A role of right middle frontal gyrus in reorienting of attention: a case study - PubMed (original) (raw)
A role of right middle frontal gyrus in reorienting of attention: a case study
Shruti Japee et al. Front Syst Neurosci. 2015.
Abstract
The right middle fontal gyrus (MFG) has been proposed to be a site of convergence of the dorsal and ventral attention networks, by serving as a circuit-breaker to interrupt ongoing endogenous attentional processes in the dorsal network and reorient attention to an exogenous stimulus. Here, we probed the contribution of the right MFG to both endogenous and exogenous attention by comparing performance on an orientation discrimination task of a patient with a right MFG resection and a group of healthy controls. On endogenously cued trials, participants were shown a central cue that predicted with 90% accuracy the location of a subsequent peri-threshold Gabor patch stimulus. On exogenously cued trials, a cue appeared briefly at one of two peripheral locations, followed by a variable inter-stimulus interval (ISI; range 0-700 ms) and a Gabor patch in the same or opposite location as the cue. Behavioral data showed that for endogenous, and short ISI exogenous trials, valid cues facilitated responses compared to invalid cues, for both the patient and controls. However, at long ISIs, the patient exhibited difficulty in reverting to top-down attentional control, once the facilitatory effect of the exogenous cue had dissipated. When explicitly cued during long ISIs to attend to both stimulus locations, the patient was able to engage successfully in top-down control. This result indicates that the right MFG may play an important role in reorienting attention from exogenous to endogenous attentional control. Resting state fMRI data revealed that the right superior parietal lobule and right orbitofrontal cortex, showed significantly higher correlations with a left MFG seed region (a region tightly coupled with the right MFG in controls) in the patient relative to controls. We hypothesize that this paradoxical increase in cortical coupling represents a compensatory mechanism in the patient to offset the loss of function of the resected tissue in right prefrontal cortex.
Keywords: dorsal attention network; endogenous attention; exogenous attention; frontal lobe tumor resection; reorienting of attention; resting state fMRI; right middle frontal gyrus; ventral attention network.
Figures
Figure 1
Coronal slices taken 6 mm apart starting posteriorly at y = 22 and showing the extent of the tumor resection in the right hemisphere. The resection encompassed right superior frontal gyrus and right middle frontal gyrus, including Brodmann areas 9, 46, and 10. Right inferior frontal gyrus was almost completely spared. In Talairach normalized space, the resection extended from x of 0 (midline) to about 50 mm, y of 23 to y of 66 mm (anterior tip of brain) and z of −4 to z of 50 mm (superior tip of brain).
Figure 2
Schematic showing the various tasks administered to patient and controls. (A) Schematic of the Endogenous Cueing Task. (B) Schematic of the Exogenous Cueing Task. (C) Schematic of the Exogenous Cueing Task with Explicit Reorienting. ISI, Inter-stimulus Interval is the time between the cue and stimulus. ISI for the Endogenous Cueing Task was fixed at 100 ms; ISI for Exogenous Cueing Task was 0, 100, 250, 500 or 700 ms; ISI for the Exogenous Cueing Task with Explicit Reorienting was 100, 400 or 800 ms. Subjects were instructed to indicate the orientation of the Gabor Patch with a button press during the Response window (Gray Fixation).
Figure 3
Average accuracy (A) and reaction time (RT) data (B) for age-matched controls (N = 10) and the patient for the Endogenous Cueing Task. Dark gray bars represent performance on validly cued trials. Light gray bars represent performance on invalidly cued trials. Unshaded bars show performance on Neutral and No-Cue trials. Error bars represent standard error of the mean for the control group. Diamond markers indicate performance of the patient. The patient and control group showed similar facilitation effects in accuracy and RT (i.e., faster and more accurate on valid relative to invalid trials).
Figure 4
Average accuracy (A) and Reaction Time (RT) data (B) for age-matched controls (N = 10) and the patient for the Exogenous Cueing Task. Dark gray bars represent performance on validly cued trials. Light gray bars represent performance on invalidly cue trials. Unshaded bars show performance on No-Cue trials. Error bars represent standard error of the mean for the control group. Diamond markers indicate performance of the patient. The patient showed similar facilitation effects as the control group for short ISI but not for long ISI trials.
Figure 5
Average accuracy (A) and reaction time (RT) data (B) for controls (N = 5) and the patient for the Go/No-Go Task. Dark gray bars represent performance on Go trials. Unshaded bars represent performance on No-Go trials when subjects were expected to withhold their response (i.e., yellow box in the simple task, and yellow box preceded by an odd number of blue boxes in the complex task). Light gray bars represent performance on complex No-Go trials when subjects were expected to press a button (yellow box preceded by even number of blue boxes). Error bars represent standard error of the mean for the control group. Diamond markers indicate performance of the patient. The patient performed as accurately as controls on all trial types but was slower to respond on Simple Go and Complex Go trials.
Figure 6
Average accuracy (A) and reaction time (RT) data (B) for age-matched controls (N = 10) and the patient for the Exogenous Cueing Task with Explicit Reorienting. Dark gray bars represent performance on validly cued trials. Light gray bars represent performance on invalidly cued trials. Unshaded bar shows performance on No-Cue trials. Errors represent standard error of the mean for the control group. Diamond markers indicate performance of the patient. The patient was as accurate as controls on all trial types but showed faster RTs for the implicitly cued 800 ms ISI condition. When explicitly cued during the long 800 ms ISI, the patient's RT data did not differ from controls.
Figure 7
(A) Axial slices showing the location of clusters in right superior parietal lobule (SPL) and right orbitofrontal cortex (OFC) where the patient showed significantly higher connectivity (>4-SD beyond mean of control group) with left MFG seed than controls. L, Left; R, Right. (B) Bar plot showing the mean normalized correlation values in right SPL and right OFC regions of interest (ROIs) in controls (bars) and the patient (diamond markers). Error bars represent standard error of the mean of correlation values for the control group.
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