 Some say that all pathways directly antagonize each other in a "push pull" fashion, while others support the "center surround theory", in which one focused input into the cortex is protected by inhibition of competing inputs by the rest of the indirect pathways.The basal ganglia contains many afferent glutamatergic inputs, with predominantly GABAergic efferent fibers, modulatory cholinergic pathways, significant dopamine in the pathways originating in the ventral tegmental area and substantia nigra, as well as various neuropeptides.Neuropeptides found in the basal ganglia include substance P, neurokinin A, cholecystokinin, neurotensin, neurokinin B, neuropeptide Y, somatostatin, dynorphin, enkephaline.