Dopamine modulates default mode network deactivation in elderly individuals during the Tower of London task.

Montreal Neurological Institute, McGill University, Quebec, Canada.
Neuroscience Letters (Impact Factor: 2.06). 08/2009; 458(1):1-5. DOI: 10.1016/j.neulet.2009.04.025
Source: PubMed

ABSTRACT Task-induced deactivation is frequently reported in the ventro-medial prefrontal cortex (vmPFC) and posterior cingulate cortex (PCC), regions considered to belong to the default mode network. To investigate the effect of dopamine on task-induced deactivation, we used positron emission tomography to measure cerebral blood flow during performance of the Tower of London task before and after administration of the dopamine receptor agonist apomorphine in six healthy volunteers (49-66 years old) and six Parkinson disease patients (52-69 years old). Although task-induced deactivation was observed in the vmPFC and PCC in both groups and in both conditions, an inverse correlation between activation and problem complexity was observed in the vmPFC only in the apomorphine condition.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Specific brain regions have consistently been reported to be activated during resting state period, and they were described as being part of a particular network called the default-mode network (DMN). It has been shown that the DMN would deactivate during goal-directed tasks, but the actual relationship between them is still a matter of debate. In a previous study, we reported a specific pattern of activation of the frontostriatal regions during a set-shifting task in which these regions were increasing their activity as set-shifts were performed continuously and decreasing when the same rule was executed repeatedly. The present study aimed at assessing the relationship between the frontostriatal regions and the DMN. We hypothesized that the DMN would be anticorrelated with the frontostriatal regions so the DMN would be more deactivated as set-shifts are executed for a long period, but would start increasing when the same rule is being executed for a long period. Here, 15 participants underwent functional magnetic resonance imaging while performing a card-sorting task. We observed increased activity in the frontostriatal regions as more set-shifts are being performed while the DMN gets more deactivated. Interestingly, as decreased activity was observed in the frontostriatal regions during the execution of the same rule for a long period, the DMN showed increasing activity. We argue that there is an anticorrelation between the frontostriatal regions and the DMN, but also that the DMN could show positive activation during performance of a familiar goal-directed task.
    European Journal of Neuroscience 01/2015; 41(6). DOI:10.1111/ejn.12821 · 3.67 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Converging evidence from epidemiological, clinical and neuropsychological research suggests a link between cannabis use and increased risk of psychosis. Long-term cannabis use has also been related to deficit-like “negative” symptoms and cognitive impairment that resemble some of the clinical and cognitive features of schizophrenia. The current functional brain imaging study investigated the impact of a history of heavy cannabis use on impaired executive function in first-episode schizophrenia patients. Whilst performing the Tower of London task in a magnetic resonance imaging scanner, event-related blood oxygenation level-dependent (BOLD) brain activation was compared between four age and gender-matched groups: 12 first-episode schizophrenia patients; 17 long-term cannabis users; seven cannabis using first-episode schizophrenia patients; and 17 healthy control subjects. BOLD activation was assessed as a function of increasing task difficulty within and between groups as well as the main effects of cannabis use and the diagnosis of schizophrenia. Cannabis users and non-drug using first-episode schizophrenia patients exhibited equivalently reduced dorsolateral prefrontal activation in response to task difficulty. A trend towards additional prefrontal and left superior parietal cortical activation deficits was observed in cannabis-using first-episode schizophrenia patients while a history of cannabis use accounted for increased activation in the visual cortex. Cannabis users and schizophrenia patients fail to adequately activate the dorsolateral prefrontal cortex, thus pointing to a common working memory impairment which is particularly evident in cannabis-using first-episode schizophrenia patients. A history of heavy cannabis use, on the other hand, accounted for increased primary visual processing, suggesting compensatory imagery processing of the task.
    Neurology Psychiatry and Brain Research 10/2014; 9(4):TBC. DOI:10.1016/j.npbr.2014.09.002 · 0.10 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, a simple and stable composite electrode based on the intrinsically conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and Nafion (R), an ion-exchange polymer, was successfully fabricated by drop-coating the blended commercially available PEDOT:PSS aqueous dispersion and Nafion (R) solution on the surface of a glassy carbon electrode (GCE). PEDOT:PSS was used as the matrix, while Nafion (R) was employed to improve the immobilization stability of the composite films and adhesion to the electrode surface in comparison with PEDOT:PSS films. Cyclic voltammetry, differential pulse voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy were utilized to characterize the properties of this composite electrode. The as-proposed composite electrode displayed good water-stability. Meanwhile, the composite electrode was applied to electrochemical sensing of dopamine, and the performance of PEDOT:PSS Nafion (R) composite film was evaluated. The obtained results demonstrated that PEDOT:PSS Nafion (R) composites are promising candidates for modification of electrode material used in electrochemical sensing and other electrocatalytic applications.
    Journal of the Serbian Chemical Society 01/2013; 78(9):1397-1411. DOI:10.2298/JSC120927036Y · 0.89 Impact Factor