Vakalopoulos C
171 McKean Street, North Fitzroy, Melbourne 3068, Australia.
Med Hypotheses. 2007;68(3):574-600. doi: 10.1016/j.mehy.2006.08.013. Epub 2006 Oct 27.
Unilateral neglect is a devastating condition, which manifests as a loss of a person's spatial awareness opposite the damaged side of the brain. It challenges our conception of the seat of the soul and its explanation is at the heart of the mind-body problem. A heuristic definition of the dorsal stream of a modality is here based on the categorization of parietal networks by the cerebellar component of motor efference copy. Taking this premise, the proprioceptive space of a stimulus is established as a concept in this paper. It is proposed that unilateral neglect is typically a dysfunction of proprioceptive space of a stimulus associated with lesions of the dorsal stream. Furthermore, most experimental findings of unilateral visual neglect (and by extrapolation, other sensory modalities), can be explained by two developmental mechanisms by which the proprioceptive space of a stimulus is encoded in the parietal cortex. Its right and left hemisphere representation can be dissociated from the hemifield of presentation of perceptual information, such that the left hemifield can have a left hemisphere representation through callosal connections and likewise, the right hemifield can have a right hemifield representation. The processing of a sensory stimulus in either parietal hemisphere is dynamically determined as shown by experimental modulation of performance. A theory of historical precedence will provide a developmental background to the organization of proprioceptive space and will invoke separate models according to specified terms of engagement. A model based on the expansion and contraction of the proprioceptive space of a stimulus as a gradient across both hemispheres and modulated by concurrent proprioceptive state will be differentiated from a model that is non-graduating but competitive and lacks such modulation. In other words, the dorsal representation of a sensory stimulus in the former case is shared to a varying degree by the two parietal hemispheres, whereas in the latter case the representation of left and right aspects of the same object stimulus is strictly divided between the two hemispheres. A further hypothesis of a dorsoventral gradient of the peripheral and foveal components of proprioceptive space characterizing dorsal stream networks will predict the double dissociation revealed by experimental paradigms. It will explain why some patients show neglect only in foveal while others only in peripheral vision. The paper proposes to unify neglect, extinction and optic ataxia on the one hand, and spatial and object-based neglect on the other hand, under a singularly proficient paradigmatic structure. A binding model as described is a component theory that acknowledges how the involved pathways or transitional zones in a pathway may contribute to a differential clinical picture as one progresses from posterior to anterior parietal cortex. Finally, a brief discussion is given on how autistic subjects neglect spatial cues and the inability of a spatial cognitive transformation underlies the impairments postulated for 'a theory of mind'.
单侧忽视是一种严重的病症，表现为患者对大脑受损侧对侧的空间感知丧失。它挑战了我们对灵魂所在之处的认知，其解释是身心问题的核心。本文基于运动传出副本的小脑成分对顶叶网络的分类，给出了一种关于某一感觉模态背侧通路的启发式定义。基于这一前提，本文将刺激的本体感觉空间确立为一个概念。有人提出，单侧忽视通常是与背侧通路损伤相关的刺激本体感觉空间的功能障碍。此外，单侧视觉忽视（以及由此推断的其他感觉模态）的大多数实验结果，可以通过两种发育机制来解释，即刺激的本体感觉空间在顶叶皮层中是如何编码的。其左右半球的表征可以与感知信息呈现的半视野分离，这样左半视野可以通过胼胝体连接具有左半球表征，同样，右半视野可以具有右半视野表征。如实验对表现的调节所示，任一顶叶半球对感觉刺激的处理是动态确定的。一种历史优先理论将为本体感觉空间的组织提供一个发育背景，并将根据特定的参与条件调用不同的模型。一个基于刺激本体感觉空间在两个半球上作为梯度的扩展和收缩并由并发本体感觉状态调节的模型，将与一个非渐变但具有竞争性且缺乏这种调节的模型区分开来。换句话说，在前一种情况下，感觉刺激的背侧表征在一定程度上由两个顶叶半球共享，而在后一种情况下，同一物体刺激的左右方面的表征在两个半球之间严格划分。关于本体感觉空间的外周和中央凹成分的背腹梯度表征背侧通路网络的进一步假设，将预测实验范式所揭示的双重分离。这将解释为什么一些患者仅在中央凹视觉中表现出忽视，而另一些患者仅在外周视觉中表现出忽视。本文提议在一个独特的有效范式结构下，一方面将忽视、消退和视觉性共济失调统一起来，另一方面将基于空间和基于物体的忽视统一起来。所描述的一个捆绑模型是一种成分理论，它承认当一个人从后顶叶皮层向前顶叶皮层进展时，所涉及的通路或通路中的过渡区域可能如何导致不同的临床症状。最后，简要讨论了自闭症患者如何忽视空间线索，以及空间认知转换的无能是如何构成“心理理论”所假定的损伤的基础的。
