GAD1 and Alzheimer disease: Moreover, the balance of excitatory and inhibitory neuronal activity in the hippocampus is thought to be required for normal learning and memory [46], while an imbalance due to the loss of hippocampal GABAergic interneurons including GAD67+ cells and PV+ cells has been implicated in the pathogenesis of cognitive impairment in Alzheimer's disease (AD) [18], [47].