Default Mode Network in the Effects of ¿9-Tetrahydrocannabinol (THC) on Human Executive Function

Evidence is increasing for involvement of the endocannabinoid system in cognitive functions including attention and executive function, as well as in psychiatric disorders characterized by cognitive deficits, such as schizophrenia. Executive function appears to be associated with both modulation of active networks and inhibition of activity in the default mode network. In the present study, we examined the role of the endocannabinoid system in executive function, focusing on both the associated brain network and the default mode network. A pharmacological functional magnetic resonance imaging (fMRI) study was conducted with a placebo-controlled, cross-over design, investigating effects of the endocannabinoid agonist ¿9-tetrahydrocannabinol (THC) on executive function in 20 healthy volunteers, using a continuous performance task with identical pairs. Task performance was impaired after THC administration, reflected in both an increase in false alarms and a reduction in detected targets. This was associated with reduced deactivation in a set of brain regions linked to the default mode network, including posterior cingulate cortex and angular gyrus. Less deactivation was significantly correlated with lower performance after THC. Regions that were activated by the continuous performance task, notably bilateral prefrontal and parietal cortex, did not show effects of THC. These findings suggest an important role for the endocannabinoid system in both default mode modulation and executive function. This may be relevant for psychiatric disorders associated with executive function deficits, such as schizophrenia and ADH

fMRI guided rTMS evidence for reduced left prefrontal involvement after task practice

Contains fulltext : 130274.pdf (publisher's version ) (Open Access)Introduction: Cognitive tasks that do not change the required response for a stimulus over time ('consistent mapping') show dramatically improved performance after relative short periods of practice. This improvement is associated with reduced brain activity in a large network of brain regions, including left prefrontal and parietal cortex. The present study used fMRI-guided repetitive transcranial magnetic stimulation (rTMS), which has been shown to reduce processing efficacy, to examine if the reduced activity in these regions also reflects reduced involvement, or possibly increased efficiency. Methods: First, subjects performed runs of a Sternberg task in the scanner with novel or practiced target-sets. This data was used to identify individual sites for left prefrontal and parietal peak brain activity, as well as to examine the change in activity related to practice. Outside of the scanner, real and sham rTMS was applied at left prefrontal and parietal cortex to examine their involvement novel and practiced conditions. Results: Prefrontal as well as parietal rTMS significantly reduced target accuracy for novel targets. Prefrontal, but not parietal, rTMS interference was significantly lower for practiced than novel target-sets. rTMS did not affect nontarget accuracy, or reaction time in any condition. Discussion: These results show that task practice in a consistent environment reduces involvement of the prefrontal cortex. Our findings suggest that prefrontal cortex is predominantly involved in target maintenance and comparison, as rTMS interference was only detectable for targets. Findings support process switching hypotheses that propose that practice creates the possibility to select a response without the need to compare with target items. Our results also support the notion that practice allows for redistribution of limited maintenance resources.11 p

EEG decoding of spoken words in bilingual listeners: from words to language invariant semantic-conceptual representations

Spoken word recognition and production require fast transformations between acoustic, phonological, and conceptual neural representations. Bilinguals perform these transformations in native and non-native languages, deriving unified semantic concepts from equivalent, but acoustically different words. Here we exploit this capacity of bilinguals to investigate input invariant semantic representations in the brain. We acquired EEG data while Dutch subjects, highly proficient in English listened to four monosyllabic and acoustically distinct animal words in both languages (e.g., "paard"-"horse"). Multivariate pattern analysis (MVPA) was applied to identify EEG response patterns that discriminate between individual words within one language (within-language discrimination) and generalize meaning across two languages (across-language generalization). Furthermore, employing two EEG feature selection approaches, we assessed the contribution of temporal and oscillatory EEG features to our classification results. MVPA revealed that within-language discrimination was possible in a broad time-window (~50-620 ms) after word onset probably reflecting acoustic-phonetic and semantic-conceptual differences between the words. Most interestingly, significant across-language generalization was possible around 550-600 ms, suggesting the activation of common semantic-conceptual representations from the Dutch and English nouns. Both types of classification, showed a strong contribution of oscillations below 12 Hz, indicating the importance of low frequency oscillations in the neural representation of individual words and concepts. This study demonstrates the feasibility of MVPA to decode individual spoken words from EEG responses and to assess the spectro-temporal dynamics of their language invariant semantic-conceptual representations. We discuss how this method and results could be relevant to track the neural mechanisms underlying conceptual encoding in comprehension and production

Brain tumor patients with impaired cognitive flexibility do not efficiently update functional connectivity within the fronto-parietal network

