Transcallosal connectivity of the human cortical motor network

The organizational and architectural configuration of white matter pathways connecting brain regions has ramifications for all facets of the human condition, including manifestations of incipient neurodegeneration. Although diffusion tensor imaging (DTI) has been used extensively to visualize white matter connectivity, due to the widespread presence of crossing fibres, the lateral projections of the corpus callosum are not normally detected using this methodology. Detailed knowledge of the transcallosal connectivity of the human cortical motor network has therefore remained elusive. We employed constrained spherical deconvolution (CSD) tractography - an approach that is much less susceptible to the influence of crossing fibres, in order to derive complete in-vivo characterizations of white matter pathways connecting specific motor cortical regions to their counterparts and other loci in the opposite hemisphere. The revealed patterns of connectivity closely resemble those derived from anatomical tracing in primates. It was established that dorsal premotor cortex (PMd) and supplementary motor area (SMA) have extensive interhemispheric connectivity - exhibiting both dense homologous projections, and widespread structural relations with every other region in the contralateral motor network. Through this in-vivo portrayal, the importance of non-primary motor regions for interhemispheric communication is emphasized. Additionally, distinct connectivity profiles were detected for the anterior and posterior subdivisions of primary motor cortex. The present findings provide a comprehensive representation of transcallosal white matter projections in humans, and have the potential to inform the development of models and hypotheses relating structural and functional brain connectivity.

Renaissance Humanism and Ethnicity before Race:The Irish and the English in the Seventeenth Century

Inspired both by debates about the origins of the modern ideology of race and also by controversy over the place of Ireland and the Irish in theories of empire in the early modern Atlantic world, <em>Renaissance Humanism and Ethnicity before Race</em> argues that ethnic discourse among the elite in early modern Ireland was grounded firmly in the Renaissance Humanism and Aristotelianism which dominated all the European universities before the Enlightenment. Irish and English, Catholic and Protestant, all employed theories of human society based on Aristotle’s <em>Politics</em> and the natural law of the medieval universities to construct or dismantle the categories of civility and barbarism. The elites operating in Ireland also shared common resources, taught in the universities, for arguing about the human body and its ability to transmit hereditary characteristics. Both in Ireland and elsewhere in Europe, these theories of human society and the human body underwent violent changes in the late seventeenth century under the impact of the early Enlightenment. These changes were vital to the development of race as we know it.