One size fits null

STUDY OBJECTIVES: Event-related potential (ERP) studies on attentional brain processes in insomnia disorder (ID) have yielded inconsistent findings. Such inconsistencies may relate to small sample sizes, limited corrections for multiple comparisons, and the possibility of heterogeneity within the clinical population. We aimed to overcome these limitations by studying ERP responses both across and within subtypes in a larger sample of ID.

METHODS: ERPs were recorded in 201 participants with ID and 70 normal sleeper controls (NS) with an auditory oddball task. Participants with ID were subtyped using a validated multivariate trait profile. Analyses evaluated subtype-specific and nonspecific deviations using both conventional ERP components as well as cluster-based permutation tests.

RESULTS: All five subtypes were well-represented in the ID sample (subtypes 1-5 respectively N = 31, 83, 28, 29 and 19). ERP component analyses with false discovery rate corrections revealed no evidence for differences between the heterogeneous ID group and NS. However, subtype-specific analyses revealed that ERPs were significantly altered, but in different ways for different subtypes. Specifically, ERP component analyses revealed stronger N100 amplitudes for standards and deviants both in subtypes 2 and 3, and a lower P300 amplitude and longer P300 latency for deviants in subtype 3. Cluster-based permutation tests on ERPs corroborated the P300 amplitude effect for deviants in subtype 3, with subtype 3 and 4 additionally showing a smaller difference between deviant and standard P300 amplitudes.

CONCLUSION: Our findings indicate that ID is a heterogeneous disorder. Ignoring subtype identity dilutes ERP alterations occurring only in specific insomnia subtypes.