Quote Originally Posted by vegas giants
A fetus has the same eeg as a brain dead patient until well after 20 weeks. They are brain dead
Actually it is not biologically asinine. The neural connections simply have not developed. No connections = no brain waves = an eeg similar to brain dead.
Abstract
Human brain development is a protracted process that begins in the third gestational week (GW) with the differentiation of the neural progenitor cells and extends at least through late adolescence, arguably throughout the lifespan. The processes that contribute to brain development range from the molecular events of gene expression to environmental input. Critically, these very different levels and kinds of processes interact to support the ongoing series of events that define brain development. Both gene expression and environmental input are essential for normal brain development, and disruption of either can fundamentally alter neural outcomes. But neither genes nor input is prescriptive or determinative of outcome. Rather brain development is aptly characterized as a complex series of dynamic and adaptive processes that operate throughout the course of development to promote the emergence and differentiation of new neural structures and functions. These processes operate within highly constrained and genetically organized, but constantly changing contexts that, over time, support the emergence of the complex and dynamic structure of the human brain (Waddington 1939; Morange 2001; Stiles 2008).
This paper will review some of the major events that contribute to the development of the human brain from its early embryonic state through adolescence.
Two of the most important pathways in the brain are the ones that transmit sensorimotor information, the thalamocortical (TC) and corticothalamic (CT) pathways. The TC relays sensory and motor information from the receptors in the retina, cochlea, muscle or skin to the sensorimotor regions of the neocortex via the major subcortical sensorimotor relay, the thalamus. The CT pathway completes the feedback loop by transmitting information from cortex back to the thalamus. These essential pathways begin to form in the later part of the second trimester in humans, and are
complete by GW 26 (Kostovic and Jovanov-Milosevic 2006). The cells of the transient subplate layer of the developing brain (see Fig.*9b) play an essential role in establishing these pathways. When TC axons arrive at the developing cortex during GW22 they do not immediately make connections with neurons in the primary input layer of cortex (layer 4). Rather, they initially make connections with the neurons of the subplate layer. The TC-subplate connections last for approximately 4*weeks, during which time the subplate neurons make connections with neurons in cortical layer 4. The subplate neurons appear to provide instructive input to the TC neurons during this period. In the absence of subplate neuron signaling, normal patterns of connectivity between TC axons and layer 4 cortical neurons do not develop. A similar pattern of instructive connectivity is seen in the development of the CT pathway. Prior to the establishment of connections between neurons from the deep layers of cortex (layers 5 and 6) and the thalamus, subplate neurons extend and establish connections with thalamic neurons. It is thought that the subplate connections may serve to guide the CT axons to their positions in the thalamus. Once the TC and CT pathways are complete, the subplate neurons retract their connections and the cells themselves gradually die off.
The Basics of Brain Development
