Identification and Quantification of the Murine Visual Cortex Activity by Functional MRI

Abstract

Purpose: To understand the visual pathway, it is important to identify and quantify the responses of each part in the visual system from the retina in the eye to the visual areas in the brain. The visual cortex activity has been examined by action potentials from electrodes within the brain of experimental animals. Furthermore, functional magnetic resonance imaging (fMRI) is utilized to visualize human visual cortex recently. However, fMRI visualization of visual cortex activities in small animals such as mice has not well documented to date. Here we report that fMRI visualization of the murine visual cortex activity in awake.

Methods: All animal experiments were conducted in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research, and were approved by Institutional Animal Care and Use Committee of the Keio University School of Medicine. To test awake mice using fMRI, we performed an operation to fix a 2×3×20mm plastic plate on parietal bone of C57BL6/j mice with local anesthesia. These mice were adapted for head fixing and MRI sounds for a couple of days after the operation till fMRI examination. To obtain the visual cortex activity, light stimulation was repeated for 5 times (10 seconds duration, 60 seconds interval) on right eye with 5 Hz blue light. Analysis was performed with SPM12 (Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, London, UK) and tailored software in MATLAB.

Results: Bilateral occipital lobe and lateral geniculate nucleus response in the C57BL6/j mice by 5 Hz blue light stimulation with fMRI was observed. Most significant voxel located 2.56mm, 0.88mm, -2.88mm(x,y,z from Bregma line). This area matched with V1 area. These response are quantifiable and statistically significant compared with baseline signal (p<0.05, FWER corrected).

Conclusions: We tested the murine visual cortex activity in awake by light stimulation with fMRI. The responses　from primary and secondary visual cortex were identified and quantifiable. These data indicated that fMRI is effective to detect the murine visual pathway and response.