Chapter 24 – The Changing Brain and Cognitive Functioning: Comprehensive Study Notes

Memory loss is common, but structural brain changes are normal and highly variable.
Microscopic: Neural dendrites shrink (fewer synapses), impairing learning/memory; neurons generally shrink.
Macroscopic: Brain volume declines from early adulthood, accelerating post-60, especially in the prefrontal cortex (PFC) and hippocampus.
Functional: PFC decline affects motor behavior and working memory; hippocampal decline impacts information storage/retrieval and Alzheimer's.
Myelin sheath thins, leading to $ext{loss} > ext{gain}$ and slower neural transmission.
Neurogenesis/Plasticity: New neuron generation slows after midlife; brain compensates via functional reorganization (e.g., bilateral activation).

CRUNCH: Older adults use extra neural resources (PFC) at lower task loads, limiting resources for harder tasks.
STAC: Increased PFC activity forms “neural scaffolds” to offset structural damage.
Consensus: Compensation maintains daily function but uses cognitive reserve.

Cognitive changes are diverse. Mild lapses are normal; dramatic impairment suggests a major neurocognitive disorder (e.g., Alzheimer’s).

Normal forgetting (e.g., lost keys) differs from dementia, which involves severe, pervasive memory loss affecting daily life (e.g., forgetting conversations, failing to recognize family).

Explicit (Declarative): Conscious recall (facts/events) declines.
Implicit (Procedural): Unconscious skills (e.g., driving) generally spared.
Semantic: Generalized knowledge shows small decline in speed/accuracy; “tip‐of‐the‐tongue” (TOT) events are common.
Episodic: Autobiographical events show the largest normative decline, a key target in Alzheimer’s.
Working Memory (WM): Temporary storage; the central executive (attention, monitoring) is vulnerable, leading to difficulty inhibiting irrelevant info. Dual-task deficits but self-paced tasks help.

Sustained focus maintained; flexible shifting and divided attention decline. Inhibition weakens, increasing distractibility.

Universal slowing; more time needed for decisions, due to reduced myelination/connectivity. Differences diminish if time is not a factor.

Performance drops for quick, meaningless problems. However, everyday, experience-based problems show stable or improved performance due to crystallized intelligence.

Crucial to distinguish normal vs. pathological decline. Training, environmental supports, and sensory aids can help. Public safety decisions (e.g., driving) balance independence/risk. Societal views should emphasize plasticity and compensatory strengths.