Functional MRI of the brain is briefly reviewed. The two methods used in fMRI to capture hemodynamic changes induced by brain activation are described. One is to measure regional CBF change by the inflow signal for a single slice image and the other is to acquire BOLD images where the image contrast is generated by the magnetic susceptibility of red cells containing paramagnetic deoxyhemoglobin. With these types of measurements, many images are taken rapidly in time sequence at a constant image acquisition mode and thus one can follow the brain activation in real time. Various early applications of fMRI to sensory stimulations, motor responses and some of cognitive functions are described and the potentials of fMRI are discussed. The feasibility of fMRI to use in stroke field is high and the merit of the method is expected to be extremely useful in the field.
Brief ischemic insults protect against injury following subsequent longer and otherwise damaging periods of ischemia, although such protective effects have usually been quite variable. Selective changes in gene expression are considered good candidates for mediators of the tolerance phenomenon, and the stress protein, hsp72, has received considerable attention in this regard. In recent experiments we have monitored the interval of ischemic depolarization following brief periods of occlusion and have identified depolarization thresholds for tolerance, for injury and for various changes in gene expression. While hsp72 is clearly inducible after moderate insults that do not injure neurons, our results indicate that neuronal protection can be achieved by even milder insults that do not appreciably induce hsp72, but that do induce immediate-early genes of the Fos and Jun families with lower depolarization thresholds. In addition, these studies provide the basis for a reproducible model in which mechanisms of tolerance can be further studied.