Positron emission tomography (PET) was performed in normal volunteers during a serial recall task under the influence of irrelevant speech comprising both single item repetition and multi-item sequences. An interaction approach was used to identify brain areas specifically related to the irrelevant speech effect. We interpreted activations as compensatory recruitment of complementary working memory processing, and decreased activity in terms of suppression of task relevant areas invoked by the irrelevant speech. The interaction between the distractors and working memory revealed a significant effect in the left, and to a lesser extent in the right, superior temporal region, indicating that initial phonological processing was relatively suppressed. Additional areas of decreased activity were observed in an a priori defined cortical network related to verbal working memory, incorporating the bilateral superior temporal and inferior/middle frontal cortices extending into Broca's area on the left. We also observed a weak activation in the left inferior parietal cortex, a region suggested to reflect the phonological store, the subcomponent where the interference is assumed to take place. The results suggest that the irrelevant speech effect is correlated with and thus tentatively may be explained in terms of a suppression of components of the verbal working memory network as outlined. The results can be interpreted in terms of inhibitory top-down attentional mechanisms attenuating the influence of the irrelevant speech, although additional studies are clearly necessary to more fully characterize the nature of this phenomenon and its theoretical implications for existing short-term memory models.
BackgroundEvidence has been accumulating that it may be possible to achieve prevention in psychotic disorders. The aim of the Prevention Of Psychosis (POP) study is to reduce the annual incidence of psychotic disorders in a catchment area population through detection and intervention in the prodromal phase of disorder. Prodromal patients will be recruited through information campaigns modelled on the Scandinavian early Treatment and Intervention in Psychosis (TIPS) study and assessed by low-threshold detection teams.Methods/DesignThe study will use a parallel control design comparing the incidence of first episode psychotic disorders between two Norwegian catchment areas with prodromal detection and treatment (Stavanger and Fonna) with two catchment areas without a prodromal intervention program (Bergen and Østfold). The primary aim of the current study is to test the effect of a Prodromal Detection and Treatment program at the health care systems level. The study will investigate: 1) If the combination of information campaigns and detection teams modelled will help in identifying individuals (age 13–65, fulfilling study inclusion criteria) at high risk of developing psychosis early, and 2) If a graded, multi-modal treatment program will reduce rates of conversion compared to the rates seen in follow-along assessments.DiscussionPositive results could potentially revolutionize therapy by treating risk earlier rather than disorder later and could open a new era of early detection and intervention in psychosis. Negative results will suggest that the potential for psychosis is determined early in life and that research should focus more on genetically linked neurodevelopmental processes.If we can identify people about to become psychotic with high accuracy, we can track them to understand more about how psychosis unfolds. Appropriate intervention at this stage could also prevent or delay the onset of psychosis and/or subsequent deterioration, i.e., social and instrumental disability, suicide, aggressive behavior, affective- and cognitive deficits.Trial registrationCurrent Controlled Trials ISRCTN20328848. Registered 02 November 2014.
Irrelevant speech impairs the immediate serial recall of visually presented material. Previously, we have shown that the irrelevant speech effect (ISE) was associated with a relative decrease of regional blood flow in cortical regions subserving the verbal working memory, in particular the superior temporal cortex. In this extension of the previous study, the working memory load was increased and an increased activity as a response to irrelevant speech was noted in the dorsolateral prefrontal cortex. We suggest that the two studies together provide some basic insights as to the nature of the irrelevant speech effect. Firstly, no area in the brain can be ascribed as the single locus of the irrelevant speech effect. Instead, the functional neuroanatomical substrate to the effect can be characterized in terms of changes in networks of functionally interrelated areas. Secondly, the areas that are sensitive to the irrelevant speech effect are also generically activated by the verbal working memory task itself. Finally, the impact of irrelevant speech and related brain activity depends on working memory load as indicated by the differences between the present and the previous study. From a brain perspective, the irrelevant speech effect may represent a complex phenomenon that is a composite of several underlying mechanisms, which depending on the working memory load, include top-down inhibition as well as recruitment of compensatory support and control processes. We suggest that, in the low-load condition, a selection process by an inhibitory top-down modulation is sufficient, whereas in the high-load condition, at or above working memory span, auxiliary adaptive cognitive resources are recruited as compensation. D
The irrelevant speech effect illustrates that sounds that are irrelevant to a visually presented short-term memory task still interfere with neuronal function. In the present study we explore the functional and effective connectivity of such interference. The functional connectivity analysis suggested an interaction between the level of irrelevant speech and the correlation between in particular the left superior temporal region, associated with verbal working memory, and the left medial temporal lobe. Based on this psycho-physiological interaction, and to broaden the understanding of this result, we performed a network analysis, using a simple network model for verbal working memory, to analyze its interaction with the medial temporal lobe memory system. The results showed dissociations in terms of network interactions between frontal as well as parietal and temporal areas in relation to the medial temporal lobe. The results of the present study suggest that a transition from phonological loop processing towards an engagement of episodic processing might take place during the processing of interfering irrelevant sounds. We speculate that, in response to the irrelevant sounds, this reflects a dynamic shift in processing as suggested by a closer interaction between a verbal working memory system and the medial temporal lobe memory system.
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