Elsevier

New Ideas in Psychology

Volume 36, January 2015, Pages 30-37
New Ideas in Psychology

Default-mode network activity and its role in comprehension and management of psychophysiological insomnia: A new perspective

https://doi.org/10.1016/j.newideapsych.2014.08.001Get rights and content

Abstract

Psychophysiological insomnia (PI) is a common sleep disorder in which numerous variables interact. The mechanisms responsible for the etiology and maintenance of PI, though far from completely understood, point to the existence of hyperarousal of several systems. The frequent occurrence of ruminations and worries with a self-referential component (related or not with sleep complaints) during the pre-sleep period, and daytime wakefulness, seems to relate to the functions which have been associated with default-mode network (DMN) activity. This neural network seems to be involved in introspective thinking as well as emotional and episodic memory processing, among others. In this paper, we propose that PI may be conceptualized as a disorder associated with overactivity of some brain areas of DMN. Accordingly, it is also suggested that cognitive-behavioral therapy for insomnia (CBT-I), a kind of non-pharmacological treatment, may alter the function of this network, improving symptoms of patients, and overall quality of life.

Introduction

Approximately 10–15% of the general population has insomnia and this is considered as being one of the most common sleep disorders with an estimated incidence of 3–5% of new cases each year (Drake & Roth, 2006). Psychophysiological insomnia (PI) is a sleep disorder with clear-cut classification criteria in terms of medical diagnosis and covers complaints in starting, maintaining sleep, or experiencing non-restorative sleep. According to the second edition of International Classification of Sleep Disorders - ICSD-2 of the American Academy of Sleep Medicine (AASM, 2005), this is a diagnosis that includes high cognitive, physiological, and emotional arousal levels associated with negative conditioning between some stimuli or spatial/temporal cues and sleep behaviors.

As suggested in the literature, insomnia (particularly conditioned insomnia) seems to be a fluctuating disorder. This is evident when we analyze the amount of pathophysiologic models that have been proposed to explain it (Bootzin, 1972, Espie et al., 2006, Harvey, 2002, Kales et al., 1976, Lundh and Broman, 2000, Morin, 1993, Ong et al., 2012, Perlis et al., 1997, Spielman et al., 1987). All these models, mainly psychological in their origins, gave consistency to the two hypotheses explaining insomnia development and maintenance processes: hyperarousal and failure to inhibit wakefulness, respectively (Perlis, Shaw, Cano, & Espie, 2011). The hyperarousal hypothesis states that in patients with insomnia there is a widespread activation of several systems (e.g., cognitive, physiological, emotional, cortical), which consequently prevents the person to relax. The concept of hyperarousal was recognized to be of major importance in the understanding of PI. However, sleep researchers have not yet reached a consensus on which dimensions this concept covers (Riemann et al., 2010).

On the other hand, the failure to inhibit wakefulness account suggests that the difficulty in inhibiting activation typical of wakefulness period is the principal disturbing process in PI (Espie et al., 2006). In practice, it is feasible to accept the complementarity of both hypotheses (Perlis et al., 2011). It is likely that these two processes may relate to two distinct profiles of patients with insomnia. Although interesting, we do not have yet evidence to support this claim.

Many studies have concluded that bedtime is the period of day in which individuals are more available to deal with emotionally arousing cognitions (Harvey, 2005). For example, people tend to focus on the concerns regarding the organization and management of the following day, to elaborate a retrospective of the past day, to remember past traumatic events, or to anxiously anticipate the future, or generate negative expectations related to own sleep behavior, among many others (Watts, Coyle, & East, 1994). Accordingly, it is easy to understand that intrusive and dysfunctional thoughts related with the self play a key role in PI.

As already mentioned, there are many models proposed for understanding the etiology and maintenance of PI. Nevertheless, it should be noted that the behavioral or psychological models are the most studied and well-known ones, with the added advantage, but also the challenge, of integrating neurobiological, biochemical, physiological, and even immunological variables (Talbot & Harvey, 2010).

In this article, we will present some provisional ideas suggesting that the new developments in neuroscience, in particular, pertaining to the brain's default-mode network (DMN) study will bring important advances for insomnia's conceptualization and treatment.

Section snippets

The default-mode network

The function of the DMN is currently one of the most studied topics in the field of cognitive neuroscience. In general, it concerns to a relatively well-defined set of brain areas which have a higher level of activation when the subjects are not focused on a specific external task mobilizing their explicit attentional resources (i.e., goal-oriented task or attention demanding task). For this reason, it is also called a task-negative network (Raichle & Snyder, 2007). In spite of this, it is

Insomnia as a self-referential processing disorder: the DMN dysfunction pathway

Until now, we enlightened that DMN has an important role in many human functions and may be disrupted in several disorders. The most studied disorders have been the Alzheimer's disease, major depression, anxiety disorders, schizophrenia, autism, and attention-deficit/hyperactivity disorder. However, the DMN dysfunction hypothesis has been examined also in other disorders beyond neuropsychiatric ones (e.g., Kornelsen et al., 2013, Liu et al., 2013, Tregellas et al., 2011, Violante et al., 2012,

Specificities regarding the study of the DMN in insomnia

Taking into account some main characteristics of PI (e.g., intrusive thoughts/cognitive arousal) and the functions that appear to be hypothetically related to the DMN, we think it is very important in clinical practice and neurobiological research to study how the regions of DMN modulate their activity in these patients compared with matched control samples taken from general population, without sleep complaints or other neuropsychiatric disorders. It should be outlined that the scientific

Implications for treatment

If future research validates the hypotheses that (a) there is a significant correlation between activity of DMN's regions and the cognitive experiences that patients often report, and (b) that this association is significantly different from control samples (i.e., individuals without sleep disorders), psychotherapeutic techniques derived from cognitive therapies may be strategies to favor in the management of insomnia, giving strength to the idea that all insomnia treatment packages must

Concluding remarks

We think that the model of impaired DMN function and the raised provisional hypotheses we propose in this paper, can be integrated in other comprehensive models of insomnia that already exist (e.g., Espie's psychobiological inhibition model). In clinical practice, it is common to observe that different explanatory models can be used successfully to different patients with PI diagnosis.

It will be helpful to foster future research on the putative role of different functional clusters within DMN

Acknowledgment

First author has a PhD Grant from the Portuguese Foundation for Science and Technology (FCT – Fundação para a Ciência e a Tecnologia) with the following reference: SFRH/BD/77557/2011.

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