Week 5 Flashcards
What is the lateral geniculate nuclei
90% if fibres terminate here in primates
Pathway responsible for conscious visual attention
Retinal input to LGN accounts for 10% of synapses
Visual cortical feedback accounts for 30% of synapses
How many layers does the LGN have
6
what are the 6 layers seperated into
Parvo + Magno
Konio
What are the Magno layers
1+ 2 layers = larger cells
What are the Parvo layers
3 + 4+ 5 + 6 = smaller cells
What are the Konio cell layer
interlayers
even smaller cells
koniocells
Which are the contralateral eye fibres
1, 4, 6 layers
What are ipsilateral eye fibres
2, 3, 5 layers
what is the purpose for the LGN
-Important regulatory function
-Regulates strength of signals sent to cortex and pre-sorts info into significant streams
-Amplify differences in illumination ie. Edge and contrast
-Emphasise sudden changes in simulation
-Integrate across large retinal areas
What is the superior colliulus
multisensory midbrain structure
controls:
Integration of visual and auditory signals
Direction of visual attention
What are Parvo cells
and what they do
-Colour opponent – differentially sensitive to colour - red/green pathway
-Retinal fields are 2-3x smaller than magno cells
-Important for analysing spatial detail
What are Magno cells
and what they do
-Cells not differentially affected by colour
-Response depends on relative intensity of centre and surround
-Respond vigorously to fast abrupt fluctuations in light intensity within their RFs
What are Konio cells
and what they do
Colour opponent – differentially sensitive to colour – blue/yellow pathway
Some respond to sound and touch as well as visual stimulation
What is the Vision cortex (V1)
Primary visual cortex
Anatomically split into 6 layers
What is layer 4 of the visual cortex
4a + 4b + 4c
What is Layer 4c of the Visual Cortex
Layer 4c: 4calpha + 4cbeta
Most input arrives in layer 4c
Magnocellular pathway terminates in 4calpha
Parvocellular pathway terminates in 4cbeta
what are VEPs
visual evoked potentials
Microelectrode methods cannot be used routinely to record from single neurones in human visual cortex
VEP can be recorded using small leads attached to the scalp (special conductive cream)
These are non-invasive
How VEPs conducted
- VEPs can be regarded as an objective analogue of psychophysical detection
- Can be recorded whilst participant views specific stimuli e.g. size colour
- Electrical potentials arise from activities of neurones in V1 and recorded from the occipital cortex:
1. Standard electrode positioning
2. Standard stimuli
Why use VEP
Provide info about visual processing
Objectively monitor visual maturation in babies and children
Detect pathology in children and adults
Patient whom you refer to the hospital may end up having visual electrophysiology
What is Optic Neuritis
-Inflammatory demyelination of optic nerve fibres
-Slowing down of conduction velocity
-Increased latency of P100
-May be associated with multiple scleosis
