Mind wandering, emotional lability and sleep quality are currently mostly independently investigated but are all interlinked and play a major role is adult attention-deficit/ hyperactivity disorder (ADHD). Emotional lability is a core feature of the disorder, excessive mind wandering has recently been linked to symptoms and impairments of ADHD and poor sleep quality is experienced by a clear majority of adults with ADHD.
Mind wandering, emotional lability and sleep quality are currently mostly independently investigated but are all interlinked and play a major role is adult attention-deficit/ hyperactivity disorder (ADHD).
Emotional lability is a core feature of the disorder, excessive mind wandering has recently been linked to symptoms and impairments of ADHD and poor sleep quality is experienced by a clear majority of adults with ADHD.
All three phenomena lead to functional impairment in ADHD, however their relationship to each other and to ADHD symptom severity is not well understood.
Mind wandering was found to lead to emotional lability which in turn lead to ADHD symptom severity; and poor sleep quality was found to exacerbate mind wandering leading to ADHD symptoms.
ADHD and emotional lability
Attention-deficit/hyperactivity disorder (ADHD) is a pervasive neurodevelopmental disorderaffecting 5–6% of children and 3–4% of adults [1,2]. In both children and adults ADHD is characterized by age-inappropriate and impairing levels of inattention, hyperactivity and impulsivity . According to DSM-5 measures of emotional lability can be used in a supportive capacity to help establish the diagnosis of adult ADHD. This can include a number of symptoms such as high irritability, changing moods or low frustration threshold . Emotional lability is also a prominent feature of borderline personality disorder and bipolar disorder , which are both common comorbidities of ADHD [5,6]. However, it has been argued that emotional lability in adults with ADHD is not related to comorbid conditions, but is a core feature of the disorder . This is supported by multiple lines of evidence: emotional lability is present in adults with ADHD without psychiatric comorbidities , it responds well to ADHD medication [9,10] and is related to functional impairment beyond other symptoms of ADHD . Moreover, genetic studies indicate shared genes explain the strong link of ADHD to emotional lability .
ADHD and mind wandering
Mind wandering is an omnipresent life experience, when our mind drifts away from a primary task and focuses on internal, task-unrelated thoughts and images. It has been defined as a shift of attention from the external environment towards inner, self-generated, task-unrelated and stimulus-independent thoughts, decoupled from immediate sensory perceptions [13,14]. It is estimated that up to 50% of our daily lives are spent in a mind wandering state [15,16]. Mind wandering can be spontaneous and unintentional, which is often detrimental to the task at hand and have little strategic value to the individual; or deliberate, when it may be related to strategic thinking about future plans . Excessive spontaneous mind wandering has recently been proposed as a candidate mechanism leading to the symptoms and impairments of ADHD, as it correlates strongly with ADHD symptom domains and impairment scores [, , , ], and mind wandering is closely associated with default mode network (DMN) activity [, , ] and dysregulation of the DMN is a prominent feature of ADHD . Mind wandering and ADHD symptoms have been examined predominantly in populations of college students not diagnosed with ADHD [25,18,20,26]. These studies found that spontaneous mind wandering is positively associated with ADHD symptom severity , both when measured in the laboratory as well as in daily life . Participants with a childhood diagnosis of ADHD reported more task-unrelated thoughts compared with other participants .
ADHD and sleep quality
Poor sleep quality and the resulting sleep deprivation have profound consequences on daily human functioning, negatively affecting cognition and emotion . Lack of good quality sleep disrupts normal wakefulness resulting in inattention [, , ]. Excessive daytime sleepiness due to disrupted sleep is extremely common in the general population  as well as in children and adults with ADHD [32,33]. Furthermore, adults with ADHD report higher excessive daytime sleepiness relative to healthy controls . A variety of sleep problems are associated with ADHD . It is estimated that up to 78% of adults with ADHD experience sleep problems [36,37] and report lower sleep quality than neurotypical controls [, , , ]. Sleep problems are thought to add to lower quality of life in ADHD, and are also associated with poorer academic performance, obesity, as well as more negative relations with carers . Sleep disorders may also generate ADHD-like symptoms which can make differential diagnosis challenging [43,44]. There is a positive correlation between mind wandering and poor sleep quality or difficulty falling asleep in the general population  and a single night of sleep deprivation can increase mind wandering. Poor sleep quality as well as a range of sleep problems has also been linked to difficulties in emotion regulation and negative mood [, , ].
