Vallar G
Dipartimento di Psicologia, Università di Roma La Sapienza, Italy.
Philos Trans R Soc Lond B Biol Sci. 1997 Oct 29;352(1360):1401-9. doi: 10.1098/rstb.1997.0126.
In patients with lesions in the right hemisphere, frequently involving the posterior parietal regions, left-sided somatosensory (and visual and motor) deficits not only reflect a disorder of primary sensory processes, but also have a higher-order component related to a defective spatial representation of the body. This additional factor, related to right brain damage, is clinically relevant: contralesional hemianaesthesia (and hemianopia and hemiplegia) is more frequent in right brain-damaged patients than in patients with damage to the left side of the brain. Three main lines of investigation suggest the existence of this higher-order pathological factor. (i) Right brain-damaged patients with left hemineglect may show physiological evidence of preserved processing of somatosensory stimuli, of which they are not aware. Similar results have been obtained in the visual domain. (ii) Direction-specific vestibular, visual optokinetic and somatosensory or proprioceptive stimulations may displace spatial frames of reference in right brain-damaged patients with left hemineglect, reducing or increasing the extent of the patients' ipsilesional rightward directional error, and bring about similar directional effects in normal subjects. These stimulations, which may improve or worsen a number of manifestations of the neglect syndrome (such as extrapersonal and personal hemineglect), have similar effects on the severity of left somatosensory deficits (defective detection of tactile stimuli, position sense disorders). However, visuospatial hemineglect and the somatosensory deficits improved by these stimulations are independent, albeit related, disorders. (iii) The severity of left somatosensory deficits is affected by the spatial position of body segments, with reference to the midsagittal plane of the trunk. A general implication of these observations is that spatial (non-somatotopic) levels of representation contribute to corporeal awareness. The neural basis of these spatial frames includes the posterior parietal and the premotor frontal regions. These spatial representations could provide perceptual-premotor interfaces for the organization of movements (e.g. pointing, locomotion) directed towards targets in personal and extrapersonal space. In line with this view, there is evidence that the sensory stimulations that modulate left somatosensory deficits affect left motor disorders in a similar, direction-specific, fashion.
在右半球有病变、常累及顶叶后部区域的患者中，左侧躯体感觉（以及视觉和运动）缺陷不仅反映了初级感觉过程的紊乱，还具有与身体空间表征缺陷相关的高级成分。这个与右脑损伤相关的额外因素在临床上具有相关性：与左侧脑损伤患者相比，右脑损伤患者的对侧偏身感觉缺失（以及偏盲和偏瘫）更为常见。三项主要的研究线索表明存在这种高级病理因素。（i）患有左侧半侧空间忽视的右脑损伤患者可能表现出躯体感觉刺激处理保存的生理证据，但他们并未意识到这一点。在视觉领域也获得了类似的结果。（ii）特定方向的前庭、视觉视动以及躯体感觉或本体感觉刺激可能会改变患有左侧半侧空间忽视的右脑损伤患者的空间参照系，减少或增加患者同侧向右方向误差的程度，并在正常受试者中产生类似的方向效应。这些刺激可能会改善或加重忽视综合征的多种表现（如个人空间和周边空间的半侧空间忽视），对左侧躯体感觉缺陷的严重程度（触觉刺激检测缺陷、位置感觉障碍）也有类似影响。然而，这些刺激改善的视觉空间半侧空间忽视和躯体感觉缺陷是独立的，尽管相关，但却是不同的障碍。（iii）左侧躯体感觉缺陷的严重程度受身体各节段相对于躯干矢状面的空间位置影响。这些观察结果的一个普遍含义是，空间（非躯体定位）表征水平有助于身体感知。这些空间参照系的神经基础包括顶叶后部和额叶前运动区。这些空间表征可以为组织指向个人空间和周边空间目标的运动（如指向、移动）提供感知 - 运动前接口。与此观点一致的是，有证据表明调节左侧躯体感觉缺陷的感觉刺激以类似的、特定方向的方式影响左侧运动障碍。
