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Faculty Detail     Name FRANKLIN R AMTHOR   Campus Address CH 229 Zip 1170 Phone 205-934-2694 E-mail amthorfr@uab.edu Other websites

Faculty Appointment(s) Appointment Type Department Division Rank Secondary  Neurobiology  Neurobiology Associate Professor Center  Civitan International Research Center  Civitan International Research Center Center  General Clinical Research Center  Comprehensive Neuroscience Center

Graduate Biomedical Sciences Affiliations Medical Scientist Training Program  Neuroscience  Neuroscience Graduate Program  Neurosciences

Research/Clinical Interest Title Description My early training in electrical engineering at Cornell University evolved into an interest in artificial neural nets like the Perceptron, which were developed to solve visual perception problems. I am particularly interested in how complex behavior emerges in the CNS via neural computations such as those that can be investigated in the retina. To date, little is known about how biological neural systems actually compute anything interesting. One place in the central nervous system that is computationally very interesting is the retina, because retinal ganglion cells are the first locus in the visual system of highly specific and nonlinear analyses such as motion and directional selectivity. Complex response properties of retinal ganglion cells clearly involve interactions between bipolar and amacrine cell inputs to the ganglion cell dendritic arborization, and integrative properties of the ganglion cell dendritic tree itself. However, despite the importance of the ganglion cell dendritic morphology in their function, the morphologies of most mammalian retinal ganglion cells having complex response properties were unknown as little as ten years ago. My first major research effort during the last ten years has been to identify, by intracellular recording and staining, all the major ganglion cell classes in a mammalian retina (rabbit), including directionally selective, orientation-selective and edge-detecting ganglion cells. My colleagues and I have shown that the morphologies of different physiological classes of rabbit retinal ganglion cells are distinct, and typically associated with important physiological properties of each class. More recently I have shown that the dendritic trees of some retinal ganglion cells can be described as having a fractal dimension, corresponding to its need to fill two dimensional space. My current research, supported by the National Eye Institute, seeks to determine how the entire ensemble of mammalian retinal ganglion cells apportions and codes information about the visual environment for transmission to the brain. I am particularly interested in how the temporal coherence of firing among nearby ganglion cells may help "bind" or code aspects of the visual input beyond the firing rate of any one cell by itself. I am also investigating the retinal circuitry and mechanisms underlying complex receptive field properties, and determining where in the brain each type of retinal ganglion cell projects, and what, therefore, is its role is in various aspects of visual acuity and perception. Most recently, I have developed the ability to optically image the responses of many neurons simultaneously in an isolated retina preparation, and will be using this technique to simultaneously study the responses of a large portion of the retinal network to visual stimulation. I have previously been supported by the Sloan Foundation, and the Office of Naval Research to investigate the computational aspects of the mechanism of directional selectivity in retina. Directional selectivity is particularly robust in the On-Off directionally selective ganglion cells of the rabbit retina, being independent of object contrast, shape and velocity. I am using linear and nonlinear analyses of the responses to complex stimuli, in conjunction with electrotonic models of ganglion cell dendritic trees, to test biophysical hypotheses about the synaptic mechanisms and integrative properties underlying the nonlinear selectivity for direction of motion. A goal is to relate these biophysical properties to a computational algorithm for direction of motion in sufficient detail to synthesize the function. My long term interests include research on several kinds of artificial neural nets that function in a more biophysically realistic manner than those currently in vogue. I also am interested in biomedical instrumentation relevant to visual and other neural prostheses, particularly sensory prostheses for the blind, and for diagnosis of eye and visual function disease.

Selected Publications  Publication PUBMEDID Amthor FR, Keyser KT and Dmitrieva NA. (2002) Effects of the destruction of starburst-cholinergic amacrine cells by the toxin AF64A on rabbit retinal directional selectivity. Visual Neuroscience 19: 495-509.  12511082  Reed BT, Amthor FR, and Keyser KT. (2002) Rabbit retinal ganglion cell responses mediated by "-bungarotoxin-sensitive nicotinic acetylcholine receptors. Visual Neuroscience 19:427-438.  12511076  Tjepkes, DS and Amthor FR. (2000) The role of NMDA channels in rabbit retinal directional selectivity. Visual Neuroscience 17(2): 291-302.  10824683  Merwine DK, Grzywacz NM, Tjepkes DS and Amthor FR. (1998). Non-monotonic contrast behavior in directionally selective ganglion cells and evidence for its dependence on their GABAergic input. Visual Neuroscience 15(6): 1129-1136.  9839977  Grzywacz NM, Merwine DK and Amthor FR. (1998). Complementary roles of two excitatory pathways in retinal directional selectivity. Visual Neuroscience 15(6): 1119-1128  9839976  Grzywacz NM, Amthor FR and Merwine DK (1998) Necessity of acetylcholine for retinal directionally selective responses to drifting gratings in rabbit. J. Physiol. 512.2: 575-581.  9763645  Grzywacz NM, Tootle JS and Amthor FR (1997) Is the input to a GABAergic or cholinergic synapse the sole asymmetry in rabbit’s retinal directional selectivity? Visual Neurosci. 14: 39-54.  9057267  Amthor FR, Grzywacz NM and Merwine DK. (1996) Extra-receptive field facilitation in On-Off DS ganglion cells of the rabbit retina. Visual Neuroscience 13(2): 303-310.  8737281  Amthor FR and Oyster CW. (1995) Spatial organization of retinal information about movement detection. Proc. Natl. Acad. Sci. USA. 92(9): 4002-4005.  7732021  Merwine DK, Amthor FR and Grzywacz NM. (1995) The interaction between center and surround of rabbit retinal ganglion cells. J. Neurophysiol. 73(4): 1547-1567.  7643166

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