NEUROPLASTICITY ACROSS THE LIFESPAN: MECHANISMS, MODULATORS, MALADAPTATION AND TRANSLATIONAL FRONTIERS

Abstract

Neuroplasticity, the capacity of the nervous system to alter its structure, function and connectivity in response to intrinsic and extrinsic stimuli, has moved from a developmental curiosity to a central organising principle of contemporary neuroscience and a plausible therapeutic target across neurology, psychiatry, pharmacology and rehabilitation medicine. This condensed review synthesises current mechanistic and translational evidence within a single integrated framework. Four interdependent pillars of plasticity are delineated: synaptic modification, comprising long-term potentiation, long term depression, spike-timing dependence, metaplasticity and homeostatic scaling; structural remodelling, comprising spine turnover, dendritic and axonal growth, pruning and activity-dependent myelination; neurogenesis; and system-level functional reorganisation, comprising map plasticity, vicariation and diaschisis. These neuron-centred processes are permitted or constrained by a supporting tissue environment of astrocytes, microglia, oligodendrocytes, extracellular matrix and the neurovascular unit, and converge on a common molecular substrate dominated by calcium-dependent glutamatergic signalling, brain-derived neurotrophic factor-TrkB transduction, transcriptional and epigenetic control, and neurosteroid modulation. Plastic capacity follows a non-monotonic lifespan trajectory, being high and experience expectant during critical periods, progressively gated in adulthood, and attenuated but not abolished in senescence. Critically, plasticity is directionally neutral: identical mechanisms underwrite skill acquisition and recovery on the one hand, and central sensitisation, addiction, dystonia and epileptogenesis on the other. The current interventional armamentarium is appraised, spanning task-specific rehabilitation, aerobic exercise, cognitive and social enrichment, structured psychological techniques including clinical hypnosis, sleep and dietary optimisation, non-invasive and paired neuromodulation, plasticity-promoting pharmacology, brain-computer interfaces and artificial-intelligence-guided personalisation, with the maturity of supporting evidence graded for each. Persistent obstacles include biomarker non equivalence, heterogeneity of dose and timing, short follow-up, and unresolved ethical questions concerning equitable access, neural data privacy and the therapy-enhancement boundary. The decisive translational challenge is no longer whether plasticity can be induced, but whether it can be reliably steered.