Workshop 6 Description:

Workshop 6: Neuroscience issues in early development
Organizers: Ken Miller and Fred Wolf

In the mammalian nervous system, a classic example of pattern formation is the formation of "maps". These include the continuous mapping of the sensory periphery (e.g. the retina, or a fingertip) onto a central structure, preserving topographic relationships, and the continuous mapping of derived stimulus features such as the dominant eye or the preferred stimulus orientation for driving a central visual neuron. Theories of map formation generally involve an interplay between a number of elements: topographic matching of molecular gradients across axons and across the target structure; activity-dependent rules for synaptic growth or stabilization that typically lead to the outcome "neurons that fire together, wire together"; the patterns of activation of the input axons, in some cases driven by the patterns of sensory stimulation; and the interplay of input drive and intrinsic circuitry, both of which are simultaneously developing, in determining patterns of activation in the target structure.

In recent years, there has been great progress in elucidating the molecules involved in topographic map formation and the often non-intuitive effects on the maps of perturbing them, and models are playing a key role in making sense of these observations. There has also been great progress in understanding the dynamical mechanisms underlying feature map formation, and this theoretical work is leading to a new class of experiments involving perturbation of feature maps even in adulthood. Some aspects of feature map formation show "critical periods" -- specific developmental time windows during which abnormal sensory experience greatly alters feature maps, and outside of which the maps are relatively impervious to alterations of sensory experience. Recent years have seen enormous progress in understanding the mechanisms underlying critical periods, in particular with the demonstration that maturation of inhibition in the target structure can be necessary and sufficient to initiate the critical period. This presents enormous challenges for theorists to understand how these changes in target circuitry can radically alter the sensitivity of the development process to changes in input statistics. The workshop will articulate these challenges.

In addition, theory also addresses how particular neuronal response features are learned, a separate question from the organization of preferred features into continuous maps. Recent years have seen progress in understanding mechanisms for development of spatiotemporal, rather than merely spatial, response features such as selectivity for the direction of motion of a stimulus, and in understanding how certain nonlinear response features ("complex cells") can arise. Many open questions exist, including the computational function of observed learning rules, and how different nearby neurons can learn to detect quite diverse features from the same overall set of inputs; these questions too will be discussed in the workshop.