Table 2:

Summary of metabolites detected by proton MRS and findings

Metabolite of Interest	Key Properties	Findings for Patients with Depression Relative to Controls
Glu/Glutamine	Complex signal Requires difference technique at intermediate field strengths	Decreased Glu/Gln in anterior cingulate^19,56,57 Decreased Glu/Gln in amygdala-hippocampus⁵⁸ Decreased Glu/Gln in prefrontal cortex⁶² Elevated Glu in occipital cortex⁵⁹ Reduction of Glx (mainly Glu and Gln) in depressive disorder but elevation in bipolar disorder⁶⁰ Response to treatment: increased levels with ECT¹⁹
GABA	Complex signal Requires different technique at intermediate field strengths	Decreased in occipital cortex^59,61 Decreased in occipital and anterior cingulate cortex⁶³ Decreased in prefrontal cortex⁶² Response to treatment: patients who were most severely depressed and who had lowest GABA concentrations showed largest increase after SSRI treatment⁵⁹
NAA or NAA/Cr	Only present in neurons Change reflects loss or decreased function of neurons	Decreased NAA/Cr in thalamus⁶⁴ Decreased NAA in caudate⁶⁵ Meta-analysis: no significant differences in NAA between depressed and healthy subjects in basal ganglia and frontal lobe structures⁵⁰
Cr+PCr	Reflects tissue energetics ∼7.8 μmol/g¹¹⁷	No significant differences in Cr levels in frontal lobe structures between depressed and healthy subjects⁵⁰
Cho	Concentration of pool: ∼2 μmol/g¹¹⁷ Reflects mobile Cho (TMA) moieties Cho concentration rate limiting step in acetylcholine synthesis Dynamic equilibrium with acetylcholine and phospholipid pathways	Mixed findings Meta-analysis: elevated in basal ganglia⁵⁰ Response to treatment: choline elevation reverses with antidepressant treatment⁵⁰
mIns	Diverse role in central nervous system (gliosis, cytoskeleton, cellular signaling)	Generally negative findings in anterior cingulate cortex, basal ganglia Mixed results for prefrontal cortex⁵⁴

Note:—ECT indicates electroconvulsive therapy; SSRI, selective serotonin reuptake inhibitor; TMA, trimethylamine.