3.1.1. Impulsivity/Impulsiveness
Even though impulsivity is broadly understood as a concept that encompasses a multitude of behaviors or responses that are poorly conceived, premature, inappropriate, and that frequently result in unwanted or deleterious outcomes [
11], in the articles selected for this current review, most authors refer to impulsivity as a multidimensional construct. This seems to be a general consensus in the current literature [
12,
13]. However, the dimensions of interest vary considerably from one study to the next. Here is a brief description of the different studies and their respective definition of impulsivity.
Firstly, Barratt’s Impulsiveness Scale (BIS) derived from Barratt’s three factor model of impulsivity [
14,
15] is a self-report questionnaire and seems to be the most commonly used to assess impulsivity in a TBI population. According to this model, there are three dimensions to impulsivity: Motor impulsivity which refers to acting without thinking, cognitive impulsivity which refers to quick decision taking and non-planning impulsivity which refers to a present orientation. McHugh and Wood examined the relation between impulsivity and decision making after brain injury using the BIS-11 [
16]. They demonstrated that the TBI group’s decision-making was more impulsive than the control group’s and that the TBI participants scored higher on all three dimensions of the BIS-11. Greve and collaborators also used the BIS-11 this time to differentiate TBI patients at risk for impulsive aggression from those who are not [
4] and in another study aiming to observe the use of cognitive strategies in TBI patients with problems with impulsive aggression [
17]. Similarly, Floden, Alexander, Kubu, Katz, & Stuss used the BIS-11 in an effort to distinguish impulsivity from risk-taking [
18]. They, however, specified that their definition of impulsivity is closer to the motor and non-planning subscales. Ferguson and Coccaro, in a study aiming to determine if a history of mild or moderate TBI was associated with impulsivity and aggression, also used the BIS-11 [
19].
In another study of impulsivity, Votruba
et al. aimed to assess impulsivity after TBI using different measures (
i.e., rating scales, questionnaires and performance tasks) in relation to direct behavioral observation [
10]. To do so, they focused on the mode of expression of these impulsive behaviors, either motor or verbal. They define an impulsive act (motor impulsivity) as being an action that the patient performs spontaneously, without evidence of preconsideration, and that has potential for negative consequences for the patient or others. More specifically, the authors observed dangerous acts, impersistences of action, disruptive behaviors, inappropriate acts, sexual actions, self-injurious actions and perseverated actions. According to the same authors, an impulsive statement (verbal impulsivity) is a statement made spontaneously, without evidence of preconsideration, with potential for negative consequences for the patient or others. Votruba and colleagues specifically targeted impersistent statements, inappropriate interruptions, inappropriate statements, sexual statements and perseverated statements for this dimension. The results of this study suggest that, even though rating scales completed by rehabilitation therapists (as opposed to self-reports) converged with verbal impulsivity and some performance tasks converged with motor impulsivity, direct observation of behaviors is the most accurate measure of impulsivity.
Similarly, in a study by Aeschleman and Imes, impulsivity was assessed by direct observation using four distinct categories [
20]. These categories were verbal impulsivity which was defined as yelling out abusive comments or verbally threatening to engage in destructive behavior, gestural impulsivity which required the use of body language to convey threat or insult, physical impulsivity which was operationalized as striking out at another person or object and making actual physical contact with person/object, tempting to strike out but missing the target, or throwing objects and finally a category named “other” which, according to the authors, includes other incidents in which the participant clearly acted in an impulsive manner, but the behavior does not fall into the above categories (e.g., walking out of class). The first two categories are similar to those defined in the study conducted by Votruba and colleagues [
10].
