Simultaneous BOLD fMRI and fiber-optic calcium recording in rat neocortex

Area of Science:

• Neuroscience
• Neuroimaging

Background:

• Functional magnetic resonance imaging (fMRI) using blood oxygen level-dependent (BOLD) contrast is a key tool for brain activity research.
• The precise relationship between BOLD signals and underlying neural activity is not fully understood.

Purpose of the Study:

• To investigate the relationship between neuronal activity, glial activity, and fMRI BOLD signals.
• To clarify the cellular mechanisms contributing to BOLD responses in the rat somatosensory cortex.

Main Methods:

• Simultaneous recording of fMRI BOLD signals and fiber-optic fluorescent calcium indicator signals in rat somatosensory cortex.
• Electrical forepaw stimulation at varying frequencies (1-10 Hz) to evoke neural responses.
• Astrocyte-specific staining and two-photon microscopy to identify glial network activity.

Main Results:

• Neuronal calcium signals showed frequency-dependent adaptation.
• Slower calcium signals were observed in astrocyte networks, indicating glial involvement.
• BOLD responses could be predicted from neuronal signals alone when glial activity was absent.
• Glial activation introduced additional prolonged components to the BOLD signal.

Conclusions:

• fMRI BOLD signals are complex and influenced by both neuronal and glial activity.
• Combined fMRI and fiber-optic recordings offer a powerful approach to dissecting the cellular basis of BOLD signals.
• Understanding glial contributions is crucial for accurate interpretation of fMRI data.