ABSTRACT
Objective To explore the role of the prefrontal cortex in semantic encoding of unrelated word pairs by using functional near-infrared spectroscopy (fNIRS). Method Forty-eight subjects were presented unrelated pairs of Chinese words under both the nonsemantic and semantic encoding conditions. Under the nonsemantic condition, subjects judged whether the two words had similar orthographic structures; under the semantic condition, they generated a sentence involving the presented word pairs. The changes of regional blood volume associated with the cognitive tasks were measured by using fNIRS equipment which was a continuous optical imager. Result The regions that corresponded to the prefrontal regions showed greater activation under semantic than nonsemantic condition in both left and right hemispheres, although the extent of the activation was larger in the left than right prefrontal regions. This result was consistent with other neuroimaging studies on unrelated word pairs processing, but did not conform to the strict interpretations of the hemispheric encoding/retrieval asymmetry model (HERA). Conclusion This study suggests that material specificity is one of the important factors to influence hemispheric asymmetry in memory encoding. When associations between items are required, right prefrontal regions participate in the encoding processing as well. It also indicates that fNIRS imaging is a viable method of investigating higher level cognitive processing such as memory.
ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the changes in near infrared spectroscopy (NIRS) absorptive properties induced by cerebral ischemia.</p><p><b>METHODS</b>A dual wavelength (760 nm and 850 nm) NIRS system measuring total hemoglobin concentration changes was constructed. Twenty Sprague-Dawley rats were used to set up middle cerebral artery occlusion (MCAO) model that had a stable ischemia focus on the cortex. We used NIRS to localize the ischemia focus that was confirmed with magnetic resonance imaging (MRI) and triphenyltetrazonlium chloride brain staining. The cortical ischemia area and the geometric configuration of the NIRS topograms were compared with those from MRI and the anatomical samples for the same rat.</p><p><b>RESULTS</b>The reconstructed NIRS topograms showed that there was an optical density decreased area on the left cortex of the rats with MCAO model. The mean ischemia area as shown in NIRS images was 19.50 mm2 (19.50 +/- 0.35 mm2, n = 20). Anatomical samples showed that the mean ischemic area located in the NIRS measurement area was 18.46 mm2 (18.46 +/- 0.38 mm2, n = 20). For MRI, the mean ischemia area located in the NIRS measurement area was 20.71 mm2 (20.71 +/- 0.27 mm2, n = 20). There were no significant differences among NIRS, MRI and anatomical samples (F(2,57) = 2.47, P > 0.05) for defining the ischemia area. The results showed that there was a significant correlation among NIRS, MRI (r = 0.782, P < 0.05) and anatomical sample (r = 0.851, P < 0.05) for the same cortical ischemia area. Meanwhile, the location and geometric configuration of the ischemia focus shown by NIRS were identified by MRI and anatomical samples, though the NIRS images had worse spatial resolution.</p><p><b>CONCLUSIONS</b>NIRS showed a good agreement with MRI and anatomical samples in the ischemic area and location determination of the infarction focus for the rat MCAO model. The study suggests that NIRS can non-invasively trace cortical hemodynamic changes induced by ischemia in real time.</p>