Retinotopic mapping in cat visual cortex using high-field functional magnetic resonance imaging.

In the field of neuroscience, there has always been a need for imaging techniques that provide high-resolution, large field-of-view measurements of neural activity. Functional MRI has this capability, but the link between the blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal and neural activity is indirect. High magnetic field strengths (>3 T) improve the strength and specificity of the BOLD signal, but there are additional concerns about imaging artifacts at high field. We have tested the capabilities of ultra high field fMRI in the anesthetized juvenile cat, demonstrating rapid, non-invasive retinotopic mapping of early visual areas. Maps of topographic organization and measured cortical magnification factors are in good agreement with electrophysiological studies. Measurement precision was estimated at 1 mm. This mapping, performed with an MRI scanner at ultra high field (9.4 T), demonstrates the capabilities of high-resolution functional mapping of the visual system at ultra high field.