Any ideas about the neural mechanism underlying the ASMR sensation?
I found one study that looked at ASMR and the Default Mode Network (DNM). The DMN consists of the medial prefrontal cortex, medial temporal gyri, bilateral inferior parietal cortices, precuneus and posterior cingulate gyrus. In the study, the DMN of 11 individuals with ASMR was compared with 11 controls. 

The DMN of individuals with ASMR showed significantly less functional connectivity than that of controls. The DMN of individuals with ASMR also demonstrated increased connectivity between regions in the occipital, frontal, and temporal cortices, suggesting that ASMR was associated with a blending of multiple resting-state networks. This atypical functional connectivity likely influences the unique sensory-emotional experiences associated with ASMR.

Reference:

D. L. (2008). The brain’s default network: Anatomy, function, and relevance to disease. Annals of the New York Academy of Sciences, 1124, 1–38. doi:10.1196/annals.1440.011