Ingestion of HIV-carrying lymphocytes by microglial cells probably propagates the infection in the brain. The inflammatory cytokines that are produced by microglial cells are intended to kill viruses and other pathogens but damage also brain cells and myelin. This contributes to the brain damage from viral encephalitis, multiple sclerosis, and HIV encephalitis . The white matter of the cerebral hemispheres and spinal cord consists of myelin, oligodendroglia, astrocytes, microglia, and blood vessels. It contains no neurons.
Pyramidal cells project their axons to targets away from their points of origin.
Stellate cells receive afferents and form intracortical networks. The mix of pyramidal and stellate cells varies in different cortical fields and correlates with cortical function. The subiculum and entorhinal cortex are interposd between the hippocampus and the temporal neocortex. The hippocampus receives extensive afferents from association cortex and limbic areas, and projects to the thalamus, hypothalamus, and cortex. The hippocampus is important for the process of declarative memory, i.e. the memory for facts and events, but is not a storage depot for old memories.