Download T2 - Center for Neural Basis of Cognition

Active Vision: Memory, Attention and Spatial
Representation in Parietal Cortex
Carol Colby
Rebecca Berman
Cathy Dunn
Chris Genovese
Laura Heiser
Eli Merriam
Kae Nakamura
Richard Saunders
Department of Neuroscience
Center for the Neural Basis of Cognition
University of Pittsburgh
Department of Statistics
Carnegie Mellon University
Laboratory of Neuropsychology,NIMH
1) Remapping in monkey area LIP and
extrastriate visual cortex
2) Remapping in split-brain monkeys
Behavior
Physiology
3) Remapping in human cortex
LIP memory guided saccade
Stimulus On
Saccade
Stimulus appears outside of RF
Saccade moves RF to stimulus location
Single step task
Spatial updating or remapping
The brain combines visual and corollary discharge
signals to create a representation of space that
takes our eye movements into account
LIP Summary
Area LIP neurons encode attended spatial locations.
The spatial representation of an attended location is remapped
when the eyes move.
Remapping is initiated by a corollary discharge of the eye
movement command.
Remapping produces a representation that is oculocentric: a
location is represented in the coordinates of the movement
needed to acquire the location.
Remapping allows humans and monkeys to perform a spatial
memory task accurately.
Extrastriate Summary
Remapping occurs at early stages of the visual hierarchy.
Corollary discharge has an impact far back into the system.
Remapping implies widespread connectivity in which many
neurons have rapid access to information well beyond the
classical receptive field.
Vision is an active process of building representations.
1) Remapping in monkey area LIP and
extrastriate visual cortex
2) Remapping in split-brain monkeys
Behavior
Physiology
3) Remapping in human cortex
Stimulus appears outside of RF
Saccade moves RF to stimulus location
What is the brain circuit that produces remapping?
The obvious pathway:
forebrain commissures (FC)
Are the forebrain commissures necessary for
updating visual signals across the vertical
meridian?
Behavior in double step task
Physiology in single step and double step task
Attain fixation
FP
FP
T1
T1 appears
T2
FP
T1
T2 flashes briefly
T1
Saccade to T1
T2
Saccade to T2
Attain fixation
FP
FP
T1
T1 appears
T2
FP
T1
T2 flashes
Transfer of visual signals
WITHIN
T2
T1
T2
WITHIN
T2
T1
T2 T2’
WITHIN
VISUAL-ACROSS
T2
T2
T1
T2 T2’
T1
T2
WITHIN
VISUAL-ACROSS
T2
T2
T1
T2 T2’
T1
T2
T2’
Is performance impaired on visual-across sequences
in split-brain monkeys?
WITHIN
VISUAL-ACROSS
T2
T2
T1
T2 T2’
T1
T2
T2’
Central
Within
Central
Across
Across
Within
Day 1: Initial impairment for visual-across
Monkey
C
Monkey
E
Within Central Across
Across Central
Within
correct
incorrect
TRIALS
1-10
60-70
120-130
Within Central Across
Across Central Within
First day saccade endpoints
Vertical eye position (degrees)
Monkey C
Monkey E
Horizontal eye position (degrees)
Last day saccade endpoints
Vertical eye position (degrees)
Monkey C
Monkey E
Horizontal eye position (degrees)
Learning? Or a monkey trick?
Central
Within
Central
Across
Across
Within
no monkey tricks..
Both monkeys really update
the visual representation
Monkey EM
Monkey CH
Are the forebrain commissures necessary for
updating spatial information across the vertical
meridian?
No. The FC are the primary route but not the only
route.
What are LIP neurons doing?
Stimulus appears outside of RF
Saccade moves RF to stimulus location
SINGLE
STEP
STIMULUS
ALONE
SACCADE
ALONE
Population activity in area LIP
SINGLE
STEP
DOUBLE
STEP
Split Brain Monkey Summary
The forebrain commissures normally transmit remapped
visual signals across the vertical meridian but they are not
required.
