The ability of the nervous system to maintain normal function is the stuff of legend.  This is well exemplified by the "Giraffe Neck" syndrome.  There are, however, a number of other clinical syndromes which serve to illustrate the effects of diminished neuronal reserve.  Some examples are:

"Sundowner's" Syndrome 
In older individuals who have experienced multiple small strokes to the brain they may appear to be neurologically intact when they arise in the morning refreshed from sleep and neurologically impaired at night after a tiring day.  "Sundowner's" Syndrome has been the bane of young interns and residents who have admitted neurologically impaired patients to the hospital at night only to find them neurologically intact in the morning when presenting their case to their attending physician.

"Post-Polio" Syndrome
The neurologic sequela of poliomyelitis were devastating to many individuals in the mid-part of the 20th century.  For those who were lucky enough to experience sensible rehabilitation good recoveries were possible.  The "post-polio" syndrome refers to the onset, in recovered polio patients, of progressive weakness of the lower extremities in their fourth through sixth decades of life.  Because these individuals had lost their neuronal reserve in childhood they were becoming progressively impaired because of the neuronal population decrease from the process of aging alone.