1. Introduction
Traumatic brain injury (TBI) often leads to pervasive emotional and cognitive changes, including increases in boredom and depression, and decreases in motivation [
1,
2,
3,
4]. A great deal of research, including work from our own lab, has shown a consistent and strong relationship between the constructs of boredom and depression [
5,
6,
7]. Importantly, we recently showed that although the two experiences are highly correlated (r = 0.72), they can be shown to be psychometrically distinct [
6].
Work in our lab has also shown that boredom should not be considered a unitary construct [
8]. The Boredom Proneness Scale (BPS) [
5], most commonly used to evaluate susceptibility to boredom, has consistently been shown to have two prominent factors that account for the variance on this measure—the internal and external stimulation subscales. It should be noted that the factor structure of the BPS is far from uncontroversial—although many studies have sought to determine the factor structure of the BPS, the data has produced anywhere from two to eight factors [
7]. However, the perceived need for either internal or external stimulation represents the two factors most commonly observed in all of these factor analytic studies [
7,
9]. This distinction harks back to an earlier one made by Greenson [
10] between an agitated and an apathetic bored state. In short, the difference between these two states lies in their motivational status. The agitated boredom prone individual experiences boredom as an aggressively dissatisfying state—they are motivated to engage in something pleasurable and stimulating, but every attempt to do so fails to satisfy them. This discrepancy between the desire to be stimulated and a failure to extract that stimulation from the environment leads to a sense of agitation—hence, the so-called agitated boredom prone individual. In contrast, the apathetic boredom prone individual may perceive their environment to be dull and monotonous, but experiences no desire to alter that experience. In other words, the apathetic boredom prone individual sees things as unstimulating, but is not motivated to redress that fact.
Recent work in our lab exploring the relationship between boredom and attention supports the distinction between the agitated and apathetic boredom prone subtypes. Others had already demonstrated a link between boredom and attention, suggesting that lapses in everyday attention (e.g., pouring orange juice on your cereal) and reduced mindfulness actually
lead to both boredom and depression [
11,
12]. In this context, boredom (and potentially depression) arises as a consequence of a
disengaged mind—an individual less capable of attending appropriately to their surroundings [
12]. Our work found that it was the apathetic boredom prone individual who most prominently showed such lapses in everyday attention. In contrast, the agitated boredom prone individual was insensitive to errors of performance on a sustained attention task [
8]. That is, the agitated boredom prone individual did not slow their reaction times on trials subsequent to an error, as would normally be expected [
8,
13]. This same kind of insensitivity to having made an error is evident in TBI patients [
13]. Indeed, there is a wealth of research demonstrating poor sustained attention and concentration in patients with TBI [
3,
13,
14,
15,
16]. It may be the case that the poor sustained attention evident in TBI will, in turn, lead to increased levels of boredom [
11,
12].
Given the distinct boredom subtypes discussed above, and the fact that both boredom and depression represent major impediments to rehabilitation [
2,
17], it is important to investigate whether the commonly observed relationship between the two affective constructs is driven primarily by the need for external or internal stimulation. The current study aimed to explore the relationship between boredom and depression following TBI, a population of patients who report experiencing high levels of both.
A priori, we expected the moderate-to-severe TBI group to have the highest BPS scores, given prior research suggesting this population experiences elevated levels of boredom [
4]. Furthermore, based on previous results [
6], we expected that boredom and depression would be highly correlated in all groups. However, we hypothesized that this relationship would be strongest in the moderate-to-severe TBI group.
4. Discussion
We investigated the relationship between depression and boredom in patients with varying degrees of TBI, where boredom has been reported to be pervasive [
1,
2,
4]. All three groups evidenced a strong correlation between boredom and depression, as shown in previous work (
Figure 1) [
6,
7]. This relationship warrants further investigation. Our earlier work showed that the two constructs do indeed represent distinct affective states and that any commonalities in the items on each scale cannot account for the strong relationship [
6]. In addition, at least one study looking at the effects of pharmacological treatment (citalopram) for depression in cancer patients [
20] found that depressive and boredom symptoms ameliorate along different time scales (depressive symptoms are alleviated more rapidly than self-reported boredom). This provides further support to the notion that the two constructs tap into different subjective experiences and that boredom does not simply reflect a symptom or epiphenomenon of depression. Regardless, it is not clear at this stage what underlying mechanisms may be common to the two experiences and what, if any, the causal relationship is between the two. It is also worth pointing out that depression and boredom may manifest in distinct ways in different patient populations.
