Ralph D. Freeman

Research Interests

Our laboratory is concerned with the neural organization of central visual pathways in the brain. We are interested in how visual information is detected, encoded, and transmitted. We seek to determine the neural basis of specific aspects of visual performance. In addition to the consideration of normal visual organization, we are interested in development and plasticity of vision.

Research Summary

Our laboratory is concerned with the neural organization of central visual pathways in the brain. We are interested in how visual information is detected, encoded, and transmitted. We seek to determine the neural basis of specific aspects of visual performance. In addition to the consideration of normal visual organization, we are interested in development and plasticity of vision. What is genetically determined and what is shaped by the visual environment? In addition, we are interested in questions concerning neural-metabolic coupling in the cerebral cortex. Our approach is to try to formulate physiologically plausible hypotheses or models whose predictions are subject to experimental verification. We then design and perform experiments that are specifically intended to test the predictions of the hypotheses or models. Our experimental approaches are neurophysiological and involve extracellular microelectrode recordings from single or multiple neurons. Most of our work concerns striate or extra-striate visual cortex but we also address questions that require recording in early visual pathways. We are able to record from small groups of cells simultaneously by use of several adjacent electrodes. This allows cross-correlation analysis to be used between different combinations of cell pairs, which provides insights about functional connections between neurons. Conventional and elaborate visual stimulation techniques are used. In this way, a variety of visual parameters can be studied simultaneously. Most of our work is of a quantitative nature we  use extensive  computer applications.

Selected Publications

Thompson, J.K., Peterson,  M., and Freeman, R.D. (2004) High resolution neurometabolic coupling revealed by focal activation of visual neurons. Nature Neuroscience.  7: 919-920

Li, B., Peterson, M., Thompson, J.K., Duong, T., and Freeman, R.D. (2005) Cross-orientation suppression: monoptic and dichoptic mechanisms are different. Journal of Neurophysiology 94: 1645-1650

Thompson J.K., Peterson M.R., Freeman R.D. (2005) Separate spatial scales determine neural activity-dependent changes in tissue oxygen within central visual pathways.  Journal of Neuroscience.  25: 9046-9058

Peterson, M., Li, B., and Freeman, R.D. (2006) Direction selectivity of neurons in the striate cortex increases as stimulus contrast is decreased.  Journal of Neurophysiology. 95: 2705-2712

Li, B., Thompson J.K., Duong, T., Peterson M.R., and Freeman, R.D. (2006) Origins of cross-orientation suppression in the visual cortex. Journal of Neurophysiology. 96: 1755-1764

Allen, E.A. and Freeman, R.D. (2006) Dynamic spatial processing originates in early visual pathways. Journal of Neuroscience. 26:11763-11774