Habituation refers to the brain's inhibitory mechanism against sensory overload and its brain correlate has been investigated in the form of a well-defined event-related potential, N100 (N1). Fibromyalgia is an extensively described chronic pain syndrome with concurrent manifestations of reduced tolerance and enhanced sensation of painful and non-painful stimulation, suggesting an association with central amplification of all sensory domains. Among diverse sensory modalities, we utilized repetitive auditory stimulation to explore the anomalous sensory information processing in fibromyalgia as evidenced by N1 habituation.
Auditory N1 was assessed in 19 fibromyalgia patients and age-, education- and gender-matched 21 healthy control subjects under the duration-deviant passive oddball paradigm and magnetoencephalography recording. The brain signal of the first standard stimulus (following each deviant) and last standard stimulus (preceding each deviant) were analysed to identify N1 responses. N1 amplitude difference and adjusted amplitude ratio were computed as habituation indices.
Fibromyalgia patients showed lower N1 amplitude difference (left hemisphere: p = 0.004; right hemisphere: p = 0.034) and adjusted N1 amplitude ratio (left hemisphere: p = 0.001; right hemisphere: p = 0.052) than healthy control subjects, indicating deficient auditory habituation. Further, augmented N1 amplitude pattern (p = 0.029) during the stimulus repetition was observed in fibromyalgia patients.
Fibromyalgia patients failed to demonstrate auditory N1 habituation to repetitively presenting stimuli, which indicates their compromised early auditory information processing. Our findings provide neurophysiological evidence of inhibitory failure and cortical augmentation in fibromyalgia. WHAT'S ALREADY KNOWN ABOUT THIS TOPIC?: Fibromyalgia has been associated with altered filtering of irrelevant somatosensory input. However, whether this abnormality can extend to the auditory sensory system remains controversial. N!00, an event-related potential, has been widely utilized to assess the brain's habituation capacity against sensory overload. WHAT DOES THIS STUDY ADD?: Fibromyalgia patients showed defect in N100 habituation to repetitive auditory stimuli, indicating compromised early auditory functioning. This study identified deficient inhibitory control over irrelevant auditory stimuli in fibromyalgia.