Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Comparative Study
Relationship between saccadic eye movements and cortical activity as measured by fMRI: quantitative and qualitative aspects.
We investigated the quantitative relationship between saccadic activity (as reflected in frequency of occurrence and amplitude of saccades) and blood oxygenation level dependent (BOLD) changes in the cerebral cortex using functional magnetic resonance imaging (fMRI). Furthermore, we investigated quantitative changes in cortical activity associated with qualitative changes in the saccade task for comparable levels of saccadic activity. All experiments required the simultaneous acquisition of eye movement and fMRI data. ⋯ A comparison of saccade parameters revealed that saccade frequency and cumulative amplitude were comparable between the two tasks, whereas reaction times were longer in the "anti" task than the pro task. The latter finding is taken to indicate a more demanding cortical processing in the "anti" task than the "pro" task, which could explain the observed difference in BOLD activation. We hold that a quantitative analysis of saccade parameters (especially saccade frequency and latency) is important for the interpretation of the BOLD changes observed with visual stimuli in fMRI.
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The purpose of this study was to determine whether the transport of small hydrophilic molecules across the blood-brain barrier (BBB) during focal cerebral ischemia could be altered by a topical application of endothelin-1 (ET-1) in the ischemic cortex (IC). Forty minutes after middle cerebral artery (MCA) occlusion, patches of 10 nM ET-1 (low-endothelin group), 100 nM ET-1 (high-endothelin group), or normal saline (control group) were placed on the IC of rats for a 20-min period. One hour after MCA occlusion, transfer coefficient (Ki) of [14C-alpha-]aminoisobutyric acid (14C-AIB) or regional cerebral blood flow (rCBF) was determined. ⋯ However, in the High-endothelin group (n=8), the Ki of the IC was not different from that of the CC (6.9+/-2.1 vs 5.6+/-2.3 microl/g per minute) and 42% lower than that of the control group. The rCBF was not affected by 100 nM of ET-1 [control (n=6): IC 53+/-18 ml/100 g per minute, CC 94+/-23 ml/100 g per minute; high-endothelin (n=6): IC 49+/-15 ml/100 g per minute, CC 98+/-24 ml/100 g per minute]. Our data suggest that the application of endothelin-1 in the IC could reduce the transfer coefficient of small hydrophilic molecules across the BBB during focal ischemia.