Rochat and colleagues, as for them, use a very different definition of impulsivity [
6]. In their studies on post-TBI impulsivity, they refer to Whiteside and Lynam’s conceptualization of impulsivity [
6,
13]. According to this specific theory, which is based on the Five Factor Model of personality [
21], there are four dimensions to impulsivity which can be measured with a rating scale (either self-report or relative-report) called the UPPS scale. Urgency refers to the tendency to experience and act on strong impulses frequently under conditions of negative affect [
22] and positive affect [
23], (lack of) premeditation refers to the inability to think and reflect on the consequences of an act before engaging in that act [
22], (lack of) perseverance refers to an individual’s inability to remain focused on a task that may be boring or difficult [
22] and finally sensation seeking refers to the tendency to enjoy activities that are exciting and to the willingness to try new experiences. Rochat and colleagues have not only demonstrated that the relative-reported version of this questionnaire had adequate factor structure in a TBI sample, but have also shown, as expected, that urgency, (lack of) premeditation and (lack of) perseverance increased following brain injury and that sensation seeking decreased [
6].
The Dysexecutive questionnaire (DEX) [
24] is a measure of executive dysfunction frequently used in TBI studies [
25,
26,
27,
28] In this questionnaire, impulsivity is assessed by a single question and is defined as acting without thinking and doing the first thing that comes to mind.
In a study in which the nursing staff observed adverse behaviors in a rehabilitation setting in patients who have suffered from TBI or stroke [
29], a behavior rating form developed specifically for the present study was used. Adverse behaviors such as restlessness, wandering, impulsiveness and verbal aggression where observed. Impulsiveness was defined as sudden movements or motions that indicated lack of behavioral or verbal control over oneself and was among the most observed and frequent adverse behaviors.
In the Behavioral Dysexecutive Syndrome Inventory, a structured interview, impulsivity, combined with irritability and aggressiveness, is considered to be one of 12 domains of interest in the evaluation of behavioral changes by informants of patients who have suffered from severe traumatic brain injury, stroke, mild cognitive impairment, Alzheimer disease, multiple sclerosis, and Parkinson disease [
30]. The authors do not, however, present a definition of impulsivity in this study.
Dixon and colleagues [
31,
32,
33] use a very different narrow definition of impulsivity. In their studies of patients who have suffered from TBI, impulsivity is conceptualized as the selection of a smaller reinforcer that comes in a shorter delay rather than a delayed larger reinforcer.
3.1.3. Inhibitory Control
Inhibitory control has been associated to orbitofrontal damage and has been linked to the ability to engage in goal-directed behavior. Patients with damage in this region are abnormally distractible, and have difficulty controlling impulsivity and instinctual behavior [
40]. More specifically, the author mentions that patients who have suffered from damage to the orbital prefrontal cortex have abnormalities that seem to be the result of deficits in inhibitory control such as altered emotions and cognitions and emotional and social behavior.
According to Wood, the ability to self-regulate social behavior is undermined by reduced inhibitory control of emotion and behavior and a lack of inhibitory control results in a tendency to act impulsively without thought of consequences and is often associated with a lack of concern for social values [
41]. This lack of concern reflects a change of personality following TBI (more specifically to the orbito-frontal cortex) and is often referred to as pseudo-psychopathy or acquired sociopathy. According to the author, these personality changes are usually associated with poor social judgment and short-lived enthusiasm for ill-judged projects, euphoric mood, sometimes accompanied by emotionally labile and erratic behavior, with low tolerance of frustration, leading to irritability and impulsive aggression.
Also, a few other authors have related a lack of inhibitory control to impulsive aggression following TBI. More specifically, Lishman used the concept of inhibitory control to distinguish impulsive aggression from episodic aggression following TBI [
42]. According to this author, a lack of inhibitory control can be explained by defective modulatory mechanisms associated with injuries in the prefrontal cortex as opposed to episodic aggression which is of a neurochemical nature. Similarly, Grafman and colleagues theorized that a lack of inhibitory control is the underlying cause of impulsive aggression [
43].
