The present invention relates to novel 6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one derivatives as negative allosteric modulators (NAMs) of the metabotropic glutamate receptor sub-type 2 (“mGluR2”) of Formula I: The invention is also directed to pharmaceutical compositions comprising such compounds, to processes for preparing such compounds and compositions, and to the use of such com-pounds and compositions for the prevention or treatment of disorders in which the mGluR2 subtype of metabotropic receptors is involved.