Mod 2 - Liana Flashcards
Transcranial Magnetic Stimulation (TMS) over Primary Visual Cortex- effect?
Artificial V1 activation
- flash of white light
= phosphene
ecstasy user V1 excitability
negative correlation between frequency of use and threshold –> suggests ecstacy users have more excitable visual cortex
Sensory Integration
- combination of incoming info from multiple senses
- e.g. visual + hearing
- superior colliculus
- contains retinotopic map
- but also get incoming info from medial colliculus re auditory info
ventriloquist illusion
The ventriloquist illusion occurs due to the sound source being mislocalised towards a synchronous but spatially discrepant visual event (in this case, the puppets mouth moving).
- if a good puppeteer, we experience it as if sound is coming from the puppet, not the puppeteer
- visual system is very spatial acute, but auditory is not
- brain might decide based on visual, bc knows its more accurate
- same for movie, speakers on the side
MT (non-human primates) = V5 (humans), neurons have preference for:
- direction of motion
- speed of motion
What do the cortical Visual Pathways - dorsal and ventral - code for
- The dorsal stream codes motion and location = “where” pathway
- The ventral stream processes detailed stimulus features and object identity = “what” pathway?
V4
= colour and form = what (ventral stream)
cortical vs subcortical vision in humans
cortical = 90% of neurons project here (V1) - really important for humans,
conscious, phylogenetically newer
subcortical = 10% of neurons project here (superior colliculus), some is unconscious, phylogenetically older
in what layer of the superior colliculus are the neurons that receive information from the retinal ganglion cells located?
superficial layers
mapping on superior colliculus
- retinotopic
- y axis stretch across the top
- distorted, with more neurons for analysis of central vision
knockout cortical visual area on one side =
contralateral cortical blindness/neglect
sprague effect
lesioned subcortical visual area on opposite side to cortical visual area knockout
= started responding to both sides again
explanation of sprague effects
release of inhibition (cut inhibitory fibres) to subcortical area on same side as cortical damage = hyperactive = restored orientation
Visual cortex vs. superior colliculus damage - localisation (orient to sunflower seed) and discrimination tasks (maze to find hidden seed) - RESULTS AND CONCLUSION
- Cortical damage could do localisation task but not discrimination
- Subcortical damage could do discrimination but not localisation
= double dissociation = opposite results
Conclude: cortical for more complex tasks, subcortical for basic visual orienting
blindsight
- no conscious awareness of seeing a light but eyes moved towards where light was
- response was there, visual system working, so retinotectal pathway (subcortical)
blindsight experiment with distractor
- slower reaction time when distractor in blind hemifield
- this distraction effect would also increase reaction time for people with normal vision
Conclude: the subcortical visual pathway in humans may play an important role in orienting toward visual stimuli.
Unilateral damage to primary auditory cortex (A1) (compared to V1)
not nearly as devastating as damage to V1 bc neurons from ears project to both sides of the brain (bilateral projections)
EMG vs EOG
- Electromyography (EMG) records muscle activity
- Electrooculography (EOG) records movement of the eyes
where in SC are neurons for reflexive eye movement?
Deeper into the superior colliculus
types of cells/preferences for reflex movements in SC
Some cells are just visual or just motor, some are responsive/fire with both - important for integration of motor and visual systems
neurons have preferences for direction and distance of movement (amplitude) within the field
which way will eyes move if you stimulate cells deep in the R SC
left
mapping of occularmotor in SC
movement fields tend to code for eye movements into the same area of the visual field represented by the retinotopically organised visual receptive field of the neurons just above them in the superficial layers
smallest saccades = [central vision] = rostral SC
largest saccades = caudal SC
retinotopic map (superficial layer of SC) is info about central vision at top/rostral SC and info from peripheral vision at caudal SC
Effects of unilateral SC damage on reflexive saccades
- ipsi = moving towards hemi on same size as damage = same reaction time as control
- contra = movement opposite direction to damage = much slower, but could still move eyes
Fixation cells
these cells are more excited in fixation task, triggered by something in environment projecting onto central vision
Opponent processes in occularmotor reflexes?
