Resting state BOLD signal periodicity in low-back pain patient's hippocampus

Abstract

We report here the case of a low-back pain individual who shows rhythmic fluctuations in hippocampal neural activity. Resting state functional magnetic resonance imaging (fMRI) studies record signal over time without extrinsic stimuli and may be used to assess functional connectivity between regions. Functional connectivity can be evaluated by measuring the correlations in spontaneous fluctuations of blood oxygen level dependent (BOLD) signals from different regions across the brain, providing a systems level evaluation of the integration of individual regions within an intrinsic neural network. This case was detected in a study examining opioid treatment effects on the human brain. During our analysis, we discovered that one participant possessed hippocampal BOLD signal fluctuations with exact periodicity, 0.023Hz, pre-treatment and post-treatment. The resting state BOLD signal pattern is strikingly similar to on/off task design BOLD signal time courses, here mimicking 22s on and 22s off. This frequency fluctuation in the BOLD signal persisted beyond the resting state scan and could be seen in both heat-pain and cold-pain task scans, where the tasks paradigms (20s on and 30s off, and 20s on and 32s off, respectively) were not synced with the BOLD signal fluctuations. Additionally, the BOLD signal fluctuations did not correlate with head motion, heart rate, or respiratory rate. Due to the oddity in the BOLD signal observed in the participant's hippocampus, we asked the participant to return for a third scan, over a year after the first scan. We repeated the same resting state functional scan protocol. The 0.023-Hz BOLD signal periodicity within the hippocampus was still observable. This is the first report we know of where someone exhibits such periodicity in the BOLD signal fluctuations in the resting state. We report here the case of a low-back pain individual who shows rhythmic fluctuations in hippocampal neural activity. Resting state functional magnetic resonance imaging (fMRI) studies record signal over time without extrinsic stimuli and may be used to assess functional connectivity between regions. Functional connectivity can be evaluated by measuring the correlations in spontaneous fluctuations of blood oxygen level dependent (BOLD) signals from different regions across the brain, providing a systems level evaluation of the integration of individual regions within an intrinsic neural network. This case was detected in a study examining opioid treatment effects on the human brain. During our analysis, we discovered that one participant possessed hippocampal BOLD signal fluctuations with exact periodicity, 0.023Hz, pre-treatment and post-treatment. The resting state BOLD signal pattern is strikingly similar to on/off task design BOLD signal time courses, here mimicking 22s on and 22s off. This frequency fluctuation in the BOLD signal persisted beyond the resting state scan and could be seen in both heat-pain and cold-pain task scans, where the tasks paradigms (20s on and 30s off, and 20s on and 32s off, respectively) were not synced with the BOLD signal fluctuations. Additionally, the BOLD signal fluctuations did not correlate with head motion, heart rate, or respiratory rate. Due to the oddity in the BOLD signal observed in the participant's hippocampus, we asked the participant to return for a third scan, over a year after the first scan. We repeated the same resting state functional scan protocol. The 0.023-Hz BOLD signal periodicity within the hippocampus was still observable. This is the first report we know of where someone exhibits such periodicity in the BOLD signal fluctuations in the resting state.