When planning fails: Individual differences and error-related brain activity in problem solving.

The neuronal processes underlying correct and erroneous problem solving were studied in strong and weak problem-solvers using functional magnetic resonance imaging (fMRI). During planning, the right dorsolateral prefrontal cortex was activated, and showed a linear relationship with the participants' performance level. A similar pattern emerged in right inferior parietal regions for all trials, and in anterior cingulate cortex for erroneously solved trials only. In the performance phase, when the pre-planned moves had to be executed by means of an fMRI-compatible computer mouse, the right dorsolateral prefrontal cortex was again activated jointly with right parahippocampal cortex, and displayed a similar positive relationship with the participants' performance level. Incorrectly solved problems elicited stronger bilateral prefrontal and left inferior parietal activations than correctly solved trials. For both individual ability and trial-specific performance, our results thus demonstrate the crucial involvement of right prefrontal cortex in efficient visuospatial planning

18F-FDG PET during stereotactic body radiotherapy for stage I lung tumours cannot predict outcome: a pilot study

(18)F-Fluorodeoxyglucose positron emission tomography (FDG PET) has been used to assess metabolic response several months after stereotactic body radiotherapy (SBRT) for early-stage non-small cell lung cancer. However, whether a metabolic response can be observed already during treatment and thus can be used to predict treatment outcome is undetermined. Ten medically inoperable patients with FDG PET-positive lung tumours were included. SBRT consisted of three fractions of 20 Gy delivered at the 80% isodose at days 1, 6 and 11. FDG PET was performed before, on day 6 immediately prior to administration of the second fraction of SBRT and 12 weeks after completion of SBRT. Tumour metabolism was assessed semi-quantitatively using the maximum standardized uptake value (SUV(max)) and SUV(70%). After the first fraction, median SUV(max) increased from 6.7 to 8.1 (p = 0.07) and median SUV(70%) increased from 5.7 to 7.1 (p = 0.05). At 12 weeks, both median SUV(max) and median SUV(70%) decreased by 63% to 3.1 (p = 0.008) and to 2.5 (p = 0.008), respectively. SUV increased during treatment, possibly due to radiation-induced inflammation. Therefore, it is unlikely that (18)F-FDG PET during SBRT will predict treatment success

Observation of Static Pictures of Dynamic Actions Enhances the Activity of Movement-Related Brain Areas

Physiological studies of perfectly still observers have shown interesting correlations between increasing effortfulness of observed actions and increases in heart and respiration rates. Not much is known about the cortical response induced by observing effortful actions. The aim of this study was to investigate the time course and neural correlates of perception of implied motion, by presenting 260 pictures of human actions differing in degrees of dynamism and muscular exertion. ERPs were recorded from 128 sites in young male and female adults engaged in a secondary perceptual task.Our results indicate that even when the stimulus shows no explicit motion, observation of static photographs of human actions with implied motion produces a clear increase in cortical activation, manifest in a long-lasting positivity (LP) between 350–600 ms that is much greater to dynamic than less dynamic actions, especially in men. A swLORETA linear inverse solution computed on the dynamic-minus-static difference wave in the time window 380–430 ms showed that a series of regions was activated, including the right V5/MT, left EBA, left STS (BA38), left premotor (BA6) and motor (BA4) areas, cingulate and IF cortex.Overall, the data suggest that corresponding mirror neurons respond more strongly to implied dynamic than to less dynamic actions. The sex difference might be partially cultural and reflect a preference of young adult males for highly dynamic actions depicting intense muscular activity, or a sporty context

Transcranial direct current stimulation of the prefrontal cortex modulates working memory performance: combined behavioural and electrophysiological evidence

The present study demonstrates that tDCS can alter WM performance by modulating the underlying neural oscillations. This result can be considered an important step towards a better understanding of the mechanisms involved in tDCS-induced modulations of WM performance, which is of particular importance, given the proposal to use electrical brain stimulation for the therapeutic treatment of memory deficits in clinical settings

Cognition-induced modulation of serotonin in the orbitofrontal cortex: A controlled cross-over PET study of a delayed match-to-sample task using the 5-HT2a receptor antagonist [18F]altanserin

Behavioral and cellular studies indicate that serotonin interacting with the 5-HT2a receptor (5-HT2aR) is involved in cognitive processes supporting working memory (WM). However, 5-HT receptor neuroimaging studies directly relating WM-induced neuronal activations to concomitant changes in the availability of 5-HT receptors as a functional measure for serotonin release are lacking. This controlled cross-over PET study aimed to identify brain regions with WM-induced changes in the binding potential (BP(nd)) of the 5-HT2aR antagonist [(18)F]altanserin. Ten young males underwent a delayed match-to-sample task using photographs of faces and a control task. The BP(nd)s for both conditions were calculated by applying Ichise's noninvasive plot. Statistics were performed with the SPM toolbox statistical nonparametric mapping (SnPM3) particularly suited for analyzing whole-brain PET data in an exploratory way. A higher BP(nd) for [(18)F]altanserin during WM versus control was found in the orbitofrontal cortex (OFC) pointing towards an increased [(18)F]altanserin/5-HT2aR interaction in OFC while BP(nd) decreases during WM were not found. Furthermore, no BP(nd) changes in regions known from functional neuroimaging studies to be more specifically involved in WM were identified. These findings may suggest that the increased [(18)F]altanserin BP(nd) under WM challenge and hence the increased availability of 5-HT2aR reflects a decrease in local OFC serotonin. As the OFC plays a prominent role in decision-making and supports cognitive processes related to the central executive functions of WM it might be modulated by the serotoninergic system via the 5-HT2aR in order to support and optimize basic cognitive functions

Attenuation Correction of Cerebellum in PET/MR Data

Abstract:Most approaches of modelling neuroreceptor PET studies apply the cerebellum as reference area. Therefore, it is mandatory that the respective attenuation correction (AC) method for reconstructing the emission data is most appropriate regarding cerebellar areas. PET data from PET/MR scanners require alternative AC methods. These ought to be tested with respect to the performance within the cerebellum. This study aimed to compare various AC methods for PET/MR data focussing on the cerebellum. Data of 16 subjects undergoing 18 FDG imaging in the Siemens 3TMR-BrainPET scanner and a whole head CT scan at the same day were used. The latter were transformed to CT-based attenuation maps (AM CT ). The MR images were used to obtain AMs using the Boston-MGH method (AM MGH ), the London-UCL method (AM UCL ), the CT-template-based (AM CT-Juel ) and Tx-template-based (AM Tx-Juel ) Juelich methods. BrainPET emission data were reconstructed with the five AM s . Using the SUIT tool the cerebellum was extracted from the MR images and normalized to a cerebellum VOI atlas. The cerebellum of the PET data was extracted by applying the same parameters. Correlation plots with regression equations, coefficients of determination R 2 , normalized and absolute normalized errors (NErr) between AM CT and the other four AM s were calculated. The values of cerebellar NErr varied to a high extent between the four AC methods. In one subject AM MGH showed the lowest NErr (3.03±1.60%), in three participants the AMUCL performed best (NErr from -0.13±2.33% to 0.91±2.93%), in three others the AM Tx-Juel had the best results (NErr from -1.24±3.01% to 0.86±2.07%), while for the remaining seven subjects the AM CT-Juel performed best (NErr from -2.08±0.94% to 7.98±3.43%). Our results demonstrate that the quantitation of radiotracer uptake in the cerebellum is very susceptible to the respective attenuation correction applied to the PET data. This, in turn, has to be considered in neuroreceptor modelling studies which rely on the cerebellum as reference