Single neurons in area LIP continue to encode remapped
stimulus traces in split-brain animals.
1) Remapping in monkey area LIP and
extrastriate visual cortex
2) Remapping in split-brain monkeys
Behavior
Physiology
3) Remapping in human cortex
Remapping in human cortex
Task and predictions
Parietal cortex
Striate and extrastriate visual cortex
Remapping in a split brain human
Functional Imaging Predictions
1) Robust activation in cortex ipsilateral to the
stimulus.
2) Ipsilateral activation should be smaller than the
contralateral visual response.
3) It should not be attributable to the stimulus alone
or to the saccade alone.
4) Ipsilateral activation should occur around the time
of the saccade.
Contralateral Visual Response
(Fixation Task)
Ipsilateral Remapped Response
Ipsilateral Remapped Response
Visual and Remapped Responses
Human Parietal Imaging Summary
Remapping in humans produces activity in parietal cortex
ipsilateral to the visual stimulus.
Remapped activity is lower amplitude than visual activity.
The activity cannot be accounted for by the stimulus or the
saccade alone.
Remapped activity occurs in conjunction with the eye
movement.
Remapping in human cortex
Task and predictions
Parietal cortex
Striate and extrastriate visual cortex
Remapping in a split brain human
Contralateral Visual Response
Ipsilateral Remapped Response
Remapping in Multiple Visual Areas
Magnitude of Remapped Response
Remapping in human cortex
Task and predictions
Parietal cortex
Striate and extrastriate visual cortex
Remapping in a split brain human
Intact Subjects
Split Brain Subject
Parietal Responses in Split Brain and Intact Subjects
Human Imaging Summary
Remapping in humans produces activity in the hemisphere
ipsilateral to the stimulus.
Human Imaging Summary
Remapping in humans produces activity in the hemisphere
ipsilateral to the stimulus.
Remapped activity is present in human parietal, extrastriate
and striate cortex.
Human Imaging Summary
Remapping in humans produces activity in the hemisphere
ipsilateral to the stimulus.
Remapped activity is present in human parietal, extrastriate
and striate cortex.
Remapped visual signals are more prevalent at higher levels
of the visual system hierarchy.
Human Imaging Summary
Remapping in humans produces activity in the hemisphere
ipsilateral to the stimulus.
Remapped activity is present in human parietal, extrastriate
and striate cortex.
Remapped visual signals are more prevalent at higher levels
of the visual system hierarchy.
Remapping occurs in parietal and visual cortex in a split brain
human subject.
Conclusions
Remapping of visual signals is widespread in monkey cortex.
Conclusions
Remapping of visual signals is widespread in monkey cortex.
Split-brain monkeys are able to remap visual signals across
the vertical meridian.
Conclusions
Remapping of visual signals is widespread in monkey cortex.
Split-brain monkeys are able to remap visual signals across
the vertical meridian.
Remapped visual signals are present in area LIP in split-brain
monkeys.
Conclusions
Remapping of visual signals is widespread in monkey cortex.
Split-brain monkeys are able to remap visual signals across
the vertical meridian.
Remapped visual signals are present in area LIP in split-brain
monkeys.
Remapped visual signals are robust in human parietal and
visual cortex.
Conclusions
Remapping of visual signals is widespread in monkey cortex.
Split-brain monkeys are able to remap visual signals across
the vertical meridian.
Remapped visual signals are present in area LIP in split-brain
monkeys.
Remapped visual signals are robust in human parietal and
visual cortex.
In a split-brain human, remapped visual signals are present in
parietal and visual cortex.
Conclusions
Remapping of visual signals is widespread in monkey cortex.
Split-brain monkeys are able to remap visual signals across
the vertical meridian.
Remapped visual signals are present in area LIP in split-brain
monkeys.
Remapped visual signals are robust in human parietal and
visual cortex.
In a split-brain human, remapped visual signals are present in
parietal and visual cortex.
Vision is an active process of building representations from
sensory, cognitive and motor signals.