The basis for the concept of executive functioning (EF) arose in the 1840s in the initial efforts by scientists to understand the functions of the frontal lobes generally and the prefrontal cortex (PFC) specifically (Harlow, 1848, 1868; Luria, 1966). Indeed, the concept predates the term “EF” by more than 120 years. The concept of EF was at first defined by default as what the prefrontal lobes do (Pribram, 1973, 1976); they are, as Pribram said, the executive brain. The term “EF” came out of these earlier efforts to understand the neuropsychological functions mediated by the prefrontal or premotor regions of the brain. This history has led to a conflating of the term “EF” with the functions of the PFC and vice versa.
Over time, this conflation has led to a circularity of reasoning in that the functions of the PFC are said to be EF while EF is then defined back to the functions of the PFC. It has also led to a slippage in the discourse on EF between two separate levels of analysis (Denckla, 1996). One is the neuropsychological level involving thought (cognition), emotion, and verbal or motor action (behavior); the other is the neuroanatomical level involving the localization of those neuropsychological functions to specific regions of the brain and their physiological activity. But EF is not exclusively a function of the PFC given that the PFC has various networks of connections to other cortical and subcortical regions as well as to the basal ganglia, amygdala and limbic system, and cerebellum (Denckla, 1996; Fuster, 1989, 1997; Luria, 1966; Nigg & Casey, 2005; Stuss & Benson, 1986). The PFC may well engage in certain neuropsychological functions that would not be considered to fall under the umbrella of EF, such as simple or automatic sensory–motor activities, speech, and olfactory identification, to name just a few.
Thus, despite an extensive history concerning the nature of EF and of the functions of the PFC, several significant problems continue to exist in the definition of the term “EF,” its conceptualization, and its measurement. EF is a term describing psychological functions and is therefore a construct at the psychological level of analysis. If our understanding of EF is to advance, the concept of EF and its nature must be defined separately and specifically at the psychological level without reference to the neurological level being an essential part of that definition. Such a cross-referencing of levels is of interest to neuropsychology in determining what specific brain regions engage in what specific functions. But this activity requires that we have such functions properly defined at the psychological level first before we can determine what brain networks give rise to that psychological function. If EF and its larger purposes in human life are not well defined and developed, only confusion can reign at the neurological level as one searches for the neural networks that supposedly underlie a vaguely defined and poorly crafted psychological construct, perhaps in vain.
This book was written to address four related problems that currently exist in the concept of EF. First, there is neither a consensus definition of EF nor an explicit operational definition of the term that can simply, clearly, and efficiently determine which human mental functions can be considered executive in nature and which ones cannot be so classified. Simply put, What is EF? When definitions are too general or vague, as is EF, they leave considerable opportunity for misinterpretation as well as for including within the term’s conceptual realm excessive semantic baggage that would easily have been pared away had the definition had greater clarity and precision.