Due to the subjective nature of<unk> , there are many hypotheses presented as to the underlying causation. Since the condition by definition is an inability to recognize the human body and its parts, the disorder could stem from a language deficit specific to body parts. On the other hand, the patient could suffer from a disrupted body image or a variation of the inability to separate parts from whole. It is also believed that<unk>  has multiple underlying causes that cannot be categorized as either language-specific or body-image-specific. The rarity of<unk> , frequently combined with the manifestation of other psychoneurological disorders, makes the prime cause extremely difficult to study. In many cases, one of these accompanying conditions—often aphasia—could be masking the patient's<unk>  altogether. Brain Lesions Animation. Parietal lobe of the left cerebral hemisphere. Although it is still unclear what precise deficits in brain function cause the symptoms of<unk> , the location of brain damage is not as ambiguous.<unk>  is most often attributed to lesions in the parietal lobe of the left hemisphere of the brain. However, it is also believed that the disorder can be caused by general brain damage as well. Many different types of brain lesions can cause<unk> ; however, neoplastic lesions seem to be the most common. “Pure”<unk>  is often seen with smaller lesions, as larger lesions tend to create other unseen deficits that can confuse or mask the appearance of the symptoms of<unk> —such as aphasia, as discussed above. The parietal lobe is involved in the integration of sensory information and visuospatial processing. The left parietal lobe, specifically, is important to the understanding of language and mathematics, and has a more prominent role for right handed people. Mental Representations of Body Schema Lesions in the left parietal lobe are thought to disrupt one or more of four putative mental representations of body schema. The deficiencies associated with the disease seem to arise from a dysfunction in the mental representation of the body; however, the human psyche interprets its body schema and orientation in space through various sources of representation systems. According to Felician et al. (2003), the notion of body schema can be categorized into four tiers of mental representation: Level Type Description 1 Lexical and Semantic Representations of the Body At the first level, the mind anchors its body image to refer to body-related conceptual knowledge, associated with speech and language recognition. For instance, the identification of body parts are attributed to fundamental knowledge of the names and titles, rather than the physical locations and relationships of body parts. 2 Category-specific Visuospatial Representations of the Body On the second tier, unlike semantic representation, the visuospatial schema specifies the structural position of parts over the body surface. In particular, it relates to the local relationship between body parts and the boundaries between them. 3 Classical Notion of Postural Schema On a third level, the classical notion of postural schema emerges, which draws from various sources of sensory afferences. Information from proprioceptive, tactile, visual, auditory, and vestibular systems is consolidated to construct an on-line, three-dimensional and dynamic representation of the body in space, a “somatosensory representation.” 4 Motor Representations Finally, the skeletal-muscular system provides motor representations that participate in the formation and preservation of the somatosensory representations.
Autotopagnosia
Integrative agnosia
Visuospatial dysgnosia
Apperceptive agnosia
Finger agnosia
Hemispatial neglect
Phonagnosia
Associative visual agnosia