Abstract The spatial location of an object can be repre- sented in the brain with respect to different classes of reference frames, either relative to or independent of the subject’s position. We used functional magnetic reso- nance imaging to identify regions of the healthy human brain subserving mainly egocentric or allocentric (ob- ject-based) coordinates by asking subjects to judge the location of a visual stimulus with respect to either their body or an object. A color-judgement task, matched for stimuli, difficulty, motor and oculomotor responses, was used as a control. We identified a bilateral, though main- ly right-hemisphere based, fronto-parietal network in- volved in egocentric processing. A subset of these re- gions, including a much less extensive unilateral, right fronto-parietal network, was found to be active during object-based processing. The right-hemisphere lateral- ization and the partial superposition of the egocentric and the object-based networks is discussed in the light of neuropsychological findings in brain-damaged patients with unilateral spatial neglect and of neurophysiological studies in the monkey. Key words Spatial reference frames · Mid-sagittal plane · Object-based · Spatial · Hemineglect · Right hemisphere Introduction The spatial location of an object may be, in principle, represented with reference to two fundamental classes of spatial coordinate frames: egocentric and allocentric (see, e.g., Howard and Templeton 1966; Lacquaniti 1997). In the egocentric frames, the position of objects is encoded with reference to the body of the observer or, more specifically, to relevant body parts, such as the head, trunk, and/or arm. Egocentric representations of objects may be used for the organization of goal-directed movements, such as reaching a target or avoiding a dan- gerous stimulus. In the allocentric coordinate frames, by contrast, objects are primarily represented with reference to their spatial and configurational properties, such as the relationships among their different component parts and among different objects in the environment. Representa- tions encoding the configurational properties of objects may be useful for their identification. Objects, in ecolog- ical conditions, are typically seen from a variety of ego- centric (observer-based) perspectives, suggesting a close interaction between body- and object-based reference frames. Experimental support for this broad distinction comes from two main sources of evidence. Neurophysiological studies in the monkey have demonstrated the existence of both body- and object-based representations in the brain. In the posterior parietal cortex, neurons coding vi- sual information in egocentric (body- and body part-cen- tered) coordinates have been found in area 7a (Andersen et al. 1985), area LIP (Andersen et al. 1990), area VIP (Duhamel et al. 1997), and area PO (Galletti et al. 1993). Units with similar properties were also found in the pre- motor cortex (area 6: Fogassi et al. 1992; Graziano et al. 1994). On the other hand, neurons whose firing rate is modulated by the specific location inside an object, where a saccade has to be directed independent of the object position and orientation, have been found both in the posterior parietal cortex (area LIP: Breznen et al. 1999) and in the frontal lobe (supplementary eye fields: Olson and Gettner 1995). G. Galati · G. Vallar · L. Pizzamiglio Laboratory of Neuropsychology, Fondazione Santa Lucia, Via Ardeatina 306, 00179 Roma, Italy G. Galati · E. Lobel · D. Le Bihan SHFJ, Department of Medical Research, CEA, Orsay, France L. Pizzamiglio Department of Psychology, Università di Roma “La Sapienza”, Roma, Italy E. Lobel · A. Berthoz LPPA, Collège de France and CNRS, Paris, France G. Vallar Department of Psicology, Università di Milano-Bicocca, Milano, Italy Exp Brain Res (2000) 133:156–164 Digital Object Identifier (DOI) 10.1007/s002210000375 RESEARCH ARTICLE Gaspare Galati · Elie Lobel · Giuseppe Vallar Alain Berthoz · Luigi Pizzamiglio · Denis Le Bihan The neural basis of egocentric and allocentric coding of space in humans: a functional magnetic resonance study Received: 26 July 1999 / Accepted: 10 February 2000 / Published online: 11 April 2000 © Springer-Verlag 2000