It was perhaps surprising that there was not a more stark difference in boredom proneness in the TBI groups given the documented subjective reports of elevated boredom in TBI [
1,
4]. It may be the case that the BPS lacks sensitivity with this population. In addition, TBI patients may, in fact, show elevated levels of boredom proneness
relative to premorbid levels, which we were not able to measure here. In addition, many of our moderate-to-severe TBI patients had suffered their injury many years prior to testing (
Table 1). Although this represents a highly speculative conjecture, it may well be the case that boredom levels subside with age, in general, and with time post injury, in particular, both possibilities that require further research.
The control and mild-TBI groups showed a relationship between depression and age, such that depressive symptoms
increased with age. One would have expected to see a similar pattern in the moderate-to-severe TBI group, especially if one considers that in this population, depressive symptoms will be likely to increase with increasing insight into the patient’s condition. Therefore, while initially lower levels of insight may prove to be prophylactic for depression in TBI [
4], as insight is gained, depressive symptoms should be more likely to appear. Further research is needed to determine the course of depressive symptoms in TBI. The small sample size here prevents us from making any reasonable speculation about the lack of an association between depression and age in the moderate-to-severe TBI group.
When full BPS scores were considered, results showed a trend towards a stronger relationship between boredom and depression in the mild and moderate-to-severe TBI groups than in controls. This is not surprising, given the high incidence of post-injury depression in patient groups [
4,
21]. In all three groups, the relationship between boredom and depression was largely driven by the perceived need for external stimulation from the environment. This relationship was stronger in both TBI groups when contrasted against controls, although the difference only approached significance for the mild TBI group. This failure to satisfy a need for external stimulation could plausibly lead to both boredom and depression simultaneously. Given our prior work showing that boredom and depression are indeed two distinct affective states [
6], along with other work showing that they respond to pharmacological treatment along different time scales [
20], it is nevertheless plausible that boredom and depression can be experienced independently and that the failure to satisfy a need for external stimulation could lead to one or either affective state in isolation. As such, it remains an open question as to why a perceived need for external stimulation—and presumably the failure to satisfy that need—could lead to boredom in one instance and depression in another? This is perhaps particularly pertinent when taking into consideration one of the cardinal difficulties of patients with depression, who commonly suffer from recursive negative self-evaluations that, on face value, are
internal evaluations [
18]. Although completely speculative at this stage, two potential explanations can be considered; first, the failure to garner satisfactory stimulation from the environment may be
interpreted in distinct ways by bored
vs. depressed individuals. The bored individual, particularly those who see the experience as aggressively dissatisfying [
8,
10], may attribute the failure to be stimulated as external to themselves—that is, there is something wrong with the world. In contrast, the depressed individual may interpret the same experience as an internal failure—there is something wrong with me. This, of course, requires further research to examine the cognitive appraisal and attribution styles of both depressed and bored individuals (see [
22,
23,
24] for a discussion of coping styles and depression following brain injury). The second possibility is that depression and boredom follow one from one another in a temporal manner, with depression arising only after prolonged boredom or disengagement from the environment [
12], both of which are known to cause feelings of hopelessness and helplessness—hallmark features of depression [
25,
26]. Of course, the opposite temporal sequence could also occur, with boredom following on as a consequence of depressive symptoms or episodes. Clearly, further research is required to longitudinally investigate the time course of boredom and depression, especially in TBI patients.
The findings presented here may have implications for the treatment of depression, in general, and in patients who have suffered brain injury, in particular. One popular therapeutic approach to the treatment of depression is behavioural activation therapy [
27], which attempts to engage the patient in the pursuit of a hierarchy of self-generated goals with rewards given for success. Boredom, as a stand-alone affective experience [
6], may represent a serious impediment to this approach. That is, the agitated boredom prone individual [
8,
10] is, by definition,
already motivated to engage in activities, but fails to see or experience the pleasure in doing so. In the context of behavioural activation therapy, asking such a patient to engage
more may be futile. Instead, it may be more important to address the disconnection between the individual’s high level of motivation to engage with the environment and the perceived failure to satisfy those desires. As such, a therapeutic approach that focuses more on cognitive appraisal to realistically experience the environment may be more successful in the treatment of depression in patients who are prone to agitated boredom.
Why boredom and depression are more strongly correlated in patients with TBI should be the focus of further research. It may simply be that reduced cognitive resources in TBI mean that these patients are more vulnerable to both affective states. Alternatively, one brain region commonly affected in TBI, and known to be dysfunctional in patients with depression, is the orbitofrontal cortex (e.g., [
28]). This brain region is known to be important for representing the reward value of stimuli [
29]. A failure to accurately register or respond to external reinforcers may play a significant role in both boredom and depression. With the relatively small samples sizes tested here, coupled with the fact that our groups were not matched on key demographics (
i.e., age and education) and there was, at least in the moderate-to-severe TBI group, a long time post injury, it is difficult to address these specific hypotheses.
