Table 2.

This table depicts the mean ± standard deviations of all neurometabolites in OCD and HV, displayed for anterior cingulate cortex, supplementary motor area, and occipital cortex and compared between groups

Metabolites	OCD group (M ± SD)	HV group (M ± SD)	t-test	DF	p-value	d	p-FDR	NAA-corr F-test	DF	p-value	ηp2	p-FDR
ACC
GABA	2.71 ± 0.43	2.86 ± 0.42	−1.29	58	0.10	−0.33	0.15	4.58	(1,57)	0.03	0.074	0.04
Gln	3.37 ± 0.58	3.21 ± 0.48	1.18	58	0.12	0.30	0.14	1.11	(1,57)	0.29	0.019	0.29
Glu	12.63 ± 0.82	12.20 ± 0.74	−2.08	58	0.02	0.53	0.04	5.66	(1,57)	0.02	0.090	0.03
Glx (Glu + Gln)	16.00 ± 1.13	15.41 ± 0.98	2.13	58	0.02	0.55	0.06	5.68	(1,57)	0.02	0.091	0.05
NAA	12.63 ± 0.94	12.51 ± 0.92	0.48	58	0. 61	0.13	0. 61	NA	NA	NA	NA	NA
Glu/GABA	4.73 ± 0.64	4.34 ± 0.61	618U	NA	0.006	0.10${}^{{\mathrm{\eta }}_{\mathrm{p}}{}^2}$	0.03	8.65	(1,57)	0.005	0.13	0.02
SMA
GABA	3.41 ± 0.97	3.31 ± 0.83	450U	NA	0.41	0.0008${}^{{\mathrm{\eta }}_{\mathrm{p}}{}^2}$	1.00	0.04	(1,56)	0.84	0.001	1.00
Gln	2.53 ± 0.93	2.40 ± 0.85	0.56	57	0.29	0.14	0.69	0.28	(1,56)	0.59	0.005	1.00
Glu	12.64 ± 0.97	12.50 ± 1.28	0.50	59	0.45	0.13	0.61	0.03	(1,58)	0.86	0.000	0.86
Glx (Glu + Gln)	15.34 ± 1.38	14.90 ± 1.82	1.03	57	0.30	0.27	1.00	0.80	(1,56)	0.37	0.014	1.00
NAA	15.37 ± 1.42	15.14 ± 1.43	0.64	59	0.26	0.16	0.78	NA	NA	NA	NA	NA
Glu/GABA	4.00 ± 1.09	3.97 ± 0.98	445U	NA	0.44	−0.0004${}^{{\mathrm{\eta }}_{\mathrm{p}}{}^2}$	0.88	0.07	(1,56)	0.79	0.001	1.00
OCC
GABA	2.55 ± 0.55	2.48 ± 0.48	0.51	54	0.30	0.13	0.36	0.25	(1,53)	0.62	0.005	0.77
Gln	3.88 ± 0.64	4.05 ± 0.52	−1.12	56	0.13	−0.29	0.25	1.15	(1,55)	0.29	0.021	0.72
Glu	10.39 ± 0.78	10.08 ± 0.60	1.70	54	0.09	0.44	0.25	1.65	(1,55)	0.20	0.029	1.0
Glx (Glu + Gln)	14.27 ± 1.01	14.01 ± 1.14	0.93	56	0.17	0.24	0.25	0.43	(1,57)	0.51	0.007	0.85
NAA	14.79 ± 1.05	14.57 ± 1.06	0.84	58	0.40	0.21	0.40	NA	NA	NA	NA	NA
Glu/GABA	4.23 ± 1.02	4.18 ± 0.80	1.46	54	0.15	0.05	0.25	0.03	(1,53)	0.85	0.001	0.85

To minimise concentration levels being contaminated with noise, and to avoid excluding abnormal data points that are population specific and may be clinically relevant, % Cramér-Rao Lower Bound and concentration levels outside the mean ± 2 SD were excluded, following procedure from Frangou et al.⁹⁷ and as suggested by Kreis⁸⁰. All metabolites were normalised using (Cr + PCr), corrected for grey and white matter and cerebral spinal fluid of each individual voxel, within subjects. The F-test values are the results of an ANCOVA using NAA as covariate to correct as a measure of neuronal integrity. The bold formatting shows the significant p-values and the metabolites that were measured for each significant test. For the ACC voxel the sample size for Glu and GABA in the OCD group was (n = 30) and in HV (n = 30). For the SMA voxel the sample size for Glu in the OCD group was (n = 31) and in the HV it was (n = 30), for GABA in the OCD group it was (n = 30) and in the HV the sample size was (n = 29). Lastly, for the OCC voxel the sample size for Glu in the OCD group was (n = 30) and in the HV it was (n = 28), for GABA in the OCD group it was (n = 27) and in the HV the sample size was (n = 29). All tests were two sided except for ACC and SMA glutamate, glutamine and GABA level comparisons across groups. The data for this table are provided in the Source Data file.

ACC anterior cingulate cortex, SMA supplementary motor area, OCC occipital cortex, GABA γ-amino-butyric acid, Glu glutamate, Gln glutamine, Glx Glu + Gln, NAA N-acetylaspartate, Cr creatine, PCr Phosphocreatine, t independent sample t-test, U Mann–Whitney U test, F Analysis of Covariance, NAA-c corrected for NAA levels, M mean, SD standard deviation, HV healthy volunteers, OCD obsessive-compulsive disorder, p-FDR p-value corrected for False Discovery Rates⁹⁸, DF degrees of freedom, d Cohen’s d, η_p² partial eta-square.