Magnetic resonance image connectivity analysis provides evidence of central nervous system mode of action for parasacral transcutaneous electro neural stimulation - A pilot study

Abstract

Parasacral transcutaneous electriconeural stimulation (pTENS) is a common treatment modality for patients with overactive bladder (OAB). Its mechanism of effectiveness has yet to be elucidated. Recent studies with fMRI in adults with implanted sacral nerve stimulators impute its effectiveness on changes in the brain involving the anterior cingulate cortex (ACC) and prefrontal cortex (PFC). The study set out to evaluate brain connectivity utilizing functional MRI to the outline the mechanism of action of pTENS in the brain. Ten adult volunteers without urinary tract symptoms underwent fMRI. Electrodes were placed on the skin at sacral level (S2) (Experimental Stimulation - pTENS) and on the right scapular region (Sham Stimulation - sTENS). Stimulation was done twice on each site for 6min at a frequency of 10Hz and pulse width of 260 μs and intensity determined by the motor threshold. A 6min resting state fMRI was also done twice as control. Functional connectivity data was acquired during each state (resting, pTENS and sTENS). Standard functional connectivity preprocessing was performed. Seed connectivity was examined to investigate changes in ACC functional connectivity between the stimulations and resting-state conditions. Significance was assessed at p<0.05 corrected for multiple comparisons. For all conditions (pTENS, sTENS, and rest), standard patterns of ACC connectivity were detectable with strong connectivity between the ACC and subcortical regions and between the ACC and the frontal lobe. Functional connectivity between ACC seed and the dorsal lateral prefrontal cortex (DLPFC) was significantly increased during pTENS compared to rest. sTENS did not increase connectivity between the ACC seed and DLPFC when compared to rest. Preliminary results indicate that ACC is a major site of activation during pTENS. Increased connectivity between ACC and DLPFC may be a possible mechanism of pTENS effectiveness, which appears to be specific to pTENS compared to sTENS. This study is limited to the small size at this time which prevents further investigation at other sites in the brain. The study confirms our original aim which was to define if parasacral TENS actually has a central effect.