Introduction. Since Lezak coined the term executive functions to refer to the mental capabilities that are considered essential for performing efficacious, creative and socially acceptable behaviour, they have gradually grown in importance in neuropsychological research. Different models have been proposed to explain their nature, but there is no general agreement as to whether we are dealing with a unitary construct or a multimodal processing system with independent, but interconnected, components. With the aim of gaining a deeper knowledge of the structure of this construct, researchers have conducted lesion, neuroimaging and, more recently, factorial analysis studies, the latter being seen as a promising methodology for expanding our knowledge about such a generic concept as the executive functions. DEVELOPMENT. The purpose of this study is to carry out a systematic review of factorial models of attention and executive control in adults, between the years 1991 and 2016, using the PubMed, OvidSP and PsycINFO databases. Altogether, 33 papers were reviewed. Based on the literature, an integrating proposal of the executive functions is put forward.

Conclusions. Although we do not have just one single model that can account for the complexity of the executive functions, there does seem to be general agreement on their multidimensionality. In factorial analyses, there is strong evidence of updating, inhibition and alternation, although there are also studies that propose novel factors. Our integrating proposal aims to combine the executive processes found in the literature with their corresponding neuroanatomical correlates, and defends the stance that the ideal methodology should use information from lesion studies, neuroimaging techniques and psychometric-computational models.

Introduction of the ‘Model of executive functions based on factorial analyses’

Executive functions have been defined as processes that associate ideas, movements, and actions and guide them to problem solving, but Muriel Lezak first uses the term in 1982 [1] referring to mental abilities essential for effective, creative, and socially accepted behavior with four components: formulation of goals (ability to generate and select desirable states in the future), planning (selection of actions, elements and sequences necessary to achieve an objective), development (ability to initiate, stop, maintain and change between planned actions) and execution (ability to monitor and correct activities). The alteration of these capabilities may involve problems of initiation, modification, control or interruption of action, and resulting in a decrease in spontaneous behavior and an increase in perseverance and impulsivity.

Executive functions are considered a set of skills involved in generating, supervising, regulating, executing, and readjusting appropriate behaviors to achieve complex objectives, especially those that are novel to the individual and require a creative solution [2]. In this sense, in our daily life we face situations for which we do not have a predetermined plan of action, so Lezak’s assertion that executive functions are the central axis that guides adaptive and socially acceptable behaviors is not exaggerated.

The role they have played in neuropsychological research is highlighted, and there are multiple models that attempt to clarify the processes involved in executive functions and their relationship with different brain regions, preferably the prefrontal cortex.

The nature of executive functions

In the context of the functional diversity of the frontal cortex, one of the crucial debates about the nature of executive functions is framed: whether they constitute a unitary construct or a multimodal multiple processing system with different independent, yet interrelated, components. The view of executive functions as a nonspecific and adaptable system assumes that there are, a priori, no regions specialized in particular functions, but rather different areas of the prefrontal cortex respond in a coordinated manner when the system must solve new challenges.

Thus, executive functions overlap with the concept of fluid intelligence or the ability to optimally adapt our cognitive resources to the changing demands of the environment. Current models tend to lean toward the second hypothesis [2,3], although there is still controversy as to whether they are functionally unspecific, but highly adaptable, unitary mechanisms or relatively modular,  hierarchical, specialized processes [4,5]. In this paper we assume the idea that executive functions cannot be understood as a unitary construct, but as a set of multiple processes with different independent components, but with intimate relationships to each other.

Nevertheless, we are aware that this approach creates an epistemological problem if we consider that the brain is a system of high complexity (it possesses specialized elements and its connections are not due to chance) with emerging properties (the most complex processes cannot be explained by the simple sum of the processes of lower level) and whose main function is to make predictions to act in a flexible way in changing environments to achieve adaptation, survival and the quality of this survival.

Searle’s Emergence Approach

Searle’s approach to emergence, applied to this topic, would lead us to question whether executive functions, conceived as the ‘sum of a set of lower-level processes’, can fall into the error that so-called executive functions are a reality with emerging properties that arise from the sum of lower-level processes, but that cannot be explained by the simple sum of them, but when they are joined new processes emerge [6,7].

Factorial analysis of the ‘Model of executive functions based on factorial analysis’.

In recent years, factorial analysis has been used to identify the components of executive functioning, as it is considered a useful tool that allows knowing the structure of the cognitive processes that underlie the performance observed in the execution of tests considered ‘executive’. However, in spite of this utility promising, is not without limitations that reduce the power of generalization of conclusions: heterogeneity in population samples and neuropsychological evaluation tests makes it difficult to compare results between papers or the idea that finding low correlations between evidence does not necessarily reflect the independence of the underlying processes, but may be due to different concepts of executive functions put forward by different authors.

The purpose of this paper is to carry out an exhaustive review of the factorial models proposed in the bibliography, to conclude with a proposal of factors involved in executive functioning. We intend to provide a model based on in processes that help to clarify terminological and conceptual aspects, taking as an initial idea the existence of a general consensus that assumes that there are several processes involved under this ‘conceptual umbrella’ called executive functions.

Therefore, our proposal pretends to be a ‘starting point’ to initiate the path that leads to a model of executive functions based on cognitive processes with the repercussion that it would entail to establish evaluation protocols capable of ‘capturing’ the differentiating aspects in different ‘dysexecutive’ subjects and the implications that, in turn, it would have to establish more effective rehabilitation programs.