左前额叶参与非相关词对的语义编码过程──来自光学成像的佐证

通过研究左前额叶在非相关同对的语义编码过程中的作用，探讨近红外光学成像技术用于脑高级认知活动检测的可行性。被试在两种实验条件下分别学习视觉呈现的20个汉字非相关词对，要求被试或将词对组成一个有意义的句子(深加工)，或判断两个词是否具有相同的结构组合(浅加工)。光学成像器即时记录连续光透过额骨及前额皮层后760nm和850nm的漫射光强变化，以此推测相应脑组织的血容量变化。结果表明，与浅加工相比，左下前额叶在深加工时的血容量增多，尤其是背外侧部分。

LEFT PREFRONTAL LOBE CONTRIBUTED TO SEMANTIC ENCODING OF UNRELATED WORD PAIRS: A NEAR-INFRARED SPECTROSCOPY STUDY

In addition to positron emission tomography (PET) and functional magnetic resona nce imaging (fMRI) that can measure brain function in vivo, near-infrared spectr oscopy (NIRS) is being used in various fields of neuroscience. In the near-infra red region, light with wavelength of 760nm and 850nm have different characterist ics of absorbing two different states of hemoglobin (Hb), the oxyhemoglobin(O2Hb) and deoxyhemoglobin (HHb). The relative metabolic changes of O2Hb, HHb an d the total of them, the blood volume within the measured regions, can be detect ed. This study explored the feasibility of NIRS in detecting higher brain functi on, by investigating the role of the left prefrontal lobe in semantically encodi ng unrelated word pairs. The subjects studied unrelated word pairs that were vis ually presented under both semantic and shallow conditions. In semantic (or deep ) task, subjects were asked to form a sentence including the two words, while in perceptual (or shallow) task, they were asked to judge whether the two words ha d the same orthographic structures. Optical imager measured the relative changes of 760nm and 850nm absorption when the continuous light diffused through the le ft prefrontal lobe during the encoding tasks. In terms of intensity change, the regional blood volume change could be measured. Finally, subjects performed the recognition task. The results showed that recognition performance was better in semantic task than that in the perceptual task. Correspondingly, t he blood volume of the left prefrontal lobe, especially the dorsal part, increas ed in the semantic task as compared with the perceptual task. The proportion of the activated subjects out of the total subjects was higher in regions C and D t han in regions A and B. It demonstrated that the left prefrontal lobe contribute d to semantic encoding of unrelated word pairs. The present research also sugges ted that NIRS can be used to measure higher brain function non-invasively, for e xample, memory process.