Neuroplasticity Study Guide

📖 Core Concepts Neuroplasticity – the brain’s capacity to reorganize neural connections via growth, pruning, and functional changes. Scale – ranges from single‑synapse modifications to whole‑cortex remapping. Forms – homologous‑area adaptation, cross‑modal reassignment, map expansion, compensatory masquerade, structural vs. functional plasticity. Synaptic Basis – activity‑dependent changes in synaptic strength (LTP = strengthening, LTD = weakening) and intrinsic excitability. Molecular Drivers – phosphorylation of synaptic proteins, gene‑expression cascades, acetylcholine signaling, mitochondrial energy, BDNF, IGF‑1, VEGF. Developmental Gradient – plasticity is highest in early childhood, declines but persists into adulthood. Adaptive vs. Maladaptive – activity‑dependent (beneficial) versus maladaptive (e.g., chronic pain, addiction) remodeling. --- 📌 Must Remember Hebbian principle – “neurons that fire together wire together” (simultaneous firing → new/strengthened synapses). LTP/LTD – core mechanisms for memory formation and pruning. Critical periods – early life windows where sensory input (e.g., vision, language) produces maximal cortical re‑mapping. Exercise → BDNF – acute bout ↑ circulating BDNF (moderate effect), chronic training ↑ resting BDNF and gray‑matter volume. Ketamine & psychoplastogens – rapid‑acting antidepressants that boost dendritic spine number within hours. Cross‑modal plasticity – loss of a sense (e.g., blindness) leads to recruitment of the deprived cortex for other modalities. Constraint‑induced therapy – forces use of the impaired limb, driving cortical reorganization after stroke/TBI. Age‑related gene decline – synaptic‑plasticity gene expression drops after age 40, accelerating after 70. --- 🔄 Key Processes Activity‑Dependent Synaptic Strengthening (LTP) Repetitive high‑frequency stimulation → NMDA receptor activation → Ca²⁺ influx → kinase cascade → AMPA receptor insertion → ↑ synaptic efficacy. Activity‑Dependent Synaptic Weakening (LTD) Low‑frequency stimulation → modest Ca²⁺ rise → phosphatase activation → AMPA receptor removal → ↓ synaptic efficacy. Map Expansion (e.g., taxi driver hippocampus) Repeated spatial navigation → ↑ dendritic branching in posterior hippocampus → larger cortical representation. Cross‑Modal Reassignment Sensory loss → deafferented cortex becomes responsive to another modality → functional recruitment via training/rehab. Exercise‑Induced Neurotrophic Cascade Aerobic activity → ↑ BDNF, IGF‑1, VEGF → enhanced neurogenesis & synaptic plasticity → gray‑matter growth. Rehabilitation‑Driven Reorganization (stroke/TBI) Targeted motor training → movement representation shifts to neighboring cortex → functional recovery. --- 🔍 Key Comparisons Structural vs. Functional Plasticity – Structural: changes in gray‑matter volume, synapse number; Functional: alterations in firing patterns/network connectivity. Homologous‑Area Adaptation vs. Cross‑Modal Reassignment – Homologous: same function moves to opposite‑hemisphere counterpart; Cross‑modal: different sensory modality takes over a deprived region. Adaptive Plasticity vs. Maladaptive Plasticity – Adaptive: improves performance/compensation; Maladaptive: leads to chronic pain, addiction, or inefficient network activity. Ketamine (psychoplastogen) vs. Traditional Monoamine Antidepressants – Ketamine: rapid spine growth, effect within hours; Traditional: ↑ monoamines first, clinical effect delayed weeks. Early vs. Late Cochlear Implantation – Early (2–4 yr) → normal auditory cortical development; Late → limited plasticity, poorer outcomes. --- ⚠️ Common Misunderstandings “Adult brain is hard‑wired.” → Adult cortex retains capacity for synaptic remodeling and map reallocation. All plasticity is beneficial. → Maladaptive changes underlie chronic pain, addiction, and some post‑stroke deficits. Exercise only improves mood, not brain structure. → Proven increases in gray‑matter volume and BDNF‑driven neurogenesis. Neuroplasticity stops after childhood. → Persists lifelong, though magnitude and critical‑period mechanisms change. Ketamine works by boosting serotonin. → Its primary acute effect is spine and synapse formation, not monoamine elevation. --- 🧠 Mental Models / Intuition “Neural wiring is a garden.” → Synapses are like plants: activity waters (strengthens) them, lack of use weeds (prunes) them. “Brain maps are flexible rubber sheets.” → Stretch (map expansion) with practice, shift (reallocation) after injury, compress (maladaptive) under chronic stress. “Energy = plasticity.” → Mitochondrial ATP fuels the remodeling; think of a construction site needing power. --- 🚩 Exceptions & Edge Cases Sensory deprivation in early life – can cause excessive cross‑modal reassignment, sometimes leading to hyper‑sensitivity. Nicotine chronic use – may reduce plasticity by damaging nicotinic receptors despite its acute cholinergic activation. ADHD medication – normalizes fronto‑parietal activation only while on drug; off‑medication may revert. Exercise‑induced BDNF – single bout raises BDNF transiently; chronic training needed for sustained baseline elevation. --- 📍 When to Use Which Rehabilitation choice – Use constraint‑induced therapy for focal motor deficits; add functional electrical stimulation when voluntary movement is minimal. Imaging modality – MRI/CT for structural changes; functional MRI or EEG for functional network reorganization. Pharmacologic strategy for depression – Start with SSRI for gradual neuroplasticity; switch to ketamine or psychoplastogen if rapid response required. Sensory loss intervention – Early cochlear implantation (≤ 4 yr) for auditory plasticity; visual‑to‑auditory training for blind individuals to harness cross‑modal plasticity. --- 👀 Patterns to Recognize Repeated high‑frequency stimulation → LTP (memory formation). Chronic low‑frequency or disuse → LTD or synaptic loss (skill decay). Spatial learning tasks → hippocampal posterior enlargement (map expansion). Injury → neighboring cortical shift (functional reallocation). Regular aerobic exercise + aging → gray‑matter preservation. --- 🗂️ Exam Traps Distractor: “Neuroplasticity only occurs in the cortex.” → Wrong; hierarchical reorganization occurs throughout the brain. Trap: “All dopamine‑related changes are adaptive.” → In addiction, dopaminergic reinforcement leads to maladaptive structural changes. Misleading choice: “Ketamine works by increasing serotonin levels.” → Incorrect; its primary mechanism is rapid dendritic spine growth. Confusing option: “Cross‑modal reassignment requires loss of the original sense.” → Actually, it can also occur when the original cortex is damaged, not just sensory loss. False statement: “BDNF rises only after chronic exercise.” → Acute bouts also elevate BDNF; chronic training amplifies the response.