VIP and Parkinson disease: In contrast, regional changes in gradients in PD-NC compared with controls were only correlated with inhibitory (total, VIP and SST) but not excitatory neuronal distribution, and with oligodendrocytes (ρ = 0.199, pspin = 0.018, qspin = 0.049); regions richer in excitatory neurons and poorer in oligodendrocytes were more likely to show contraction in SC-G1 values in PD-NC.