Measuring the neural response to continuous intramuscular infusion of hypertonic saline by perfusion MRI

Lawson Health Research Institute, The University of Western Ontario, London, Ontario, Canada.
Journal of Magnetic Resonance Imaging (Impact Factor: 3.21). 03/2012; 35(3):669-77. DOI: 10.1002/jmri.22814
Source: PubMed


To determine the extent to which arterial spin labeling (ASL), a functional magnetic resonance imaging technique that directly measures cerebral blood flow (CBF), is able to measure the neural activation associated with prolonged experimental muscle pain.
Hypertonic saline (HS) (5% NaCl) was infused into the brachioradialis muscle of 19 healthy volunteers for 15 min. The imaging volume extended from the dorsal side of the pons to the primary somatosensory cortices, covering most of the cortical and subcortical regions associated with pain perception.
Using a numerical scale from 0 to 10, ratings of pain intensity peaked at 5.9 ± 0.5 (mean ± SE). Group activation maps showed that the slow infusion of HS evoked CBF increases primarily in bilateral insula, with additional activation in right frontal regions. In the activated areas, CBF gradually increased at the onset of HS infusion and was maintained at relatively constant levels throughout the remainder of the infusion period. However, the level and extent of activation were smaller than observed in previous studies involving acute muscle pain.
This study demonstrates the ability of ASL to measure changes in CBF over extended periods of time and that the neural activation caused by muscle pain is paradigm specific.

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    • "The insula is typically activated during neuroimaging studies of acute experimental pain in healthy subjects and clinical pain syndromes, where the strength and range grow significantly as the pain threshold intensity is increased[2021]. As a key region in the endogenous pain modulation system, it is likely that the functional association between the insula and other brain regions is changed when experiencing pain. "
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    ABSTRACT: Functional magnetic resonance imaging studies have shown that the insular cortex has a significant role in pain identification and information integration, while the default mode network is associated with cognitive and memory-related aspects of pain perception. However, changes in the functional connectivity between the default mode network and insula during pain remain unclear. This study used 3.0 T functional magnetic resonance imaging scans in 12 healthy subjects aged 24.8 ± 3.3 years to compare the differences in the functional activity and connectivity of the insula and default mode network between the baseline and pain condition induced by intramuscular injection of hypertonic saline. Compared with the baseline, the insula was more functionally connected with the medial prefrontal and lateral temporal cortices, whereas there was lower connectivity with the posterior cingulate cortex, precuneus and inferior parietal lobule in the pain condition. In addition, compared with baseline, the anterior cingulate cortex exhibited greater connectivity with the posterior insula, but lower connectivity with the anterior insula, during the pain condition. These data indicate that experimental low back pain led to dysfunction in the connectivity between the insula and default mode network resulting from an impairment of the regions of the brain related to cognition and emotion, suggesting the importance of the interaction between these regions in pain processing.
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    ABSTRACT: Over the past two decades, modern brain imaging techniques such as functional magnetic resonance imaging, positron emission tomography (PET), magnetoencephalography (MEG), and electroencephalography (EEG) have revolutionized our understanding of pain. Using such tools, in conjunction with carefully conceived experimental manipulations and sophisticated image analysis methods, scientists have begun unraveling the complexities of the neural processes underlying the pain experience as well as its modulation by a variety of factors (e.g. cognitive or emotional state, genetic makeup, and pharmacological or behavioral interventions). Brain imaging studies are also contributing to a change in the way we perceive chronic pain, as they have revealed that the brains of patients with pain disorders are characterized by structural, functional, and neurochemical alterations, some of which might have causal roles in the pathophysiology of pain conditions. In this chapter, we will discuss the advances that neuroimaging studies have brought to our understanding of pain, as well as the limitations and future implications of research in this field. In particular, this chapter concentrates on magnetic resonance imaging (MRI) studies, with brief mention of other imaging techniques. While tools such as PET, single-photon emission computed tomography, MEG, EEG, and other techniques have undoubtedly provided significant contributions to this field, MRI has arguably been proved to be among the most powerful techniques for the investigation of pain processing, given that it allows for the assessment of functional, structural, perfusion, connectivity, and neurochemical correlates of pain.
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