Key Terms
Concise definitions for terms used throughout this guide
The following definitions are provided for quick reference. Full context for each appears in the relevant section of the guide.
Acetylcholine
A neurotransmitter released during focused attention that plays a central role in encoding new memories. Choline, its dietary precursor, is found in eggs and liver.
Allostatic Load
The cumulative physiological cost of repeated or prolonged activation of the body's stress-response systems, including effects on brain structures involved in memory and emotional regulation.
Anterior Mid-Cingulate Cortex (aMCC)
A brain region associated in early-stage research with persistence, effortful goal pursuit, and resilience to age-related cognitive decline. The popular claim that specific discomfort practices directly grow this region runs ahead of the current, mostly associational evidence.
BDNF (Brain-Derived Neurotrophic Factor)
A protein that supports the growth, survival, and connectivity of neurons. Reliably increased by aerobic exercise, and the leading proposed mechanism linking exercise to the structural brain changes described in Section 6.
Default Mode Network (DMN)
A set of brain regions that becomes more active during unfocused rest than during externally directed tasks. Associated with self-referential thought, future planning, and creative incubation — suppressed by constant external stimulation.
Dopamine
A neurotransmitter primarily involved in motivation and reward prediction rather than pleasure itself. Encodes the gap between expected and actual outcomes, and typically dips below baseline after a spike — the mechanistic basis of the post-reward "trough."
Ego Depletion
The theory that self-control draws on a single limited resource that depletes with use. A large, pre-registered multi-lab replication found no meaningful effect, substantially weakening confidence in this specific mechanism — though the everyday experience of declining performance across a demanding day is real and better explained by other factors.
Neurogenesis
The generation of new neurons. Whether meaningful adult hippocampal neurogenesis occurs in humans throughout life is currently unresolved in the scientific literature, with high-quality studies reaching opposing conclusions.
Neuroplasticity
The brain's capacity to physically change its structure and connectivity in response to experience. Well established for existing-connection strengthening and grey matter changes in task-relevant regions, at any adult age.
Prediction Error
The gap between an expected outcome and the actual outcome, encoded by dopamine neurons in reward learning and by related mechanisms in skill and knowledge learning. A larger error produces a stronger adjustment signal.
Reward Prediction Error
See Prediction Error and Dopamine — the specific application of prediction-error signalling to reward learning, first demonstrated by direct recordings from dopamine neurons.
Synapse
The junction between two neurons where chemical neurotransmitters are released and received, forming the basic unit of communication in the nervous system.
Synaptic Plasticity
The strengthening or weakening of synaptic connections based on use — the cellular basis of learning and memory.