Magnetic Resonance Imaging (MRI)

Animal imaging of brain systems offers exciting opportunities to better understand the neurobiology of pain and analgesia. Overall functional studies have lagged behind human studies as a result of technical issues including the use of anesthesia. Now that many of these issues have been overcome including the possibility of imaging awake animals, there are new opportunities to study whole brain systems neurobiology of acute and chronic pain as well as analgesic effects on brain systems de novo (using pharmacological MRI) or testing in animal models of pain.

RATIONALE AND OBJECTIVES: There is evidence that drug addiction is associated with increased physiological and psychological responses to stress. In this pilot functional magnetic resonance imaging (fMRI) study we assessed whether a prototype behavioral addiction, pathological gambling (PG), is likewise associated with an enhanced response to stress.

OBJECTIVE: To examine biochemical differences in the anterior cingulate cortex (ACC) and insula during the interictal phase of migraine patients. We hypothesized that there may be differences in levels of excitatory amino acid neurotransmitters and/or their derivatives in migraine group based on their increased sensitivity to pain.

The hypothalamus has been implicated in migraine based on the manifestation of autonomic symptoms with the disease, as well as neuroimaging evidence of hypothalamic activation during attacks. Our objective was to determine functional connectivity (FC) changes between the hypothalamus and the rest of the brain in migraine patients vs. control subjects. This study uses fMRI (functional magnetic resonance imaging) to acquire resting state scans in 12 interictal migraine patients and 12 healthy matched controls.

We have entered a new era in understanding CNS circuitry involved in acute and chronic pain. The ability to objectively measure a pain or analgesic state of the brain using non-invasive methods that define neural activation provides the possibility for top-down approaches to drug discovery. These brain maps represent the specific brain state. In the future, correlations with such states and behavioral, genetic, epigenetic or other chemical markers may help define specific diagnostic tools and novel approaches to drug discovery.

This review and meta-analysis aims at summarizing and integrating the human neuroimaging studies that report periaqueductal gray (PAG) involvement; 250 original manuscripts on human neuroimaging of the PAG were identified. A narrative review and meta-analysis using activation likelihood estimates is included. Behaviors covered include pain and pain modulation, anxiety, bladder and bowel function and autonomic regulation. Methods include structural and functional magnetic resonance imaging, functional connectivity measures, diffusion weighted imaging and positron emission tomography.

Functional magnetic resonance imaging was used to study patients with chronic neuropathic pain involving the maxillary region (V2) of the trigeminal nerve in patients with spontaneous pain and evoked pain to brush (allodynia). Patients underwent two functional scans (2-3 months apart) with mechanical and thermal stimuli applied to the affected region of V2 and to the mirror site in the unaffected contralateral V2 region, as well as bilaterally to the mandibular (V3) division. Patients were stimulated with brush, noxious cold, and noxious heat.

Spatial Independent Component Analysis (ICA) decomposes the time by space functional MRI (fMRI) matrix into a set of 1-D basis time courses and their associated 3-D spatial maps that are optimized for mutual independence. When applied to resting state fMRI (rsfMRI), ICA produces several spatial independent components (ICs) that seem to have biological relevance - the so-called resting state networks (RSNs). The ICA problem is well posed when the true data generating process follows a linear mixture of ICs model in terms of the identifiability of the mixing matrix.

A typical fMRI data analysis proceeds via the generalized linear model (GLM) with Gaussian noise using a model based on the experimental paradigm. This analysis ultimately results in the production of z-statistic images corresponding to the contrasts of interest. Thresholding such z-statistic images at uncorrected thresholds suitable for testing activation at a single voxel results in the problem of multiple comparisons.

The human trigeminal system mediates facial pain and somatosensory processing. The anatomic location of neuronal substrates and axonal pathways of the trigeminal system have previously been characterized with conventional in vitro methods. The present investigation implemented diffusion tensor imaging (DTI) and probabilistic tractography to first segment the peripheral trigeminal circuitry, trigeminal nerve branches (ophthalmic, maxillary, and mandibular nerves), ganglion, and nerve root.