Is Consciousness Rooted in Neuron Synchronization in the Cortex?
A study conducted by scientists at the Picower Institute shows that consciousness depends not just on the joint activity of neurons in the cerebral cortex, but on their synchronized interaction. Propofol disrupts this interaction and desynchronizes cortical neurons. This may explain the loss of consciousness during anesthesia.
Through experiments on mice, researchers found that under the influence of propofol, sensory information still reaches the brain, but the spread of signals across the cortex is disrupted. This suggests that consciousness requires synchronized communication throughout the brain, and propofol’s effect in limiting this connection may explain its role in “switching off” consciousness. Propofol is used as a sedative and as an anesthetic. Although its exact mechanism of action is not fully understood, it is widely used in surgery.
How the Experiment Was Conducted
The experiment was performed on mice. To capture the activity of individual neurons and assess their communication, EEG electrodes were placed on the mice’s skulls. First, scientists measured cortical neuron activity while the mice were awake, and then under the influence of propofol. In both states, the animals received stimuli: auditory and tactile (air was blown onto their faces).
The researchers discovered that under propofol anesthesia, sounds and tactile sensations still triggered neural activity in the area of the cortex that receives incoming sensory information (the superior temporal gyrus). However, measurements of neural and broader oscillatory activity showed that signals did not spread to three other cortical areas that process stimuli at a higher level (the posterior parietal cortex, area 8A, and the prefrontal cortex), as was observed during wakefulness. While awake, such stimulation increased alpha/beta frequency activity in all cortical areas. Under anesthesia, the alpha and beta frequency response was reduced in the superior temporal gyrus, and in higher cortical areas, electrical waves disappeared entirely.
Key Findings
Along with reduced activity, the researchers noted a decrease in sensory information detected in the brain as it moved up the cortical hierarchy. The primary area that perceives stimuli provided some information to the decoder, but in higher structures, it could not be extracted.
The important conclusion from this study is that the cortex must synchronize its structures so they are “on the same wavelength.” Only then can incoming sensory information be adequately processed. For this to happen, stimuli must travel the full path through the cortical hierarchy: first to the “receiver,” and then to specialized processing centers. Under anesthesia, these pathways are cut off, and stimuli do not reach the specialized processing zones.
This scientific work provides valuable insights into how anesthesia affects consciousness and the perception of sensory information, shedding light on the nature of consciousness itself.