Cerebral metabolism and consciousness.
Level 5 - mechanism / opinion, no new human data
Narrative review and theoretical synthesis of human and animal metabolic data
PubMed 12806834 · doi:10.1016/s1631-0691(03)00071-4
What was done
The authors synthesized findings from in vivo carbon-13 (13C) magnetic resonance spectroscopy and calibrated functional magnetic resonance imaging (fMRI) combined with electrophysiological recordings. Studies evaluated the relationship between the glutamate-glutamine cycling rate (Vcyc), glucose oxidation (CMRglc(ox)), cerebral metabolic rate of oxygen (CMRO2), and neuronal spiking rates across awake humans and anesthetized rats under sensory stimulation.
What was found
Vcyc and CMRglc(ox) were stoichiometrically linked, showing that approximately 80% of total energy derived from cerebral glucose oxidation supports processes related to glutamate neurotransmission. Percentage changes in energy consumption (delta CMRO2%) measured via calibrated fMRI matched percentage changes in neuronal spiking rates (delta nu%) measured by direct electrode recordings during stimulation at two depths of anesthesia.
Why it matters
The findings establish that the high baseline energy consumption of the resting brain reflects active, ongoing neuronal communication rather than passive metabolic maintenance. This biophysical link between metabolic consumption and neuronal firing supports theoretical models of consciousness, such as the global neuronal workspace, and suggests that loss of consciousness under anesthesia stems directly from suppression of total neuronal firing.
Limits
The abstract provides a narrative synthesis without specifying sample sizes, systematic search criteria, or quantitative variance for the cited measurements. The translation from rat electrophysiology and anesthesia models to subjective human consciousness relies on correlational and theoretical reasoning.
Cited by
- supports Approximately 80% of brain energy consumption is dedicated to glutamatergic neurotransmission.