BDNF and Postural instability: Furthermore, after the group with a low plasma exosomal BDNF level (Q1) was distinguished from the groups with optimal plasma exosomal BDNF levels (Q2–4), the severity of postural instability and gait disturbance (PIGD)-associated motor symptoms were found to be significantly worse in the low plasma exosomal BDNF level group (Figure 3).