Is autotopoagnosia real? EC says yes. A case study

Abstract

We report a case of pure autotopagnosia (AT) following a left subcortical vascular accident. The absence of any language disorder, general mental deterioration or other cognitive impairments in this patient allowed an in-depth study of AT. Several tests of body representation and object and animal representation, as well as tests assessing semantic skills were administered to verify current interpretations of AT. Results showed a clear-cut dissociation between defective performances in body representation tests and normal performances on tests involving other kinds of stimuli.

The patient’s performances were particularly defective on tests relying on visuo-spatial body representation, but her semantic and linguistic knowledge seemed to be spared. This dissociation between different aspects of body representation supports Sirigu et al.’s hypothesis that multiple, partially independent systems are involved in body knowledge. In agreement with this hypothesis, in the present patient AT seems be due to a deficit in a system that processes the structural properties and relative position of single body parts.

The present results, reporting the first observation of a subject not affected by any cognitive impairment other than AT, strongly support the existence of a system specifically devoted to body representation.

Introduction

Autotopagnosia (AT) is the inability to localize body parts either on one’s own body, on the examiner’s body or in a picture. It is generally associated with a lesion of the left parietal lobe, often with a neoplastic etiology [7]. The most frequent errors are pointing to a contiguous body part or to one semantically related to the target [27]. A deficit is often observed in naming and in describing the functions of body parts [13], [24], [30] or in determining their spatial relationships [6].

Despite the clinical notoriety of AT, it is still not clear whether it is a specific disorder of a specific system devoted to body representation (i.e. body schema) or whether it is the consequence of other cognitive deficits. In fact, AT patients are frequently affected by other cognitive disorders, especially aphasia. The nature and severity of this latter disorder has influenced the interpretation of AT, so that it has been attributed either to a linguistic impairment [22], [24], [16], [13], [25] or to the inability to analyze a whole into its parts [9], [11], [23], [30].

However, in the last 20 years some studies of single cases have been reported that attempted to determine whether a body schema defect or other cognitive deficits are responsible for AT. Ogden [18] reported AT in a non-aphasic patient (JPB) with a left parietal lobe lesion, who also showed constructional apraxia, extra-personal and personal neglect, right–left confusion, finger agnosia and dressing apraxia. Ogden interpreted this case as due to loss of the ability to generate the body image. The mental imagery deficit was specific for body representation since, despite his inability to localize human body parts, JPB was still able to indicate single parts of animals and objects.

Semenza [26] described a similar case in a mild aphasic patient. Her localization deficit was body specific and she performed object part localization tests flawlessly.

Two more cases of AT were recently reported [8] with a dissociation between good naming, recognition and use of body parts and severe inability to localize the same parts on verbal command. In one patient (a left-handed man), the lesion was confined to the right parietal cortex and in the other one, to the left parietal cortex. Denes [8] argued that in these cases AT was due to the impairment of a specific neural circuit in the language dominant hemisphere that encodes both one’s own and others’ body position.

Also Buxbaum and Coslett [2] reported AT in a patient (GL) who showed lesions in the left frontal, temporal, parietal and occipital and in the right parietal lobes following a head injury. Transcortical motor aphasia and apraxia also affected GL, who required supervision and assistance in daily life activities involving his own body, such as grooming and dressing. A series of well designed experiments led Buxbaum and Coslett [2] to state that in this case AT was due to a deficit in a specific representation system that processes the structural descriptions of human bodies.

Some AT patients without linguistic defects are affected by dementia (i.e. [28]). In these cases, the presence of a general cognitive decline makes it difficult to assert that AT is due to the impairment of a specific system that represents the body as it appears, and the spatial relationship between its parts, even when it is a rather isolated deficit.

In the present paper, we report a new case of AT in EC, a patient who did not show any other cognitive impairment. Since no other case has been described up until now that shows such pure AT, we decided to further investigate this body schema impairment. In particular, we set out to determine whether AT is due to a more general impairment or to a specific deficit of a system specifically devoted to processing body representation and to verify present models of body representation.

Two different models propose that body representation is processed by multiple systems. Paillard [20] hypothesized that two different mechanisms process the “what” and “where” aspects of body representation. According to Paillard [20], a deficit in one of the two systems will impair the ability to perceptually identify body features in body images or to localize body parts, regardless of the task.

Instead, Sirigu et al. [28] hypothesized that four different systems, which may be selectively impaired by brain damage, process different aspects of body representation:

• a semantic and lexical representation, involved in naming body parts and in recognizing their specific functional relations;

• a category-specific, visuo-spatial representation, processing structural properties and position of single parts as well as their boundaries;

• an emergent body-reference system, processing a dynamic, actual body image based on vestibular, somatosensory and visual inputs and

• motor representation system.

EC’s performances on different body-involving tasks will help us understand whether body knowledge is processed by multiple representations.