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  1. INTRODUCTIONIn the stop-task, a fast choice response to a visual stimulus must be withheld when an auditory signal is unpredictably presented after a short delay. Successful stops are associated with a larger frontocentral negative event-related potential (ERP) in the N1 latency range than failed stops, here referred to as the ‘switch-ERP’. ACUE - PASSIVE ANT R ERP (n=14)* fMRI (n=8) In adult patients with attention deficit hyperactivitydisorder (ADHD), this effect is absent,suggesting a disturbed link between the ability to switch attention from visual to auditory stimuli and subsequent inhibitory control (Bekker et al., 2005a,b). .31uV .03uV/cm2 Z=52 VCUE - PASSIVE -8.00 *Same pattern of effects for n=8 Voltage 1300 ms CSD 3.20 AIM We investigate the mechanisms of this hypothesized switch-ERP and ask whether it involves a modality-specific or supra-modal process. Valid - Invalid Auditory Visual Auditory Valid Auditory Invalid Visual valid Visual Invalid -8.00 ANT 140 R -1.20 Z=29 Neural Correlates of Cross-Modality Attentional Switching Evelijne M. Bekker, Santani Teng, David M. Horton, George R. Mangun Center for Mind and Brain, University of California, Davis RESULTS: TARGETS Performance Invalidly cued targets evoked longer reaction times, especially in the auditory modality (F(1,13)=13.5,p<.01; F(1,7)=5.6,p<.05), and smaller variability of responding (F(1,13)=4.5,p<.05; F(1,7)=9.9, p<.02). Scalp distributions and fMRI indicated similar fronto-parietal activation when preparing for upcoming target in either modality. Difference waves reveals specific biasing in sensory areas. Event-Related Potentials Invalid trials elicited more negativity than valid trials from 100-160 msec. This effect was largest at Cz (F(4,10)=3.7,p<.05), and did not interact with modality. VCUE - ACUE .10uV .01uV/cm2 -8.00 ANT R -3.20 3.20 Voltage 1300 ms CSD 8.00 X,Y,Z=-53,-24,9 X,Y,Z=-8,-92,10 METHODS Subjects ERP: 14 right-handed, healthy subjects participated (age=23.3 (3.6), 7 males). fMRI: 8 of those tested with ERPs (age=24.3(4.3), 5 males). SUMMARY/CONCLUSION Invalidly cued targets elicited a larger N1 than validly cued targets (replication of switch-ERP effect). Scalp distributions suggest similar although not identical generators across modalities. fMRI data shows activity in posterior parietal and superior prefrontal areas, in line with previous cross-modality switching studies (Shomstein and Yantis, 2004). In addition, TPJ activity previously reported for invalid trials in visuo-spatial studies was found (not shown here) (Corbetta et al., 2000). Symbolic cues activated fronto-parietal attentional control regions. In contrast to Foxe et al. (2005), no modality differences were found for control. However, difference waves did reveal sensory specific biasing in line with both Shomstein and Yantis (2004) and Foxe et al. (2005). Task Symbolic visual cues validly or invalidly signaled the modality of an upcoming target. Passive cues did not require preparation.Subjects pressed a button with the index/middle finger of the right hand upon presentation of a grating (visual) or a tone (auditory) with a high/low frequency. RESULTS: CUES Symbolic cues elicited more positivity from – ms, and more negativity from – ms. Auditory cues elicited more positivity/less negativity at posterior sites. • REFERENCES • Bekker et al. (2005a). The pure electrophysiology of stopping. Int.J.Psychophysiol.; • 55:191-8. • Bekker et al. (2005b): Disentangling deficits in adults with ADHD. Arch.Gen. Psych.; • 62:1129-36. • Corbetta et al. (2000). Voluntary orienting is dissociated from target detection in • human posterior parietal cortex. Nat.Neurosci.; 3:292-7. • Foxe et al. (2005). Biasing the brain's attentional set (I): cue driven deployments of • intersensory selective attention. Exp. Brain Res.; 166: 370-92. • Shomstein and Yantis (2004). Control of attention shifts between vision and audition • in human cortex. J. Neurosci.; 24:10702-6. Data Acquisition EEG: 128 leads, 0.05-30Hz, A/D=250Hz, re-reference left mastoid fMRI: 3T, EPI w/ TR=2000, TE=25, 34 axial slices, 4mm, interleaved FUNDING AND CONTACT This study was supported by NIMH grant MH55741, and by NWO (Netherlands Organization of Scientific Research) Talent Fund. Correspondence: embekker@ucdavis.edu

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