نقشه های شناختی در غفلت از تصویرسازی

Patients with imagery neglect (RI+) show peculiar difficulties in orienting themselves in the environment. Navigational impairments could be due to a deficit in creating or using a mental representation of the environment (Guariglia, Piccardi, Iaria, Nico, & Pizzamiglio, 2005) or, according to the BBB model (Burgess, Becker, King, & O’Keefe, 2001), to a specific deficit in a mechanism that transforms an allocentric representation into an egocentric one and vice versa. Previous studies, however, do not allow discerning between a deficit in forming or in using a cognitive map, taking no notice of the fact that these are two different abilities underlain by different neuroanatomical areas, which could be independently impaired. Furthermore, the BBB model has never been verified in a population of brain-damaged patients. Therefore, we administered two tasks that separately assess the ability to create and use a cognitive map of the environment to 28 right brain-damaged patients (4 patients with imagery neglect and 4 patients with perceptual neglect) and 11 healthy participants. RI+ patients showed no specific deficit in creating or using a cognitive map, but failed to transform an egocentric representation of the environment into an allocentric one and vice versa, as predicted by the BBB model.

Patients affected by imagery neglect (RI+), that is, a deficit in processing the left side of a mental image (Bisiach & Luzzatti, 1978), have difficulty with topographical orientation (Guariglia et al., 2005, Nico et al., 2008 and Piccardi, 2009). For example, Palermo, Nori, Piccardi, Giusberti, & Guariglia, (2010) described the case of a patient with imagery neglect who had difficulty orienting himself in the environment. Furthermore, group studies using a human version of the Morris Water Maze showed that RI+ patients had deficits in finding a target location in a rectangular environment (Guariglia et al., 2005 and Nico et al., 2008). Guariglia et al. (2005) found that in RI+ patients navigational deficits arise from defective processing of mental representations of the environment (i.e. cognitive maps). The BBB model (Burgess et al., 2001 and Byrne et al., 2007), which quantitatively describes the interactions between brain regions involved in spatial memory and mental imagery, provides another interpretation of navigational deficits in RI+. According to this model, the spatial orientation difficulties of individuals with RI+ could arise from a specific deficit in a mechanism that transforms allocentric representations into egocentric ones and vice versa. The BBB model (Burgess et al., 2001 and Byrne et al., 2007) assumes that an egocentric representation of space, that is, the locations of all landmarks visible from a subject's current location in space or from a location the subject recalls from previous experiences, is maintained in the parietal cortex, and that an allocentric representation of object locations is constructed in the parahippocampal regions and projected to the hippocampus, where long-term spatial memories are stored. The idea of separate egocentric representations in parietal areas from allocentric representations in temporal areas goes back to the literature about the dorsal and ventral streams (Milner and Goodale, 1995 and Dijkerman et al., 1998), that is to the idea that the dorsal stream supports the representation of the locations of stimuli in the various egocentric reference frames appropriate to sensory perception and motor action while the ventral stream supports the visual perceptual processes related to object recognition. In the BBB model these two types of representation are supposed to interact. In particular, the BBB model postulates the existence of a transformation circuit, which transforms allocentric representations of space into egocentric ones and allows the recall of locations and identities of environmental boundaries relative to one's own location and orientation; the same circuit transforms egocentric representations of space into allocentric ones. The authors suggest that the format transformation (from-egocentric-to-allocentric and vice versa) is mediated by the retrosplenial cortex/intraparietal sulcus, and by using the representation of head-direction found along Papez's circuit (Byrne et al., 2007 and Bird and Burgess, 2008). At the present state of the art, data do not allow accepting or rejecting either or both of these interpretations. Furthermore, although the BBB model has received some support from experimental data, it has never been tested directly in brain-damaged patients. Indeed, the assumption of the deficit in imagery neglect patients derives from a review of previous studies and a computer implementation. And results obtained using the Human Morris Water Maze (Guariglia et al., 2005 and Nico et al., 2008) in previous studies in brain-damaged patients do not clarify whether RI+ patients have a problem in creating a cognitive map or in using it. This task requires subjects to memorize a target point after they perform an active searching task. They have to move around in a rectangular environment, which can be completely devoid of visual cues or contain two landmarks, until they find the target point they have to memorize. Then, they have to reach the target point in a series of subsequent trials carried out soon after the end of the searching (immediate reaching) and after a 30-min delay spent in a different environment (delayed reaching). Patients with imagery neglect showed a specific deficit in the immediate and the delayed reaching tasks both when landmarks were present and when they were absent. Although this experimental paradigm is useful in confirming the presence of specific navigational disorders in RI+, it does not clarify whether failure to reach the target point is due to a deficit in the ability to create a cognitive map or to use a well-developed cognitive map. Inasmuch as creating and using a cognitive map are two different abilities (Iaria et al., 2007 and Palermo et al., 2008), underlain by different neuroanatomical areas (Iaria et al., 2007 and Wolbers and Buchel, 2005) that could be independently damaged, the issue about the nature of the navigational deficit in imagery neglect (i.e. whether it is due to a defect in forming a map or in using it) seems relevant to clarify the role of extra-hippocampal areas in navigation processing. In the present study, we aimed to investigate (a) how the imagery deficits of patients with imagery neglect affect their ability to create and use cognitive maps and (b) to verify the predictions of the BBB model in a population of right brain-damaged patients using two tests that allow selectively assessing the ability to form maps, use cognitive maps and transform allocentric representations of the environment into egocentric ones and vice versa. In the first test, we assessed the ability to develop cognitive maps from real navigation of a novel environment (“egocentric experience”); and in the second one, we assessed the ability to use cognitive maps acquired by studying a blueprint of a different novel environment (“allocentric experience”). Both tests assess the ability to use acquired knowledge of the novel environments by relying on allocentric and egocentric representations.

