跨顱磁刺激在認知神經科學研究的角色

The Application of Transcranial Magnetic Stimulation in Cognitive Neuroscience

現代認知神經科學家使用許多先進的儀器作為研究工具，譬如fMRI、PET、ERPs、MEG、跨顱磁刺激儀（Transcranial Magnetic Stimulation，以下簡稱TMS）。在這眾多的工具中到底有什麼重要性，能提供給研究者什麼樣新的資訊？在認知神經科學的研究上最主要是在探討產生行為的大腦神經機制，在這些眾多的儀器中可以用三種向度區分，時間訊息的優越性，空間訊息的優越性，相關程度以及因果關係。每一種儀器都有其優越的地方，譬如EEG和MEG可提供精確時間向度上的訊息，而fMRI在空間向度上則可以提供準確的空間資訊。然而，他們可能都有一個共同的盲點是他們只能提供相關性的訊息，但是無法提供研究者行為與大腦之間的因果關係。要瞭解因果關係，在過去都是以腦傷病人來做研究，但由於病人的案例取得不易，研究者只能夠被動的等待病人。現在，研究者可以利用TMS來干擾特定大腦區域，確立大腦特定區域和行為之間的因果關係，且可以探討在較精細的時間點大腦特定區域對行為的影響。TMS所造成的影響是一種可逆轉的短暫干擾效果，並不會對受試者造成無法回復的影響。本文將以視覺科學與注意力的研究為例，介紹TMS在認知神經科學上所扮演的重要角色。

Many brain imaging techniques, such as fMRI, ERPs and MEG, help correlate brain activation and cognitive processes. To investigate the mechanisms of cognitive processes researchers need to go beyond the correlation evidence in order to determine the link of causality and necessity between brain activation and cognition, which were conventionally established by lesion studies. Transcranial magnetic stimulation (TMS), a noninvasive technique, frees researchers from some of the limitations of lesion experiments. For instance, TMS can introduce a disruption in processing in many regions of cortex to create “an ideal patient.” A second advantage is that TMS disruption can be applied to very discrete areas (~1cm square) whereas brain lesions often involve much larger and diffuse areas. Thirdly, the disruption that TMS induces is entirely reversible. Fourthly, TMS can provide the exact time frame of an area’s involvement in the processing of a task, which is not possible with lesion studies. Consequently, researchers can use this newly developed technology to investigate the neural mechanisms of behavioral plasticity. With the said advantages, TMS has been applied as a “transient lesion” technique in the society of Cognitive Neuroscience worldwide. The theoretical backgrounds and the current development of TMS studies will be reviewed in this article.