NeuroImage
-
We applied diffusion tensor tractography (DTT), a recently developed MRI technique that reveals the microstructures of tissues based on its ability to monitor the random movements of water molecules, to the visualization of peripheral nerves after injury. The rat sciatic nerve was subjected to contusive injury, and the data obtained from diffusion tensor imaging (DTI) were used to determine the tracks of nerve fibers (DTT). The DTT images obtained using the fractional anisotropy (FA) threshold value of 0.4 clearly revealed the recovery process of the contused nerves. ⋯ The FA values of the peripheral nerves were more strongly correlated with axon-related (axon density and diameter) than with myelin-related (myelin density and thickness) parameters, supporting the theories that axonal membranes play a major role in anisotropic water diffusion and that myelination can modulate the degree of anisotropy. Moreover, restoration of the FA value at the lesion epicenter was strongly correlated with parameters of motor and sensory functional recovery. These correlations of the FA values with both the histological and functional changes demonstrate the potential usefulness of DTT for evaluating clinical events associated with Wallerian degeneration and the regeneration of peripheral nerves.
-
We used the [F-18]FDG micro PET neuroimaging technique to investigate changes in brain activity induced by acute stress in rats. Animals were given immobilization stress for 1 or 2 h, or 1-h stress followed by 1-h recovery, after which their brains were scanned. Plasma corticosterone levels measured at various time points in separate groups of rats showed a rapid increase during stress and slower decrease after termination of the stress. ⋯ Additional brain areas such as the septum and prelimbic cortex now showed deactivation during recovery. Changes in glucose metabolism in the dorsal hippocampus and hypothalamus exhibited a highly significant negative correlation, supporting the view that the hippocampus is involved in regulating the stress response of the hypothalamo-pituitary-adrenal axis. The advantages and limitations of the [F-18]FDG micro PET used in this study are discussed.
-
Meta Analysis
Functional topography in the human cerebellum: a meta-analysis of neuroimaging studies.
Clinical, experimental and neuroimaging studies indicate that the cerebellum is involved in neural processes beyond the motor domain. Cerebellar somatotopy has been shown for motor control, but topographic organization of higher-order functions has not yet been established. To determine whether existing literature supports the hypothesis of functional topography in the human cerebellum, we conducted an activation likelihood estimate (ALE) meta-analysis of neuroimaging studies reporting cerebellar activation in selected task categories: motor (n=7 studies), somatosensory (n=2), language (n=11), verbal working memory (n=8), spatial (n=8), executive function (n=8) and emotional processing (n=9). ⋯ Emotional processing involved vermal lobule VII, implicated in cerebellar-limbic circuitry. These data provide support for an anterior sensorimotor vs. posterior cognitive/emotional dichotomy in the human cerebellum. Prospective studies of multiple domains within single individuals are necessary to better elucidate neurobehavioral structure-function correlations in the cerebellar posterior lobe.
-
Cervical spinal cord displacements have recently been measured in relation to the cardiac cycle, substantiating that cord motion in this region reduces both the sensitivity and reproducibility of functional magnetic resonance imaging of the spinal cord (spinal fMRI). Given the ubiquitous and complex nature of this motion, cardiac gating alone is not expected to sufficiently remove these errors, whereas current modeling approaches for spin-echo methods are not specific to motion artifacts, potentially eliminating function-related data along with components of motion-related noise. ⋯ With this approach, the components of motion-related signal fluctuation are modeled, along with functionally-relevant signal changes (i.e., those components fitting the stimulus paradigm), to account for the effects of spinal cord and cerebrospinal fluid (CSF) motion in a thorough, yet discerning, manner. By analyzing 100 previously acquired half-Fourier turbo spin-echo (HASTE) spinal fMRI data sets, along with a collection of null-task data, we show that the implementation of RESPITE reduces the occurrence of both type I (false-positive) and type II (false negative) errors, effectively increasing the specificity (5-6%) and sensitivity (15-20%) to neuronal activity.
-
Fibromyalgia syndrome (FMS) is characterized by widespread pain. Studies with functional neuroimaging support the hypothesis of central pain augmentation in FMS. We tested this in our study with a novel paradigm of tonic pain induced by a single stimulus. ⋯ Additionally the first Eigenvariates in those areas which show an interaction between both factors were determined over the time course of pain stimulation. Differences of activation in the fronto-cingulate cortex, the supplemental motor areas, and the thalamus were found between both groups with distinct differences in BOLD-signals changes over the time course of pain stimulation, even during anticipation of pain. Our results support the hypothesis that central mechanisms of pain processing in the medial pain system, favourable cognitive/affective factors even during the anticipation of pain, may play an important role for pain processing in patients with FMS.