Unit 4 Notes Flashcards
stroke
- brain cells suddenly die because of lack of oxygen
- caused by hemorrhage or ischemia
hemorrhage stroke
-weakened or ruptured blood vessel leaks into surrounding brain
ischemia stroke
- obstruction within blood vessel leading to brain
- blockage
prevalence of stroke
-most prevalent in southern US b/c of unhealthy eating
photoreceptors
- detect light and convert into neural impulses
- release nts in response to light detection
- align retina
- pint toward back of head
ganglion cells
- transmit info from retina to thalamus (LGN)
- have long axons that extend to the brain
- axons from the optic chiasm, optic nerve, and optic tract
rods
- detect dim light
- no color vision
- poor resolution
- don’t give a ton of info
cones
- color vision
- high acuity b/c neurons linked one to one
- dense in fovea
fovea
- back of eye at center of retina
- responsible for sharp central vision
- dense with cones
cortical representation of fovea
- cortical magnification of fovea even though it is a small structure
- suggest abundance of photoreceptors (large receptive field)
- makes sense b/c of fovea role in sharp vision
why no blood vessels near fovea
-light can’t penetrate through blood vessels to hit photoreceptors
receptive field
-region of space in which the presence of stimuli will alter the firing of neurons
tapetum lucidum
- night vision
- layer of tissue behind retina reflects light back to photoreceptors increasing availability of stimulus
right and left
- right side of each retina projects to right cerebral hemisphere
- left side of each retina projects to left hem.
- right side of each retina receives image of visual world on left side of the head
- left side of each retina receives visual world on right side of head
nasal retina
- part of retinal closest to nasal bones
- visual info that crosses and travels contralaterally to cortex
temporal retina
- part of retina nearest to temporal bone
- visual info that travels ipsilaterally to cortex
optic tract
-continuation of optic nerve that runs from optic chiasm to LGN
optic chiasm
- where optic nerves partially cross
- images of nasal retinal cross
- images of temporal retina do not
- half of tracts cross; half don’t
optic nerve
- transmits info from retina to brain
- cranial nerve II
- considered part of CNS
- myelinated axons
lateral geniculate
- primary relay center for visual info received from retina
- located in thalamus
ipsilateral eye projections
-hit LGN layers 5, 3, and 2
contralateral eye projections
-hit LGN layers 6, 4, and 1
magnocellular layer LGN
- LGN layers 1 and 2
- large cells with large receptive fields
- respond to movement, depth, and contrast
- rods
parvocellular layer LGN
- LGN layers 3-6
- small cells with small receptive fields
- respond to position and color
- cones
koniocellular layer LGN
- zone of small cells between M and P layers of LGN
- provide visual cortex with info about short wavelength color (blue)
on center cell responses
- ) central illumination
- ) annular illumination
- ) diffuse illumination
central illumination
-on center cells respond best when spot of light shone onto central part of receptive field
annular illumination
- on center response followed by light shone on surrounding area
- suppresses discharges of on center cells
- discharges restored when surround turned off
diffuse illumination
- illumination of entire receptive field
- weak discharge becuse center and surround antagonize each other’s effects
optic disk
- where ganglion axons exit eye and converge to form optic nerve
- no rods or cones present
- “blind spot”
- beginning of optic nerve
- entry point for major blood vessels that supply the eye
off center cell responses
- neuron excited when light shone onto surrounding of off-center receptive field
- once activated by on surround, response slows or stops when central area of field is illuminated
- restore signaling when central field is turned off
hermann grid
- grey blobs perceived at intersections of white grid on black background
- blobs disappear when looking directly at intersection
- optical illusion caused by lateral inhibition
lateral inhibition
- capacity of excited neuron to reduce activity of its neighbors
- sharpens response to localized stimulus- contrast
- rods at center of stimulus send “light” signals to brain
- rods in periphery of stimulus send “dark” signals to brain
area 17 (V1)
- primary visual field
- located posteriorly in occipital lobe
- striate cortex- myelinated axons visible
- processes info about static and moving objects
- pattern processing
- 6 layers
part of retina detecting right visual field
- left temporal
- right nasal
part of retina detecting left visual field
- right temporal
- left nasal
retinotopic maps
- info from 6 layers of LGN maintain topography when traveling to 6 layers of area 17
- integration of info from many neurons
- increase in complexity of processing further into cortex
damage to right LGN
-become blind in left visual field (right temporal and left nasal)
notable thing about human visual cortex
- subdivision of layer 4
- where most LGN fibers end
4C alpha and 4B layer of visual cortex
-receive input from magnocellular layers of LGN
circle of Willis
- vascular structure under brain
- common location of aneurism
- arrangement of arteries creates redundancies, which allows for vascular “back-up” if an artery were to become blocked
aneurysm
- abnormal widening or ballooning of portion of an artery due to weakness of the vessel wall
- dangerous if ruptures
pituitary tumor
- midline structure
- tumor puts pressure on middle of optic chiasm
- suppresses nasal retina input
- limits peripheral vision b/c nasal detects lateral vision
- pituitary also secrets prolactin, so abnormal levels would indicate
layer IV C of striate cortex
- innervates superficial (higher layers)- II and III
- binocular processing (info from both eyes) begins
ocular dominance columns
- portions of visual cortex that get input from one one verses the other
- variation in eye preference
