Optimized RF excitation for anatomical brain imaging of the occipital lobe using the 3D MDEFT sequence and a surface transmit coil
ABSTRACT An RF excitation scheme is presented for anatomical imaging of occipital brain areas at 3T using the 3D modified driven equilibrium Fourier transform (MDEFT) sequence and a transmit-receive surface coil. Surface coils operated in the transmit mode usually display a high B(1) inhomogeneity. This causes variations of the flip angle and impairs fat saturation, resulting in blurring, signal losses, and artifacts due to high scalp intensities. A composite binomial pulse with one spectral component for water selective excitation and one spatial component for B(1) inhomogeneity compensation is presented. It is shown experimentally that the pulse prevents image blurring and reduces the scalp signal considerably. The total pulse duration of only 2.4 ms is compatible with the relatively short repetition times (TRs) required for MDEFT imaging. The method is particularly useful for certain applications in neuroimaging that require technical equipment that is too large for standard coils or should not be exposed to RF fields.
- SourceAvailable from: Tanja Endrass[Show abstract] [Hide abstract]
ABSTRACT: Obsessive-compulsive disorder (OCD) is associated with dysfunctional brain activity in several regions which are also involved in the processing of motivational stimuli. Processing of reward and punishment appears to be of special importance to understand clinical symptoms. There is evidence for higher sensitivity to punishment in patients with OCD which raises the question how avoidance of punishment relates to activity within the brain's reward circuitry. We employed the monetary incentive delay task paradigm optimized for modeling the anticipation phase of immediate reward and punishment, in the context of a cross-sectional event-related FMRI study comparing OCD patients and healthy control participants (n = 19 in each group). While overall behavioral performance was similar in both groups, patients showed increased activation upon anticipated losses in a medial and superior frontal cortex region extending into the cingulate cortex, and decreased activation upon anticipated rewards. No evidence was found for altered activation of dorsal or ventral striatal regions. Patients also showed more delayed responses for anticipated rewards than for anticipated losses whereas the reverse was true in healthy participants. The medial prefrontal cortex has been shown to implement a domain-general process comprising negative affect, pain and cognitive control. This process uses information about punishment to control aversively motivated actions by integrating signals arriving from subcortical regions. Our results support the notion that OCD is associated with altered sensitivity to anticipated rewards and losses in a medial prefrontal region whereas there is no significant aberrant activation in ventral or dorsal striatal brain regions during processing of reinforcement anticipation.01/2013; 2:212-20. DOI:10.1016/j.nicl.2013.01.005
- [Show abstract] [Hide abstract]
ABSTRACT: Research indicates that dysfunctional food reward processing may contribute to pathological eating behaviour. It is widely recognized that both the amygdala and the orbitofrontal cortex (OFC) are essential parts of the brain's reward circuitry. The aims of this fMRI study were (1) to examine the effects of food deprivation and calorie content on reward processing in the amygdala and the OFC, and (2) to examine whether an explicit evaluation of foods is necessary for OFC, but not amygdalar activity. Addressing the first aim, healthy females were presented with high and low calorie food pictures while being either hungry or satiated. For the second aim, attention focus was manipulated by directing participants' attention either to the food or to a neutral aspect. This study shows that hunger interacts with the energy content of foods, modulating activity in the posterior cingulate cortex, medial OFC, insula, caudate putamen and fusiform gyrus. Results show that satiated healthy females show an increased reward processing in response to low calorie foods. Confirming our hypothesis, food deprivation increased activity following the presentation of high calorie foods, which may explain why treatments of obesity energy restricting diets often are unsuccessful. Interestingly, activity in both the amygdala and mOFC was only evident when participants explicitly evaluated foods. However, attention independent activity was found in the mPFC following the high calorie foods cues when participants where hungry. Current findings indicate that research on how attention modulates food reward processing might prove especially insightful in the study of the neural substrates of healthy and pathological eating behaviour.Behavioural brain research 12/2008; 198(1):149-58. DOI:10.1016/j.bbr.2008.10.035
- [Show abstract] [Hide abstract]
ABSTRACT: Anxiety disorders have been linked to a hyperactivated cortico-amygdalar circuitry, but the amygdala's role in the pathophysiology of obsessive-compulsive disorder (OCD) remains unclear. This fMRI study examined the cortico-limbic correlates of individually tailored symptom provocation in 14 unmedicated OCD patients and 14 controls. In addition to OCD-relevant pictures, aversive and neutral control stimuli were included. Patients showed increased fronto-striatal activation to OCD-relevant stimuli contrasted with both control categories. Briefly presented symptom-related triggers elicited stronger amygdala engagement in patients than in controls. This effect, however, did also occur to aversive stimuli and was not symptom specific. Augmented amygdala involvement in patients reflects general emotional hyperarousal. Symptom-specific frontal activation points towards a sustained endeavor to suppress exaggerated emotional responses to OCD triggers.Psychophysiology 02/2010; 47(4):728-38. DOI:10.1111/j.1469-8986.2010.00980.x