise the dorsal stream?

A

DORSAL STREAM = WHERE PATHWAY
Y-CELLS = PARASOL CELLS (M-CELLS) = MAGNOCELLULAR LAYER OF LGN = DORSAL STREAM

45
Q

What is the route if the dorsal stream?

A

ROUTE
• V1 > dorsally > posterior parietal cortex
• Passes through MT (V5), MST and regions of the posterior parietal cortex

46
Q

What is the purpose of the dorsal stream? Lesion?

A

PURPOSE
• This pathway figures in the perception of spatial locations among objects & motion direction
• Lesions in posterior parietal cortex = inability to perform visually guided movement/inability to select a response location on the basis of a visual landmark

47
Q

What is Zeki’s 4 pathways for working in parallel?

A
  1. Colour: parvocellular V1 (blobs) - V2 - V4
    ( Parvo, ventral )
  2. Motion: magnocellular V1 (4B) - V2-MT
    (Magno, dorsal)
  3. Form system 1 = linked to P1 and colour V1 (blobs) - V2-V4
  4. Form system 2= linked to M1 and motion V1 (4B) V2-V3
48
Q

V2

A

• Ventral/parvo pathway
• 3 separate visual maps
• THICK stripes = visual ORIENTATION map (input form V1 layer 4b)
• THIN strips = COLOUR map (input form blobs of V1)
• INTERSTRIPES = DISPARITY map (stereopsis/depth) (input from V1 interblobs)

49
Q

V3

A

• Parallel part of the magnocellular system
• DORSAL stream

• Receives information from THICK stripes of V2, input is mainly from layer 4b of V1

• Dorsal (top) V3 = receives input & projects it to the posterior parietal cortex
• Ventral (bottom) V3 = stronger connections with inferior temporal cortex

50
Q

V4

A

• Nearly everything converges into V4
• 1st area in VENTRAL stream to show attentional modulation
• Orientation, spatial frequency, colour
• Objects of intermediate complexity, NOT complex patterns

51
Q

What is the inferno temporal cortex?

A

• Ventral/parvo pathway
• Main target for V4 neurons
• Essential for pattern recognition
• Some cells respond best to faces

52
Q

V5/MT?

A

• Magnocellular inputs, dorsal stream
• Input from V3 & thick stripes of V2 & 4b of V1 (directionally sensitive neurons)

• Cells respond to motion and depth
• Responds to any neuron moving in the right direction (responds to almost any pattern or contrast - NOT flicker

• Poor colour selectivity
• Transient
Columnar architecture - neurons with similar motion preferences near each other, orderly progression of motion direction
• RECEPTIVE FIELD: directionally sensitive, large RFs

53
Q

What is the MST?

A

• Medial superior temporal area
• Next to MT
• Large RF
• Respond selectively to complex optic flow fields: expansion, contraction & rotation
• Involved in 3D motion perception

54
Q

What are component cells?

A

COMPONENT CELLS: found in V1 and MT. They respond to single gratings moving in a preferred direction (e.g. horizontal to the right). They do not respond to plaids moving in a preferred direction (preferred component is absent.

55
Q

What are pattern cells?

A

PATTERN CELLS: found in MT only. They respond to overall plaids moving in a preferred direction. These cells do not respond well simply to components moving in preferred direction. Therefore, MT cells must respond well to pattern.

56
Q

Summary of the Parvocellular pathway?

A

• X/midget/p-cells > parvocellular layers of LGN (layers 3, 4, 5, 6)
• LGN feeds to the blobs of V1
• Ventral stream: V1 > V2 (thin) > V4 > IT > Posterior temporal cortex
• Detail - what stream

57
Q

Summary of the magnocellular pathway??

A

• Y/parasol/m-cells > magnocellular layers of LGN (layers 1, 2)
• LGN feeds to layer 4b of V1
• Dorsal stream: V1 > MT + MST > Posterior parietal cortex
• Motion - where stream

58
Q

What is the retinotopic map?

