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