Transcutaneous electrical stimulation and vibration of neck muscles in neglect

Four neglect patients without visual field defects, one with a lesion of the right basal ganglia and three with a right, predominantly parietal lesion, were examined with a cancellation and a copying task before, during and after neck muscle vibration, during transcutaneous electrical stimulation of neck muscles and during vibration of hand muscles on the left side. In all patients, neck muscle vibration improved task performance, while transcutaneous electrical stimulation and hand vibration had little or no effect. The present results demonstrate that the effect of neck muscle vibration cannot be explained as arousal and activation due to unspecific sensory stimulation on the contralesional side of the body. They rather argue for the assumption that the compensatory effect of neck muscle vibration on neglect is an effect induced by the predominant activation of afferent Ia nerve fibres and their specific contribution to the central representation of egocentric space.     

Mirror writing resulting from an egocentric representation disorder: A case report

Abstract

We describe the case of a 74-year-old man with selective apraxia for transitive gestures (gestures of object use) following a left temporo-parietal infarction. We document his neuropsychological progress over 2 years and assess his praxic abilities according to the best-developed cognitive model of praxis. Strikingly, PF was unable to pantomime transitive gestures in every test modality (verbal command, imitation, photographs of objects and handling actual tools), but could still execute symbolic (e.g. salute) and meaningless gestures. He was able to discriminate and recognize transitive gestures as well as controls. His praxic impairment has persisted through the years in the absence of dementia. His inability to use tools cannot be accounted for on the basis of a visual agnosia, impaired language comprehension or a classic ideomotor apraxia. Such a selective deficit of transitive gestures is incompatible with the cognitive model proposing that the production of all meaningful gestures (symbolic and transitive) requires a final common pathway. Rather, these findings indicate a selective deficit in the production system, which is inefficient at implementing specific representations for complex object-related gestures. Our findings also support a dissociation between semantic (what) and functional (how) knowledge of an object.     

Assessment and Functional Impact of Allocentric Neglect: A Reminder from a Case Study

SR suffered a right hemispheric stroke more than 3 years ago, and now lives with left-sided hemiparesis and chronic spatial neglect due to damaged white matter pathways connecting the frontal, temporal and parietal regions. We report here that SR suffers from both viewer-centered (i.e., egocentric) and object-centered (i.e., allocentric) spatial neglect. Notably, unlike most neuropsychological and functional assessments that focus on egocentric deficits, a specialized neuropsychological figurative discrimination test (the Apples test) revealed SR’s allocentric neglect. Further, using assessments sensitive to detect functional deficits related to allocentric neglect, we observed SR’s difficulty in reading and using clocks, reflecting his object-centered errors in these everyday activities. SR’s case suggests that allocentric-specific assessments, both neuropsychological and functional, are valuable in standard neglect examinations, particularly to predict daily function after stroke. We recommend that neglect-related functional disability be distinguished further with respect to allocentric spatial deficits, and functional assessments for allocentric neglect should be validated in future large sample studies. Identifying allocentric neglect early, and learning about its influence on daily function, may enhance care quality and facilitate effective rehabilitation planning for stroke recovery.     

The role of egocentric and allocentric abilities in Alzheimer's disease: A systematic review

A great effort has been made to identify crucial cognitive markers that can be used to characterize the cognitive profile of Alzheimer's disease (AD). Because topographical disorientation is one of the earliest clinical manifestation of AD, an increasing number of studies have investigated the spatial deficits in this clinical population. In this systematic review, we specifically focused on experimental studies investigating allocentric and egocentric deficits to understand which spatial cognitive processes are differentially impaired in the different stages of the disease. First, our results highlighted that spatial deficits appear in the earliest stages of the disease. Second, a need for a more ecological assessment of spatial functions will be presented. Third, our analysis suggested that a prevalence of allocentric impairment exists. Specifically, two selected studies underlined that a more specific impairment is found in the translation between the egocentric and allocentric representations. In this perspective, the implications for future research and neurorehabilitative interventions will be discussed.     

Numbers are represented in egocentric space: Effects of numerical cues and spatial reference frames on hand laterality judgements

Convergent findings demonstrate that numbers can be represented according to a spatially oriented mental number line. However, it is not established whether a default organization of the mental number line exists (i.e., a left-to-right orientation) or whether its spatial arrangement is only the epiphenomenon of specific task requirements. To address this issue we performed two experiments in which subjects were required to judge laterality of hand stimuli preceded by small, medium or large numerical cues; hand stimuli were compatible with egocentric or allocentric perspectives. We found evidence of a left-to-right number–hand association in processing stimuli compatible with an egocentric perspective, whereas the reverse mapping was found with hands compatible with an allocentric perspective. These findings demonstrate that the basic left-to-right arrangement of the mental number line is defined with respect to the body-centred egocentric reference frame.     

