Faculty Bibliography

In this paper, we describe a nonlinear image representation based on divisive normalization that is designed to match the statistical properties of photographic images, as well as the perceptual sensitivity of biological visual systems. We decompose an image using a multi-scale oriented representation, and use Student's t as a model of the dependencies within local clusters of coefficients. We then show that normalization of each coefficient by the square root of a linear combination of the amplitudes of the coefficients in the cluster reduces statistical dependencies. We further show that the resulting divisive normalization transform is invertible and provide an efficient iterative inversion algorithm. Finally, we probe the statistical and perceptual advantages of this image representation by examining its robustness to added noise, and using it to enhance image contrast.

BACKGROUND: Fibers containing galanin (GAL) enlarge and hyperinnervate cholinergic basal forebrain (CBF) nucleus basalis (NB) neurons in late-stage Alzheimer's disease (AD), yet the physiological consequences of this phenomenon are unclear. OBJECTIVE: To determine whether GAL hyperinnervation of cholinergic NB neurons modulates the expression of genes critical to cholinergic transmission [e.g. acetylcholine (ACh) metabolism and ACh receptors] in AD. METHODS: Single-cell gene expression profiling was used to compare cholinergic mRNA levels in non-GAL-hyperinnervated NB neurons in tissue autopsied from cases classified as having no cognitive impairment (NCI) or late-stage AD (AD/GAL-) and in GAL-hyperinnervated (AD/GAL+) NB neurons from the same AD subjects. RESULTS: AD/GAL+ cells displayed a significant upregulation in choline acetyltransferase (ChAT) mRNA expression compared to NCI and AD/GAL- cells. CONCLUSION: GAL fiber hyperinnervation of cholinergic NB neurons upregulates the expression of ChAT, the synthetic enzyme for ACh, suggesting that GAL regulates the cholinergic tone of CBF neurons in AD