fixation cells inhibited when saccade cells active, and vice versa
Fixation offset reflex
- faster movement when fixation stimulus disappears as peripheral stimulus presented
- fixation overlap trial = fixation cells firing more rapidly = more inhibition of movement cells = slower movement
fixation offset effect (FOE)
= indication of how strong your fixation reflex is
- big FOE = strong fixation reflex
TMS held over superior prefrontal cortex or superior parietal lobe, meausuring voluntary and reflexive eye movements
TMS causes temporary lesion - disrupts cell activity - inhibitory effect
- voluntary movement slowed down towards contralateral side as coil, not ipsi
- no significant change with parietal lobe stimulation, or reflexive eye movement
Frontal eye field
- frontal lobe, not part of primary motor strip
- receives visual information indirectly,
- also projects down to the SC in the brain stem
Damage to FEF
delayed voluntary eye movements contralesional
reflexive vs voluntary eye movements - speed
reflexive = a lot faster bc less circuitry, direct connection from retinal ganglion to superior colliculus
voluntary = slower bc more connections
visual control system at birth
At birth, cortico-subcortical projections aren’t fully developed (top down control)
Fixation offset effect for babies
- much slower to move eyes to target stimulus when overlap with fixation stimulus
- babies can get really locked on to central fixation — 1-2 mo especially
Anti saccade task
- look away from stimulus
- measure when reflexive (oops) and correct anti saccade movements
- lots of oops = problem with imposing this top down control, controlling reflexive
- get more accurate, faster as you get older as cortico-subcortical projections develop
Anti saccade task with people with damage to FEF on one side
- more reflexive eye movements contralesionally
- ipsilateral = all good
- hard time suppressing reflexive movements
Anti saccade task with healthy adult aging
- natural deterioration of brain tissue, particularly frontal lobe
- loose a bit of top down control as you age
- more mistakes, slower
covert attention
paying attention without making eye contact
EEG activity when covert attention directed at target
= stronger EEG activity
but note attending one part = neglecting another part
Cortical vs SC neurons in visual control
Cortical neurons important for voluntary movement of attention
Superior colliculus important for reflexive movements
Exogenous (cued) vs. Endogenous Movements of Attention
- can respond to asterisk faster when location cued → directs attention here
- for both endogenous and exogenous tasks
= attention helps facilitate search/behaviour
→ as long as cue is accurate
When cue followed by a long delay before asterisk…
- slows you way down
inhibition of return
inhibition of return
- reflexive attention
- inhibitory process to where you just searched so you don’t keep going back to the same guy in the banana costume when looking for your friend in yellow
- aids efficiency of attention/visual system
Flanker task
- test of cortical, top down mechanisms
- distractor above or below central item
- reaction times slower when distractor incongruent (indicates wrong response) rather than indicating correct (congruent) = flanker effect
flanker task with healthy aging
- show larger flanker effects - less able to ignore distraction
- links to higher car accident rate when older
prenatal developments - 3 steps
-
division
- stem cells
-
migration
- make its way along other cellular processes (glia) to where they will reside
- from inside out
-
differentiation
- can become neurons or glia, different types
formation of ocular dominance columns
over the course of early postnatal development, the inputs from the two eyes segregate into ocular dominance columns
rewiring of baby ferret’s brains so visual info to A1 – findings
- Retinotopic organisation in primary auditory cortex - single cell recordings
- Still responding normally to visual world
Experiment: TMS over V1 in blind and visually impaired people
- damage before LGN - so no brain damage (thalamus, V1 all OK)
- most with residual vision or previous visual experience reported phosphenes
- the 8 congenially blind participants did not
mental imagery in sighted and congenitally blind adults
- 6 congenially blind, 6 blindfolded seeing adults
- fMRI - subtraction condition = abstract words
- recorded activation of primary visual cortex in both groups
- for congenially blind people, mental imagery may be more based on touch, smell etc
Training & plasticity: A1 and M1
- more of brain responding when trained, compared to untrained
- rapid changes, after just 3 weeks of training
- effect still there 8 weeks post training
The aging brain & aerobic exercise
aerobic exercise - sweating and elevated HR = increased hippocampal vol, improved accuracy of spatial memory