Kruskal–Wallis ANOVAs with group (C, RN−, RN+, RI + ) as independent variable and scores on the different tasks (learning 1 – egocentric experience; map drawing 1 – egocentric experience; navigation 1 – egocentric experience; learning 2 – allocentric experience; map drawing 2 – allocentric experience; navigation 2 – allocentric experience) as dependent variable showed no significant differences among groups in the learning 1 – egocentric experience (H(3,33) = 5.36; n.s.), the navigation 1 – egocentric experience (H(3,33) = 4.51; n.s.), the learning 2 – allocentric experience (H(3,33) = 7.11; n.s.) or the map drawing 2 – allocentric experience (H(3,33) = 5.93; n.s.). But statistical analysis showed significant differences in the map drawing 1 – egocentric experience (H(3,33) = 10.82; p = 0.01) and the navigation 2 – allocentric experience (H(3,33) = 11.77; p < 0.01). Results of Mann–Whitney U tests showed that in the map drawing 1 – egocentric experience RI+ patients drew maps with significantly fewer elements than the C participants (U4,11 = 2; p < 0.01) and RN− patients (U4,14 = 5; p = 0.01). No differences were detected between RI+ and RN+ (U4,4 = 5; n.s.), RN+ and C (U4,11 = 7.5; n.s.), RN+ and RN− (U4,14 = 21; n.s.) or between RN− and C (U14,11 = 44; n.s.). In the navigation 2 – allocentric experience, results of the Mann–Whitney U tests showed that both RN+ and RI+ patients had significantly greater difficulty in navigating from one point to another inside the convention center with respect to the C participants (U4,11 = 3; p < 0.01 and U4,11 = 2; p < 0.01 respectively) and RN− patients (U4,14 = 9; p < 0.05 and U4,14 = 10; p < 0.05 respectively). No differences were detected between RI+ and RN+ (U4,4 = 6; n.s.) or between RN− and C (U14,11 = 56; n.s.). See Fig. 3 for details. Full-size image (26 K) Fig. 3. Means and s.d. of the performance in the experimental tasks by the different groups (C, RN−, RN+, RI + ). Figure options However, as showed in Fig. 4 the kind of errors made by RN+ and RI+ in the navigation 2 – allocentric experience task was different. Indeed, RN+ made errors only when a left turn was necessary to reach the target location (see Fig. 4a) while RI+ made errors also when a right turn was required (see Fig. 4a). Further, most of errors were made by RI+ when their position inside the environment did not match the alignment of the studied map (see Fig. 4b). Full-size image (28 K) Fig. 4. Errors made by RN+ and RI+ patients in the navigation 2 – allocentric experience task. This picture show errors made by RN+ and RI+ patients while performing the navigation task, both in successful (subject reaches the goal by not direct way, thus making directional errors) and in unsuccessful trials (subject fails in reaching the goal). a) The graph shows errors made when a left turn was necessary to reach the target room (left turns) or when a left turn was not necessary (not left turns). b) Errors were classified according to the position of the patient inside the environment in reference to the alignment of the studied map. Aligned: patient's position matched with the alignment of the studied map. Misaligned: patient's position inside the environment did not match with the alignment of the studied map. .