Prosopagnosia and Capgras Syndrome - Term Paper Example

Until as recent as 1990, prosopagnosia and Capgras were seen as two very different and unrelated disorders. In order to conceptualize this, it is prudent that we first establish both a theoretical and practical understanding of the underlying characteristics, signs and symptomology of the two disorders. First and foremost, prosopagnosia is a disorder classically characterized as an inability to visually recognize faces despite otherwise normal visual and mental function (Caldara, Schyns , Mayer, Smith, Gosselin & Rossion, 2005). One of the defining characteristics of the disorder is that the individual is able to recognize people via other cues: such as voice or other visual traits (e.g., size, gait, mannerism, clothes, hairstyle, or even facial features (mustache, scar, blemish, or even style of make-up)). Such findings illustrate that individuals with prosopagnosia typically have otherwise intact visual and mental functioning. For example, individuals with prosopagnosia, in general, are able to make fine visual discriminations (e.g., they often show intact reading abilities) (Caldara, Schyns , Mayer, Smith, Gosselin & Rossion, 2005). Prosopagnosia in isolation is extremely rare, but if prosopagnosia is considered as one symptom among other visual or neuropsychological deficits, the frequency of occurrence is much higher (Caldara, Schyns , Mayer, Smith, Gosselin & Rossion, 2005). According to Kumral, Bayulkem, Atac, and Alper (2004), the typical cause of prosopagnosia is posterior cerebral artery infarcts (PCAI). The posterior cerebral arteries are paired arteries that supply part of the midbrain, the subthalamic nucleus, the basal nucleus, the thalamus, the medial inferior temporal lobe, and the occipital and occipitoparietal cortices (Maulaz, Bezerra, & Bogousslavsky, 2005). Thus a stroke that disrupts blood flow of the posterior cerebral arteries typically result in infarcts (i.e., areas of tissue death due to lack of oxygen) in the regions supplied by these arteries. Although most individuals show evidence of bilateral damage, a few individuals with prosopagnosia have damage restricted to the right hemisphere (Wada & Yamamoto, 2002). Among vision researchers, there is a growing consensus that a right hemisphere lesion is necessary, if not sufficient, to cause prosopagnosia (e.g., see Mattson, Levin, & Grafman, 2000). The lesions causing prosopagnosia are generally located in the infero-medial part of the temporo-occipital cortex, specifically the fusiform gyrus, the lingual gyrus, and the posterior part of the parahippocampal gyrus (Bouvier & Engel, 2005). Neurological imaging studies (e.g., PET and fMRI investigations) conducted on neurologically intact individuals have identified a small area within the right midfusiform gyrus that shows maximal activation to face stimuli (e.g., Kanwisher et al., 1997) and has been termed the fusiform face area (FFA, Kanwisher et al., 1997). Interestingly, in a meta-analysis of 73 prosopagnosic cases, Bouvier and Engel (2005) found that area of maximal lesion overlap was a small area in the right inferior occipital gyrus and included the FFA once again showing the importance of this region to face recognition. Prosopagnosics often have a number of other deficits such as achromotopsia (a severe deficit in color perception), topographical disorientation, (see Griisser & Landis, 1991, and Bouvier & Engel, 2005, for reviews), and visual field defects, especially in the upper left quadrant (Bouvier & Engel, 2005). In a meta-analysis of 92 cases of achromatopsia and 100 cases of prosopagnosia (note that there were not 192 separate cases in the meta-analysis as many of the individuals had both disorders), Bouvier and Engel (2005) found that 72% of the 92 cases of achromatopsia also had prosopagnosia. As Bouvier and Engels (2005) paper was primarily a meta-analysis of achromatopsia, the precise percentage of the 100 cases of prosopagnosia who also had achromotopsia was not reported. Achromatopsia is typically associated with a bilateral or right unilateral lesion of the temporo-occipital cortex (Zeki, 1990). Another deficit frequently associated with both prosopagnosia and achromotopsia is topographical disorientation, with four types of topographical disorientation often being described: a) egocentric disorientation (in which the individual is unable to represent the location of objects with respect to self, typical lesion site is posterior parietal cortex), b) heading disorientation (in which the individual is unable to represent direction of orientation with respect to external environment, typical lesion site is posterior cingulate gyrus), c) landmark agnosia (in which the individual is unable to represent the appearance of salient environmental stimuli (or landmarks), typical lesion site is the lingual gyrus), and d) anterograde disorientation (in which the individual is unable to create new representations of environmental information, typical lesion location is the parahippocampal gyrus) (Aguirre & DEsposito, 1999). (See Figure 6 for an illustration showing the aforementioned locations). Note that these regions are adjacent to those associated with prosopagnosia and achromatopsia. A third deficit often associated with prosopagnosia is visual field defect, specifically a left superior quadrantanopia (i.e., blindness in the left upper quadrant of visual field) (Bouvier & Engel, 2005; Meadows, 1974). Note the unique pattern of deficits typically associated with prosopagnosia and the fact that the majority of these disorders (prosopagnosia, achromatopsia, and topographical disorientation) are associated primarily with lesions to adjacent regions of the right cerebral cortex. Capgras’ Syndrome, first identified by Capgras & Reboul-Lachaux (1923) is a rare disorder whereby the afflicted individual is plagued by the delusionary belief that an individual close to him/her [most likely a spouse or another very close family member] has been replaced with and individual who appears to be identical to the family member but is believed to be an imposter. The underlying delusion exhibited in Capgras’ Syndrome is classified. It was originally described in the psychiatric literature and has many psychodynamic interpretations (Capgras & Reboul-Lachaux, 1923). Most of the literature provides an very colorful interpretation of this phenomenon and it has been described in very esoteric terms such as “ego splitting and projection in defense of overwhelming erotic or aggressive impulses directed at a parental figure or intensive ambivalent feelings directed toward a significant other, such as a spouse or sibling" (Sullivan, Cavenor, Maltbie, & Silverstein, 1978, p. 275). O’Reilly & Malhatra (1987) delineates Capgras’ Syndromes as a delusionary condition which manifests itself in a distorted state with behavioral correlates of intolerable ambivalence. This ambivalence is present to an exacerbated extent and causes psychological disturbance that can only be defused by the existence of doubles. Berson (1983) posits that this syndrome is most typically seen in schizophrenics [mainly paranoid schizophrenics] although in very few cases, there was evidence of neuropathological involvement. He delineates clear and concise inclusionary diagnostic criteria. These criteria include the presence of pathologic psychical splitting, paranoia, psychosis and rudimentary changes in interpersonal relationships. Currently, there is a great deal of ambiguity in the classification of Capgras Syndrome as there is evidence that the underlying etiology may be neuropathlogical or psychopathological or an intricate combination of the two (Bienenfield & Brott, 1989). Furthermore, ambiguity can be seen in the notion that some individuals feel that there is a gender-based component with the majority of individuals suffering from this disorder being female (Vogel, 1974). (Moskowitz, 1975) describes the etiology of this disorder as being related to an underlying dysfunctional family system. The neuropathological component for this disorder can be seen in the notion that there is a comorbid reduction in monoamine oxidase activity (Sullivan et al., 1978), hypothyroidism (Fish-bain, 1989; Madakasira & Hall, 1981), or head trauma (Weston & Whitlock, 1971). In fact, Joseph, OLeary, and Wheeler (1990) examined twelve (12) patients suffering from Capgras’ Syndrome and noted that there was significantly more atrophy of the bilateral frontal and temporal lobes when compared to the control group. A superficial examination of these two disorders leads us to believe that these disorders are inherently different in nature as Capgras’ Syndrome proves to have significantly more behavioral correlates while prosopagnosia proves to be predominately neuropathological in nature. Essentially, these two disorders were conceived as different and unrelated entities until Ellis & Young (1990) set out to explain the delusionary component of Capgras’ syndrome by undertaking an intricate study of the mechanism involved in the inability to visually recognize faces despite otherwise normal visual and mental function (Mayer & Rossion, 2005). This link can be further established by an intricate examination of patients who have acquired prosopagnosia do display physiological responses to the display of familiar faces. These physiological responses can be detected when skin conductance responses (SCRs) are measured. Bauer (1984) suggests that the same paradoxical relationship exists in individuals afflicted with Capgras’ syndrome. He purports that there is a bimodal method of resolving this paradox—a ventral route between visual cortex and the higher centers that run along the inferior longitudinal fasciculus. This is essentially the principle route of recognition. Additionally there is a less prominent route, a dorsal route, which entrails transport by way of the inferior parietal lobule. This is responsible for conveying the affective nature of face recognition. Bauer (1984) further purports that these routes are distinctive entities and as a direct result, they can compensate for neurological deficits individually. Renault, Signoret, DeBruille, Breton & Bolgert (1989) establish a causal relationship between damage to the ventral routes and prosopagnosia whereby damage in this area manifests itself in the inability to consciously recognize distinctive faces. Conversely, if the dorsal route is intact some facial discrimination is possible on an unconscious level. Tranel, Damasio & Damasio (1995) illustrated a disconnect between the ability to recognize a face and the results obtained on skin conductance response tests among two different groups of patients with different neurological deficits. The first group of individuals studied had occipitemporal lesions and the second group had ventromedial frontal lesions. The first group exhibited very poor facial recognition but good covert recognition. The second group exhibited good overt recognition while exhibiting no underlying difference in skin conductance response when showed both familiar and unfamiliar faces. De Haan et al. (1987) & Young (1994) utilized an alternative approach to studying the underlying similarities the neurological mechanism of prosopagnosia and Capgras’ Syndrome. In so doing, they were able to illustrate the somewhat transient nature of the two disorders in that prosopagnosic patient were able to show marked improvements in facial processing when such activity was paired with priming and matching tasks. This was irrespective of any conscious experience with regards to finding previously seen faces. Furthermore, Ellis & Young (1990) posit that the delusionary aspect of Capgras’ Syndrome may be illustrative of a neurological deficit whereby the ventral route is intact while there is a disconnect in the dorsal route. This effectively manifests itself in the condition whereby the individual afflicted with Capgras’ Syndrome is able to readily recognize faces despite the fact that the signal is lacking. The absence of the signal effectively and efficiently leads to the underlying delusionary belief. In prosopagnosia, however, the converse may occur whereby faces that are not recognized on the conscious level may elicit autonomic response. 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