NeuroImage
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There is a large body of evidence that the serotonergic system plays an important role in the transmission and regulation of pain. Here we used positron emission tomography (PET) with the serotonin transporter (SERT) tracer [(11)C]DASB to study the relationship between SERT binding in the brain and responses to noxious heat stimulation in a group of 21 young healthy volunteers. Responses to noxious heat stimuli were assessed in a separate psychophysical experiment and included measurements of pain threshold, pain tolerance, and responses to phasic noxious heat stimuli and to a long lasting (7-minute) tonic noxious heat stimulus. ⋯ Finally, the VOI analysis revealed a positive correlation between pain tolerance and SERT binding in the hypothalamus (r=0.53; p=0.02) although this was not seen in the parametric analysis. These data extend our earlier observation that cortical 5-HT receptors co-determine responses to tonic but not to phasic pain. The negative correlation between SERT binding in the hypothalamus and insula with tonic pain ratings suggests a possible serotonergic control of the role of these areas in the modulation or in the affective appreciation of pain.
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The calibration of functional magnetic resonance imaging (fMRI) for the estimation of neuronal activation-induced changes in cerebral metabolic rate of oxygen (CMRO(2)) has been achieved through hypercapnic-induced iso-metabolic increases in cerebral blood flow (CBF). Hypercapnia (HC) has been traditionally implemented through alterations in the fixed inspired fractional concentrations of carbon dioxide (F(I)CO(2)) without otherwise controlling end-tidal partial pressures of carbon dioxide (P(ET)CO(2)) or oxygen (P(ET)O(2)). There are several shortcomings to the use of this manual HC method that may be improved by using precise targeting of P(ET)CO(2) while maintaining iso-oxia. ⋯ The variability of the calibration constant obtained under HOP (M(HOP)) was 0.3-0.5 that of the HCP one (M(HCP)). In addition, M-variances with precise gas targeting (M(HCP) and M(HOP)) were less than those reported in studies using traditional F(I)CO(2) and F(I)O(2) methods (M(HC) and M(HO), respectively). We conclude that precise controlled gas delivery markedly improves BOLD-calibration for fMRI studies of oxygen metabolism with both the HCP and the more precise HOP-alternative.
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Recovery of function following lesions in the nervous system requires adaptive changes in surviving circuitries. Here we investigate whether changes in cerebral activation are correlated to spinal cord atrophy and recovery of functionality in individuals with incomplete spinal cord injury (SCI). 19 chronic SCI individuals and 7 age-comparable controls underwent functional magnetic resonance imaging (fMRI) while performing rhythmic dorsiflexion of the ankle. A significant negative correlation was found between the activation in the ipsilateral motor (M1) and bilateral premotor cortex (PMC) on one hand and the functional ability of the SCI participants measured by the clinical motor score on the other. ⋯ There was a tendency for a negative correlation between cerebral activation in ipsilateral S1, M1 and PMC and the amplitude of motor evoked potentials in the tibialis anterior muscle elicited by transcranial magnetic stimulation, but this did not reach statistical significance. There was no correlation between motor score or spinal cord dimensions and the volume of the cortical motor areas. The observations show that lesion of descending tracts in the lateral part of the spinal cord results in increased activation in ipsilateral motor and sensory areas, which may help to compensate for the functional deficit following SCI.
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This fMRI study was set up to explore how cognitive empathy, i.e. the cognitive inference on another person's affective state, can be characterized as a distinct brain function relating to pre-existing neurofunctional concepts about mentalizing and empathy. In a 3 Tesla MRI scanner 28 healthy participants were presented with four different instructions randomly combined with 32 false-belief cartoon stories of 3 subsequent pictures free of direct cues for affective states, like e.g. facial expressions. Participants were instructed to judge affective or visuospatial changes from their own (1st person perspective) or the protagonists' (3rd person perspective, 3rdpp) perspective. 3rdpp-judgements about affective states differed from visuospatial 3rdpp judgements by a significantly higher activation of the anterior mentalizing network (dorsomedial prefrontal cortex, anterior superior temporal sulcus, temporal poles) and the limbic system (left amygdala and hippocampus). ⋯ The simultaneous activation of the cortical mentalizing network and the amygdala indicates that cognitive empathy actually involves reference to own affective states in the observer. Notably, the cognitive reference to own affective states activated the mentalizing network as well. Moreover our results support pre-existing ideas about a functional anterior-posterior subdivision of the mentalizing network, depending on affective content and 3rd person perspective of cognition.
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White matter (WM) lesions are the classic pathological hallmarks of multiple sclerosis (MS). However, MRI-based WM lesion load shows relatively poor correlation with functional outcome, resulting in the "clinico-radiological paradox" of MS. Unlike lesion based measures, volumetric MRI assessment of brain atrophy shows a strong correlation with functional outcome, and the presence of early atrophy predicts a worse disease course. ⋯ We earlier reported another neurodegenerative feature in this model, the presence of deep gray matter T2 hypointensity in thalamic nuclei. Future studies utilizing this model will allow us to investigate key components of MRI detectable neurodegenerative feature development, their tissue correlations and associations with functional outcome measures. These studies are expected to pave the way to a better understanding of the substrate of disability in MS models.