The term “executive functioning” is used traditionally to refer to a set of integrated higher-order processes that determine goal-directed and purposeful behavior. By supervising and coordinating underlying cognitive, behavioral, and emotional processes, executive functions allow the orderly execution of daily life activities. Executive functions include the ability to formulate goals, solve problems, anticipate the consequences of actions, plan and organize behavior, initiate relevant behaviors, inhibit irrelevant behaviors, and monitor and adapt behavior to fit a particular task or context [9]. Higher-level attentional processes responsible for allocating attention across more than one task, actively shifting attention between tasks, and selectively sustaining attention while inhibiting irrelevant information, also fall within the broad rubric of executive functioning [13, 14]. Working memory, defined as a process that allows the short-term storage, maintenance, and manipulation of information [15], is also intimately related to attention-executive functioning. The “executive” aspect of working memory is the ability to actively manipulate and control transitory information in the mind [16].

Attention-executive functions are also related to emotional and behavioral self-regulation, and metacognitive processes [14, 17]. Metacognition, or simply thinking about thinking, is a set of processes that involves metacognitive knowledge or beliefs, self–monitoring, and self–control that work together to enable self-regulation [12, 18]. Metacognitive knowledge is the moment-to-moment and more stable beliefs about one’s cognitive abilities. The ability to self-monitor one’s performance and use the resulting internal feedback to adapt to changes in the environment or task demands (a process labeled self-control) is also an integral aspect of metacognition. There is some debate as to whether metacognition is in fact a core “executive” function or rather reflects a distinct superordinate process at the highest level of the cognitive system [12, 18]. Nonetheless, there seems to be general consensus that metacognitive self-regulatory skills are mediated by the frontal lobes, are frequently disrupted following traumatic brain injury (TBI), and are critical to the execution of self-directed complex behaviors [12, 14, 17–25].

Recent developments in cognitive neuroscience, aided by advances in brain imaging methodologies (e.g., diffusion-tensor imaging–DTI; functional magnetic resonance imaging–fMRI), have led to number of new empirically driven, theoretical perspectives of attention-executive functioning. We will briefly review these perspectives with an emphasis on their relevance to the nature and rehabilitation of attention-executive impairments following TBI.

Posner and Peterson [26] have described an approach to understanding attention-executive processes based on principles of large-scale distributed neural networks [27]. Cognitive-neuropsychological and neuroimaging studies have identified distinct attentional networks for alerting, orienting, and executive control [26, 28–30]. The alerting attention network, which is characterized by reciprocal connections between right frontal and parietal regions, involves the ability to reach and sustain preparedness for potential stimuli [31]. The orienting attention network includes the superior and inferior parietal lobes, frontal eye fields, superior colliculus, and the pulvinar and reticular thalamic nuclei, and involves the ability to make covert shifts in attention [31]. The executive attention network involves the anterior cingulate, medial frontal cortex, and lateral prefrontal cortex, and underlies the capacity to use relevant information, ignore irrelevant information, and resolve conflicts among competing sources of information [31]. It is worth noting that the capacity for conflict resolution is a developmental process, which in early life evolves from the need for resolution (or delay) of emotional needs [32].

Niogi and colleagues [33] examined the operations of these attention networks in relation to structural connectivity of white matter tracts. They demonstrated distinct and separable relationships between attention components and structural connectivity, providing evidence of discrete networks. Alerting was related to the posterior limb of the internal capsule, which contains thalamic-parietal connections. Orienting was related to the splenium of the corpus callosum containing interhemispheric tracts connecting regions including the frontal eye fields and posterior parietal regions. The executive-conflict effect correlated with structural integrity of the anterior cingulate region, as expected. Niogi and colleagues also demonstrated an association between decreased performance of the executive network after TBI and reduced fractional anisotropy within the anterior corona radiata, including projections to the anterior cingulate gyrus [34].

The initial investigations of attentional networks were directed at establishing the efficiency and independence of functions involving alerting, orienting, and executive attention [35]. More recently, investigations have demonstrated consistent interactions among attention networks [36]. For example, the alerting and orienting system will typically operate together in real-world situations where a single event indicates both when and where a relevant stimulus occurs [30], suggesting that both of these networks serve a more general preparatory function [37].

This anticipatory function is likely a general, integral feature of higher cognitive processing, especially attention-executive processes [38]. Ghajar and Ivry [39] have described an anticipatory neural network involving the prefrontal-inferior parietal areas that provides a feed-forward mechanism that reduces performance variability by generating a “predictive brain state.” This framework suggests that through the generation of moment-to-moment predictions about the immediate future, and the comparison of these predictions with sensory feedback, individuals will be less distracted by irrelevant information which will facilitate goal-oriented behavior. Disruption of this network may represent a fundamental defect after TBI resulting in a variety of deficits, including impairments of sustained attention, poor self-monitoring of errors, and loss of goal-directed behavior.

