Long-term motor training induced changes in regional cerebral blood flow in both task and resting states.

Neuroimaging studies of functional activation often only reflect differentiated involvement of brain regions compared between task performance and control states. Signals common for both states are typically not revealed. Previous motor learning studies have shown that extensive motor skill training can induce profound changes in regional activity in both task and control states. To address the issue of brain activity changes in the resting-state, we explored long-term motor training induced neuronal and physiological changes in normal human subjects using functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). Ten healthy subjects performed a finger movement task daily for four weeks, during which three sessions of fMRI images and two sessions of PET images were acquired. Using a classical data analysis strategy, we found that the brain activation increased first and then returned to the pre-training, replicating previous findings. Interestingly, we also observed that motor skill training induced significant increases in regional cerebral blood flow (rCBF) in both task and resting states as the practice progressed. The apparent decrease in activation may actually result from a greater increase in activity in the resting state, rather than a decrease in the task state. By showing that training can affect the resting state, our findings have profound implications for the interpretation of functional activations in neuroimaging studies. Combining changes in resting state with activation data should greatly enhance our understanding of the mechanisms of motor-skill learning

CBF changes during brain activation: fMRI vs. PET

The changes in regional cerebral blood flow (rCBF) associated with the changes in neuronal activity are routinely measured both by positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) techniques. However, direct comparison has not been performed to determine similarities and differences of PET and fMRI techniques in determining the rCBF response to brain activation. In the present study, a quantitative comparison of the functional rCBF maps obtained by PET and fMRI are made by performing an activation study in a single group of subjects under precisely controlled conditions and using identical visual stimuli. Twelve healthy volunteers participated in the activation study using the visual checkerboard stimulation with flip frequency at 8 Hz. By selecting the conjunctive pixels which activated on both PET and fMRI maps, the change in rCBF measured by fMRI was 36.95 ± 2.54%, whereas the value measured by PET was 38.79 ± 2.63%. Our results have demonstrated that there is no statistically significant difference (P = 0.22) in the measurements of rCBF change between MRI and PET methods. © 2004 Elsevier Inc. All rights reserved.link_to_subscribed_fulltex

Molecular mechanisms of complement evasion: learning from staphylococci and meningococci

The complement system is a crucial component of the innate immune response in humans. Recent studies in Staphylococcus aureus and Neisseria meningitidis have revealed how these bacteria escape complement-mediated killing. In addition, new structural data have provided detailed insights into the molecular mechanisms of host defence mediated by the complement system and how bacterial proteins interfere with this process. This information is fundamental to our understanding of bacterial pathogenesis and may facilitate the design of better vaccines