Functional mapping of the cerebellar cortex usingpH sensitive dyes: An optical approach

Despite it's simple architecture, much remains to be learned about the functional organization of the cerebellar cortex. Debate regarding the relationship between the anatomy and function still exists and centers on two questions: First, how do the two most prominent architectures, the parasagittal and transverse shape the spatial characteristics of the response to peripheral input? Second, how do the parasagittal and transverse architectures define the processing of information through the cerebellar cortex?; This thesis builds upon initial observations by our laboratory using optical imaging techniques that peripheral stimulation activates parasagittal zones in the rat cerebellar cortex. However, the cerebellar afferents or circuit elements responsible for this parasagittal signal were not known. Extending that study, this thesis uses optical imaging to test the hypothesis: Hypothesis I. The parasagittal bands evoked by peripheral stimulation are due to the activation of Purkinje cells by climbing fiber afferents.; The second half of this thesis investigates whether peripheral stimulation also activates the transverse architecture of the cortex. Since the evidence for or against the activation of parallel fibers is limited, the thesis tests the following hypothesis: Hypothesis II. Peripheral stimulation functionally engages the parallel fiber{09}system.; To test these two hypotheses on the parasagittal and transverse functional architectures of the cerebellar cortex, neuronal activation was monitored optically using a high-speed digital camera and the pH sensitive dye, neutral red. Neutral red transduces shifts in pH into epifluorescent signals that were recorded both spatially and temporally. Electrical stimulation of the surface of the rat cerebellar cortex, contralateral inferior olive, and/or the ipsilateral face was used to activate cerebellar afferents and cortical elements. A wide range of stimulus frequencies was also used to delineate the optimal activation parameters and to characterize the source of the optical signals.; Quantification of the patterns of activity was accomplished using several analytical techniques. These included image subtraction and statistical thresholding to obtain activation maps and two-dimensional Fourier analysis to quantify the strengths and spatial frequencies of different patterns of activity. Singular value decomposition (SVD) was used to segregate individual components of the complex signal in space and time.