Cerebral metabolism and consciousness

Area of Science:

• Neuroscience
• Biophysics
• Neuroimaging

Background:

• In vivo 13C magnetic resonance spectroscopy (MRS) measures brain metabolism.
• The glutamate-glutamine cycle (Vcyc) and glucose oxidation (CMRglc(ox)) are key metabolic pathways.
• Understanding brain energy consumption is crucial for interpreting functional imaging data.

Purpose of the Study:

• To quantitatively measure brain metabolism and neuronal activity.
• To investigate the relationship between energy consumption and neurotransmission.
• To re-evaluate baseline brain activity in functional imaging.

Main Methods:

• Utilized in vivo 13C MRS to detect 13C label turnover from glucose.
• Measured Vcyc and CMRglc(ox) in awake humans and anesthetized rats.
• Employed calibrated fMRI to measure energy consumption (delta CMRO2%) and correlated with neuronal firing rates (delta nu %).
• Distinguished neuronal responses from different brain regions.

Main Results:

• Vcyc and CMRglc(ox) are stoichiometrically related in both humans and rats.
• Approximately 80% of glucose oxidation energy supports glutamate neurotransmission.
• High resting brain activity was observed, supporting a reinterpretation of functional imaging data.
• Quantitative biophysical relationships between energy consumption and neuronal activity were established.
• Anesthesia reduced neuronal firing rates, correlating with loss of consciousness.

Conclusions:

• The brain exhibits high resting activity, significantly supporting neurotransmission and potentially consciousness.
• Quantitative links between energy use and neuronal activity offer new insights into brain function.
• Findings align with global workspace theories of consciousness and neuronal processing.