Introduction to Functional MRI Daniel Bulte Centre for Functional MRI of the Brain University of Oxford Outline • • • • • • fMRI as a tool in neuroscience What is MRI? Neuronal firing, blood flow and BOLD A basic fMRI experiment What can fMRI be used for? Integrating modalities Functional MRI Phrenology Gall and Spurzheim (1810) Functional localization Brodmann’s anatomical areas Functional Localisation • • • • • • Brain injury and surgical cases Direct electrode stimulation/recording PET - blood flow and metabolism EEG - scalp potentials from neuronal firing fMRI - blood oxygenation MEG - magnetic field from neuronal firing MRI vs FMRI What is MRI? • Nuclear Magnetic Resonance (NMR) • Interaction between nuclei and strong magnetic field • In most MRI we only worry about protons (1H) Nuclear Spin M magnetic moment spin M=0 Location invariance Visual hemi-field Left Right Regardless of hemi-field, words engage the region more than consonant letter strings Cohen et al (2002) fMRI studies of hand movement FMRI signal Task paradigm: rest move rest move time rest move rest SMA PMCc M1i M1c fMRI reveals different activity patterns in disease control stroke preSMA PMCdr SMA PMCdc PMCv CMA Spinal cord M1 Possible confounds •Performance •attention Changes in the FMRI activity during affected hand movements after therapy Pre Aff hand (left) Post THERAPY Unaff hand (right) Pre ansen-Berg et al, Brain, 2002 Post Changes in FMRI activity are specific to patients who improve Pre Improver: Aff hand (L) Post THERAPY Nonimprover: Aff hand (L) Pre Post Correlation vs Causation • Imaging techniques show us correlations between a brain activity state and a task • Imaging techniques cannot tell us whether activation in a particular brain area is necessary for performance of a task • To this we need to use interference techniques Integrating Modalities MRI can’t everything (quite) Diffusion Imaging • Measure self diffusion of protons • In white matter areas diffusion is greatest in fibre direction “Virtual dissection” of fibre tracts Superior longitudinalBroca’s fasiculus area Wernicke’s area Insular fibres Temporal fibres Catani et al, NeuroImage Why MRS? • MRI provides structural/anatomical and physical information • Signal from water protons • MR Spectroscopy (MRS) provides biochemical, physical and molecular information 4.0 3.0 2.0 ppm Rapid modulation of GABA during motor learning ▲- learning; ■ - random ,◊ - control •The visible GABA signal in the sensorimotor cortex decreased rapidly during motor learning, but not during random tracking movements; •GABA modulation was specific to learning and not a general result of performance of motor task Floyer et al EEG in the Scanner Simultaneous EEG/fMRI: 32 channel EEG, Brainamps, 3T Siemens Allegra, © Cognitive Neuroscience Lab Singapore EEG in the Scanner EEG in the Scanner In Summary • fMRI uses the NMR phenomenon to generate images and exploits the magnetic properties of blood to measure oxygenation changes in the brain • Careful design of experiments to answer useful questions • Data analysis methods that account for the temporal and spatial effects of BOLD contrast ... The Tools • Stimulus presentation – Visual/Auditory/Somatosenory presentation – Response (button box etc.) – Software • Must be MR safe – Not ferromagnetic – Potential heating effects – Introducing...Outline • • • • • • fMRI as a tool in neuroscience What is MRI? Neuronal firing, blood flow and BOLD A basic fMRI experiment What can fMRI be used for? Integrating modalities... the blood flow response to the activation site • Temporal Resolution – The peak in blood flow increase is around seconds after the activation A Basic fMRI Experiment The Tools • High field MRI