The elevator illusion results from the combination of body orientation and egocentric perception

Perception of body orientation and apparent location of objects are altered when humans are using assisted means of locomotion and the resultant of the imposed acceleration and gravity is no longer aligned with the gravitational vertical. As the otolithic system cannot discriminate the acceleration of gravity from sustained inertial accelerations, individuals would perceive the resultant acceleration vector (GiA) as the vertical. However, when subjects are aligned on the GiA, an increase in the magnitude of GiA induced a lowering of the apparent visual horizon (i.e. “elevator illusion”). The main aim of this study was to quantify the contribution of body and egocentric perception in the elevator illusion. While being exposed to 1 G and 1.3 G and aligned on the GiA acceleration, subjects (N = 20) were asked (1) to set a luminous target to the subjective horizon, (2) to set a luminous target on “straight ahead” position (egocentric task) and (3) to rotate a tilting tube to their subjective perception of body orientation. Results showed that increasing GiA lowered horizon and egocentric settings and induces a backward body tilt perception. Moreover, the elevator illusion can be expressed as the additive combination of two processes: one that is dependent on body tilt perception, and the other that is dependent on egocentric perception. Both misperceptions in hypergravity may be considered to be a consequence of excessive shearing of the otolith organs. However large inter-individual differences in body tilt perception were observed. This last result was discussed in terms of the contribution of extravestibular graviceptors.     

Spatial and temporal dynamics of visual search tasks distinguish subtypes of unilateral spatial neglect: Comparison of two cases with viewer-centered and stimulus-centered neglect

We developed a computerised test to evaluate unilateral spatial neglect (USN) using a touchscreen display, and estimated the spatial and temporal patterns of visual search in USN patients. The results between a viewer-centered USN patient and a stimulus-centered USN patient were compared. Two right-brain-damaged patients with USN, a patient without USN, and 16 healthy subjects performed a simple cancellation test, the circle test, a visuomotor search test, and a visual search test. According to the results of the circle test, one USN patient had stimulus-centered neglect and a one had viewer-centered neglect. The spatial and temporal patterns of these two USN patients were compared. The spatial and temporal patterns of cancellation were different in the stimulus-centered USN patient and the viewer-centered USN patient. The viewer-centered USN patient completed the simple cancellation task, but paused when transferring from the right side to the left side of the display. Unexpectedly, this patient did not exhibit rightward attention bias on the visuomotor and visual search tests, but the stimulus-centered USN patient did. The computer-based assessment system provided information on the dynamic visual search strategy of patients with USN. The spatial and temporal pattern of cancellation and visual search were different across the two patients with different subtypes of neglect.     

Increase of the hippocampal theta activity in the Morris water maze reflects learning rather than motor activity

The change in the percentage of rat hippocampal high-frequency theta activity from being immobile and awake to swimming behaviour was calculated for three groups of rats, trained in either place learning, cue learning or egocentric learning in the Morris water maze. The place-learning-trained rats showed an increase in the percentage of theta activity, along with a significant reduction in escape latency over the last 3 days of training. No changes were observed in the other two groups. Because the motor activity displayed by the three groups of rats was similar, we suggest that the increase in the percentage of theta activity concomitant with place-learning training could be related to the processing of information by the hippocampus, rather than to the displayed motor activity.     

Selective rotation of egocentric spatial representation following right putaminal hemorrhage

Although the role of frontoparietal cortex in spatial egocentric processing is well established, recent animal-lesion and human functional imaging studies have suggested that the neostriatum may also be a critical modulator in the processing of body-centred spatial orientation. We describe here a patient with right putamen-centred hemorrhage who exhibited a consistent counterclockwise rotation of approximately 90 degrees when drawing and writing from memory. A more detailed assessment with a series of representational clock tests demonstrated that the rotation was present only in tasks requiring the use of egocentric cues. In the absence of external cues the patient would adopt and maintain a stable but incorrectly-oriented egocentric representation of the imagined or recollected object. By contrast, performance could be rectified by presentation of correctly-oriented stimuli. These findings suggest that the putamen is part of a circuit underlying egocentric, as opposed to allocentric, representation of space in humans.     

自我中心言语理论及其对聋生言语康复教育的启示

自我中心言语是儿童言语和思维发展过程中的一个重要现象。在介绍皮亚杰和维果茨基关于自我中心言语的相关理论后，本文对聋生言语康复教育中的一些问题进行了探讨。