High-resolution fMRI of macaque V1.
To understand the physiological mechanisms underlying the blood-oxygenation-level-dependent (BOLD) signal, the acquisition of data must be optimized to achieve the maximum possible spatial resolution and specificity. The term "specificity" implies the selective enhancement of signals originating in the parenchyma, and thus best reflecting actual neural activity. Such spatial specificity is a prerequisite for imaging aimed at the elucidation of interactions between cortical micromodules, such as columns and laminae. In addition to the optimal selection of functional magnetic resonance imaging pulse sequences, accurate superposition of activation patterns onto corresponding anatomical scans, preferably acquired during the same experimental session, is necessary. At high resolution, exact functional-to-structural registration is of critical importance, because even small differences in geometry, that arise when different sequences are used for functional and anatomical scans, can lead to misallocation of activation and erroneous interpretation of data. In the present study, we used spin-echo (SE) echo planar imaging (EPI) for functional scans, since the SE-BOLD signal is sensitive to the capillary response, together with SE-EPI anatomical reference scans. The combination of these acquisition methods revealed a clear spatial colocalization of the largest fractional changes with the Gennari line, suggesting peak activity in Layer IV. Notably, this very same layer coincided with the largest relaxivity changes as observed in steady-state cerebral blood volume measurements, using the intravascular agent monocrystalline iron oxide nanoparticles (MION).
Goense
Jozien B M
JB
Department of Physiology of Cognitive Processes, Max-Planck Institute for Biological Cybernetics, 72076 Tübingen, Germany. jozien.goense@tuebingen.mpg.de
Zappe
Anne-Catherin
AC
Logothetis
Nikos K
NK
D000465:Algorithms; D000818:Animals; D002196:Capillaries; D002560:Cerebrovascular Circulation; D017352:Echo-Planar Imaging / Q000379:methods; D005290:Ferric Compounds / Q000494:pharmacology; D052203:Ferrosoferric Oxide / Q000494:pharmacology; D007091:Image Processing, Computer-Assisted; D008251:Macaca; D008279:Magnetic Resonance Imaging / Q000379:methods*; D053758:Nanoparticles; D010100:Oxygen / Q000378:metabolism*; D012039:Regional Blood Flow
D005290:Ferric Compounds; C499827:monocrystalline iron oxide nanoparticle; C000499:ferric oxide; D010100:Oxygen; D052203:Ferrosoferric Oxide