Parcellation of human periaqueductal gray at 7-T fMRI in full and empty bladder state: The foundation to study dynamic connectivity changes related to lower urinary tract functioning

Aims: The periaqueductal gray (PAG) is a brain stem area involved in processing signals related to urine storage and voiding. The PAG is proposed to be responsible for projecting afferent information from the bladder to cortical and subcortical brain areas and acts as a relay station projecting efferent information from cortical and subcortical areas to the pons and spinal cord. Here, we use 7-Tesla functional magnetic resonance imaging to parcellate the PAG into functionally distinct clusters during a bladder filling protocol. Methods: We assess the similarity between parcellation results in empty and full bladder states and show how these parcellations can be used to create dynamic response profiles of connectivity changes between clusters as a function of bladder sensations. Results: For each of our six healthy female participants, we found that the agreement between at least one of the clusters in both states resulting from the parcellation procedure was higher than could be expected based on chance (p ≤.05), and observed that these clusters are significantly organized in a symmetrical lateralized fashion (p ≤.05). Correlations between clusters change significantly as a function of experienced sensations during bladder filling (p ≤.05). Conclusions: This opens new possibilities to investigate the effects of treatments of lower urinary tract symptoms on signal processing in the PAG, as well as the investigation of disease-specific bladder filling related dynamic signal processing in this small brain structure.