Despite the lack of correlations with FR in PD, our findings seem to align with those of Muralidharan and colleagues (Muralidharan et al., 2016), who showed that GPi neuronal FRs may not directly correlate with motor severity but exhibit variability across the disease severity continuum in Parkinsonian non-human primates (initially increasing, then decreasing, then increasing again at mild, moderate, and severe disease manifestations, respectively). Here, GPI is linked to Parkinson disease.