Murphey Dona K, Maunsell John H R
Department of Neuroscience, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA.
Curr Biol. 2007 May 15;17(10):862-7. doi: 10.1016/j.cub.2007.03.066. Epub 2007 Apr 26.
The extent to which areas in the visual cerebral cortex differ in their ability to support perceptions has been the subject of considerable speculation. Experiments examining the activity of individual neurons have suggested that activity in later stages of the visual cortex is more closely linked to perception than that in earlier stages [1-9]. In contrast, results from functional imaging, transcranial magnetic stimulation, and lesion studies have been interpreted as showing that earlier stages are more closely coupled to perception [10-15]. We examined whether neuronal activity in early and later stages differs in its ability to support detectable signals by measuring behavioral thresholds for detecting electrical microstimulation in different cortical areas in two monkeys. By training the animals to perform a two-alternative temporal forced-choice task, we obtained criterion-free thresholds from five visual areas--V1, V2, V3A, MT, and the inferotemporal cortex. Every site tested yielded a reliable threshold. Thresholds varied little within and between visual areas, rising gradually from early to later stages. We similarly found no systematic differences in the slopes of the psychometric detection functions from different areas. These results suggest that neuronal signals of similar magnitude evoked in any part of visual cortex can generate percepts.
视觉大脑皮层中各区域在支持感知能力方面的差异程度一直是大量推测的主题。研究单个神经元活动的实验表明，视觉皮层后期的活动比早期的活动与感知的联系更为紧密[1 - 9]。相比之下，功能成像、经颅磁刺激和损伤研究的结果被解释为表明早期阶段与感知的耦合更为紧密[10 - 15]。我们通过测量两只猴子不同皮层区域中检测电微刺激的行为阈值，来研究早期和后期神经元活动在支持可检测信号能力方面是否存在差异。通过训练动物执行二选一的时间强制选择任务，我们从五个视觉区域——V1、V2、V3A、MT和颞下皮层获得了无标准阈值。每个测试部位都产生了可靠的阈值。阈值在视觉区域内和区域间变化很小，从早期到后期逐渐升高。我们同样没有发现不同区域心理测量检测函数斜率的系统差异。这些结果表明，在视觉皮层任何部位诱发的幅度相似的神经元信号都能产生感知。
