On the dynamics of cortical development: synchrony and synaptic self-organization

Abstract

We describe a model for cortical development that resolves long-standing difficulties of earlier models. It is proposed that, during embryonic development, synchronous firing of neurons and their competition for limited metabolic resources leads to selection of an array of neurons with ultra-small-world characteristics. Consequently, in the visual cortex, macrocolumns linked by superficial patchy connections emerge in anatomically realistic patterns, with an ante-natal arrangement which projects signals from the surrounding cortex onto each macrocolumn in a form analogous to the projection of a Euclidean plane onto a Möbius strip. This configuration reproduces typical cortical response maps, and simulations of signal flow explain cortical responses to moving lines as functions of stimulus velocity, length, and orientation. With the introduction of direct visual inputs, under the operation of Hebbian learning, development of mature selective response “tuning” to stimuli of given orientation, spatial frequency, and temporal frequency would then take place, overwriting the earlier ante-natal configuration. The model is provisionally extended to hierarchical interactions of the visual cortex with higher centers, and a general principle for cortical processing of spatio-temporal images is sketched.

Two Visual Pathways in Primates Based on Sampling of Space: Exploitation and Exploration of Visual Information

“…Even further, the presence of retinotopic maps in higher order areas in the ventral visual pathway in both non-human (Boussaoud et al, 1991; Rajimehr et al, 2014) and human (Larsson and Heeger, 2006; Sayres and Grill-Spector, 2008; Schwarzlose et al, 2008; Arcaro et al, 2009; Kravitz et al, 2010; Cichy et al, 2011) primates would mean that the appearance of a stimulus will cause a substantial part of the ventral visual pathway to potentially respond. However, biological and energetic constraints, including but not limited to the competition for limited metabolic resources (Wright and Bourke, 2013) preclude all neurons from firing at the same time, which occurs if neurons and areas specialize to inform on features over and above spatial location. In other words, metabolic constraints drive spontaneous symmetry-breaking along dimensions other than physical space, and the emergence and development of selectivity—at the single-cell level as well as the group or columnar level—for features such as color, orientation, objects, faces etc.…”

Further Work on the Shaping of Cortical Development and Function by Synchrony and Metabolic Competition

“…Basole et al, 2006) throughout cells surrounding a singularity, as was diagramed in our earlier theoretical paper (Wright and Bourke, 2013). …”

“…As postnatal learning begins, the antenatal organization would be progressively overwritten. The organization of the connection overwriting can be inferred from our explanation of object representation and feature tuning in V1, as previously cited in the Introduction (Wright and Bourke, 2013). As a property of the antenatal evolution of the connections, any small segment of a moving visual object, projected to the visual cortex as a stimulus pattern, O P , is transmitted with axonal delays to each cortical column surrounding an OP singularity as a mapped transformed pattern, O p $\begin{array}{c}left{O}_{P}false(K_x,K_y,{\text{v}}_{x}false)false(tfalse)\to O_{p}false(k_x,k_y,\omega false)false(t+|P-p|/\nu false)\end{array}$ where v x is the velocity of the stimulus pattern moving over the visual cortex along axis x to cross the classical receptive field of the macrocolumn, K x , K y , k x k y are dominant spatial frequencies of the visual object's projection and mapped response respectively, ω is the temporal frequency of response, ν is the speed of electrocortical wave transmission, and…”

“…Under the added assumption that values of ε qr are initially random, geometrical solutions for positions of cell bodies creating maximum co-resonance, and thus maximizing each subset of J in Equation (5b), predict anatomically realistic patterns and response properties (Wright and Bourke, 2013) in mature columnar cortex.…”

“…In an attempt to account for the above findings, we (Wright and Bourke, 2013) argued that in the process of embryonic development in the visual cortex, macrocolumns linked by superficial patchy connections become arranged so as to project signals to and from the surrounding cortex onto each macrocolumn in a pattern analogous to projection of a Euclidean plane onto a Möbius strip.…”