Insomnia disorder is associated with increased amygdala reactivity to insomnia-related stimuli

Abstract

Study objectives: Alterations in emotional reactivity may play a key role in the pathophysiology of insomnia disorder (ID). However, only few supporting experimental data are currently available. We evaluated in a hypothesis-driven design whether patients with ID present altered amygdale responses to emotional stimuli related and unrelated to the experience of insomnia and, because of chronic hyperarousal, less habituation of amygdala responses.

Design: Case-control study.

Setting: Departments of Psychiatry and Psychotherapy and of Radiology of the University of Freiburg Medical Center.

Participants: There were 22 patients with ID (15 females; 7 males; age 40.7 ± 12.6 y) and 38 healthy good sleepers (HGS, 21 females; 17 males; age 39.6 ± 8.9 y).

Interventions: N/A.

Measurements and results: In a functional magnetic resonance imaging session, five different blocks of pictures with varying emotional arousal, valence, and content (insomnia-relatedness) were presented. Pictures were presented twice to test for habituation processes. Results showed that patients with ID, compared to HGS, presented heightened amygdala responses to insomnia-related stimuli. Moreover, habituation of amygdale responses was observed only in HGS, but not in patients with ID who showed a mixed pattern of amygdala responses to the second presentation of the stimuli.

Conclusions: The results provide evidence for an insomnia-related emotional bias in patients with ID. Cognitive behavior treatment for ID could benefit from strategies dealing with the emotional charge associated with the disorder. Further studies should clarify the role of ID with respect to habituation of amygdala responses.

Keywords: International Affective Picture System; amygdala; emotional arousal; emotional bias; emotional reactivity; emotional valence; habituation; insomnia disorder.

Figure 1

Task design and an example stimulus for each category. Pictures were presented in an functional magnetic resonance imaging block design. Each block included four pictures of the same type of stimuli lasting 5 sec each. Stimuli were presented twice in order to test habituation processes of amygdala responses. Within each category, the second presentation of the pictures started after all pictures were presented for a first time. The Neut_low blocks always preceded all other blocks types. Apart from these constraints, the presentation of the pictures and the sequences of blocks were randomized.

Figure 2

Amygdala reactivity (means ± standard error) to the four Contrasts (C1_Neut_moderate; C2_Neg_ moderate; C3_Neg_high; C4_Sleep_Neg_moderate) in patients with insomnia disorder (ID) and in heavy good sleepers (HGS) with respect to the first appearance of each stimulus. * P < 0.05; ** P < 0.001.

Figure 3

Voxelwise explorative Group × Contrast analyses (performed using the Analysis of Functional NeuroImages program GroupAna), conducted for the first appearance of each stimulus, revealed a cluster of activation in the left amygdala (orange areas).