- observable with radioactive tracer injected into animal eye and carried from retina to LGN to cortex
- cells in one layer of LGN project to aggregates of target cells in layer 4 that are separate from those supplied by the other eye
what generates ocular dominance columns
-axons from LGN segregation and crossing after layer IV of cortex
orientation selectivity
- simple cells of striate cortex respond to certain orientation of bars of light
- setting up edge detection
simple cells
- found mainly in layers 4 and 6 of visual cortex
- respond to pattern of light in certain orientation in a small receptive field
- each cell has distinct and specific response
- degree of response dependent on bar of light width and angle orientation
cortical fields derived from fovea
-most excited by narrower bars of light b/c “represents” an on-center stimuli and of center surround
orientation pinwheels
- range of different orientations that drive cells maximally
- orientation organization laid on top of visual dominance patterns
- each portion of cortex sensitive to certain orientation
- visual cortex has LOTS of organized layers
synthesis of simple cell get receptive field
- produced from convergence of inputs from LGN neurons
- LGN neurons have receptive fields in retina that are aligned identical to receptive fields of simple cells in cortex
- LGN cells that project to particular simple cell in particular fashion that simple cell is sensitive to
- get receptive fields from many LGN cells
4C beta and 4A of visual cortex
-receive input from parvocelluar LGN
complex cells
- in layers 2, 3, 5, and 6
- receive input from the simple cells
- sensitive to orientation of light/dark border (edges)
binocular fusion
-simple cells in visual cortex respond to similar visual stimuli in either eye
demonstrating ocular dominance columns
- destroy small group of cells in one layer of the LGN and examine cortex for degenerating terminals
- can also be changed by removing eye
- eye or LGN cells that are still there has an increase in ocular dominance
haptic sense
- recognizing objects through touch
- complex task further downstream in cortex
complex cells and importance of orientation
- cells are sensitive to specific edge (ex: horizontal, vertical, etc)
- if completely invert stimulus, cell has inhibitory response as opposed to excitatory
complex cells and relative unimportance of position
-cell responds vigorously to every vertically oriented edge, no matter where in the receptive field
end stopping
- cells respond more vigorously when whole stimulus fits in receptive field
- if extend beyond receptive field, don’t fire as much
- back edge of stimulus causes cell to respond more vigorously
simple and complex example
- multiple simple cells respond to vertical line (in specific position)
- all vertical simple cell projections lead to single complex cells
- target complex cells respond best to any vertical line within its receptive field
binocular cells
- first see in visual cortex superficial to layer 4
- where integration of two eyes is occuring
beyond striate cortex pathways
- ) dorsal stream
- ) ventral stream
* outer layers of brain
dorsal stream
- focused on spatial processing
- how things are moving around
- where things are in space
- “where” pathway
- V1, V2, V3, MT, other dorsal areas
ventral stream
- focused on object shape and color
- “what” pathway
- recognizing face
- V1, V2, V3, V4, IT, other ventral areas
- DON’T process motion
originate at V1
- > V2 -> V3 -> MT or V4
- if MT -> MST -> dorsal areas
- if V4 -> IT -> ventral ventral areas
MT
- middle temporal (V5)
- critical area in primates for processing visual motion
lesion to MT
- extreme difficulty perceiving motion
- snapshots, rather than fluid motion
- every now and then new view
- really choppy
- Ex: overshoot when pouring coffee
MST
- medial superior temporal
- getting most input in MT
- role in visual motion and navigation
- involved in optic flow
IT
- inferior temporal cortex
- complex objects
- face recognition
V4
- big role in color
- simple geometric objects
optic flow
- things flowing past eyes
- generated as you are moving
- shifts if turning
why see ground move when playing guitar hero
- during play MST is fired up (optic flow)
- even when stimulus stops, MST still active for a bit
- habituation- habitual activity with MST, so don’t notice optic flow
para-hypocampal place area (PPA)
- area of brain that identifies landmarks
- experiment with response to houses
- ventral stream structure
fusiform face area
- behind PPA
- recognize faces
- ventral stream structure
grandmother cells
- hypothetical neuron that represents a complex but specific concept or object
- activated when person see or hears
- sensibly discriminates
- big role in face recognitions
vision
- perception combines individually identified properties of visual objects
- achieved by simultaneous parallel processing of visual pathways
parallel processing
- ability to carry out multiple operations or tasks simultaneous
- ability of brain to divide and interpret visual input by color, motion, shape, and depth
MEG
- used to identify zones of activity
- sensitive machine that detects tiny brain waves
MUA
- multi unit activity
- used to identify receptive fields
- rarely used in humans b/c requires sticking electrode in brain
EEG
-focuses on surface of brain activity
fMRI at rest with eyes closed
- how much of brain using when doing absolutely nothing
- brain is still very active
- already using more than 10% doing nothing
- at rest using 15% of brain
fMRI when telling traumatic story out loud
- trying to see all of brain firing at once
- frontal, temporal, limbic, and occipital firing
- using 30% of brain
to determine importance of structure
- ) correlation
- ) necessity
- ) sufficiency- can it generate behavior by itself
neurons and behavior
-is there a correlation between activity and behavior
large giant interneuron
-role in flip behavior response to sneaking up on crawdad
limitation of fMRI
-can’t see individual neurons
