Oyachi H, Ohtsuka K
Department of Ophthalmology, School of Medicine, Sapporo Medical University, Japan.
Invest Ophthalmol Vis Sci. 1995 Jun;36(7):1441-9.
Previous neurophysiological studies in the monkey have shown that the posterior parietal cortex (PPC) is involved in the control of memory-guided saccades. In this study, the authors investigated the effect of focal transcranial magnetic stimulation (TMS) over the posterior parietal cortex on accuracy of memory-guided saccades in humans to clarify the cortical region related to controlling memory-guided saccades.
Single TMS pulses were applied systematically at various locations over the parietal cortex during memory-guided saccades in human subjects. Each subject was instructed to fixate on a central target until the target was extinguished. A lateral target was flashed for 100 msec with unpredictable direction and amplitude. The subject executed a saccade to the remembered position of the previously flashed target in total darkness when the central target was extinguished. Transcranial magnetic stimulation was applied after the extinction of the central target with various latencies. Stimulation sites were identified by three-dimensional magnetic resonance imaging (MRI).
Transcranial magnetic stimulation of the right PPC degraded accuracy of rightward and leftward memory-guided saccades in all subjects, when TMS was applied 100 msec after the offset of the central target. On the other hand, TMS of the left PPC showed no effects on accuracy of memory-guided saccades. Systematic error of saccade amplitude appeared as a hypometria for rightward saccades. Three-dimensional MRI revealed that the effective stimulation site was located over the posterior portion of the intraparietal sulcus and the superior part of the angular gyrus of the right hemisphere.
These findings strongly suggest that the right PPC is involved in maintaining spatial accuracy of remembered target locations of memory-guided saccades in humans.
先前对猴子的神经生理学研究表明，后顶叶皮质（PPC）参与记忆引导扫视的控制。在本研究中，作者调查了经颅磁刺激（TMS）作用于人类后顶叶皮质对记忆引导扫视准确性的影响，以明确与控制记忆引导扫视相关的皮质区域。
在人类受试者进行记忆引导扫视期间，在顶叶皮质的不同位置系统地施加单个TMS脉冲。指示每个受试者注视中央目标，直到目标消失。一个侧向目标以不可预测的方向和幅度闪烁100毫秒。当中央目标消失时，受试者在完全黑暗中向先前闪烁目标的记忆位置执行扫视。在中央目标消失后，在不同潜伏期施加经颅磁刺激。通过三维磁共振成像（MRI）确定刺激部位。
当在中央目标消失后100毫秒施加TMS时，对所有受试者右侧PPC进行经颅磁刺激会降低向右和向左记忆引导扫视的准确性。另一方面，左侧PPC的TMS对记忆引导扫视的准确性没有影响。扫视幅度的系统误差表现为向右扫视时的运动减退。三维MRI显示，有效刺激部位位于右半球顶内沟后部和角回上部。
这些发现强烈表明，右侧PPC参与维持人类记忆引导扫视中记忆目标位置的空间准确性。