The term
inhibitory control has also been used in relation to emotional regulation. Cattran, Oddy and Wood define emotional regulation as the ability to exercise inhibitory control over how we express and/or direct our emotions in different forms of social interaction [
44]. According to these authors, inhibitory control is the mechanism that allows anticipatory reactions that help us judge the consequences of our behavior and a lack of inhibitory control is associated, according to the authors, with emotionally labile and impulsive behavior, often in the form of irritability and poor temper control. In this study, the authors developed a questionnaire to measure emotional regulation after acquired brain injury called the BIRT (Brain Injury Rehabilitation Trust) Regulation of Emotions Questionnaire (BREQ).
3.1.4. Inhibition/Disinhibition
In most of the articles consulted for the following review, it seems that disinhibition is synonymous with impulsivity. As an illustration of this, in Neuropsychological assessment, when searching for disinhibition, the authors invite the reader to see also impulsivity [
45]. Similarly, according to Constantinidou, Wertheimer, Tsanadis, Evans and Paul, both impulsivity and disinhibition belong to the same domain of executive functions: Initiation and planning [
46]. Also, in a study evaluating conversational abilities in TBI patients, impulsivity and disinhibition constitute one factor representing impulsive or disinhibited conversational behaviors (saying rude or embarrassing things) [
47]. More specifically, this factor encompasses speaking too quickly, saying or doing things others might consider rude or embarrassing, allowing people to assume wrong impressions from the conversations, answering without taking time to think about what the other person has said, having trouble using a tone of voice to get the message across, getting “sidetracked” by irrelevant parts of the conversation and losing track of conversations in noisy places.
For Luria, however, disinhibition is the general background on which are superimposed euphoria, impulsiveness and inadequate emotional actions [
48]. According to his model of frontally-mediated changes in personality and emotion, disinhibition is one of the two general sets of impairments (the other one being inhibition and torpidity).
For Hanna-Plady, failure to inhibit behavioral responses that are inappropriate to the environmental contingencies or fail to lead to successful goal attainment are frequent after frontal lobe injury [
49]. The author adds that this lack of inhibition often presents as behavioral impulsivity.
For Fuster, disinhibition is characterized by distractibility, difficulty in focusing and concentrating and difficulty in inhibiting interference of irrelevant stimuli [
40]. Serebro-Sorek, Shakhar and Hoofien use this definition in their study on basic attentional impairments in TBI patients and add that symptoms of disinhibition are accompanied by hyperactivity, impulsive behavior, inappropriate social behavior and unpredictable changes in affect [
50]. In this study, the authors measured disinhibition with the Behavioural Assessment Questionnaire (BAQ) in which the disinhibition items assessed the patient’s ability to reasonably plan activities, postpone her/his needs, be calm and not irritated by minor events and his or her ability to resist distractions. This questionnaire was completed by the patient’s neuropsychologist.
As mentioned earlier, the DEX is commonly used questionnaire to assess a variety of executive dysfunctions. As for the impulsivity item, disinhibition is evaluated with a single question. The item that specifically measures disinhibition evaluates if the patient says or does embarrassing things in the presence of others.
Another measure of frontal dysfunction commonly used is the Frontal Systems Behavioural rating scale (FrSBe) [
27,
51,
52,
53] and measures three domains of frontal dysfunction: Apathy, disinhibition and dysexecutive symptoms. The disinhibition scale is measured by 15 items evaluating encompassing a wide range of behaviors such as laughing or crying too easily, doing embarrassing things, making sexual comments, swearing, doing things impulsively, being overly silly, acting inappropriately, talking out of turn, not getting along with others, doing risky things, being easily angered or hyperactive, getting into trouble with the law, loss of taste or smell and lacking sensitivity to others.
