Week 8, wiring the brain
This week was concentrated on the wiring of the brain during development. It was focused on the process of how the connections between the different structures of the brain happen. The example that was given was related to the visual system. This is how the link from the optic nerves happens to the cortical layers. First was described the stages of neural structure development, i.e., cell proliferation, cell migration, and cell differentiation. Then was explained how the axons, when they differentiate, find the way to their final connections. This has three phases: pathway selection (which path to take to reach a specific location), target selection (decision of what to innervate), and address selection (find the location of the correct target). All these depend on the communication between cells, cell signaling by diffusion of chemicals or by cellular secretions. Another process that occurs is the refinement of the connections that happen before birth to adolescence. This refinement also means the loss of connections and synapses and cell elimination. An important concept that was described is the rules for synaptic modifications. One rule is called Hebb’s hypothesis, which is “neuros that fire together wire together,” and the second rule is the opposite, “neurons that fire out of sync lose their link.” These can be explained by mechanisms of synaptic plasticity involving glutamate and NMDA receptors.