What Is the Position of an Arm Relative to the Body? Neural Correlates of Body Schema and Body Structural Description

Abstract

Neuropsychological studies suggest that the human brain is endowed with two body representations: the body schema (BS), coding the orientation of one's body parts in space, and the body structural description (BSD), coding the location of body parts relative to a standard body. We used fMRI to disentangle the neural mechanisms underlying these putatively distinct body representations. Participants saw an arm or a pot's handle (stimulus: arm, handle) rotated at different angles (angle: 30 -150°). If the stimulus was an arm, subjects were instructed to imagine (1) rotating their own arm until it matched the stimulus orientation (comparing the seen arm to their own) or (2) seeing the stimulus moving toward its appropriate position on a simultaneously presented human body [comparing the arm to the one of a standard body (strategy: motor, visual imagery)]. If the stimulus was a handle, subjects were instructed to imagine (1) placing the handle on its appropriate position on a simultaneously presented pot or (2) seeing it moving toward its pot's position. The analysis of the interaction stimulus ϫ strategy revealed activation of left secondary somatosensory cortex (SII), specifically when comparing the stimulus arm to one's own. The analysis of the parameters describing the linear effect of angle revealed that neural activity of left posterior intraparietal sulcus was modulated by the stimulus's rotation, but only when relating the arm to a standard body. The results associate BS and BSD with differential neural substrates, thereby suggesting that these are independent body representations, and furthermore extend current concepts of SII function.

Bodily ownership and self-location: Components of bodily self-consciousness

“…autotopagnosia; Ogden, 1985). Virtual lesions induced by transcranial magnetic stimulation applied over the PPc affect the capacity for coding and remapping of multisensory information across different body parts (Azanon, Longo, Soto-Faraco, & Haggard, 2010;Bolognini & Maravita, 2007; see also Corradi-Dell'Acqua, Tomasino, & Fink, 2009;Lloyd, Morrison, & Roberts, 2006 for fMRI evidence). Taken together, these findings suggest that activity in the PPc is necessary to encode multisensory spatial representations of body parts centered on different reference frames.…”

Mental Imagery for Full and Upper Human Bodies: Common Right Hemisphere Activations and Distinct Extrastriate Activations

“…Classically the OBT-task is performed using an egocentric frame of reference, while the LAT-task is a control task not asking for a transformation with respect to either the egocentric nor the allocentric frame of reference. Previous research, and in particular the direct comparison between the mental imagery of one's own versus another person's full body (Corradi-Dell'Acqua et al 2009) has shown that both hemispheres are differentially involved in processing one's own as opposed to other's body (e.g., Ruby and Decety 2001;Vogeley and Fink 2003;Decety and Sommerville 2003). We note that the main interest of the present fMRI study-motivated by insights from data of neurological patients with illusory own body perceptions (Blanke et al 2004;)-was to distinguish mechanisms of mental imagery concerning the full body from those of the upper body with respect to the LAT control task.…”

Does thumb posture influence the mental rotation of hands?

“…Evidence for motor imagery being involved in mental rotation of body parts comes from clinical cases [e.g., 3,4,12,16] and from neuroimaging studies (see [22] for review). Further studies proposed that mental rotation tasks can be solved by different strategies, involving visual imagery or motor imagery [2,11], and that the choice of strategy might depend on the type of stimuli [21] or the instructions [20]. One argument that has been brought forward in favour of a motor imagery strategy is the posture effect.…”