8. Discussion
The growing evidence summarized in this review supports a paradigm shift in the understanding of brain aging—from a model of progressive decline to one of dynamic adaptation [2,3,4,5,6,7,8,11,12,13,51,52]. Rather than a passive loss of neural resources, the aging brain displays a remarkable ability to reorganize its structure and function to preserve cognition [15,16,20,45,46,47,48,53,70,71,72,85]. This adaptive neuroplasticity, underpinned by molecular, glial, and vascular mechanisms, constitutes the biological substrate of cognitive resilience [21,22,23,24,25,26,27,28,31,55,56,57,58,59,60,61,62,63,64,65,69].
Importantly, neuromarker interpretation in aging should not rely on a simplified linear framework in which higher values are automatically equated with adaptive neuroplasticity or preserved neural health [25,26,56,57]. In older adults, increases in neuromarkers such as BDNF expression, functional connectivity strength, or regional metabolic activity may reflect compensatory responses to declining efficiency in downstream signaling pathways rather than enhanced function per se [27,28,58,59]. Evidence from neuroimaging and molecular studies indicates that such compensatory upregulation may coexist with reduced network efficiency, altered excitation–inhibition balance, or increased energetic cost during cognitive performance [60,61,62,63].
In addition, aging-related neuromarkers should not be interpreted independently of age range, cognitive status, or measurement context. Neuroimaging and electrophysiological metrics obtained during resting-state conditions may index baseline network organization, whereas task-based measures more directly reflect compensatory recruitment or neural efficiency under cognitive demand [32,33,34,35,36]. Importantly, these patterns vary across the aging spectrum, with younger-old adults often exhibiting flexible compensatory engagement, while older-old individuals may show overactivation associated with reduced performance or increased neural cost [37,38,39,40,41].
Thus, the functional meaning of a given neuromarker is context-dependent and influenced by age range, cognitive status, task demands, and interactions with other biological signals, including inflammatory and vascular factors [64,65,66,69]. As a result, similar neuromarker profiles may carry fundamentally different implications in cognitively resilient older adults compared with individuals at risk for cognitive decline, underscoring the need for cautious and integrative interpretation when evaluating biomarkers of adaptive plasticity in aging populations [29,30,31,67].
However, the heterogeneity of findings across studies underscores that neuroplasticity is not uniformly beneficial. Some compensatory activations may reflect inefficiency rather than resilience, particularly when overactivation of frontal or parietal networks accompanies declining cognitive performance [17,45,46,47,48,72,85,101]. Disentangling adaptive from maladaptive reorganization therefore remains a major conceptual challenge. Future research should integrate longitudinal designs and mechanistic approaches to distinguish compensatory recruitment that sustains function from neural responses that precede cognitive exhaustion [17,18,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,54,66,67,70,71,72,74,75,82,99,100,101,102].
Another critical point concerns the bidirectional relationship between behavior and biology. Lifestyle factors—such as physical activity, intellectual engagement, and social interaction—can modulate neurotrophic signaling, network organization, and metabolic efficiency [21,22,23,24,49,50,55,88,89,90,91,92,93,94,95], thereby creating a feedback loop between experience and brain biology. Conversely, molecular deficits, including reduced BDNF availability or impaired neurovascular coupling, may constrain the effectiveness of behavioral interventions [21,22,23,24,25,26,27,28,55,56,57,60,61,62]. This interplay highlights the necessity of multilevel models that integrate molecular, network, and behavioral dimensions to fully capture the determinants of cognitive resilience [17,18,45,46,47,48,54,72,75,85,99,100,101,102].
Beyond biological factors, environmental and experiential determinants play a critical role in shaping adaptive neuroplasticity and cognitive resilience in aging. Educational attainment, occupational complexity, physical activity, and sustained cognitive engagement have been consistently associated with more efficient network organization, preserved functional connectivity, and modulation of neurotrophic signaling pathways in older adults [21,22,23,24,49,50,55,88,89,90,91,92,93,94,95]. These factors contribute to cognitive reserve, influencing how neural systems respond to age-related stressors and modifying the functional expression of neuromarkers observed in neuroimaging and molecular studies.
Consequently, similar neuromarker profiles may therefore reflect distinct underlying mechanisms depending on an individual’s environmental background and life-course exposures. For example, increased functional connectivity or metabolic activity may support resilience in individuals with higher cognitive reserve, while representing compensatory strain or inefficiency in less enriched contexts [17,18,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,54,66,67,72,74,75,82,99,100,101,102]. Integrating environmental determinants into neuromarker-based models is thus essential for accurate interpretation and for advancing precision approaches to cognitive aging.
Importantly, resilience should not be conflated with resistance to aging, but rather conceptualized as adaptive recalibration in response to age-related biological change [17,18,54,70,71,72,99,100,101,102]. The presence of preserved or reorganized neural networks does not imply the absence of pathology, but instead reflects the engagement of compensatory mechanisms that maintain functional homeostasis [17,45,46,47,48,72,85,101]. Integrating multimodal neuromarkers within this framework enables a more nuanced view of brain aging—one characterized not by inevitable loss, but by the dynamic balance between degeneration and adaptation. This perspective aligns with the emerging paradigm of precision cognitive aging, which emphasizes individualized trajectories shaped by biological, environmental, and experiential factors [19,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,54,66,67,74,75,82,83,84,85,86,102].