PMC2080822_01
A The panel illustrates the encoding block design. Vagus nerve stimulation (VNS) was set to a 30 second 'on' / 66 second 'off' cycle (red line at bottom of figure A) as the patient viewed randomised 1 second presentations of positive, negative and neutral words (illustrated as magenta, green and blue 'events'. During the first of three encoding blocks, the patient was scanned using fMRI, signalling the onset of the VNS prior to scanning by a buttonpress.. B Across later recognition memory blocks, performed 20 minutes after each of the three encoding blocks, the patient made significantly more recognition errors to words encoded when the stimulator active (i.e. in the 30 second 'on' period). This effect was almost entirely attributable to interference with the encoding of negative words (which, compared to normative data was relatively enhanced when the stimulator was 'off'). The bar chart depicts the subject's recognition memory performance for each word category across all recognition blocks (filled = stimulator 'on' at encoding).. C Activity in a discrete set of brain regions reflected the selective behavioural impact of VNS on the encoding of negative words. VNS enhanced the activity brainstem (pons) ventromedial prefrontal cortex, right anterior insula/lateral orbitofrontal (area 47) cortex and frontal pole during the processing of negative (but not positive or neutral) words that were subsequently recognized. Interestingly activity within these regions, particularly area 47 and frontal pole also predicted subsequent forgetting of words during the first encoding task, illustrated in a conjunction analysis depicted in 2 panels on the right. Significant activity relating to this interaction is plotted on a normalised T2*weighted echoplanar volume from the subject to illustrate fully the field of view. Data is presented at P<0.001, uncorrected for clusters of 10 or more contiguous voxels. Peak coordinates and magnitudes of the effects are given in Table 1.
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F1
VNS (20Hz, 500 microsecs, 2.25 mAmp) was set at a 30 seconds-'on' and 66 seconds-'off' cycle during each encoding block (changed from a duty cycle of 30 seconds-'on', 3 minutes-'off') (Fig. 1A).