Fink G R, Marshall J C, Weiss P H, Toni I, Zilles K
Institute of Medicine, Forschungszentrum Jülich, 52425, Jülich, Germany.
Neuropsychologia. 2002;40(2):119-30. doi: 10.1016/s0028-3932(01)00087-2.
Manual line bisection and a perceptual variant thereof (the Landmark test) are widely used to assess visuospatial neglect in neurological patients, but little is known about the cognitive strategies involved. In the Landmark test, one could explicitly compare the lengths of the left and right line segments; alternatively, one could compute the centre of mass of the display. We here investigate with functional MRI if these cognitive strategies modulate the neural mechanisms underlying judgements whether pre-transected horizontal lines are correctly bisected (the Landmark test) in normal volunteers. Functional neuroimaging (fMRI) was carried out in 12 healthy volunteers who judged: (a) whether the line segments on either side of the transection mark were of equal length, and (b) whether the transection mark was in the centre of the line. Line centre judgements were made significantly faster than line length comparisons. Increased neural activity common to both strategies was observed in inferior parietal lobes bilaterally and right temporooccipital cortex. Further activations, most likely reflecting general task demands like response selection and motor control, were found in the precentral gyrus bilaterally, supplementary motor area bilaterally, right anterior cingulate, right dorsolateral prefrontal cortex, cerebellar vermis, and right thalamus and right putamen. Explicit length comparisons (relative to line centre judgements) differentially activated left superior posterior parietal cortex, with a tendency toward activation of the equivalent area on the right, while the reverse comparison revealed differential activation in the lingual gyrus bilaterally and anterior cingulate cortex. The activations observed in inferior parietal cortex during task performance using either strategy are consistent with the results of lesion studies. The differential activation of superior posterior parietal cortex following length instructions suggests that explicit comparisons of spatial extent were implicated. The differential activation of bilateral occipital cortex following centre judgements suggests that the centre of a line is extracted at an early stage of visual processing.
手工直线二等分及其一种感知变体（地标测试）被广泛用于评估神经科患者的视觉空间忽视，但对于其中涉及的认知策略却知之甚少。在地标测试中，人们可以明确比较左右线段的长度；或者，也可以计算显示的质心。我们在此通过功能磁共振成像研究这些认知策略是否会调节正常志愿者判断预先横断的水平线是否被正确二等分（地标测试）时所涉及的神经机制。对12名健康志愿者进行了功能神经成像（fMRI），他们判断：（a）横断标记两侧的线段长度是否相等，以及（b）横断标记是否在线条的中心。线条中心判断的速度明显快于线条长度比较。在双侧顶下叶和右侧颞枕叶皮层观察到两种策略共有的神经活动增加。在双侧中央前回、双侧辅助运动区、右侧前扣带回、右侧背外侧前额叶皮层、小脑蚓部以及右侧丘脑和右侧壳核中发现了进一步的激活，这些激活很可能反映了诸如反应选择和运动控制等一般任务需求。明确的长度比较（相对于线条中心判断）使左侧顶上后皮层有差异地激活，右侧等效区域有激活趋势，而相反的比较则显示双侧舌回和前扣带回皮层有差异地激活。在使用任何一种策略进行任务执行期间，顶下皮层中观察到的激活与病变研究结果一致。长度指令后顶上后皮层的差异激活表明涉及对空间范围的明确比较。中心判断后双侧枕叶皮层的差异激活表明线条的中心在视觉处理的早期阶段被提取。
