Heterotopagnosia is a neuro-psychological syndrome caused by brain damage in the left parietal lobe and corresponding to an acquired inability in pointing at and locating another person's body parts. Its name comes from the Greek: "hetero" which means the other from a pair, "a" combined with "gnosis" which means without knowledge, and "topos" which means location. This clinical syndrome is distinct from autotopagnosia, another group of cognitive deficits associated with difficulties in locating body parts on one's own body. Allotopagnosia is another related disorder in which the patient cannot point at any external targets except his/her own body parts.
Causes Heterotopagnosia is a type of brain damage that affects the left parietal lobe, at the parieto-occipital junction, or in the inferior parietal lobe. The brain damage could be an ischemic or an hemorrhagic stroke, or a neurogenerative disorder affecting this region.
Symptoms Heterotopagnosia is an inability in pointing at another person's body parts associated with a spared ability in pointing one's own body parts. When the patient is asked by the examiner to point at his/her own body parts, he/she shows normal performance. However, when asked to point at the examiner's body parts, the patient erroneously points at his/her own corresponding body parts. For example, when the patient is asked "Point at the examiner's nose", the patient points at his/her own nose (so-called "self-referencing" behavior). In typical cases, the patient can point at objects, even those located on the body of other persons. In three reported observations of patients with heterotopagnosia, the ability in touching or grasping other person's body parts was spared.
Diagnosis
Clinical examination Heterotopagnosia can be detected by asking several questions: “Point to your nose”: the patient shows no error. “Point to my nose”: the patient erroneously points to his/her own nose. “Point to the door, to the ceiling, to my glasses…”: typically, the patient shows no errors for objects. “What is it called?” (the examiner points to his/her own nose”: the patient can name the nose of the examiner or any object.
Core syndrome Based on the different cases reported in the literature, the core syndrome of heterotopagnosia appears to imply: 1) an impaired capacity in pointing at another person's body parts; 2) a spared capacity in pointing at the patient's body parts; 3) a self-referencing behavior is observed when the patient fails to point at another person's body parts (except in the case).
Brain imaging Brain imaging (CT-scan or MRI or functional imaging) demonstrates a damage to the left posterior parietal, the left parieto-occipital or the inferior parietal region. According to Cleret de Langavant et al., an additional lesion in the insular region makes the syndrome of heterotopagnosia long-lasting.
Clinical cases Sixteen patients with heterotopagnosia have been reported so far in the literature. Those patients all share the striking inability in pointing at another person's body parts, despite normal performance for pointing at their own body. All patients but one show the self-referencing behavior. Despite similarities between the clinical assessments in those sixteen patients, the same tests were not proposed in all patients, yielding discrepancies in the descriptions of impairments. For example, grasping capacities were only tested in four patients and touching in one patient.
Degos et al. (1997) / Degos and Bachoud-Lévi (1998) JD Degos and AC Bachoud-Lévi described for the first time the syndrome of heterotopagnosia in nine patients after a left hemisphere stroke. In 5 of these patients, the deficit was restricted to the body of other persons (pure heterotopagnosia), while for the 4 other patients, the inability to point at external targets included both other persons' body and objects (allotopagnosia). Three patients with heterotopagnosia could perfectly point at body parts of pictures of human body and another patient with heterotopagnosia could point at body parts of a doll. The authors described for the first time the self-referencing behavior typical in heterotopagnosia and allotopagnosia, by which patients point at their own body instead of pointing at another person's one. One patient with heterotopagnosia had better performance for grasping other person's body parts than for pointing at them. Another patient with heterotopagnosia recovered from this disorder after eight days and offered a narrative of his experience: he could see the body parts of other persons but could not locate them, and acknowledged confusing between the body of other persons and his own. The authors interpreted this disorder as an impairment in the process of pointing itself.
Felician et al. (2003) O Felician and collaborators described two patients showing a typical double dissociation. The first patient suffered from autotopagnosia, with a selective deficit in pointing to own body parts and a spared ability to point to the body parts of others. The second patient demonstrated symptoms of pure heterotopagnosia, with a selective inability to point to another person's body parts, a self-referencing behavior, and a spared capacity to point to own body. The patient with heterotopagnosia could point at objects whether at a reaching distance, in the room or on the examiner's body. The patients could point at parts of animals or of complex objects. This patient could point at body parts of a picture of a human body, at parts of a mask, whether held by the examiner or onto the examiner's face, or at parts of a face visible onto a TV screen, whether still or moving. The patient with heterotopagnosia had decreased brain perfusion in the left inferior parietal lobe, while the patient with autotopagnosia had decreased perfusion in the left superior parietal lobe.
Auclair et al. (2008) L Auclair and collaborators described the case of a patient with heterotopagnosia, with impaired pointing performance for other persons’ body parts but also for other human body representations. A qualitative analysis of pointing errors showed that the patient did not exhibit a self-referencing behavior. Brain imaging identified a left parieto-occipital hemorrhagic stroke.
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