On a more cognitive level, Rieger and Gauggel use a definition of inhibition in which inhibition is measured as a deliberate and complete suppression of an ongoing motor response [
54]. The authors, therefore, target an intentional form of inhibition. The authors also add that this type of inhibition requires one of the most extreme forms of control and is required in many real life situations, where unanticipated changes in the environment suddenly make ongoing actions inappropriate. In other words, an incapacity to suppress an ongoing response might lead to inappropriate behavior in specific situations. According to the authors, in most studies this form of inhibition is measured with the Go/No-Go task. Similarly, Braun, Daigneault and Champagne demonstrated that paradigms designed to elicit commission errors (such as the go/no go paradigm or a paradigm with prestimulus warning) were the most sensitive to distinguish severe chronic TBI patients from controls [
55].
3.1.5. Dyscontrol
Lux, in an article exploring the different chronic neuropsychiatric manifestations of TBI, describes behavioral dyscontrol as being a lost or diminished regulation in the behavioral sphere that is characterized by impaired social judgment and difficulty regulating emotional function as it contributes to and integrates with behavioral output [
56]. According to the author, agitation is frequent in cases of behavioral dyscontrol, however not all cases of post TBI agitation relies on the same mechanisms. He also encourages clinician to differentiate a difficulty in integrating emotional factors and social judgment from posttraumatic delirium and from episodic dyscontrol or intermittent explosive disorder which, according to him, are all manifestations of behavioral dyscontrol, but have distinct aetiologies.
In a study on emotional change following TBI, the authors base their comprehension of behavioral and emotional dyscontrol [
57] on Kinsella, Packer and Olver’s classification of post-TBI difficulties according to which impulsivity, aggression, short-temperedness and self-centeredness are reflections of poor self-monitoring and dyscontrol (behavioral and emotional) [
58]. Tate also used that conceptualization in a study in which she opposed loss of emotional control to loss of motivation [
59].
In a study on neuropsychological complications following TBI, the authors indicate that major features of behavioral dyscontrol include lability, impulsivity and a tendency to act without regard for consequences and that it may occur in both the acute and chronic stages after TBI and in patients with different levels of severity (mild, moderate and severe brain injury) [
60]. Behavioral dyscontrol can be measured with validated behavioral dyscontrol scales [
61].
3.1.6. Regulation Deficits
Deficits in regulation can either be emotional, behavioral or cognitive. Authors have demonstrated that different types of regulation most likely rely on different types of mechanisms [
44].
Firstly, unlike disinhibition and impulsivity which, according to some authors, belongs to the initiation/planning domain of executive functions, self-regulation belongs to the regulation/effective performance domain [
46]. Similarly, Callahan defines self-regulation as self-awareness and self-monitoring [
62]. In a study on the awareness of deficits in patients who have suffered from TBI [
63], the authors used the Self-Regulation Skills Interview [
64] which is a semi-structured interview measuring emergent awareness, anticipatory awareness, strategy generation, strategy-use and strategy effectiveness.
Also on self-regulation, Hanna-Paddy mentions that self-regulatory dysfunction can take the form of difficulty in comprehending the emotional consequences of behavior, behavioral disinhibition, or self-awareness involving the inability to be aware of one’s own mental state [
49]. According to the author, self-regulatory dysfunction can also have an effect on the appreciation of humor, the ability to take another individual’s perspective, and the use of appropriate judgment in social behavior.
In a study aiming to compare the patient’s and the caregiver’s assessment of the frequency of behavioral problems after TBI [
65], the authors used the Head Injury Behaviour Rating Scale (both the self-rating scale and the relative version) [
66]. This questionnaire is composed of two subscales composed of 10 items each: The Emotional Regulation subscale and the Behavioral Regulation subscale. The emotional regulation subscale measures impatience, being depressed, anger, anxiety, irritability, being argumentative, being overly sensitive, sudden mood changes, frequent complaining and aggression. The behavioral regulation subscale measures impulsivity, difficulty in becoming interested in things, lack of motivation, poor decision making, childishness, poor insight, being overly dependent, lack of control over social behavior, lack of initiative and irresponsibility.
Finally, in a study aiming to dissociate impulsivity and risk-taking on a behavioral level, the authors suggest that impaired behavioral regulation encompasses both impulsivity and risk-taking behaviors [
18].