Does aging reduce synaptic plasticity, mitochondrial resilience, and neural reserve?

Aging is associated with biological and network changes that can reduce the brain’s capacity to tolerate neurodegenerative pathology, but the strength of evidence differs across these processes.

Clinical and physiological evidence

• Synaptic plasticity: Healthy older adults generally show smaller or less durable LTP/LTD-like responses and reduced homeostatic metaplasticity on TMS paradigms. These findings are consistent with diminished plasticity, although motor-evoked-potential and connectivity measures are indirect, variable proxies for synaptic function.
• Mitochondrial resilience: Cognitively unimpaired older adults show lower oxidative-phosphorylation efficiency, complex-I activity, and NAD+ metabolism, alongside impaired calcium handling and antioxidant defenses. Increased oxidative injury to proteins, lipids, and mitochondrial DNA further supports reduced ability to withstand metabolic stress.
• Neural reserve: Evidence most strongly supports reserve as a determinant of clinical vulnerability. Higher reserve was associated with lower incident MCI/dementia and predementia-to-dementia conversion, including after accounting for structural damage and Alzheimer biomarkers; a meta-analysis reported a pooled hazard ratio of 0.53 for higher reserve.

Mechanistic interpretation

• Impaired mitochondrial ATP production, redox control, calcium regulation, and mitophagy could amplify synaptic injury and interactions with amyloid-β, tau, and inflammation.
• Synaptic dysfunction and loss occur early in MCI/Alzheimer disease and track with cognition; longitudinal electrophysiologic network abnormalities may precede conversion to Alzheimer dementia.
• Compensatory recruitment of frontal or dorsal-attention regions can sometimes preserve task performance, but its meaning is context-dependent: hyperactivation may be adaptive, ineffective, or maladaptive. FDG-PET hypometabolism in posterior cingulate and temporoparietal cortex in MCI predicts later Alzheimer conversion.

Bottom line

• The overall claim is plausible: aging-related reductions in synaptic plasticity and mitochondrial resilience are supported, and lower neural reserve is strongly associated with greater clinical expression of neurodegenerative injury. Plasticity and mitochondrial changes are credible contributors to vulnerability, though their independent causal role remains less firmly established than that of reserve.