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Regional Brain Differences in the Effect of Distraction During the Delay Interval of a Working Memory Task

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Regional Brain Differences in the Effect of Distraction During the Delay Interval of a Working Memory Task

Florin Dolcos et al. Brain Res.

Abstract

Working memory (WM) comprises operations whose coordinated action contributes to our ability to maintain focus on goal-relevant information in the presence of distraction. The present study investigated the nature of distraction upon the neural correlates of WM maintenance operations by presenting task-irrelevant distracters during the interval between the memoranda and probes of a delayed-response WM task. The study used a region of interest (ROIs) approach to investigate the role of anterior (e.g., lateral and medial prefrontal cortex--PFC) and posterior (e.g., parietal and fusiform cortices) brain regions that have been previously associated with WM operations. Behavioral results showed that distracters that were confusable with the memorandum impaired WM performance, compared to either the presence of non-confusable distracters or to the absence of distracters. These different levels of distraction led to differences in the regional patterns of delay interval activity measured with event-related functional magnetic resonance imaging (fMRI). In the anterior ROIs, dorsolateral PFC activation was associated with WM encoding and maintenance, and in maintaining a preparatory state, and ventrolateral PFC activation was associated with the inhibition of distraction. In the posterior ROIs, activation of the posterior parietal and fusiform cortices was associated with WM and perceptual processing, respectively. These findings provide novel evidence concerning the neural systems mediating the cognitive and behavioral responses during distraction, and places frontal cortex at the top of the hierarchy of the neural systems responsible for cognitive control.

Figures

Figure 1
Figure 1
Diagram of the delayed-response working memory (WM) task with distraction. Three categories of trials were involved, as follows: 1/3 of the trials contained novel faces (High-load distracters), 1/3 contained scrambled faces (Low-load distracters), and 1/3 contained no distracters (None). Subjects were instructed to encode and maintain the memoranda into WM, look at the distracters while maintaining focus on the WM task, and then indicate by pressing a response button whether the probes were part of the memoranda or not.
Figure 2
Figure 2
Brain activity in the anterior ROIs. Lateral anterior ROIs showed similar general pattern of activity in which face distracters (High) produced greater delay activity than both scrambled (Low) and no-distraction (None) conditions. However, differences were also noticed, particularly in the MFG, IFG, and ACG. Specifically, MFG was the only PFC ROI that displayed sustained activity during the delay interval in all conditions, the IFG showed a gradient in the activation pattern (High > Low > None), and the ACG did not distinguish among the three experimental conditions (High = Low = None). S1 and S2 mark the onsets of the memoranda and the probes, respectively.
Figure 3
Figure 3
Brain activity in the posterior ROIs. Activity in IPS and FG showed both similarities and differences with the patterns observed in the anterior ROIs. First, similar to the MFG, IPS displayed sustained activity during the delay interval in all three trial types. Second, similar to the IFG, the FG showed no sustained activity for the None condition: without perceptual stimuli during the delay, the FG activity returned to baseline. Different from the anterior ROIs, activity in the posterior ROIs showed more systematically significant differences across all conditions: High > Low > None.
Figure 4
Figure 4
Anatomically-defined regions of interests (ROI) in anterior and posterior brain regions. The figure illustrates representative coronal slices showing the location in the brain of the anatomical ROIs. Analyses involved identification of active voxels (highlighted in red) in each subject, as a function of trial type, brain region, slice, hemisphere, and time point, whose activity was further examined across subjects using random-effects group analyses. SFG = Superior Frontal Gyrus, MFG = Middle Frontal Gyrus, IFG = Inferior Frontal Gyrus, ACG = Cingulate Gyrus, IPS = Intraparietal Sulcus, FG = Fusiform Gyrus, and WHM = White Matter.
Figure 5
Figure 5
Similarity between the shape of the reference waveform and the shape of the hemodynamic response (HDR) profiles of the anatomical ROIs. A. The left panel illustrates the shape of the reference waveform used to identify the active voxels; B. The right panel illustrates the shape of the average HDR profiles of the anterior and posterior ROIs that resulted from averaging the signal changes from all voxels within each anatomically defined ROI, across all three trial types and as a function of time point. The overall shape of the average HDR profiles was very similar to the reference waveform and across the ROIs.
Figure 6
Figure 6
Similarities in the number of active voxels accross the three trial types. No significant differences in the number of active voxels contributed by each distracter condition were observed, thus confirming that within each ROI the three distracter types contributed with relatively equal numbers of active voxels. The numbers of active voxels identified for each ROI are expressed in percentages relative to the total number of voxels within each anatomical ROI.

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