Background The majority of brain tumor patients suffers from cognitive deficits. These deficits can be very disruptive for a person’s daily functioning, quality of life and treatment compliance. Examining functional connectivity patterns during the performance of a cognitive task may enhance our understanding of the relationship between functional brain networks and cognitive performance. Despite the similarity in network topology across rest and task states, there are also meaningful differences in functional connectivity that are likely to be linked to cognitive performance. Currently, it is largely unknown how differences between rest and task functional connectivity patterns are related to cognitive functioning in brain tumor patients. The goal of this study was therefore to explore this relationship, whereby we focussed on cognitive flexibility. We expected less intense task-evoked network reconfiguration in patients with worse cognitive flexibility abilities. Material and Methods Resting state and functional MRI data (while performing several working memory tasks) were acquired in 50 brain tumor patients (23 meningioma, 13 low grade and 14 high grade glioma patients) before tumor resection. Performance on the “Shifting Attention Test” (SAT; part of CNS-VS) was used as an independent measure of a patient’s cognitive flexibility. Task-evoked network reconfiguration was investigated at the whole-brain and at the network level (fronto-parietal (FPN), cingulo-opercular (CON), and default mode (DMN) network). Whole-brain and network-specific connectivity matrices were created for each patient. We used the Pearson correlation value as a measure of similarity between rest and task functional connectivity patterns. For each network and for the whole brain, a linear regression (4 in total) using demographic and clinical factors, tumor characteristics and the reconfiguration measure was performed to test the relationship between the reconfiguration measure and cognitive flexibility performance while correcting for the other variables. Results We found that, across patients, SAT performance was negatively associated with the similarity of the FPN connectivity pattern between task and rest (β= -75.84, t(42)=-3.63, p<0.001). No association was found between SAT scores and degree of reconfiguration at the whole brain level or for the CON or DMN. Conclusion Our results show that cognitive flexibility problems in brain tumor patients are associated with a higher rest-task similarity in the fronto-parietal network topology. Possibly, the problems with cognitive flexibility are related to reduced capacity to update the fronto-parietal connections to changing cognitive demands. Our findings provide an important step towards individually-tailored treatment of cognitive deficits

Brain tumor patients with impaired cognitive flexibility do not efficiently update functional connectivity within the fronto-parietal network

Background The majority of brain tumor patients suffers from cognitive deficits. These deficits can be very disruptive for a person’s daily functioning, quality of life and treatment compliance. Examining functional connectivity patterns during the performance of a cognitive task may enhance our understanding of the relationship between functional brain networks and cognitive performance. Despite the similarity in network topology across rest and task states, there are also meaningful differences in functional connectivity that are likely to be linked to cognitive performance. Currently, it is largely unknown how differences between rest and task functional connectivity patterns are related to cognitive functioning in brain tumor patients. The goal of this study was therefore to explore this relationship, whereby we focussed on cognitive flexibility. We expected less intense task-evoked network reconfiguration in patients with worse cognitive flexibility abilities. Material and Methods Resting state and functional MRI data (while performing several working memory tasks) were acquired in 50 brain tumor patients (23 meningioma, 13 low grade and 14 high grade glioma patients) before tumor resection. Performance on the “Shifting Attention Test” (SAT; part of CNS-VS) was used as an independent measure of a patient’s cognitive flexibility. Task-evoked network reconfiguration was investigated at the whole-brain and at the network level (fronto-parietal (FPN), cingulo-opercular (CON), and default mode (DMN) network). Whole-brain and network-specific connectivity matrices were created for each patient. We used the Pearson correlation value as a measure of similarity between rest and task functional connectivity patterns. For each network and for the whole brain, a linear regression (4 in total) using demographic and clinical factors, tumor characteristics and the reconfiguration measure was performed to test the relationship between the reconfiguration measure and cognitive flexibility performance while correcting for the other variables. Results We found that, across patients, SAT performance was negatively associated with the similarity of the FPN connectivity pattern between task and rest (β= -75.84, t(42)=-3.63, p<0.001). No association was found between SAT scores and degree of reconfiguration at the whole brain level or for the CON or DMN. Conclusion Our results show that cognitive flexibility problems in brain tumor patients are associated with a higher rest-task similarity in the fronto-parietal network topology. Possibly, the problems with cognitive flexibility are related to reduced capacity to update the fronto-parietal connections to changing cognitive demands. Our findings provide an important step towards individually-tailored treatment of cognitive deficits

Vocational rehabilitation services for people with hearing difficulties: A systematic review of the literature

Objective: The goal of this review was to list and summarize work-related health programs for employees with hearing difficulties and to summarize the statistical evidence of the effectiveness of these programs. Methods: A systematic review was performed by searching the PubMed, EMBASE, PsycINFO, CINAHL, and The Cochrane Library databases for relevant citations. From 2313 unique citations retrieved from the search strategy, we included nine programs that met all inclusion criteria. The authors assessed the methodological quality of studies which evaluated the program's effectiveness, using the Downs and Black checklist. Results: Nine vocational rehabilitation programs for people with hearing difficulties were described. The programs differed in procedure, duration, setting, and content. In four studies, the effectiveness of the program was explored statistically. Measurements showed an improvement in general health (SF-36), communication strategies, and the degree of work readiness, but none of these studies included a control group, a power calculation, nor adjusted for confounding. Hence, the methodological quality to provide evidence of effectiveness was assessed as poor. Discussion: Existing vocational programs for employees with hearing difficulties provide relevant information to demonstrate how to implement the appropriate content of the programs. Future research is required to improve the strength of evidence of the effectiveness of vocational rehabilitation for workers with hearing difficulties. © 2013 - IOS Press and the authors. All rights reserved