Freud's Theory of Mind and Functional Imaging Experiments

¹³C in vivo NMR experiments have measured large neuronal neurotransmitter fluxes in resting rat and human brains which are coupled to brain energy consumption. In the awake, resting state this “baseline” neuronal activity accounts for ∼80% of brain energy consumption. The resting activity decreases with deepening anesthesia. In stimulated anesthetized rats, high localized somatosensory brain activity is restored by incremental changes during forepaw stimulation. Functional imaging experiments generally measure such incremental changes in activities during a task period and discard the highly active baseline. Single electrode measurements of the spiking rates in a representative population of neurons in the rat somatosensory region have been correlated with the functional imaging under the same stimulation. The population response has allowed patterns from the sensory stimulation to be distinguished from connections with the brain's global activity. In this way it is becoming possible to identify global task activities that include the organismic responses normally submerged in the large unassigned baseline activities. We propose that the high baseline plus any incremental activity supports total mental activity across all levels of mentation. In contrast to cognitive psychology, which neglects baseline and assumes that task activities are supported by measurable increments, we suggest that Freud's layers of consciousness provide a more fitting conceptual framework for understanding brain activity and its relation to mentation. Freud's topographical model of mind is consistent with the high neuronal activity that is required to support tasks, and its layered structure offers an interpretive guide to total brain activities.