Principles of Functional Magnetic Resonance Imaging and its Applications in Cognitive Neuroscience

Functional magnetic resonance imaging (fMRI) is a neuroimaging technique that provides brain activation maps with a spatial resolution of a few millimeters. The BOLD (blood oxygenation level dependent) fMRI method is the most commonly used technique. It measures the hemodynamic response to neural activity. The BOLD fMRI signal is based on the magnetic properties of the oxygenated / deoxygenated hemoglobin which is the oxygen carrier in blood. FMRI is noninvasive, and unlike in positron emission tomography (PET) individuals are not exposed to radiation. This allows data collection from the same individual over multiple sessions. The relatively high temporal resolution of fMRI compared to PET provides flexibility in experimental designs of cognitive tasks. In this paper we review the key principles of MRI physics, and the underlying metabolic, hemodynamic, and electrophysiological mechanisms of BOLD signal. We introduce frequently used experimental design paradigms and present examples. Next, we give an overview of theoretical considerations and applications of analysis methods in fMRI time series. Neural network modeling based on fMRI data is also discussed. Finally, we present an ongoing study in our laboratory to demonstrate the application of design types and analysis methods. fiule T›naz , Chantal E. Stern 1, 2, 3, 4 Center for Memory and Brain, Program in Neuroscience, Dept. of Psychology Boston University Boston, MA 02215 Athinoula A. Martinos Biomedical Imaging Center Mass General Hospital Charlestown, MA 02129 Nörolojide Yeni Teknolojiler / New Technologies in Neurology Türk Nörolo j i Dergi s i 2005; C i l t :11 Say › :1 Sayfa :8-26 ÖZET Kognitif Nörobilimde Fonksiyonel Manyetik Rezonans Görüntüleme Prensipleri ve Uygulamalar› Fonksiyonel Manyetik Rezonans Görüntüleme (fMRG), milimetrik düzeydeki lokalizasyon gücü sayesinde beyin aktivasyon haritalar› elde etmede kullan›lan bir nörogörüntüleme tekni¤idir. BOLD (blood oxygenation level dependent), di¤er bir deyiflle kan›n oksijenasyon düzeyine ba¤l› fMRG metodu, kognitif çal›flmalarda en s›k kullan›lan tekniktir. BOLD fMRG nöral aktiviteye karfl› geliflen hemodinamik yan›t› ölçer. Kandaki oksijen tafl›y›c›s› hemoglobin molekülünün, oksijen ba¤lam›fl ve serbest halleri manyetik ortamda farkl› davran›fllar sergiler. ‹flte BOLD sinyali, hemoglobin molekülünün oksijenasyon düzeyine göre de¤iflen manyetik özelliklerine ba¤l›d›r. FMRG invazif de¤ildir ve örne¤in pozitron emisyon tomografisinden (PET) farkl› olarak bireyler radyasyona maruz kalmaz. Bu özellik ayn› bireyden uzun süren ve birden çok deney seanslar›nda veri toplamay› olanakl› k›lar. FMRG’nin PET’e k›yasla zamansal çözünürlü¤ünün daha iyi oluflu da kognitif deney tasar›mlar›nda esneklik sa¤lamas› aç›s›ndan önemlidir. Bu yaz›da MRG fizi¤inin temel ilkelerini ve BOLD sinyalini oluflturan metabolik, hemodinamik ve elektrofizyolojik mekanizmalar› gözden geçirip, fMRG’de s›kl›kla kullan›lan deneysel tasar›m paradigmalar›n› örneklerle aç›klamaya çal›flt›k. Ard›ndan fMRG verilerinin analizinde kullan›lan temel yöntemlerin teorik altyap›s›n› ve uygulamas›n› özetleyip fMRG verilerine dayan›larak gelifltirilen nöral a¤ modellerini tan›tt›k.