PVALB and major depressive disorder: Parallel findings in humans, such as postmortem and MRI spectroscopy data, demonstrate reduced GABA levels in the brains of individuals with depression (e.g., Sanacora et al. 1999; for reviews, see Fee et al. 2017; Hu et al. 2023), and some postmortem studies report decreased parvalbumin interneuron counts in patients with depression (Knable et al. 2004; Konradi et al. 2011; Rajkowska et al. 2007).