A

• Visual area of brain said to contain retinotopic map
• If VF (or hemifield) is mapped onto this region so that a stimulus in a restricted part of field activates, a restricted part of visual area forms a map; whose geometry corresponds although may he distorted

• Fovea is over represented, or periphery is underrepresented- to geometry of visual field

59
Q

What is the aperture problem?

A

• Each neuron on the visual system is sensitive to visual input in a small part of the visual field, as if each neuron is looking at the visual field through a small aperture.
- The motion of a contour across a small area (E.g. RF LGN or V1) provides ambiguous information about the contour’s movement. This means that a variety of contours of different orientations moving at different speeds can cause identical responses in a motion sensitive neuron in the visual system.
• Motion perception - cells in V5 which respond to moving object, are locally ambiguous, local info that they get and are giving is not clear - because there is not a whole picture i.e. they are looking through a small aperture

60
Q

What is the grandmother cell hypothesis’ evidence for and evidence against?

A

• Evidence for:
- cells in extra striate area do have more specific stimulus requirements.
- Cells have been found in the temporal cortex which respond to very specific stimuli such as faces, hands etc

• Evidence against:
- there can’t be a cell for every object we perceive, how would we be able to perceive new objects?
- Most extra-striate areas have reciprocal connections to lower areas. The output of feature detectors is ambiguous, the same firing rate can be produced by many different stimuli - disproving the theory

61
Q

What is blindsight, its and characteristics?

A

•Blindsight is the ability of people who are cortically blind due a lesion in V1, to respond to stimuli that they do not consciously see (and deny seeing)

• Characteristics: the ability to perform much better than chance on various visual tasks within the scotoma, but denying that he/she is consciously perceiving the stimuli
• Upon damage to the striate cortex, the LGN houses residual vision and sends signals straight to the striate cortex, bypassing V1. This could explain px’s responses to visual stimuli within the scotoma. An alternative explanation is linked to the collicular subcortical system.

62
Q

What is the normal human VF?

A

• (monocular) 60 degrees nasally, 70 degrees temporally. 70 degrees above and 80 degrees below the horizontal midline.
• The binocular field is the superimposition of the two monocular fields. The visual field is separated in R and L, or quadrants separated by the horizontal and vertical midlines. The macula corresponds to the central 17 degrees, and the fovea to the central 5.2 degrees.

63
Q

What is an EEG?

A

• Graphical depiction of cortical locations used to record electrical activity from the scalp

• Dipole = a pair of equal & oppositely charged/magnetized poles separated by distance; extracellular dipole is generated by excitatory post synaptic potential at dendrite apex

• High temporal resolution of cortical disorders
• Low spatial resolution of cortical disorders

• Used for diagnosis, prognosis & treatment of epilepsy
• Low cost

64
Q

What are the EGG waveform divisions?

A

There are 5 major frequency bands
1. GAMMA (30-100Hz) - learning & consciousness
2. BETA (14-30Hz) - action & alertness. Associated with movement control rhythms
3. ALPHA (8-12Hz) - relaxation. Signature resting rhythm of neurons
4. THETA (4-8Hz) - drowsiness/slipping into sleep
5. DELTA (0.1-4Hz) - deep sleep

65
Q

What are colour vision deficiencies?

A

• Ospin = a protein which forms part of the visual pigment rhodopsin and is released by the action of light
• Red & green opsins - X chromosome - this are why males are more affected by colour deficiencies that woman - males only have 1 X, females have 2
• Y-chromosomes do not carry opsin
• Blue opsin = chromosome 7
• Rhodopsin - expressed in rod photoreceptor cells - enables animals to see in dim light

66
Q

What are the differences between protan, deutan and tritan deficiencies?

A

• A protan has the longer wavelength cone photopigment missing or it is anomalous
• A deutan has the middle wavelength cone photopigment missing or it is anomalous
• A tritan has the shorter wavelength cone photopigment missing or it is anomalous.

