Analysis of aperiodic activity in obsessive-compulsive disorder and major depression

Obsessive-compulsive disorder (OCD) is believed to be linked to alterations in the cortical excitation-inhibition (E/I) ratio. Recent studies highlight aperiodic EEG activity as a neurophysiological marker for E/I ratio. We investigated the role of aperiodic activity during resting-state EEG in a children and adolescents sample of OCD patients (n = 38), compared to healthy controls (HC) (n = 94) and patients with major depression (MDD) (n = 88). To quantify aperiodic activity in resting-state EEG, we employed the FOOOF (Fitting Oscillations & One Over F) algorithm, which extracts the aperiodic exponent from EEG data. Compared to HC, both OCD and MDD patients exhibited increased E/I ratio as shown by decreased aperiodic exponents. Controlling for age by cohort-matching and for medication and stimulant intake on the test day rendered the statistical outcome non-significant but left the qualitative pattern of the outcomes intact. We conclude that both MDD and OCD seem to come with increased E/I ratios, as indicated by the aperiodic exponent, even though this effect may be moderated by age in OCD. This renders the aperiodic exponent a promising neural marker for psychopathology. However, the absence of a significant difference between OCD and MDD indicates that this marker may not be sensitive enough to differentiate between particular psychopathologies, which may be due to the fact that they often co-exist. The potential of using aperiodic exponents to examine the effectiveness of treatments in developmental neuropsychiatry should be explored. This approach should be carefully evaluated in future studies.