F. Experimental Protocols
XII. Conclusions and Prospects
Exceptional opportunities now exist for understanding brain function from flow-based markers. Flow changes indicating changes in neuronal activity can be detected Figure 9 Stimulating a row of whiskers (the middle row C) activates the appropriate barrels (row C) and generally increases flow in the cortex of row C (shading). Different methods monitor different flow-related changes in different components of blood. Qualitative changes observed in rat barrel cortex with whisker stimulation are indicated for each technique. As shown in Fig. 8, flow may be reduced or unchanged in nearby regions that are not directly activated (not hatched). For some methods (?) the effects in cortex not directly activated have not yet been determined. (For details, see Woolsey et al., 1996.)
noninvasively. It is imperative to have a firm handle on the basis of those changes. Table 1 summarizes the salient fea- tures of each method. The cranial window technique requires a craniotomy and is invasive up to the cortical surface. It is possible to install windows chronically to over- come the limitations imposed by anesthesia, and awake, sedated subjects can be secured under the microscope.
Direct observation of single vessels is limited to compara- tively small microscopic fields. Several of these techniques can be considered together to estimate local flow changes which, depending on assumptions, approach the values from the gold standard methods. A number of the video tech- niques have been used to determine the timing, extent, and stimulus parameters in activation of cortical blood flow changes with natural stimulation. As these and other factors are further understood, they will provide useful information for the design of activation and imaging sequences (e.g., Sereno et al., 1995).
Acknowledgments
This work was supported by NIH Grants NS 28781 and NS 37372 and by an award from the Spastic Paralysis Foundation of the Illinois–Eastern Iowa District of the Kiwanis International.
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Table 1 Summary of Techniques
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