MAGNETIC RESONANCE IMAGING OF ACTIVE NEURAL PATHWAYS

THE ABILITY TO DETECT AND MEASURE NON-INVASIVELY THE PROPAGATION OF ELECTRICAL ACTIVITY ALONG A NEURAL PATHWAY IN REAL TIME AND WITH A SPATIAL RESOLUTION THAT ALLOWS THE IDENTIFICATION OF THE ANATOMICAL PATH IN THE WORKING HUMAN BRAIN IS AMONG THE MOST RELEVANT, AMBITIOUS AND SO FAR UNSOLVED PROBLEMS IN NEUROSCIENCE. TECHNOLOGIES SUCH AS ELECTRO-ENCEPHALOGRAPHY (EEG) AND MAGNETO-ENCEPHALOGRAPHY (MEG) OR FUNCTIONAL MAGNETIC RESONANCE IMAGING (FMRI) HAVE NOT ACCOMPLISHED THIS TASK YET. THE MAIN AIM OF THIS PROPOSAL IS TO DEMONSTRATE THAT A NEW TECHNIQUE GROUNDED ON BASIC ANATOMICAL, PHYSIOLOGICAL AND PHYSICAL-CHEMICAL PRINCIPLES AND DIFFUSION IMAGING THEORY WILL ALLOW US TO DERIVE DIRECT MEASUREMENTS OF ELECTRICAL ACTIVITY IN ANATOMICAL BRAIN CONNECTIONS IN VIVO. NON-INVASIVE FUNCTIONAL MAGNETIC RESONANCE IMAGING (FMRI) ALLOWS US TO MAP THE DISTRIBUTED NEURAL SYSTEMS ACTIVATED BY SPECIFIC PARADIGMS. HOWEVER, THE DYNAMIC ELECTRICAL ACTIVITY CARRIED BY THE THOUSANDS OF CONNECTIONS BETWEEN THESE BRAIN AREAS REMAINS TO BE ELUCIDATED. MEASUREMENTS OF WATER MOLECULE DIFFUSION ALONG FIBER TRACTS BY DIFFUSION MAGNETIC RESONANCE IMAGING PROVIDES A STATIC MAP THE NEURAL CONNECTIONS BETWEEN BRAIN CENTERS, BUT DOES NOT CAPTURE THE ELECTRICAL ACTIVITY ALONG THE AXONS OF THESE FIBER TRACTS. HEREIN WE PROPOSE TO TEST A MODEL FOR DIFFUSION MRI BASED ON A HYPOTHESIZED ¿ANISOTROPY REDUCTION DUE TO AXONAL EXCITATION¿ (¿AREX¿) AND EXAMINE THE POTENTIAL CHANGES IN WATER MOBILITY ACCOMPANYING THE MOVEMENT OF IONS DURING THE PROPAGATION OF ACTION POTENTIALS ALONG AXONAL TRACTS. AS THIS MODEL EXAMINES THE PERPENDICULAR MOVEMENT OF WATER MOLECULES (ACCOMPANYING THE MOVEMENT OF IONS) DUE TO THE PROPAGATION OF ACTION POTENTIALS ALONG AXONAL TRACTS, WE PROPOSE THAT THE MEASUREMENT OF WATER MOLECULE DIFFUSION THAT RELIES ON THESE DYNAMIC PROPERTIES OF AXON TRACTS BE TERMED DYNAMIC DIFFUSION IMAGING (DDI).