Human brain mapping
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Human brain mapping · Feb 2012
Nonlinear estimation of neural processing time from BOLD signal with application to decision-making.
The extraction of information about neural activity timing from BOLD signal is a challenging task as the shape of the BOLD curve does not directly reflect the temporal characteristics of electrical activity of neurons. In this work, we introduce the concept of neural processing time (NPT) as a parameter of the biophysical model of the hemodynamic response function (HRF). Through this new concept we aim to infer more accurately the duration of neuronal response from the highly nonlinear BOLD effect. ⋯ As predicted, the NPT in fusiform gyrus is close to the stimulus duration and the NPT in dorsal anterior cingulate gyrus depends on the presence of an emotional distracter. Interestingly, the NPT in right but not left dorsal lateral prefrontal cortex depends on the stimulus emotional content. The summary measures of HRF obtained by a standard approach did not detect the variations observed in the NPT.
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Human brain mapping · Nov 2011
Exploring the after-effects of theta burst magnetic stimulation on the human motor cortex: a functional imaging study.
Theta burst stimulation (TBS) is a protocol of subthreshold repetitive transcranial magnetic stimulation (rTMS) inducing changes in cortical excitability. From functional imaging studies with conventional subthreshold rTMS protocols, it remains unclear what type of modulation occurs (direction and dependency to neural activity) and whether putative effects are bound to unspecific changes in cerebral perfusion or require a functional challenge. In a within-subjects (n = 17) repeated measurement design including real TBS and a control session without stimulation, we examined neural activation in a choice-reaction task after application of intermittent TBS, a protocol, which enhances cortical excitability over the left motor cortex (M1). ⋯ No changes in rCBF at rest were observed. The data demonstrate that subthreshold intermittent TBS targets both the stimulated cortical area as well as remote areas. The facilitation changing the efficacy of neural signal transmission seems to be reflected by a BOLD signal decrease, whereas the network at rest does not appear to be affected.
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Research suggests that the majority of mild traumatic brain injury (mTBI) patients exhibit both cognitive and emotional dysfunction within the first weeks of injury, followed by symptom resolution 3-6 months postinjury. The neuronal correlates of said dysfunction are difficult to detect with standard clinical neuroimaging, complicating differential diagnosis and early identification of patients who may not recover. This study examined whether resting state functional magnetic resonance imaging (fMRI) provides objective markers of injury and predicts cognitive, emotional, and somatic complaints in mTBI patients semiacutely (<3 weeks postinjury) and in late recovery (3-5 month) phases. ⋯ Abnormal connectivity between the DMN and frontal cortex may provide objective biomarkers of mTBI and underlie cognitive impairment.
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Human brain mapping · Oct 2011
The neural correlates of intertemporal decision-making: contributions of subjective value, stimulus type, and trait impulsivity.
Making choices between payoffs available at different points in time reliably engages a decision-making brain circuit that includes medial prefrontal cortex (mPFC), posterior cingulate cortex (PCC), and ventral striatum (VS). Previous neuroimaging studies produced differing accounts of the functions of these regions, including that these regions: (1) are sensitive to the value of rewards discounted by a function of delay ('subjective value'); (2) are differentially sensitive to the availability of an immediate reward; and (3) are implicated in impulsive decision-making. In this event-related fMRI study of 20 volunteers, these hypotheses were investigated simultaneously using a delay discounting task in which magnitude of rewards and stimulus type, i.e., the presence or absence of an immediate option, were independently varied, and in which participants' trait impulsivity was assessed with the Barratt Impulsiveness Scale. ⋯ Moderation by individual differences in trait impulsivity was specific to the mPFC. Conjunction analysis showed significant overlap in mPFC and PCC for the main effects of subjective value and stimulus type, indicating these regions may serve multiple distinct roles during intertemporal decision-making. These findings significantly advance our understanding of the specificity and overlap of functions subserved by different regions involved in intertemporal decision-making, and help to reconcile conflicting accounts in the literature.
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Human brain mapping · Oct 2011
Cognitive impairment in multiple sclerosis is associated to different patterns of gray matter atrophy according to clinical phenotype.
To investigate whether cognitive impairment in multiple sclerosis (MS) patients is associated to different patterns of gray matter (GM) atrophy and T2-visible lesion distribution according to the clinical phenotype. ⋯ Distinct patterns of regional distribution of GM damage and T2-visible lesions are associated with cognitive impairment in MS patients with different clinical phenotypes. The correspondence between lesion formation and GM atrophy distribution varies in the different forms of MS.