Imaging studies have suggested that these features may result from deficits in prefrontal cortical structure and function, and thereby impaired top-down inhibitory control over limbic striatal mechanisms of drug-seeking behaviour.
While it is generally accepted that alcohol impairs top-down cognitive control and conflict monitoring, it has remained unclear whether this also applies to subliminally triggered conflicts, as alcohol may not impair automated processes to the same extent.
Therefore, substantial structural and functional evidence exists to support the hypothesis that dysfunction in the fronto-parietal network impairs top-down control of attention in PDD.
"The most obvious losers from a euro trading at $1.50 will be major Eurozone exporters to the U.S., as they will obviously find their competitiveness impaired on top of facing weaker American domestic demand," said Howard Archer, chief European economist at Global Insight in London.
A number of findings suggest that anxious individuals are impaired in top-down attentional control, even in the absence of experimenter-imposed threatening events.
Generalized increases in calcium-cAMP signaling during fatigue or stress disengage dlPFC recurrent circuits, reduce firing and impair top-down cognition.
These data strongly indicate that prefrontal cortical grey matter changes reflect, rather than pre-date, drug abuse and support the hypothesis that compulsive drug use is at least in part caused by chronic drug effects leading to impaired top-down control by prefrontal cortical processes (Jentsch & Taylor, 1999; Goldstein et al., 2004; Everitt & Robbins, 2005).
The cognitive inefficiency observed in the IA group in the present study could arise from impaired "top-down" cognitive-control processes, which have been associated with increased neural activity in the ACC [ 57], and have been observed in nicotine-dependent participants performing the Stroop and working memory tasks [ 58- 60].
Second, he said, because Aliso Creek is already federally designated as impaired, further "loading" the top of its watershed with pollutants is forbidden under the Clean Water Act.
Overlaps were determined for selections ranging from the top 1% to the top 30% most impaired connections.
