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4. Neural mechanisms of selective attention (Neural mechanisms…
4.
Neural mechanisms of selective attention
Neural mechanisms
3 dichotomies
Bottom up
V4
Pop out stimuli
salient
V1
Sudden onset
Enhanced in parietal/PFC
Conjuction
difficult to detect
multiple things to concider
non target feature
pop out
easy to detect
Top down
Effects visible from the dLGN on
dLGN
first selective visual attention
increased firing rates of attended stimulus
interaction
Spacially based
Posner task
occularmotor
flanker
Feature based
Middle temporal visual
V5
V4
Behaviorally relevant objects
Paradigms
Stroop
color is relevant
letters not
Same location
bottom up
same stimuli and then suddenly different
Overt
mostly gaze and focus spatially aligned
but can also be dissociated
Covert
Pressacadic in V4
reemergence of stimulus selectivity (?)
encodes stimulus features
Gaze control
Premotor theory of attention
mechanisms responsible for spatial attention and saccades are done by same neurons
planning saccade already facilitates perception
1 mechanism for selection of stimulus and motor response
eye movements might facilitate attention
Frontal eye field
Loss of attention when lesion in FEF
FEF responses are enhanced during covert attention
Stimulation of FEF enhances attention
Presaccadic perception
Enhancement in visually driven neuronal response prior to saccades to RF stimuli
??
V4 more responsive just before eye movement
around time of gaze shift, visual representations dominated by target (spatial and feature)
Already biased by stimulus before focus
Feature based attention
Located in VPA in PFC
neurons selective for memorized objects
Neuromodulators
Acetylcholine
Increase can enhance visual selective attention
Receptors
mAchRs
modulation of visual cortex during selective attention
nAchRs
Within V1
Thalamoreceptoric neurons
Covert attention
interaction PFC with cholinergic projections
processing sensory signals
Nicotinic
Orienting
Attentional control
Bottom up attention
Comes from nucleus basalis of Meynert, substania innominata, diagonal band of basal forebrain
Dopamine
Receptors
D1
More in PFC
Cognitive functions
Mediate activity within FEF on saccadic target selection and on visual response in V4
3 ways of alrtering V4 by dopamine
enhancement in magnitude of response to stimulation
more selective to orientation
Visual responses become less variable
Modulating long range, recurrent connections between the FEF and visual cortex
Also saccadic preparation
D2
Properties
Alter strength and reliability of converging exitatory synapses
inverted U for optimal effects
larger differences between attended and unattended stimuli
Top down
PFC
changes in DA alter selective attention
comes from midbrain: substania nigra and VTA
Noradrenaline
Comes from LC
Mostly related to arousal
but respond selectively to salient stimuli
Neurotransmitters that influence synaptic transmission broadly within neural circuits
affect slow acting receptors of many neurons
Visual selective attention
Selective processing of some visual stimuli in favor of others according to their features, identity, location, salience
Increase SNR (signal to noise ratio)
endogenous cueing
most visual info goes unused because irrelevant
LGN TRN
LGN
Attention modulates visual signal in LGN
Study
If stimulus in RF then firing with attention, lower when outside RF
TRN
Thalamic reticular nucleus
reversed pattern
Higher energy when not attended
Inhibits LGN
Shows that attention already has an effect very early on
before they reach the cortex
Summary birgit
interact
TRN inhibits LGN
TRN is exited by LGN
so TRN should be negatively related to attention and decrease inhibition, causes increase in LGN
What is RF?
Receptive Field