Post on 20-Dec-2015
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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
YellowYellow : the lesion typically involves the supramarginal gyrus at the temporoparietal junction
RedRed: variation in the exact extent of the lesionDriver 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 fieldsin parietal cortex
Andersen et al., 1985
neurons with head centered RF(in VIP)
)Duhamel et al., 1997(
Coordinate transformations
Neuronal activity in area 5dependence on eye & hand position
fixed eye position fixed hand position
1 sec
Buneo et al., 2002
What’s the coordinate system of these neurons?
PRR neuronal activity:
Reach Plans in Eye-Centered Coordinates Target Buttons Initial hand position Initial eye position
Same eye position Same hand position
optimal target position depends on
Tactile-visual processing in peripersonal space
Peripersonal space-The immediate space surrounding the body (or a
certain body part).
Extrapersonal space – unreachable.
Visual RF
Integrated visual-tactile coding of peripersonal space, centered on body
parts
Iriki A. et al., Neuroreport 1996
Tactile RF
Representation of visual information in hand-based coordinates
Graziano MS., PNAS 1999
Tactile RF
Visual stimulus trajectory
1 2 3 4 1 2 3 4
Stimulus trajectory
Resp
onse
of
neuro
n
(spik
e/s
ec)
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
M.S. Graziano et al., Science (2000)
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
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 R2
= 0.3982, P<0.002
* Also found in R. cerebellum.
Linear relationship
Makin et al 2007