NeuroImage
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Clinical Trial
Electrical impedance tomography of human brain function using reconstruction algorithms based on the finite element method.
Electrical impedance tomography (EIT) is a recently developed technique which enables the internal conductivity of an object to be imaged using rings of external electrodes. In a recent study, EIT during cortical evoked responses showed encouraging changes in the raw impedance measurements, but reconstructed images were noisy. A simplified reconstruction algorithm was used which modelled the head as a homogeneous sphere. ⋯ Image quality, assessed by blinded subjective expert observers, also improved significantly when data from the previous evoked response study were reanalysed with the new algorithm. In preliminary images collected during epileptic seizures, the new algorithm generated EIT conductivity changes which were consistent with the electrographic ictal activity. Incorporation of realistic geometry and conductivity into the reconstruction algorithm significantly improves the quality of EIT images and lends encouragement to the belief that EIT may provide a low-cost, portable functional neuroimaging system in the foreseeable future.
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Clinical Trial
Brain processing of visual sexual stimuli in healthy men: a functional magnetic resonance imaging study.
The brain plays a central role in sexual motivation. To identify cerebral areas whose activation was correlated with sexual desire, eight healthy male volunteers were studied with functional magnetic resonance imaging (fMRI). Visual stimuli were sexually stimulating photographs (S condition) and emotionally neutral photographs (N condition). ⋯ In conclusion, fMRI allows to identify brain responses to visual sexual stimuli. Among activated regions in the S condition, parietal areas are known to be involved in attentional processes directed toward motivationally relevant stimuli, while frontal premotor areas have been implicated in motor preparation and motor imagery. Further work is needed to identify those specific features of the neural responses that distinguish sexual desire from other emotional and motivational states.
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Diffusion tensor imaging is often performed by acquiring a series of diffusion-weighted spin-echo echo-planar images with different direction diffusion gradients. A problem of echo-planar images is the geometrical distortions that obtain near junctions between tissues of differing magnetic susceptibility. ⋯ This achieves the simultaneous goals of providing information on the underlying displacement field and intensity maps with adequate spatial sampling density even in distorted areas. The resulting DT maps exhibit considerably higher geometric fidelity, as assessed by comparison to an image volume acquired using a conventional 3D MR technique.
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Increased glial metabolites predict increased working memory network activation in HIV brain injury.
Deficits in attention and working memory are common in human immuno deficiency virus type 1 (HIV-1)-infected patients, but the pathophysiology of these deficits is poorly understood. Modern neuroimaging techniques, such as proton magnetic resonance spectroscopy ((1)H MRS) and functional MRI (fMRI), can assess some of the processes underlying HIV brain injury. To evaluate the model that attentional deficits in early HIV brain disease are related to brain inflammation, (1)H MRS and fMRI were performed in 14 HIV-positive subjects [acquired immunodeficiency syndrome (AIDS) dementia complex stage 1 or less]. ⋯ These findings are consistent with previous results that mild HIV brain injury is associated with increased glial activation without major involvement of neuronal abnormalities. We propose that the inflammatory glial abnormalities reduce the efficiency of neural processing, and necessitate compensatory increases in attention in patients, and associated BOLD signals, to perform a given task. The same mechanism may also contribute to cognitive dysfunction in other brain diseases that involve inflammation.
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The relative contributions of autonomic arousal and of cognitive processing to cortical activity during anticipation of pain, and the role of changes in thalamic outflow, are still largely unknown. To address these issues, we investigated with functional magnetic resonance imaging (fMRI) the activity of the contralateral mesial hemispheric wall in 56 healthy volunteers while they expected the stimulation of one foot, which could be either painful or innocuous. The waiting period was characterized by emotional arousal, a moderate rise in heart rate, and by increases in mean fMRI signals in the medial thalamus, mid- and posterior cingulate cortex, and in the putative foot area of the primary somatosensory and motor cortex. ⋯ Negatively correlated clusters predominated in the perigenual anterior cingulate and ventromedial prefrontal cortex. HR clusters had different characteristics from, and showed limited spatial overlap with, clusters whose fMRI signals were related to the psychophysical pain intensity profile; however, both cluster populations were affected by anticipation. These findings unravel a complex pattern of brain activity during uncertain anticipation of noxious input, likely related both to changes in the level of arousal and to cognitive modulation of the pain system.