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 Red 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 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 Stimulus trajectory Response of neuron (spike/sec)

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 R 2 = , P<0.003R 2 = , P<0.002 * Also found in R. cerebellum. Linear relationship

Makin et al 2007