Parallel Processing Flashcards
Difference between parallel processing and serial processing
Serial is sequential and parallel is running side by side
What are all of the systems that go to the LGN in parallel
Magno cells -2 most ventral layers Parvo cells -4 most dorsal Konio cells -interlaminar regions -between principal layers -smallest of 3 LGN
Where does LGN project to
Primarily to visual cortex
What is the smallest of the 3 LGN cells
Konio
Parvo cells are sensitive to _____
R/G color contrast
- not sensitive to movement
- 70% of retinogeniculate pathway
70% of th retinogeniculate pathway
Parvo
Magno cells are sensitive to
Rapid movement
- 10% of retinogeniculate pathway
- mostly monochromatic
- rods primarily feed into the magno pathway
10% of the retinogeniculate pathway
Magno
Konio cells respond to _____
B/Y color contrast
Cortical projection of parvo neurons
4Cb
Cortical projections of magno neurons
4Ca
Both parvo and konio neurons are characterized by
Color oppnency
- They are excited by cortina wavelengths and inhibited by others
- the sign of the response (excitatory or inhibitory) encodes info about the stimulus wavelength
- these cells play critical role in wavelength based discrimination
These cells play a critical role in wavelength based discrimination
Parvo and konio
Many cells in parvo layers manifest
R-G opponency
-input from the midget ganglion cells
Input to the parvocellualr layers
Midget ganglion cells
Konio cells exhibit ____ opponency
Blue yellow
Input to konio presumed to originate from
Small bistratisfied ganglion cells
Onion cells confined to the interlaminar regions of the LGN
May not be confined
- certain cells in the parvocellualr region of the LGN manifest B-Y properties
- unknown if these are true parvo cells or konio cels
Show weak or no color opponency
Magno cells
- generally give a response of the same sign (regardless of the stimulus wavelength)
- not capable of contributing significantly to wavelength based discriminations
Temporal properties of parvo
Sustained response to long-duration stimulus
Temporal properties of magno
- transient response to long-duration stimulus
- brief burst of activity at onset and offset
- may be due to input from transient amacrine cells
Spatial properties of parvo
S-spatial properties similar to retinal midget cells
-smaller receptive field centers provide higher spatial resolution
Spatial properties for magno
- spatial properties similar to retinal parasol cells
- larger diamter axons transmit APs faster than konio or parvo (Myelin)
- stimuli that isolate magno pathway have shorter visual latency than those that isolate parvo or konio pathways
What system has larger diameter axons to allow for faster transmitting of APs?
Magno
The division of parvo and magno in the retinogenicualte pathway
The clear division into distinct parvo and magno pathways seen in the retinogeniculate pathway is not so apparent in the cortex
-parvo and magno retinogenicualte pathways may be the predominant inputs to the cortical ventral and dorsal processing streams
May be the predominant inputs to the cortical ventral and dorsal processing streams
Parvo and magno
Magno and parvo communicating with cortical processing stream
Neither retinogenicualte pathway appears to communicate exclusively with a particular cortical processing stream
Lesion in the parvocellualr region of LGN
- vision altered in predictable manner
- reduced wavelength discrimination
- reduced high spatial frequency contrast sensitivity
- detection of high temporal frequency flicker and other visual capabilities remain unaltered
Lesion in magnocellualr region of LGN
- reduction of high temporal frequency flicker
- reduction of low spatial frequency contrast sensitivity
- unaltered wavelength discrimination
- unaltered high spatial frequency contrast sensitivity
This pathway is key to color discrimination and vVA
Parvo pathway
This system encodes fast movements and low spatial frequencies
Magno
Isoluminant gratings
- bars of varying chromaticities
- same luminance
- may isolate the parvo system
- bars are visible only due to chromatic contrast
Why isoluminant gratings isolate the parvo system
- spectral Sensitivity of a magano neuron is similar in form to the photopic luminance function
- a green bar of the isoluminant grating activates a magno cell to the same extent as a red bar
- border formed by the bars become invisible to the magno cell
- the magno pathway is “silenced” by isoluminant stimuli
- the perceptual distortions noted when viewing isoluminant stimuli-for instance, abnormal motion perception- are consistent with reduced magno contribution
Why is the isoluminant grating strategy limited?
- spectral sensitivity of magno cells varies slightly from cell to cell
- therefore unlikely that isoluminant stimuli silcene all magno neurons
- perceptions obtained using isoluminant stimuli proabably do not reflect the parvo system in isolation
Do the isoluminant gratings isolate the parvo systems?
Mostly, not 100%
Diseases and parvo, magno, konio
Certain disease can impact different pathways
- noninvasive psychophysical produces could be useful for their early and differential diagnosis
- procedures must isolate these pathways
Dx of glaucoma
- VF loss
- ONH appearance
- IOP
- VF loss already indicates a substantial proportion of ganglion cells have died
May lead to blindness
Early treatment delays progression of visual loss
Key to preventing vision loss in glaucoma
Treat early
Autopsies of POAG reveals what
Axons of larger neurons are damaged earlier than those of smaller neurons (Magno)
Which pathway is more susceptible to glaucoma damage>/
Magno
Tests to look at magno pathway in glaucoma
Frequency doubling
Healthy patient in frequency doubling
As temporal rate is increased, the patient will note the apparent spatial freqnwcy of the grating doubles
PAOG and frequency doubling
Ledimpaired
-led to the adoption of frequency doubling tech as a clinical tool
Original FDT perimeter threshold testing
- employed a four-reversal staircase procedure known as the modified binary search algorithm (MOBS)
- contrast increased until a stimulus is detected
- contrast is decreased if the stimulus is detected at a higher level
N30-1 screening test
- presents stimuli that can be detected by 99% of normal population
- if initial target not detected, it will be repeated
- if again not detected, it will be presented at a level detected by 99.5% of the normal population
- if thus target is not seen the stimulus is presented as max contrast
- sensitivity for the N30-1 test is been reported to be 78-92% and specificity between 85-100%
- the high specificity associated with this test suggests it may be useful option for large population
Why is N30-1 good for screening
High sensitivity
N30-5
Diagnosis and following glaucoma
- first stimuli presented at 95%
- repeated if not detected
- if not still, presented one that is detected by 98%, then 99% detection level
- 30s per eye
High sensitivity better for detecting VF loss for glaucoma
Humphrey matrix 800
- for early VF loss detection
- people fall asleep easily
- detects damage to M cells (magno)
- fast and easy
- doesn’t need dark room, no trial lenses or eye patches
- small
Tests with high contrasts targets are more specific for
Detecting patients with VF defects
Tests with lower contrast levels
Are more sensitive
Physiological underpinnings of FDT
Based on assumptions
- could find no characteristics of the magno cell neural response that could account for frequency doubling
- dont know why or how it works, but it does
Dyslexia
- selective impairment of reading skills in spite of normal
- intelligence
- vision
- hearing
- instruction
- motivation
Origins of dyslexia
Remain controversial
- prevailing view: primarily cognitive disorder
- there are some who believe it is due to sensory defects
Dyslexia and temporal information
Deficits in it
- magno
- flicker fusion rates abnormalities
