Analysis of brainstem activitywith fMRI during low-level of pain- a feasibility study with innocuous cold stimuli

Abstract

Background: In functional magnetic resonance imaging (fMRI)studies, there are limitedpublished data on the functional map of the human brainstem. Objective: The primary goals of this pilot study were to assess the feasibility and to map the neural activity in the human brainstem with fMRIby equal intensity by low-level of thermal stimuli on the peripheral sensors of the skin. Patients and Methods: FMRI studies of the brainstem were carried out on 6healthyindividuals in a 3T MRI machine. Noxious thermal stimuli was applied on the peripheral sensitisation nerves on the arm. FMRI data spanned from the brainstem location by a 32-head channel and analysed using a fixed-effects General Linear Model to discriminate signal intensity changes from physiological motion. The results were normalised and combined to show the activity at each location on a voxel-by-voxel basis. Areas of physiological activity were recognisedwith comparison to the number of atlases. Results: Noxious and innocuous related activation clusters were approved in thisapplied method. There were considerable activity in the midbrain, pons, medulla and reticular formation. The results of this pilot study are similar and in some anatomical regions even better with head coils than obtained with previous fMRI spinal coil studies.We obtained evidence of localization of the following nuclei by using this method, asfollows: major activities in the inferior anterior parts of pons and the junction with medulla includes the (olive and pyramids),superior cerebella pundicle, rostral portion of medulla (RMV), Broadmann areas [5,2] touch and temperature sensation areas with the innocuous stimuli; activation in the left side of the medulla the (olive and pyramids), the left side of pons, the left side of midbrain, Broadmann area [5,7] pain and temperature sensation areas with noxious stimuli. Conclusion:This pilotstudy provides useful evidenceoflow-painful and innocuous information transmitted between the peripheral nervous system and the central nervous system in healthy participants.It also demonstrates how peripheral sensitisation induces physiological changes in the brainstem correlates with noxious and innocuous thermal transmission.

Keywords

• fMRI, Pain, Brainstem, PAG, RVM, Midbrain, Rostral ventromedial medulla, Pons.