Active neural coordination of motor behaviors with internal states.

The brain continuously coordinates skeletomuscular movements with internal physiological states like arousal, but how is this coordination achieved? One possibility is that the brain simply reacts to changes in external and/or internal signals. Another possibility is that it is actively coordinating both external and internal activities. We used functional ultrasound imaging to capture a large medial section of the brain, including multiple cortical and subcortical areas, in marmoset monkeys while monitoring their spontaneous movements and cardiac activity. By analyzing the causal ordering of these different time series, we found that information flowing from the brain to movements and heart-rate fluctuations were significantly greater than in the opposite direction. The brain areas involved in this external versus internal coordination were spatially distinct, but also extensively interconnected. Temporally, the brain alternated between network states for this regulation. These findings suggest that the brain's dynamics actively and efficiently coordinate motor behavior with internal physiology.

Disassociation between fluctuation shift over frequency and glucose metabolism in motor cortex of Parkinson's disease: a hybrid PET/fMRI study.

Increased glucose metabolism and decreased low-frequency fluctuation have been consistently reported in the motor area of Parkinson's disease (PD). The reason for such seeming paradox is unclear. Here, we enrolled 34 PD patients and 25 healthy controls (HCs) for hybrid PET/fMRI scan (PET/fMRI(discovery) dataset). In addition, 2 replication datasets, namely fMRI(validation-1) and fMRI(validation-2) dataset, were also included. We computed ratio of standard uptake value (SUVr) to measure FDG-uptake. The amplitude of low-frequency fluctuations (ALFF) for the following 4 frequency bands was calculated: slow-5, slow-4, slow-3, and slow-2. We obtained a significant group-by-frequency interaction effect of ALFF in the paracentral lobule/supplementary motor area (PFWE = 0.003) and the right sensorimotor area (PFWE < 0.001) in the PET/fMRI(discovery) dataset, which could be replicated using fMRI(validation-1) and fMRI(validation-2) datasets (PFWE < 0.05). In detail, HCs exhibited power law-like fluctuation pattern, but PD patients did not. Correlation analyses further revealed significant associations between ALFF and FDG-uptake in HCs (P-values < 0.031), but not in PD (P-values > 0.28). Taken together, this study identified a fluctuation shift over frequency effect in PD patients, which further disassociated with glucose metabolism in the motor cortex.