Dissociation in accessing space and number representations in pathologic pain patients.

Space is represented by integrating egocentric and allocentric reference frames; however, little is known about the role of these independent reference frames in number representation. Using patients with unilateral pathologic pain in one limb, we investigated whether number representation is closely linked to space representation by evaluating visual subjective body-midline judgments in dark and light conditions (egocentric and allocentric space, respectively). To evaluate the number representation, pairs of numbers were read aloud to the participant, who was then asked to state the midpoint number that they intuitively perceived to be at the middle of each interval. All of the patients perceived allocentric space accurately in the light condition. However, each of the patients showed perceptual shifts in egocentric space and number representation in the dark as compared with control subjects. Direct comparison showed a consistent relationship between number representation and egocentric space. We suggest that numbers are represented spatially by integrating these independent reference frames.