Michael A. Freed, Ph.D.

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Adjunct Associate Professor of Neuroscience
Department: Neuroscience

Contact information
131 John Morgan Bldg
3620 Hamilton Walk
Department of Neuroscience
Perelmann School of Medicine
University of Pennsylvania
Philadelphia, PA 19104
B.A. (Psychology)
Yale University, 1976.
Ph.D. (Neuroscience)
University of Pennsylvania, 1985.
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Description of Research Expertise

Structure and function of the vertebrate visual system

In vitro retina and brain slices, whole cell recording, transgenic mice, computer modeling of neural circuits

At present, my research addresses the following problem: the retina contains multiple ganglion cells which send disparate messages to the visual thalamus. These messages are about color, spatial frequency, direction of motion, and the onset or offset of visual objects. How these disparate messages interact in the visual thalamus, to provide information to the cortex, is poorly understood.

Our lab is developing mouse models to investigate inhibitory mechanisms in the visual thalamus. The murine retina contains at least as many types of ganglion cell as human retinas do. The murine visual thalamus contains inhibitory neurons that provide input to thalamocortical neurons within triadic circuits, as they do in humans. Thus we express channelrhodopsin or halorhodopsin in interneurons to activate or silence them optogenetically. We also express channelrhodopsin in different types of retinal ganglion cell to activate their axons in the thalamus. These mouse models will allow us to determine how interneurons modify information transmitted to the cortex. We hypothesize that interneurons modify the temporal synchrony imposed by visual objects on the firing patterns of thalamocortical neurons.

Genetic and electronic prostheses show great promise for restoring vision in blind humans. This research will clarify how inhibition in the visual thalamus modifies messages that the retina sends to the cortex, and will contribute to the design of retinal prostheses intended to restore vision.

Selected Publications

Freed Michael A: Asymmetry between ON and OFF alpha ganglion cells of mouse retina: integration of signal and noise from synaptic inputs. The Journal of Physiology 595(22): 6979-6991, Nov 2017.

Homann Jan, Freed Michael A: A Mammalian Retinal Ganglion Cell Implements a Neuronal Computation That Maximizes the SNR of Its Postsynaptic Currents. Journal of Neuroscience 37(6): 1468-1478, Feb 2017.

Freed, Michael A: The Retina. Handbook of Visual Optics, Volume One: Fundamentals and Eye Optics. Pablo Artal (eds.). CRC Press, 1, 2017.

Freed, Michael A., Liang, Zhiyin : Synaptic noise is an information bottleneck in the inner retina during dynamic visual stimulation. Journal of Physiology 592(4): 635–651, 2014.

Liang, Zhiyin, Freed Michael A.: Cross inhibition from ON to OFF pathway improves the efficiency of contrast encoding in the mammalian retina. Journal of Neurophysiology 108(10): 2679-88, Nov 2012.

Liang, Zhiyin, Freed, Michael A.: The On pathway rectifies the Off pathway of the mammalian retina. Journal of Neuroscience 30: 5533 - 5543, 2010.

Freed, MA, Liang, Z: Reliability and frequency response of excitatory signals transmitted to different types of retinal ganglion cell. Journal of Neurophysiology 103: 1508-17, 2010.

Xu, Y., Vasudeva, V., Vardi, N., Sterling, P., Freed, M. A.: Different types of ganglion cell share a synaptic pattern. Journal of Comparative Neurology 507(6): 1871-8, 2008.

L.-L. Zhang M.A. Freed.: Two-Photon Photolysis of Glutamate Reveals Hot Spots on the Dendrites of Retinal Ganglion Cells. Investigative Ophthalmology and Visual Science 49: 5802, 2008.

Tokutake, Y., Freed, M. A.: Retinal ganglion cells - spatial organization of the receptive field reduces temporal redundancy. European Journal of Neuroscience 28: 914-923, 2008.

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Last updated: 02/16/2022
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