Egocentric and allocentric spatial references in children with Cerebral Palsy

Egocentric and allocentric spatial references in children with Cerebral Palsy Laura Barca (laura.barca@istc.cnr.it) Neuroscience and Neurorehabilitation Department Children's Hospital Bambino Gesu - IRCCS Lungomare G. Marconi 36, 00058 - Santa Marinella (Rome), Italy Giovanni Pezzulo (giovanni.pezzulo@cnr.it) Istituto di Linguistica Computazionale ‘Antonio Zampolli’, CNR, Pisa, Italy Istituto di Scienze e Tecnologie della Cognizione, CNR – Roma, Italy Enrico Castelli (enrico.castelli@opbg.net) Neuroscience and Neurorehabilitation Department Children's Hospital Bambino Gesu - IRCCS Lungomare G. Marconi 36, 00058 - Santa Marinella (Rome), Italy Abstract arm-centered (Colby, 1998). Allocentric, or object-centered frames, are external to the organism and usually centered on objects in the environment. Such coding of space has an important role in the processing of far space when objects are out of reach. Among allocentric representation, distinctions can be made when the point of reference is centered on an object of interest (object-centered) or on the environment (e.g., room-centered) (Colby, 1998). The information derived by egocentric and allocentric maps is usually integrated to allow proficient spatial processing (Burgess, 2006). However, some tasks rely more on one frame than the other. For example, pointing to a location in space within arm reach or grasping an object are likely accomplished within an egocentric framework, whereas defining the fastest route between two destinations is likely to involve an allocentric frame. Overall, selection of what spatial frame(s) of reference to use is highly action-specific. Spatial memory is supported by multiple parallel representations of the environment. Egocentric perspective (body-centered) and allocentric representations (object- centered) are integrated to allow correct interaction with the world. According to Milner and Goodale (1995, 2008), the action-related dorsal system is specialized for location of objects in space and visuo-motor integration, and uses an egocentric frame of reference. The perception-related ventral system is specialized for categorical recognition of objects and forms, and supports an allocentric frame of reference. Here we use a Distance Judgment Task to explore the use of different spatial frames in children with Cerebral Palsy (CP). Following the dorsal stream vulnerability hypothesis (Atkinson et al., 2007) children with CP might have more difficulties in egocentric judgments and in the processing of peri-personal space than controls. No significant difference emerged between CP children and controls in allocentric judgments, whereas performance was worse in egocentric judgment, indicating inefficient use of the body-centered representations. Keywords: Egocentric-allocentric spatial references; Distance Judgment task; Cerebral Palsy (CP). A number of studies showed that several regions of the cerebral cortex subserved functions involved in spatial processing, having a reach network of reciprocal connections and link with subcortical structures. In the fMRI study by Zaehle et al., (2007) participants performed a spatial judgment task based on verbal instructions. They have to define the spatial relations between different objects (allocentric condition), or the position of objects with respect to the participants (egocentric condition). A fronto- parietal network was involved in both egocentric and allocentric judgments (e.g., superior occipital gyrus, medial portion of superior parietal cortex, superior frontal gyri bilaterally), but partly separated networks mediate different spatial coding strategies. While egocentric spatial coding revealed activation mainly within the medial parts of the posterior superior parietal lobe, the use of the allocentric reference frame revealed activation in right parietal lobe, bilateral ventrolateral occipito-temporal cortex and bilateral hippocampal formation. There is also increasing evidence of the critical role of connecting circuits, and the vestibular Introduction Humans are provided with different reference systems to code the environment and its physical attributes. For example, if we have to specify the location of an object we can make use of different frames of reference: we can define its position with respect to our body (egocentric frame) or we can refer to other objects in the environment or the environment itself (allocentric frame). Egocentric coordinates are based on the organism’s position, and then linked to the specific perspective under which spatial information has been processed. Hence, these representations are particularly relevant in action planning and motor control in near space, when there is a direct interaction between body and objects. Egocentric frames have been described in relation to the different body part they are based on, such as head-centered, eye-centered, and