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Spatial representation
and coordinate frames
in the brain
Hemispheric Neglect
Unilateral Neglect: failure to
attend to (or represent) sensory
information in the left
(contralesional) side of space,
following right brain parietal injury.
Neglect as a deficit in
representation
• Bisiach & Luzzati (1978): imagining a familiar scene
(e.g., central square of Milan), from opposite view points
Parietal lesions in the right hemisphere are
commonly associated with left field neglect
Yellow : the lesion typically involves the supramarginal
gyrus at the temporoparietal junction
Red: variation in the exact extent of the lesion
Driver and Mattinagley, NNS, 1998
Common tests for Visual Neglect
• Drawing from memory
• copying pictures or words
• crossing out items
• line bisection
• reading words
“Burning house”:
Implicit processing of the unattended side
Neglect can be in egocentric and/or
allocentric reference frames
Egocentric/allocentric neglect
Scene/view/object centered neglect
Hillis & Caramazza 1990
SEF neurons show selectivity for saccade
direction
Olson 2003
An SEF neuron that shows selectivity on bar-left trials
regardless of the saccade’s physical direction
Posterior parietal cortex – parietal reach region
Eye position gain fields
in parietal cortex
Andersen et al., 1985
neurons with head centered RF
(in VIP)
(Duhamel et al., 1997)
Coordinate transformations
Neuronal activity in area 5
dependence on eye & hand position
fixed eye position
1 sec
Buneo et al., 2002
fixed hand position
What’s the coordinate system of
these neurons?
PRR neuronal activity:
Reach Plans in Eye-Centered Coordinates
Same eye position
Target Buttons
Initial hand position
Initial eye position
Same hand position
optimal target position depends on
Tactile-visual processing in
peripersonal space
Peripersonal spaceThe immediate space
surrounding the body (or a
certain body part).
Extrapersonal space –
unreachable.
Integrated visual-tactile coding of
peripersonal space, centered on body parts
Tactile RF
Iriki A. et al., Neuroreport 1996
Visual RF
Representation of visual information in
hand-based coordinates
2
3
4
1
2
3
4
Response of neuron (spike/sec)
1
Stimulus trajectory
Tactile RF
Visual stimulus trajectory
Graziano MS., PNAS 1999
The cell’s response doesn’t depend
on fixation position
Neurons with
multimodal receptive
fields were found in
areas:
-Ventral premotor
-Ventral intraparietal (VIP)
-Parietal BA 7b, 5
- Putamen
Postural bimodal neurons in area 5
respond to the seen position of the hand
M.S. Graziano et al., Science )2000(
The effect of the fake arm
M.S. Graziano et al ,.Science )2000(
The rubber hand illusion
It’s
mine!
Pointing at my hand?
Botvinick and Cohen, 1998, Nature
The rubber hand illusion in the
fMRI scanner
The rubber hand illusion
Brain activity - 2
subjective rating of the illusion
vs.
level of PM activity
R2 = 0.3969, P<0.003
* Also found in R. cerebellum.
Linear
relationship
R2 = 0.3982, P<0.002
Makin et al 2007