Development of Continuous and Discrete Neural Maps
ABSTRACT Two qualitatively different kinds of neural map have been described: continuous maps exemplified by the visual retinotopic map, and discrete maps exemplified by the olfactory glomerular map. Here, we review developmental mechanisms of retinotopic and olfactory glomerular mapping and discuss underlying commonalities that have emerged from recent studies. These include the use of molecular gradients, axon-axon interactions, and the interplay between labeling molecules and neuronal activity in establishing these maps. Since visual retinotopic and olfactory glomerular maps represent two ends of a continuum that includes many other types of neural map in between, these emerging general principles may be widely applicable to map formation throughout the nervous system.
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- "The cellular and molecular mechanisms underlying many steps of mammalian brain circuit assembly have been explored in detail. Prominent examples include growth cone navigation through intermediate choice points (Dickson, 2002), topographic mapping (Luo and Flanagan, 2007; Cang and Feldheim, 2013), and laminar specificity (Huberman et al., 2010; Robles and Baier, 2012; Baier, 2013). Among the lesser understood steps involved in circuit assembly, however, is axon-target matching. "
ABSTRACT: The mammalian eye-to-brain pathway includes more than 20 parallel circuits, each consisting of precise long-range connections between specific sets of retinal ganglion cells (RGCs) and target structures in the brain. The mechanisms that drive assembly of these parallel connections and the functional implications of their specificity remain unresolved. Here we show that in the absence of contactin 4 (CNTN4) or one of its binding partners, amyloid precursor protein (APP), a subset of direction-selective RGCs fail to target the nucleus of the optic tract (NOT)-the accessory optic system (AOS) target controlling horizontal image stabilization. Conversely, ectopic expression of CNTN4 biases RGCs to arborize in the NOT, and that process also requires APP. Our data reveal critical and novel roles for CNTN4/APP in promoting target-specific axon arborization, and they highlight the importance of this process for functional development of a behaviorally relevant parallel visual pathway. Copyright © 2015 Elsevier Inc. All rights reserved.Neuron 05/2015; DOI:10.1016/j.neuron.2015.04.005 · 15.98 Impact Factor
- "In others, such as in the gustatory system, the arrangement corresponds to the qualities of the stimuli, such that similar stimuli are represented on nearby positions of the perceptual space. Not every topographic map is a continuous function according to modern usage of the term, although a continuous function satisfies the properties of a topographic map and historically they have been used synonymously (Luo & Flanagan, 2007). However, the same principles that guide the arrangement of neurons composing a topographic map also tend towards continuous functions. "
Conference Paper: What is the Ground? Continuous Maps for Grounding Perceptual Primitives[Show abstract] [Hide abstract]
ABSTRACT: Analysis of the Symbol Grounding Problem has typically fo-cused on the nature of symbols and how they tie to perception without focusing on the actual qualities of what the symbols are to be grounded in. We formalize the requirements of the ground and propose a basic model of grounding perceptual primitives to regions in perceptual space that demonstrates the significance of continuous mapping and how it influences cat-egorization and conceptualization of perception. We also outline methods to incorporate continuous grounding into computational systems and the benefits of applying such constraints.Proceedings of the 36th Annual Conference of the Cognitive Science Society, Austin, TX; 08/2014
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- "Afferent pat-585 tern formation (termed map formation because of mapping 586 from parameter space unto neuronal space) has been more 587 easily studied in the sensory system (especially the visual). 588 The importance of chemical gradients (Sperry 1963) has been 589 well established in the retinotectal pathway with the presence 590 of two (ephrin and EphA receptors) linear countergradients 591 (Luo and Flanagan 2007) present in the afferents and in the 592 target cells, respectively. Nonlinear mapping as required for 593 higher-order TW could be conceivable by nonlinear interac-594 tions between the two gradients (Stettler et al. 2012). "
ABSTRACT: The cerebellum is a major site for supervised procedural learning and appears to be crucial for optimizing sensorimotor performance. However, the site and origin of the supervising signal are still elusive. Furthermore, its relationship with the prominent neuronal circuitry remains puzzling. In this paper, I will review the relevant information and seek to synthesize a working hypothesis that explains the unique cerebellar structure. The aim of this review was to link the distinctive functions of the cerebellum, as derived from cerebellar lesion studies, with potential elementary computations, as observed by a bottom-up approach from the cerebellar microcircuitry. The parallel fiber geometry is ideal for performing millisecond computations that extract instructive signals. In this scenario, the higher time derivatives of kinematics such as acceleration and/or jerk that occur during motor performance are detected via a tidal wave mechanism and are used (with appropriate gating) as the instructive signal to guide motor smoothing. The advantage of such a mechanism is that movements are optimized by reducing "jerkiness" which, in turn, lowers their energy requirements.Biological Cybernetics 07/2014; 108(5). DOI:10.1007/s00422-014-0618-2 · 1.93 Impact Factor