Comparison of the hemodynamic response in V1, primary motor, and association areas using functional MRI

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11, Number

5, 2000,

Part 2 of 2 Parts 10

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PHYSIOLOGY

Comparison of the Hemodynamic Responsein Vl, Primary Motor, and Association Areas Using Functional MRI Todd A. Mulderink*t,

Damn

R. Gitehuan*~S, M.-Maw4

Mesulam*$,

Todd B. Parrish*?

*Feinberg Neuroscience Institute and Northwestern Cognitive Brain Mapping Group, Cognitive Neurology and Alzheimer’s Disease Center fDepartment of Radiology, Nortwestem University Medical School, Chicago, IL $Department of Neurology, Northwestern University Medical School, Chicago, IL The purpose of this study was to investigate the hemodynamic response function (HRF) of normal, young subjects during a visually cued motor task and a spatial attention task. Introduction previous work has suggested that activation-induced hemodynamic response patterns remain relatively stable in a given cortical area. [1,2]. However, some inter-area variability has also been shown to exist even within a single subject [2,3,4]. This variability may arise from differences in vascular architectnre or potential differences in the coupling between neural activity and blood oxygenation. To date there has been no direct comparison between the HRF of primnry sensory areas (Vl and Ml) and the HRF of association centers involved in spatial attention. Given the differences in the vascular environment and possibly physiologic requirements of these areas, some variability in the shape and timing of the hemodynamic response is expected. Methods 5 healthy vohmteetx ages 22-28 war imaged wing sin&-shot 6mm slices with a 2-3mm gap, FoV=24Omm, TR=SC%s)

gradientecho echo planat imaging (6 on a 1ST scanner (Vision, Siemens) dutingperformance of a visnally cued mctm task (10 trials) and a spatial attention task (15 trisls). The event-n&ted design consisted of 30 second trials ndlizing a brief 2 second stlmnlns @xi snd the ~ofmetimemesubjectwasaskwltofixateonacrosspesentedinthemiddleofthevisual field~stimulusforthevisuallycuedmotortaskconsistedofan8Hzflashingc~~during which the subjects were instmcted b perform a complex hand movement. Tbe spatial attention task consti of 2-3 jxe.sentations of peripheml detection of a target dnting central fixation [5]. Data analysis was perfond using Brain Voyager (Brain Innovation, Germany) subseqnent to 3D motion con&ion, spatial~of5~andtemporals~ofls.Hemodynamic~curveswere generatedbyfirstlocalizing~eanatomicROisonstandardfunctiona~,andthengenaaringtfK time come data for five inditiduaJ voxels within the ROI. The data fmm the voxels were awmged togethertoformaHRFfunctionfor~pruticularanatomicROI.Curve~~weregeneratedfor primy motor and visual co&es for the visual/motor task, and sssccintion areas (cingnlate gyms, frontal eye fields, and posterior par&l) for the spatial attention task. The HRF was compared within and scmss subjects.

Figure 1 shows the hemodynamic response curves for primary motor and visual cottices and association areas involved in spatial attention for a single subject. Maximum % signal change was significantly increased in the primruy co&es as compared to association areas in all subjects. However, rise and fall slopes showed no significant differences when signal time courses were normalized.

Figure 2: Single subject hemodynamic responses in association and primary areas normalized to maximum signal change, demonstrating differences in timing

Diision

Wim the advent of rapid presentation methods of event related tMRl, it is imponant to characterize the hemodynamic tespome to impmve the detection of activation. Towards this end, we have measnred the HRF using two different paradigms for comparison of primary and wociation cortices. Sign&ant difference in the maximum 8 signal changes were noted in primary conices as compa& to ac&atim ams involved in spetial ettention (figme 1). The rising and falling slopes of the HRF were determinedtobesimilarwhenmetimecoursesweremRmalizedtomaximumsignalchange(figures 2&3). Finlhm, v;uiation was observed in the liming of the hemodynamic response with earlim positive signal changes observed in association areas in 3 of 5 subjects (fignms 2&3). Differences insignal intensity snd timing may be atnibnted to vascular smhitechne, nenmnal volume, neuronal mcmitment by the di@emnt pa&igms, snd pethaps the coupling of nenronal activity to bkod flow. These differences reflect considerable inter-subject variation. Future wo& will determine if a better understanding of these &tkwships pmdnces mom effective functional brain mapping.

Figure 3: Single subject hemodynamic responses in association and primary areas normalized to maximum signal change, demonstrating no differences in timing

Referenees 1. Buckner RL, Koutstaal W, Schacter DL, Dale AM, Rosen BR. Neuroimage, 7: 163-175; 1998. 2. Agnirre GK, Zamhn E, D’Esposito M. Nemoimage, 8:360-369: 1998. 3. Kim SG, Richter W, Ugnrbil K. Magn Reson Med 37:631-636; 1997. 4. Krnggel F, van Cramon DY. Human Brain Mapping 8:259-271; 1999. 5. Gitelman DR, Nobrr AC, Parrish TB, LsBar KS, Kim YH, Meyer JR, Mesulam MM. Brain 122(6):1093-1096;

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