Laycock Robin, Crewther David P, Fitzgerald Paul B, Crewther Sheila G
La Trobe University, Bundoora, Melbourne, VIC 3086, Australia.
Exp Brain Res. 2009 Jul;197(1):69-79. doi: 10.1007/s00221-009-1894-2. Epub 2009 Jun 19.
Although word recognition is a skill commonly expected to rely more on ventral rather than dorsal stream processing, there is some evidence for a magnocellular/dorsal impairment in dyslexia. The early rapid feedforward/feedback loop through the dorsal stream seen in primate has been suggested to allow an initial global analysis, and in human early activation of parietal attention mechanisms for detecting salient stimuli, facilitating more local level detailed ventral stream processing. To test this model in humans, transcranial magnetic stimulation (TMS) was used to probe the role of early visual cortex (V1/V2) and V5/MT+ in single word identification. TMS over V1/V2 between word onset and 36 ms post word onset disrupted accurate word discrimination, with disruption also evident at approximately 99 ms. TMS over V5/MT+ also disrupted accuracy following stimulation at approximately the same time as word onset and again at 130 ms post word onset. Thus, a role for V5/MT+ in accurate single word identification is apparent suggesting rapid triggering of attention to salient exogenous stimuli may be required prior to processing in primary and temporal cortical regions.
尽管人们通常认为单词识别技能更多地依赖腹侧而非背侧流处理，但有一些证据表明诵读困难症患者存在大细胞/背侧损伤。灵长类动物中通过背侧流的早期快速前馈/反馈回路被认为可以进行初步的全局分析，而在人类中，顶叶注意力机制的早期激活用于检测显著刺激，从而促进更局部层面的腹侧流详细处理。为了在人类中测试该模型，经颅磁刺激（TMS）被用于探究早期视觉皮层（V1/V2）和V5/MT+在单字识别中的作用。在单词开始后至单词开始后36毫秒之间对V1/V2施加TMS会干扰准确的单词辨别，在大约99毫秒时干扰也很明显。在单词开始时及单词开始后130毫秒再次对V5/MT+施加TMS也会干扰准确性。因此，V5/MT+在准确的单字识别中的作用是明显的，这表明在初级和颞叶皮质区域进行处理之前，可能需要快速触发对显著外部刺激的注意力。
