The setting in which an individual lives is the

A. cross-sectional: Cross-sectional studies compare different age groups at one time point rather than following the same individuals over time.
B. naturalistic observation: Naturalistic observation is a method of observing behavior in real settings but does not specify a long-term follow-up of the same cohort.
C. longitudinal: Longitudinal studies follow the same group of individuals across multiple time points (e.g., infancy into adulthood), matching Dr. Chang’s description.
D. experimental: Experimental studies manipulate variables and assign participants to conditions, not simply following a group over many years.

A. higher and lower brain functions: Brain death is defined as the irreversible cessation of all functions of the entire brain, including higher cortical activity and brainstem (lower) functions; this “whole-brain” criterion is what most physicians use.
B. the heartbeat: Loss of the heartbeat is circulatory or cardiac death; with mechanical ventilation and support the heart can continue beating even when the brain has irreversibly ceased functioning, so this is not the defining feature of brain death.
C. the higher cortical functions of the brain: Loss of cortical function alone (e.g., no consciousness) may produce a persistent vegetative state, but brainstem functions can remain; that situation is not equivalent to whole-brain death.
D. lower brainstem functions: Loss of brainstem function (respiratory drive, brainstem reflexes) is critical and may define brainstem death in some places, but the widely used medical definition is cessation of all brain functions (both cortical and brainstem), so lower-brainstem cessation alone doesn’t capture the full standard.