Insomnia is the most common sleep disorder and affects up to 40% of older adults. Poor cognitive functioning (i.e. concentration, attention and memory deficits), is among the most frequently complained daytime consequences of the disorder. Recent meta-analytic evidence suggests that insomnia is a risk factor for cognitive decline and Alzheimer's disease. Thus, it seems crucial to quantify the magnitude of late-life-insomnia-related cognitive impairments and to explore their reversibility after insomnia treatment. The aim of the present study is to compare performance of older adults with insomnia and normal sleeper controls on complex executive functions (EFs) tasks and to explore the effects of cognitive behavioral therapy for insomnia (CBT-I) on EFs using a randomized controlled trial design. We'll focus on EFs since 1) they are high order processes involved in a variety of cognitive and emotional processes; 2) they are understudied in late-life insomnia. The study will be conducted following the Consort guideline for randomized clinical trial. The study protocol will be submitted to the Institutional Review Board of our Department and to the WHO recognized registry of clinical trials ISRCTN for monitoring each stage of the study. Participants will be recruited at GPs in Rome and will undergo a clinical assesment following the European guidelines for the diagnosis and treatment of insomnia. EFs will be assessed using a go/no-go task, classic and emotional Stroop tasks, digit span backward, arithmetic span and letter-number sequencing tests. CBT-I will combine evidence-based cognitive and behavioral techniques for insomnia. CBT-I will be compared to a self-help program for improving sleep (CBT-I booklets). Alongside EFs, also subjective and objective sleep, as well as mood and quality of life will be considered as treatment outcomes.
Insomnia is the most common sleep disorder affecting 10% of the general population (Ohayon et al. 2002) and 40% of older adults (Foley et al. 1999). It predicts the onset of depression (Baglioni et al. 2011), cognitive decline and dementia (Bubu et al. 2017; Shi et al. 2017). Thus, it is important to detect early potential modifiable factors that may influence this trajectory.
Systematic reviews and meta-analyses conducted on cognitive functioning in adults with insomnia disorder (Shekleton et al. 2012; Fortier-Brochu et al. 2012; Ballesio 2017) support the presence of small-to-medium magnitude impairments in performance on EFs tasks associated with insomnia. However, findings in older adults are less clear, due to the small number of investigations and the lack of consistency in their results. Thus, the first part of this study (the comparison between older adults with insomnia and normal sleepers on EFs tasks) will advance the knowledge in the field providing information on the presence and magnitude of late-life-insomnia-related EFs impairments and their association with both subjective and objective sleep and quality of life.
Additionally, it is not clear whether -when present- EFs deficits are reversible after standard treatment for insomnia. Several meta-analyses support the effectiveness of CBT-I in improving sleep of adult patients with insomnia (e.g. van Straten et al. 2017, Geiger Brown et al. 2015). Promising, but yet limited in terms on number of studies, randomized trials support the effectiveness of CBT-I in improving sleep and insomnia severity in older adults with insomnia (Morin et al. 1999; Rybarczyk et al. 2005; Siversten et al. 2006; Vitiello et al. 2009). Additionally, only recently researchers begun to investigate the effects of CBT-I on daytime functioning, that is paradoxically, the reason why patients with insomnia seek clinical help (Riedel et al. 2000). Preliminary evidence in adolescent samples shows positive effects of group CBT-I on EFs (de Bruin et al. 2015). Further indirect evidence shows that CBT-I improves the functioning of prefrontal cortex, an area of the brain associated with EFs in adults (Altena et al. 2008). In older adults, Wilkens et al. (2016) failed to find significant improvements in EFs after CBT-I while Cassidy-Eagle et al. (2017) found a positive effect of CBT-I in insomnia comorbid with mild cognitive impairment. In this context, the second part of our study (the randomized controlled trial) will advance the knowledge in the field proving further direct evidence on the effects of CBT-I on cognitive functioning and extending the research to older adults.
This study encompasses several clinical implications. As aforementioned, insomnia has been shown to predict cognitive decline and dementia (Bubu et al. 2017; Shi et al. 2017). Thus, it is possible to hypothesize that improving cognitive functioning in subclinical samples may have a potential preventive effect on the onset of more severe neurological disorders. Consistently with this hypothesis, a recent aforementioned study shows that CBT-I has a positive impact of cognitive functioning of older adults with insomnia and comorbid mild cognitive impairment (Cassidy-Eagle et al. 2017). Additionally, insomnia has been longitudinally associated with the onset of major depression (Baglioni et al. 2011). Interestingly, poor EFs have been associated with impaired control of negative emotions (Nota et al. 2018) and with difficulties in emotion regulation (Ballesio et al. 2018). Thus, it is also plausible to hypothesize that improving EFs in at risk populations may potentially have a positive effect in the longitudinal trajectory from insomnia to depression.