Complementarity of BOLD and ADC-fMRI in Mapping Brain Visual Processing in the Rat

Area of Science:

• Neuroscience
• Functional Magnetic Resonance Imaging (fMRI)
• Visual Processing

Background:

• The superior colliculus (SC) is known to encode the transition from static to dynamic vision.
• Previous studies utilized blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI) in rats.
• High-frequency visual stimulation exceeding the flicker fusion threshold elicits a negative BOLD response in the visual cortex, originating from the SC.

Purpose of the Study:

• To investigate the neurovascular and neuromorphological coupling mechanisms underlying the static-to-dynamic vision transition.
• To compare brain responses to low (1 Hz) and high (25 Hz) frequency visual stimulation.
• To examine responses across different brain regions, sexes, and magnetic field strengths (9.4 and 14 T).

Main Methods:

• Employed both BOLD-fMRI and apparent diffusion coefficient (ADC)-fMRI in rats.
• Administered visual stimulation at 1 Hz and 25 Hz.
• Analyzed activity in the dorsolateral geniculate nucleus, medial and lateral SC, corpus callosum, and visual cortex.

Main Results:

• Confirmed distinct BOLD responses to low- and high-frequency stimulation.
• Identified negative BOLD specifically in the lateral SC during the transition to dynamic vision.
• Observed significant ADC-fMRI responses (reduced ADC) in the SC and corpus callosum, independent of visual frequency and BOLD sensitivity.

Conclusions:

• The transition from static to dynamic vision is characterized by specific BOLD responses in the lateral SC.
• ADC-fMRI provides complementary insights into neural activity, revealing consistent responses in the SC and corpus callosum.
• An interplay between neural activity and hemodynamic response, best characterized by dual fMRI contrasts, underlies dynamic vision processing.