Network Structure Implied by Initial Axon Outgrowth in Rodent Cortex: Empirical Measurement and Models

The developmental mechanisms by which the network organization of the adult cortex is established are incompletely understood. Here we report on empirical data on the development of connections in hamster isocortex and use these data to parameterize a network model of early cortical connectivity. Using anterograde tracers at a series of postnatal ages, we investigate the growth of connections in the early cortical sheet and systematically map initial axon extension from sites in anterior (motor), middle (somatosensory) and posterior (visual) cortex. As a general rule, developing axons extend from all sites to cover relatively large portions of the cortical field that include multiple cortical areas. From all sites, outgrowth is anisotropic, covering a greater distance along the medial/lateral axis than along the anterior/posterior axis. These observations are summarized as 2-dimensional probability distributions of axon terminal sites over the cortical sheet. Our network model consists of nodes, representing parcels of cortex, embedded in 2-dimensional space. Network nodes are connected via directed edges, representing axons, drawn according to the empirically derived anisotropic probability distribution. The networks generated are described by a number of graph theoretic measurements including graph efficiency, node betweenness centrality and average shortest path length. To determine if connectional anisotropy helps reduce the total volume occupied by axons, we define and measure a simple metric for the extra volume required by axons crossing. We investigate the impact of different levels of anisotropy on network structure and volume. The empirically observed level of anisotropy suggests a good trade-off between volume reduction and maintenance of both network efficiency and robustness. Future work will test the model's predictions for connectivity in larger cortices to gain insight into how the regulation of axonal outgrowth may have evolved to achieve efficient and economical connectivity in larger brains

Traditional Masculinity Ideology and Diagnostic Aversion Predict Symptom Expression in a Community Sample of Distressed Men

Adherence to traditional masculinity ideology (TMI) is associated with a host of negative outcomes, including higher rates of internalizing and externalizing psychopathology. However, relatively less is known about the mechanisms and contexts through which TMI affects the expression of psychological distress. In the current study, men’s aversion to being diagnosed with a mental health disorder was tested as a mediator and moderator to help clarify the relationship between TMI and symptom expression. A community sample of 72 U.S. men experiencing elevated psychological distress completed self-report questionnaires during a single session. Results demonstrated that diagnostic aversion mediated the positive association between TMI and internalizing symptoms. In addition, diagnostic aversion moderated the positive association between TMI and externalizing symptoms, such that this association was stronger among men who demonstrated higher levels of diagnostic aversion. Aversion to mental health diagnosis may be important in understanding how men who adhere to TMI manifest distress across diagnostic categories