Research Summary

The organization and development of functional maps in cerebral cortex.

Research Description

I am interested in understanding how the sensory world is represented in the mammalian brain. To study this process, I am looking at the organization and function of the primary visual cortex (V1). Individual neurons in V1 are selectively responsive to specific aspects of visual scenes - aspects such as the orientation of edges, or the eye through which a scene is viewed (ocular dominance). The process by which these neurons become selectively responsive is constrained by both genetically determined events and by the environment to which the young animal is exposed. How these selective response properties develop, become organized within a sensory area, and how this organization contributes to the perception of the world are the focus of my research.

My current goal is to understand the general rules by which many different response properties can be organized in a relatively small patch of cortex. To determine how multiple response properties are organized in the primary visual cortex, I am using a functional imaging technique, intrinsic signal imaging, to simultaneously map responses to many different types of stimuli. In the first study, the organization of 3 specific stimulus properties was investigated: stimuli that vary in the eye to which they are presented (producing a map of ocular dominance), in orientation, and in spatial frequency (the spacing of contrast). The general rules for the organization of these three maps (Issa et al., J. Neurosci. 2000) constrain models of cortical development and explain how all combinations of orientation and spatial frequency preference are represented in the primary visual cortex. Based on the relationships found among these properties, it has also been possible to suggest a general method for studying cortical maps that is directly applicable to high-resolution functional mapping in animals, and will eventually be applicable to functional imaging in humans.

Future inquiries will address the generality of these organizational and mapping rules on other response properties in cortex.

Selected Papers

Issa, N.P., Rosenberg, A., Husson, T.R. Models and measurements of functional maps in V1. J. Neurophysiol. (review). In press (2008).

Grossman, K., Ross, J., Kay, L., Issa, N.P. Glomerular activation patterns and the perception of odor mixtures. Eur. J. Neurosci. In press (2008).

Zhang, J.X., Rosenberg, A., Mallik, A.K., Husson, T.R., Issa, N.P. (2007) The representation of complex images in spatial frequency domains of primary visual cortex. J. Neurosci., 27:9310-9308.

Husson, T., Mallik, A.K., Zhang, J., Issa, N.P. (2007) Functional Imaging of Primary Visual Cortex Using Flavoprotein Autofluorescence. J. Neurosci., 27:8665-8675.

Baker, T.I., Issa, N.P. (2005) Separable cortical maps underlie population responses to complex visual stimuli. J. Neurophysiol., 94:775-787.

Issa, N.P. (2003) Inhibitory circuits in sensory maps develop through excitation. TINS, 26:456-458.

Frank, M. G., Issa, N. P., Stryker, M. P.  (2001)  Sleep enhances plasticity in the developing visual cortex. Neuron, 30:275-287.

Issa, N. P., Trepel, C., Stryker, M. P.  (2000)  Spatial frequency maps in cat visual cortex.  J. Neurosci., 20:8504-8514.

Issa, N. P., Trachtenberg, J. T., Chapman, B., Zahs, K. R., Stryker, M. P.  (1999)  The critical period for ocular dominance plasticity in the ferret's visual cortex.  J. Neurosci., 19:6965-6978

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