ADHD, mind wandering and poor sleep quality are all associated with increased rates of car accidents while driving [, , , ] and together with emotional lability they contribute to poor academic performance [63,11,64,14]. Emotional lability leads to multiple functional impairments 0 .
B) Serial multiple mediation model of mind wandering and emotional liability on the effect of sleep quality on ADHD symptom severity.
We found that mind wandering and emotional lability predicted ADHD symptom severity and that mind wandering, emotional lability and sleep quality are all linked and significantly contribute to the symptomatology of adult ADHD. The mediation models supported both our prior hypotheses. Mind wandering was found to lead to emotional lability which in turn leads to ADHD symptom severity; and poor sleep quality was found to exacerbate mind wandering leading to ADHD symptoms.
Our findings fit well into the previous findings. We confirmed that mind wandering and emotional lability are significantly linked with core deficits in adult ADHD [9,11,8,18,7,19, 20,21] and that poor sleep quality may lead to emotional dysregulation [, , ] as well as exacerbate mind wandering [65,66]. We have also confirmed an influential result that mind wandering could lead to emotional lability and negative emotions .
Mind wandering and emotional lability
In this study, we have investigated a specific hypothesis that mind wandering leads to emotional lability. This is based on one of the most influential studies in the field, investigating mind wandering in a neurotypical group, where it has been found that mind wandering was the cause, and not a consequence, of negative feelings . However, another prominent study found that negative mood can lead to more mind wandering  and today it is generally acknowledged that emotional processes play a major, if not the central, role in generation of mental content during mind wandering . It seems that mind wandering and emotional lability are so closely linked that a two-way process might be a best explanation for the existing data. Mind wandering is a cause of emotional dysregulation when the negative content of the thought, or the intrusive nature of mind wandering itself, leads to higher levels of stress, including emotional distress, which in turn enhances the level of task-unrelated, negatively-valanced thoughts. Such a mechanism seems to be especially plausible in adults with ADHD, as the mind wandering experiences in ADHD are more intrusive and excessive , and there is emotional overactivity to stressful events . Mind wandering and emotional lability in adults with ADHD are both an integral part of the disorder , and this may be underpinned by abnormal activity in the DMN [79,21]. This reasoning can be additionally supported by the fact that mindfulness-based treatments for adults with ADHD seem to be promising and the preliminary data suggest high efficacy . Mindfulness and meditation practices are known to normalize activity and connectivity in the DMN and lead to decreased mind wandering and improved emotion regulation . Further work is however needed to test the hypotheses arising from our study.
Sleep, emotional lability and mind wandering
We found a similar bi-directional relationship between sleep quality and mind wandering, which is in line with previous findings in neurotypical subjects . It seems that not only poor sleep quality and the resulting sleep deprivation leads to higher incidence of mind wandering , but also a restless wandering mind makes it harder to fall asleep. It should be noted that one of the items on the MEWS scale, which was used to measure mind wandering in our study, reads: “Because my mind is ‘on the go’ at bedtime, I have difficulty falling off to sleep” . Mind wandering and sleepiness are similar in terms of the EEGsignal and are both linked to the DMN activity . Moreover, poor sleep quality results in negative affect , which is also in line with our findings regarding sleep quality and emotional lability. As discussed above, because mind wandering and emotional lability are so closely linked via negative affect, even when poor sleep quality exacerbates one of the variables, inevitably both of them will be increased [83,45], especially in adults suffering from ADHD.
Helfer, B., Cooper, R. E., Bozhilova, N., Maltezos, S., Kuntsi, J., & Asherson, P. (2019). The effects of emotional lability, mind wandering and sleep quality on ADHD symptom severity in adults with ADHD. European Psychiatry, 55, 45–51. https://doi.org/10.1016/j.eurpsy.2018.09.006