Studies show that altitude does effect oxygen levels to the brain. An injured brain is much more sensitive to these lower levels of oxygen. Living at altitude causes the body to increase the hemoglobin in the blood to help with this. The research I have read says that this can only increase one's altitude tolerance by a few thousand feet. So, you brain may respond like you are living at 5000 feet.

Exercise helps by pushing more blood through the whole body, including the brain. HBOT (Hyper Baric Oxygen Therapy) take many sessions (80 or more) to show improvement. It appears that HBOT helps the brain grow more capillaries.

The research was done in the 1970's in New Zealand by Dorothy Gronwall, et. al. It showed a marked decrease in neurological function at 8000 feet for those with a concussion history compared to those without a concussion history. It did not attempt to look at altitude accommodation from living at higher altitudes. The decreased performance was not dependent on a recent concussion history.

A calculator I found shows that a 98% blood Oxygen saturation at sea level will be 92% at 7000 feet. Consciousness begins to be effected at 70% or so.