Simulating object-based neglect with “real position” neurons.
Poster Presentation

Massimo Silvetti
Dep. of Psychology 39, University of Rome "La Sapienza"

Eliano Pessa
Dep. of Psychology, University of Pavia

Fabrizio Doricchi
Dep. of Psychology 39, University of Rome "La Sapienza"

     Abstract ID Number: 132
     Full text: Not available
     Last modified: March 21, 2005

Abstract
The neglect syndrome is a frequent consequence of parietal-frontal right brain damage. (Mort et al., 2003; Doricchi & Tomaiuolo, 2003). Most frequently, neglect patients omit objects placed to the left of the head-body midline. More rarely, and curiously, neglect patients are able to detect all the objects around them though systematically neglecting the left side of the very same objects. This form of neglect is called “object-based“ (Olson 2003). We describe a computational model simulating a pure object-based syndrome, in which neglect is anchored to eye centred coordinates and independent from head centred ones (i.e. the eye-centred frame of reference is damaged contralesionally while the head-centred one is intact). We demonstrate that pure object based coding of space is possible when the head centred position of objects is coded by units in which response amplitude is relatively independent from eye position signals, corresponding to functional and computational properties of real-position neurons located in the occipital parietal cortex of the monkey brain (Galletti, 1993). These neurons use eye position signals to explicitly code objects locations in head-centred coordinates: however, the amplitude of their response is not directly influenced by the eye position signal (Galletti, 1993).

Doricchi, F. & Tomaiuolo, F. The anatomy of neglect without hemianopia: a key role of parietal-frontal disconnection? NeuroReport 14, 2239-2243 (2003).
Galletti, C., Battaglini, P.P. & Fattori, P. Parietal neurons encoding spatial locations in craniotopic coordinates. Exp. Brain Res. 96, 221-229 (1993).
Mort, D. J., Malhotra, P., Mannan, S. K., Rorden, C., Pambakian, A., Kennard, C., & Husain, M. The anatomy of visual neglect. Brain 126, 1-12 (2003).
Olson, C.R. Brain representation of object-centred space in monkeys and humans. Annu. Rev. Neurosci. 26, 331-354 (2003).