Multiple unit activity recorded longitudinally in rats from pubescence to old age

—Longitudinal multiple unit activity (MUA) recordings of excellent quality over time periods as long as 26 months are described. The validity of the method was demonstrated by showing persistence of specific and idiosyncratic MUA responses to controlled sensory stimulation over these long time periods. This longitudinal MUA method was used to study level of localized neuronal activity as a function of aging. In agreement with deoxyglucose data from Sokoloff's laboratory, we found significant age-related declines in inferior and superior colliculi. In addition, our results showed the advantage of a longitudinal method over a cross-sectional one in following progressive changes into old age. The further declines in midbrain MUA level (though not in forebrain level) from middle age to old age that we observed were highly significant. The deoxyglucose method, on the other hand, had failed to show this kind of progression in those midbrain sites, probably because of a survival effect, a common sampling artifact in cross-sectional studies of aging.