One of the big surprises was the size of the olfactory bulbs, part of the brain associated with processing information about smells in the environment.
See, the olfactory bulb, which processes odors, is connected to two important structures involved in memory and emotion: the hippocampus and the amygdala.
Then evidence began to emerge of young neurons in the brains of adult rats and mice, -specifically in the olfactory bulb, which processes smell, and the dentate gyrus.
医学百科 The Medicine Book (Big Ideas Simply Explained)
During the 1870s, Italian biologist and pioneering neuroanatomist Camillo Golgi produced detailed descriptions of the spinal cord and the brain's olfactory lobe, cerebellum and hippocampus.
These neurons migrate down from the olfactory placode and get embedded in the cribriform plate, which is a bone plate that separates the nasal cavity from the brain, forming the olfactory bulb.
There are a few places you produce new neurons, like the olfactory bulb, the dentate gyrus, or the hippocampus, a few places, but these are far and few between.
Scientists do have a theory of how the virus could travel to the brain: from the nose, and then upward through the olfactory bulb, which connects to the brain.