A new clinical evaluation of asomatognosia in right brain damaged patients using visual and reaching tasks

The term asomatognosia refers to a unilateral disturbance of body ownership following a cerebrovascular incident. Patients with asomatognosia consider the contralesional limbs as missing or having disappeared from awareness. This neuropsychological disorder modifies body ownership in terms of perceptual experience, visual identification and sense of belonging of contralesional body parts. In the literature, asomatognosia is usually tested by using verbal scales.

In this study, we first developed a new test to assess asomatognosia that includes a visual identification task and a reaching task. We examined 16 healthy participants and 20 right brain damaged patients. The participants were asked to identify, reach and touch their left hand when positioned in peripersonal space, in presence of an extraneous hand (belonging to the examiner). We analyzed how the deficit is modulated by the reciprocal positions in space of the two limbs, the relationship with personal neglect and the anatomical correlate using a Voxel-based Lesion Symptom Mapping (VLSM) analysis with CT data.

The results show that the asomatognosia cannot be simply considered as one of the many manifestations of personal neglect but should be taken into account as a "productive" disorder characterized by the misidentification of the own hand with an extraneous hand. The VLSM analysis of patients with asomatognosia revealed the involvement of the inferior and middle frontal lobe.

The novel task that has been developed in the present study could be used as an objective tool to measure this specific disorder of body ownership or to uncover subclinical conditions of asomatognosia.