The interaction among various aspects of attention and executive functioning has also been related to three distinct, separable anterior attentional systems by Stuss and his colleagues [40]. One attentional system maintains a general state of readiness to respond, mediated primarily by superior medical frontal structures. A second attentional system serves primarily to bias attention toward specific criteria that guide responsiveness. Dysfunction of these processes, associated with damage to the left dorsolateral prefrontal cortex, is related to deficits of task initiation and setting of response criteria. The third attentional system maintains the criteria for response selection, so that relevant aspects of the environment are consistently selected and responses to competing or irrelevant targets are inhibited. Dysfunction in this network, associated with damage to right dorsolateral frontal cortex, produces deficits in sustaining attention to criteria and conflict resolution. This characterization of an anterior attentional system has significant correspondence with the attentional networks described by Posner and Peterson [26, 41]; specifically, an attentional network devoted to maintaining alertness or readiness to respond, a second network related to orienting and setting criteria to respond, and a third network related to “executive” attentional processes of response selection and conflict resolution.

Peterson and Posner [41] more recently noted the evidence supporting two brain systems related to the orienting network, through an interaction of endogenous and exogenous stimulus control [42]. Corbetta and Shulman described segregated networks corresponding to top-down and stimulus-driven regulation of attention, related to dorsal and ventral frontal-parietal connections, respectively [42]. While initially related to specific aspects of visual attention, more recent evidence suggests that these networks are related to more general, dynamic roles of reorienting between internally directed activity and attention to the environment [37]. They also noted that the orienting function is not restricted to visual information and overlaps with information from other sensory modalities. The operations of the executive network have also been elaborated, with evidence of dual networks involved in top-down cognitive control [43, 44]. The first executive system involves a fronto-parietal network, distinct from the orienting network, that serves primarily to adapt control over performance by maintaining a stable response set (including the maintenance and prioritization of information in working memory), while a network related to the cingular-opecular connectivity (consistent with the original executive network) provides moment to moment control over performance, perhaps by providing a continuously updated account of predicted demands on cognitive resources [45, 46].

Stuss has also described a “revamped attentional model” of executive functions, based on the fractionation of frontal lobe regions corresponding to fundamental cognitive operations [8]. Three of these proposed processes and their anatomic relations correspond to the earlier formulation of an anterior attentional system [8, 40]. Within this new framework, damage to the superior medial frontal lobes is associated with decreased performance on a range of (apparently dissimilar) tasks due to a failure of “energization,” or the initiation and sustaining of any response. For example, superior medial damage might manifest as slow response on speeded tasks. Two aspects of “executive functioning” are related to the dorsolateral frontal cortices (DFC), as in the earlier model. Damage to the left DFC is related to initial task setting and goal orientation, while damage to the right DFC suggests poor monitoring of ongoing performance, deficits in sustained attention, and increased intra-individual variability. These three attentional networks can be further defined by their connections with other areas of the brain. The first is a ventral system involving orbitofrontal cortex and limbic structures related to emotional and behavioral regulation. The second is a rostral and lateral system with bidirectional connections between prefrontal cortex and posterior cortices related to “metacognitive” processes (i.e., the ability to self-monitor and self-regulate), including shifting between attention directed at the environment and internal trains of thought [47, 48]. Stuss and colleagues propose that metacognitive functions—positioned at the highest level of the cognitive system—coordinate the integration of attention-executive cognitive information with emotional and motivational processes, which ultimately guides and enables complex, purposeful behavior [8, 49]. The distinction between a more dorsal fronto-cingular-parietal pathway associated with more deliberate, slow-to-respond, volitional behavior and a ventral pathway that is more reactive (to either environmental stimuli or basic emotional states) and associated with quicker-to-respond, automatic behaviors may be another general principle of the brain’s organization of complex attention-executive functions [50]. This dissociation is also central to dual-process approaches to cognitive-affective control [51–54] and provides a framework for metacognitive strategy training methods for affective and behavioral self-regulation [55, 56].

These empirically supported models suggest that the dissolution and restoration of cognitive functioning after TBI may be informed through an understanding of the efficiency and interaction of attention-executive networks, although this approach has to date had limited influence on our understanding of cognitive recovery or the development of rehabilitation interventions. Several authors have argued that these models have important implications for the rehabilitation of attention-executive impairments [14, 57]. Metacognitive processes are critical to the ability to use internal goals and desires to direct ones’ thoughts and behaviors. Thus, metacognitive training, characterized by interventions to foster anticipation and planning, response monitoring, and self-evaluation, may be particularly beneficial in reestablishing top-down control over attention-executive cognitive, emotional, and behavioral functioning [9–12, 51, 57, 58]. Recent applications of metacognitive interventions have also emphasized the importance of addressing not only attention-executive cognitive functions, but also emotional/motivational, and behavioral functions, as these processes are anatomically and functionally related in the execution of complex, real-world behaviors [59–61].

Deficits involving self-directed attention and executive cognitive functioning, behavioral and emotional regulation, and metacognitive functioning are interrelated and commonly impaired following TBI.

Two primary approaches to intervention have been investigated in the remediation of attention-executive deficits in person with TBI: direct training and metacognitive training. Consistent with the overall goals of cognitive rehabilitation, both approaches are directed at effecting cognitive change with the ultimate goal of improving patients’ functioning in meaningful contexts, including functional activities, participation, and quality of life [9–11]. However, direct training and metacognitive training interventions differ with regard to the theoretical approach to treatment; the proposed mechanism of action; and the emphasis and delivery of treatment activities. In this section, we will review the rational, evidence-based literature, and clinical recommendations for direct training and metacognitive training interventions. Because most widely used direct training interventions involve commercially available software and treatment programs that are not in the public domain, we will not describe the specific application of this type of approach. Readers should consult the research studies referenced in this chapter for further information regarding proprietary treatment programs/materials.