Neuroscience
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The capacity to identify unanticipated abnormal cues in a natural scene is vital for animal survival. Stimulus-specific adaptation (SSA) has been considered the neuronal correlate for deviance detection. There have been comprehensive assessments of SSA in the frequency domain along the ascending auditory pathway, but only little attention given to deviance detection in the spatial domain. ⋯ The variability in neuronal spatial discriminability among the TRN population was directly related to response difference (RD) but not variance; meanwhile, further analyses attributed higher spatial sensitivity at deviant locations to larger RD. Astonishingly, a significant correlation was found between the amount of adaptation and deviant discriminability. Collectively, our results suggest that adaptation facilitates rare location discrimination by sharpening the response gap between two locations.
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To explore brain activity and the related neurochemical processes, current research focuses increasingly on the combined acquisition of 1H MR spectra and fMRI data to investigate potential associations between local metabolite resting state levels and stimulus-induced BOLD signal changes. In this study, whole-brain fMRI measurements and localized functional 1H MEGA-PRESS MRS scans were conducted at 3T in healthy subjects prior to and during acute pain stimulation to quantify resting state GABA+/tCr and Glx/tCr levels in the insular cortex together with their stimulus-induced changes and to explore associations between these neurochemical parameters with intra-regional but also inter-regional BOLD responses. Inter-regionally, a significant negative correlation between the BOLD signal of a cluster in the supplementary motor area with overlap to the mid-cingulate cortex (R = -0.56, p = 0.004) and the insular resting state GABA+/tCr was obtained. ⋯ No intra-regional association was observed between BOLD and metabolite measures. These findings point toward interactions between metabolite levels and stimulus-induced BOLD responses in brain regions belonging to the pain processing network. The combination of fMRS and fMRI provides a powerful tool to improve our understanding about the complex system of neurochemical processes and brain activity within brain networks.
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Bradykinin (BK), a component of the kallikrein-kininogen-kinin system exerts multiple effects via B1 and B2 receptor activation. In the cardiovascular system, bradykinin has cardioprotective and vasodilator properties. We investigated the effect of BK on cardiac-projecting neurons of nucleus ambiguus, a key site for the parasympathetic cardiac regulation. ⋯ BK produced a dose-dependent depolarization of nucleus ambiguus neurons, which was prevented by the B2 receptor antagonist. In vivo studies indicate that microinjection of BK into nucleus ambiguus elicited bradycardia in conscious rats via B2 receptors. In summary, in cardiac vagal neurons of nucleus ambiguus, BK activates B2 receptors promoting Ca2+ influx and Ca2+ release from endoplasmic reticulum, and membrane depolarization; these effects are translated in vivo by bradycardia.
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Theta burst stimulation (TBS) has emerged as a promising tool for the treatment of swallowing disorders; however, the short-term after-effects of brain activation induced by TBS remain unknown. Here, we measured the changes in spontaneous brain activation using the amplitude of low-frequency fluctuation (ALFF) approach in subjects who underwent different TBS protocols. Sixty right-handed healthy participants (male, n=30; female, n=30; mean age=23.5y) were recruited in this study and randomly assigned to three groups that underwent three different TBS protocols. ⋯ These findings indicate that multiple brain areas involved in swallowing regulation after stimulation of TBS over the suprahyoid muscles. cTBS induces decreased after-effects while iTBS results in increased after-effects on spontaneous brain activation. Moreover, iTBS can eliminate the after-effects of cTBS applied on the contralateral swallowing cortex and alter the activity of contralateral motor cortex and brainstem. Our findings provide a novel evidence for the short-term effect of TBS on spontaneous brain activation.
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Little is known about how the central nervous system prepares postural responses differently in anticipated compared to non-anticipated perturbations. To investigate this, participants were exposed to translational and rotational perturbations presented in a blocked (anticipated) and a random (non-anticipated) design. The preparatory setting ('central set') was measured by H-reflexes, motor-evoked potentials (MEPs), and short-interval intracortical inhibition (SICI) shortly before perturbation onset in the soleus of 15 healthy adults. ⋯ As the SLR and MLR are organized at the spinal and the LLR at the cortical level, the preparatory setting seems to mainly influence cortically mediated postural responses. However, the modulation of the H-reflex before anticipated perturbations indicates that supraspinal centers adjusted Ia-afferent transmission for the soleus in a perturbation-specific manner. Intracortical inhibition was also modulated but differentiates to a lesser extent only between perturbation conditions and unperturbed stance.