High-resolution volumetric imaging constrains compartmental models to explore synaptic integration and temporal processing by cochlear nucleus globular bushy cells

Globular bushy cells (GBCs) of the cochlear nucleus play central roles in the temporal processing of sound. Despite investigation over many decades, fundamental questions remain about their dendrite structure, afferent innervation, and integration of synaptic inputs. Here, we use volume electron microscopy (EM) of the mouse cochlear nucleus to construct synaptic maps that precisely specify convergence ratios and synaptic weights for auditory- nerve innervation and accurate surface areas of all postsynaptic compartments. Detailed biophysically-based compartmental models can help develop hypotheses regarding how GBCs integrate inputs to yield their recorded responses to sound. We established a pipeline to export a precise reconstruction of auditory nerve axons and their endbulb terminals together with high-resolution dendrite, soma, and axon reconstructions into biophysically-detailed compartmental models that could be activated by a standard cochlear transduction model. With these constraints, the models predict auditory nerve input profiles whereby all endbulbs onto a GBC are subthreshold (coincidence detection mode), or one or two inputs are suprathreshold (mixed mode). The models also predict the relative importance of dendrite geometry, soma size, and axon initial segment length in setting action potential threshold and generating heterogeneity in sound-evoked responses, and thereby propose mechanisms by which GBCs may homeostatically adjust their excitability. Volume EM also reveals new dendritic structures and dendrites that lack innervation. This framework defines a pathway from subcellular morphology to synaptic connectivity, and facilitates investigation into the roles of specific cellular features in sound encoding. We also clarify the need for new experimental measurements to provide missing cellular parameters, and predict responses to sound for further in vivo studies, thereby serving as a template for investigation of other neuron classes

Aid on Demand: African Leaders and the Geography of China's Foreign Assistance

This article investigates whether China’s foreign aid is particularly prone to political capture by political leaders of aid-receiving countries. Specifically, we examine whether more Chinese aid is allocated to the political leaders’ birth regions and regions populated by the ethnic group to which the leader belongs, controlling for indicators of need and various fixed effects. We have collected data on 117 African leaders’ birthplaces and ethnic groups and geocoded 1,650 Chinese development finance projects across 3,097 physical locations committed to Africa over the 2000-2012 period. Our econometric results show that current political leaders’ birth regions receive substantially larger financial ows from China than other regions. On the contrary, when we replicate the analysis for the World Bank, our regressions with region-fixed effects show no evidence of such favoritism. For Chinese and World Bank aid alike, we also find no evidence that African leaders direct more aid to areas populated by groups who share their ethnicity, when controlling for region-fixed effects