• BLUE = SHORT = 490nm
• GREEN = MEDIUM = 540m
• RED = LONG = 700m

67
Q

What are the pattern of inheritance for colour deficiencies?

A

• The pattern of inheritance for deutan (red-green) CVD is sex-linked recessive while tritan CVD has an autosomal dominant inheritance.
(ope = missing, anomaly = anomalous - deviating from normal - reduced sensitivity)

68
Q

What are the different types of colour vision deficiencies?

A

Can be genetic or acquired (secondary to eye disease)
• Monochromacy
- Monochromats = typically totally colour blind, may have one cone pathway in addition to rod pathway
• Dichromacy
- Dichromats = cone pigment missing, therefore only 2 cone channels
• Anomalous trichromacy
- Anomalous trichromats = have all 3 cone pigments, however one cone pigment is anomalous having a shifted peak sensitivity

• Normal colour vision - Trichromates

69
Q

What are the % of population affected with colour vision difincies for males?

A

• Protan 1.3%
- Protanomaly 1.3%
• Deuteranopia 1.2%
- Deuteranomaly 5%
• Tritanopia 0.001%
- Tritanomaly 0.0001%

• Anomalous trichromacy 6.3%
• Dichromacy 2.4%

70
Q

What are the % of population affected with colour vision difincies for females?

A

• Protan 0.02%
- Protanomaly 0.02%
• Deuteranopia 0.01%
- Deuteranomaly 0.35%
• Tritanopia 0.03%
- Tritanomaly 0.0001%

• Anomalous trichromacy 0.37%
• Dichromacy 0.03%

71
Q

What area of the brain is affected, and what is:- Aphasia and Acalculia?

A

• Frontal Lobe

• Cant speak
• Cant understand numbers

72
Q

What area of the brain is affected, and what is:- Motion deficit

A

• M5/V5

73
Q

What area of the brain is affected, and what is:- Body Schema Disruption

A

• Parietal Lobe

• Disturbances or cognitive model about arrangement of body parts and spatial relationships to objects

74
Q

What area of the brain is affected, and what is:- Prosopagnosia

A

• Fusiform gyrus - part of temporal occipital lobe

• Inability to recognise faces

75
Q

What area of the brain is affected, and what is:- Achromatopsia

A

• V4, Occipital lobe

• Loss of colour perception

76
Q

What area of the brain is affected, and what is:- Simultanagnosia (ventral)

A

• Occipito-temporal lesion
• Inability to identify more than one object at a time

77
Q

What area of the brain is affected, and what is:- Simultanagnosia (dorsal)

A

• Occipito-parietal lesion

• May appear ‘blind’, motion may further impair their ability to perceive objects

78
Q

What area of the brain is affected, and what is:- Visual spatial disorders

A

• Lateral occipital gyrus
• Difficulty localising objects in space

79
Q

What area of the brain is affected, and what is:- Visual neglect

A

• Temporo-parietal junction and posterior parietal cortex

• Attention disorder that prevents the patient from attending to stimuli on one side

80
Q

What area of the brain is affected, and what is:- Motion blindness

A

• Mid temporal gyrus

• Cant perceive motion in VF

81
Q

What area of the brain is affected, and what is:- Balint’s syndrome?

A

• Posterior parietal cortex

• Clinical signs include : Simultanagnosia, ocular apraxia

82
Q

What area of the brain is affected, and what is:- Cortical blindness

A

• V1

• Total or partial loss of vision in a normal appearing eye caused by damage to brains occipital cortex

83
Q

What area of the brain is affected, and what is:- Blindsight

A

• V1

• Cortically blind, respond to visual stimuli that they do not see

84
Q

What area of the brain is affected, when unable to deal with spatial relations AND Inability to recognise objects?

A

• Dorsal (parietal) pathway
• Temporal (ventral) pathway

(2) Tri A Visual Neuro (2 decks)

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