Finger recognition and gesture imitation in Gerstmann's syndrome (original) (raw)
Related papers
Finger posture modulates structural body representations
Patients with lesions of the left posterior parietal cortex commonly fail in identifying their fingers, a condition known as finger agnosia, yet are relatively unimpaired in sensation and skilled action. Such dissociations have traditionally been interpreted as evidence that structural body representations (BSR), such as the body structural description, are distinct from sensorimotor representations, such as the body schema. We investigated whether performance on tasks commonly used to assess finger agnosia is modulated by changes in hand posture. We used the 'in between' test in which participants estimate the number of unstimulated fingers between two touched fingers or a localization task in which participants judge which two fingers were stimulated. Across blocks, the fingers were placed in three levels of splay. Judged finger numerosity was analysed, in Exp. 1 by direct report and in Exp. 2 as the actual number of fingers between the fingers named. In both experiments, judgments were greater when non-adjacent stimulated fingers were positioned far apart compared to when they were close together or touching, whereas judgements were unaltered when adjacent fingers were stimulated. This demonstrates that BSRs are not fixed, but are modulated by the real-time physical distances between body parts. Knowledge of the spatial configuration of bodies is mediated by a representation called the body structural description, damage to which results in conditions such as autotopoagnosia 1,2 and finger agnosia 3. Following left parietal lesions, such patients fail to point to body parts on verbal command (autotopoagnosia) or to identify their fingers (finger agnosia), yet may be relatively unimpaired in skilled action 4. For example, a patient described by Sirigu and colleagues 2 was unable to answer questions assessing knowledge of the spatial relations between body parts, such as " is the wrist next to the forearm? " , but could answer questions assessing functional knowledge about body parts, such as " what are the eyes for? ". In finger agnosia, patients are impaired at tasks that require identification of the fingers, especially by naming. A typical task for assessing finger gnosis is the " in-between task " , in which participants estimate the number of unstimulated fingers in-between two touched fingers 3. In order to solve this task, the participant has to perform at least two processing stages: (1) identifying which fingers are touched, and (2) locating the touched fingers within a structural model of the hand that represents at least the touched fingers and the untouched fingers 5. Therefore, this complex coding processing cannot be solved solely using sensory representations, but requires the use of higher-level body structural representations. Studies of neurological patients 6 and healthy adults 7–9 have converged in showing that the left and right parietal cortices may mediate the structural representations of the body (BSR), though the contribution of the two hemispheres may differ qualitatively. A study by Rusconi and colleagues, using a bi-manual version of the in-between task, suggests that the connections between the left anteromedial inferior parietal lobe (a-mIPL) and the precuneus (PCN) provide the core substrate of an explicit bilateral BSR for the fingers that when disrupted can produce the typical symptoms of finger agnosia 9 , compared to the bilateral posterior parietal cortex that contributes to on-line sensorimotor representations 10. Such dissociations have traditionally been interpreted as evidence that structural representations of the body are distinct from sensorimotor representations, such as the body schema 6,11–13. The body schema is a dynamic representation of body position which operates outside of conscious awareness to guide and control skilled action 14,15. For example, Castiello and colleagues 16 have shown that when participants were asked to reach for visual objects which were suddenly displaced after reach onset, they corrected their reach trajectory more than 300 ms before they were consciously aware of the displacement 16. By contrast, the body structural description seems not to be affected by on-line sensorimotor representations of the body. For instance, an autotopagnosic patient (G.L.) who performed poorly when asked to point or identify his own or other people's body parts, nevertheless showed normal preparatory grips necessary to grasp objects 4. In healthy humans, Rusconi and colleagues 5
Neuropsychology, 2014
OBJECTIVE: Body representation is a complex process involving different sources of top-down and bottom-up information. Processing the position and the relations among different body parts is necessary to build up a specific body representation, that is, the visuospatial body map (or topological map of the body). Here we aimed to investigate how the loss of peripheral or central information affects this representation by testing amputee and brain-damaged patients. METHOD: Thirty-two unilateral brain-damaged patients (i.e., left-brain-damaged patients and right-brain-damaged patients who were or were not affected by personal neglect), 18 lower limb amputees and 15 healthy controls took part in the study. The topological body map was assessed by means of the "Frontal body-evocation subtest" (Daurat-Hmeljiak, Stambak, & Berges, 1978), in which participants have to put tiles (each representing a body part) on a small wooden board on which a head is depicted. RESULTS: Group statistical analysis showed that in amputee patients the loss of peripheral information about the right lower limb affects the ability to represent relations among different body parts as much as the loss of top-down information in brain-damaged patients with personal neglect. Single case analysis of brain-damaged patients without personal neglect showed that the topological map of the body was deficient in 1 right-brain-damaged and 2 left-brain-damaged patients. CONCLUSIONS: Studying amputee and brain-damaged patients together allowed us to highlight the importance of visuospatial information about one's own limbs and the role of both hemispheres (not only the left one) in creating an efficient topological body representation.
