Human behaviormay be conceptualized in terms of three basic functional systems: (1) cognition, which is the information processing aspects of behavior (analogous to a computer); (2) emotionality, which concerns feelings and motivation; and (3) executive functions, which governs how behavior is expressed and managed (the chief executive ofﬁcer of our brain). Lezak et al.48 provide the basic deﬁnitions for these three functional systems. The four major classes of cognitive function borrow from the language of computer operations. These classes include input, storage, processing, and output. Brain receptors and sensory systems select, acquire, classify, and integrate input information; informational storage and retrieval are the memory and learning portions of human mental function. Thinking occurs during the mental organization and reorganization of input information and storage of information. The expressive portions of cognition are the means through which information is communicated or acted upon.48 Human executive functions consist of those capacities that enable a person to engage successfully in independent, purposive, self-serving behavior. They differ signiﬁcantly from cognitive functions in a number of ways. Executive function begs the question as to how or whether a person goes about doing an act or task. On the other hand, questions about cognitive function are generally phrased in terms of what or how much. This further begs questions of how much a person knows or what that person can do. So long as the executive functions are reasonably intact, a person can sustain considerable cognitive loss and still continue to be independent, constructively self-serving, and productive.