Abstract
Neural structures change with age but there is no consensus on the exact processes involved. This study tested the hypothesis that white and grey matter in the language network changes during aging according to a “last in, first out” process. The fractional anisotropy (FA) of white matter and cortical thickness of grey matter were measured in 36 participants whose ages ranged from 55 to 79 years. Within the language network, the dorsal pathway connecting the mid-to-posterior superior temporal cortex (STC) and the inferior frontal cortex (IFC) was affected more by aging in both FA and thickness than the other dorsal pathway connecting the STC with the premotor cortex and the ventral pathway connecting the mid-to-anterior STC with the ventral IFC. These results were independently validated in a second group of 20 participants whose ages ranged from 50 to 73 years. The pathway that is most affected during aging matures later than the other two pathways (which are present at birth). The results are interpreted as showing that the neural structures which mature later are affected more than those that mature earlier, supporting the “last in, first out” theory.
Highlights
Dealing with the effects of healthy aging is one of the biggest challenges facing the world today
Significant negative correlations were found in the bilateral inferior fronto-occipital fasciculus underlying the inferior frontal cortex (IFC) (IFOF-IFC), right forceps minor underlying the medial frontal cortex (FM-MeFC), and the body of the corpus callosum
No significant positive correlations were found (Table 1 and Figure 1B). These results confirmed the DTI results, indicating that brain regions along the dorsal pathway that connects the superior temporal cortex (STC) with the IFC showed significant decline of cortical thickness with age, the part that extends to the IFC
Summary
Dealing with the effects of healthy aging is one of the biggest challenges facing the world today. The neural changes that happen during aging have been explained by the ‘‘last in, first out’’ (LIFO) theoretical principle [3,4]. Studies have shown that the late-myelinating neocortical regions are most vulnerable to aging and aging-related disease, whereas the primary motor and sensory regions that myelinate early are more resistant to these changes, only being affected at later ages [5,6]. There is evidence showing that aging-related WM change occurs in specific fiber bundles that do not follow LIFO [8,9,10]. Alternative principles such as ‘‘first in, first out’’ (FIFO) are plausible. According to FIFO, the neural structures that mature earlier would be the first to be affected after maturity
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