Body Representation Alterations in Patients with Unilateral Brain Damage
Journal of the International Neuropsychological Society : JINS, 2021
OBJECTIVE Systematic studies about the impact of unilateral brain damage on the different body representations (body schema, body structural representation, and body semantics) are still rare. Aim of this study was to evaluate body representation deficits in a relatively large sample of patients with unilateral brain damage and to investigate the impact of right or left brain damage on body representations (BRs), independently from deficits in other cognitive processes. METHOD Sixty-four patients with unilateral stroke (22 with left brain damage, LBD; 31 with right brain damage without neglect, RBD-N; 11 with right brain damage with neglect, RBD+N) and 41 healthy individuals underwent a specific battery including BR as well as control tasks. RESULTS In more than a third of the sample, selective (37.5%) and pure (31%) deficits of BR were presented and equally distributed among the different BRs (˜10% for each representation), with selective (27.2%) and pure (22.7%) body schema defici...
Hand posture and motor imagery: a body part recognition study
Objective: Recognition of body parts activates specifi c somatosensory representations in a way that is similar to motor imagery. These representations are implicitly activated to compare the body with the stimulus. In the present study, we investigate the infl uence of proprioceptive information relating to body posture on the recognition of body parts (hands). It proposes that this task could be used for rehabilitation of neurological patients. Methods: Ten right-handed volunteers participated in this experiment. The task was to recognize the handedness of drawings of a hand that were presented in different perspectives and several orientations. For drawings of a right hand, the volunteers pressed the right key, and for drawings of a left hand, they pressed the left key. The volunteers underwent two sessions: one with their hands in a prone posture and the other with their hands in a supine posture. Results: The manual reaction time was longer for perspectives and orientations for which the real movement was diffi cult to achieve. This showed that, during the task, motor representations were activated to compare the body with the stimulus. Furthermore, the subject’s posture had an infl uence in relation to specifi c perspectives and orientations. Conclusions: These results showed that motor representations are activated to compare the body with the stimulus, and that the position of the hand infl uences this resonance between the stimulus and the body part.
Journal of Neuroscience, 2009
Neuropsychological studies suggest that the human brain is endowed with two body representations: the body schema (BS), coding the orientation of one's body parts in space, and the body structural description (BSD), coding the location of body parts relative to a standard body. We used fMRI to disentangle the neural mechanisms underlying these putatively distinct body representations. Participants saw an arm or a pot's handle (stimulus: arm, handle) rotated at different angles (angle: 30–150°). If the stimulus was an arm, subjects were instructed to imagine (1) rotating their own arm until it matched the stimulus orientation (comparing the seen arm to their own) or (2) seeing the stimulus moving toward its appropriate position on a simultaneously presented human body [comparing the arm to the one of a standard body (strategy: motor, visual imagery)]. If the stimulus was a handle, subjects were instructed to imagine (1) placing the handle on its appropriate position on a simultaneously presented pot or (2) seeing it moving toward its pot's position. The analysis of the interaction stimulus × strategy revealed activation of left secondary somatosensory cortex (SII), specifically when comparing the stimulus arm to one's own. The analysis of the parameters describing the linear effect of angle revealed that neural activity of left posterior intraparietal sulcus was modulated by the stimulus's rotation, but only when relating the arm to a standard body. The results associate BS and BSD with differential neural substrates, thereby suggesting that these are independent body representations, and furthermore extend current concepts of SII function.
The sense of the body a b s t r a c t There seems to be no dimension of bodily awareness that cannot be disrupted. To account for such variety, there is a growing consensus that there are at least two distinct types of body representation that can be impaired, the body schema and the body image. However, the definition of these notions is often unclear. The notion of body image has attracted most controversy because of its lack of unifying positive definition. The notion of body schema, onto which there seems to be a more widespread agreement, also covers a variety of sensorimotor representations. Here, I provide a conceptual analysis of the body schema contrasting it with the body image(s) as well as assess whether (i) the body schema can be specifically impaired, while other types of body representation are preserved; and (ii) the body schema obeys principles that are different from those that apply to other types of body representation.
Neuropsychologia, 2010
Neuropsychological and neuroimaging studies suggest distinct body representations involved in coding one's and others’ body. Other influential theories, however, instead posit a unique model behind coding multisensory information about one's own body and visual information about others. An efficient way to further investigate this issue can be through testing individuals with anomalous anatomical and sensorimotor bodily features. In these people, the representation of their own body is held to be different with respect to the average population due to the peculiar properties of their body, and any experimental finding supposedly mediated by this representation should reflect such difference. We reviewed the most relevant studies reporting individuals with anomalous anatomical and sensorimotor bodily features engaged in (a) handedness task, (b) visual processing of biological motion and (c) visual processing of body shape. The performance in all three kinds of cognitive processes is affected by anomalous body features of the tested populations. However, the reviewed data are also in favor of a body model extrapolated by visual experience of others which mediates processing of biological stimuli and which operates in parallel, or as an alternative, to the representation of one's own body. In light of these results, pure visual and pure embodied accounts behind visual processing of biological stimuli should be reconsidered.