Role of Neuronal Activity in Visual Cortical Development
Michael Weliky
The mechanisms by which the precise patterns of synaptic connectivity are established within the visual cortex remain unclear. Molecular cues, early spontaneous neuronal activity, and visual experience have been implicated in guiding the development of cortical architecture and visual behavior. We are attempting to clarify the roles that these different mechanisms play in visual cortical as well as perceptual development. In addition, experimental and computational methods are being used to analyze cortical function and circuitry in normal animals, as well as in animals that have been raised under altered developmental conditions.
To investigate the role of neuronal activity in visual cortical development, one approach we use involves multi-electrode recording. Multi-electrode recording methods permit us to examine the correlational structure of spontaneous activity within different stages of the developing visual pathway, including the lateral geniculate nucleus (LGN) and cortex. We are analyzing the relationship of these activity patterns to the emergence of visual system functional organization, such as eye-specific and ON/OFF LGN layers and cortical orientation/ocular dominance columns. We are also developing new methods to manipulate patterns of correlated neuronal activity within the developing visual pathway and assess its effect upon cortical development and visual behavior. This is accomplished through chronic neural electrical stimulation, and, most recently, by utilizing miniature head mounted visual displays and computer generated imagery to manipulate the correlational, or statistical, structure of the animal's visual experience. We are also investigating molecular mechanisms of visual cortical development utilizing gene transfection techniques to alter expression patterns of neurotrophins and other molecules in the developing cortex. In vitro brain slice methods are being used to study the effects of these manipulations upon local cortical circuits.
My lab is also utilizing optical and multi-electrode recording methods to study adult and developing cortical functional architecture and circuitry. Questions we are addressing include 1) the development and organization of multiple cortical maps, 2) spatial and temporal population codes of visual stimuli in mature and developing cortex, and 3) plasticity of population and single cell responses during visual conditioning/learning tasks. We are using these experimental results to construct computational models of network interactions across single and multiple visual areas, and to investigate their development and role in visual processing tasks such as pattern/object segmentation and discrimination.