Human consciousness and other large scale brain functions are thought to be mediated by brain networks that involve synchronous communication between distant brain regions. Whenever the brain undergoes an altered state of consciousness, it is expected that there is an alteration in at least some of the brain networks.
For example, in sleep, general anesthesia, psychoses, and delirium, distinct changes in brain network function from the normal waking state have been detected. As we get better tools for imaging the function of different brain networks, it should be possible to measure the degree of mental fatigue, level of cooperativeness, level of honesty or engagement, degree of intoxication, level of psychosis or delirium, etc.
The image below looks at the effect of sub-anesthetic doses of the drug ketamine on four different brain networks, using fMRI. From the study: Pharmacological fMRI: Effects of subanesthetic ketamine on resting-state functional connectivity in the default mode network, salience network, dorsal attention network and executive control network – ScienceDirect
In another study, researchers examined how quickly normal brain function returned to normal healthy subjects after being kept under general anesthesia for three hours:
In the study, 30 healthy adults were anesthetized for three hours. Their brain activity was measured with EEG and their sleep-wake activity was measured before and after the experiment. Each participant was given cognitive tests—designed to measure reaction speed, memory, and other functions—before receiving anesthesia, right after the return of consciousness, and then every 30 minutes thereafter.
Analyzing EEG and test performance, the researchers found that recovery of consciousness and cognition is a process that unfolds over time, not all at once. To the investigators’ surprise, one of the brain functions that came online first was abstract problem solving, controlled by the prefrontal cortex, whereas other functions such as reaction time and attention took longer to recover.
One of the longer-term side effects of general anesthesia — usually in the elderly — is the mental state of delirium. Delirium is also common in various metabolic states and exposure to a wide range of brain altering drugs.
Delirium is an acute neuropsychiatric syndrome characterized by altered levels of attention and awareness with cognitive deficits. It is most prevalent in elderly hospitalized patients and related to poor outcomes. Predisposing risk factors, such as older age, determine the baseline vulnerability for delirium, while precipitating factors, such as use of sedatives, trigger the syndrome. Risk factors are heterogeneous and the underlying biological mechanisms leading to vulnerability for delirium are poorly understood. We tested the hypothesis that delirium and its risk factors are associated with consistent brain network changes. We performed a systematic review and qualitative meta-analysis and included 126 brain network publications on delirium and its risk factors. Findings were evaluated after an assessment of methodological quality, providing N=99 studies of good or excellent quality on predisposing risk factors, N=10 on precipitation risk factors and N=7 on delirium. Delirium was consistently associated with functional network disruptions, including lower EEG connectivity strength and decreased fMRI network integration. Risk factors for delirium were associated with lower structural connectivity strength and less efficient structural network organization. Decreased connectivity strength and efficiency appear to characterize structural brain networks of patients at risk for delirium, possibly impairing the functional network, while functional network disintegration seems to be a final common pathway for the syndrome.
Psychosis is another abnormal mental state that is coming within the diagnostic reach of advanced brain imaging. Better tools are needed, but it is likely that better tools are coming.
The studies linked below look at the changes in brain networks during various levels of sleep, anesthesia, and parasomnias.
The pattern of interconnections between brain functional regions appears to differentiate sleep-related perceptions from hallucinations, creating a point of difference with regards to the transfer of information between functional networks.
Compromised signal propagation to the prefrontal cortex appears common to both phenomena, explaining the failure of top-down control and inhibitory influences in hallucinations (row 2, table 1 ), 81 , 82 but the point of rarity may lie in the extent and severity of this disconnection.
- In REM sleep, connectivity between higher-order association and prefrontal areas, and unimodal sensory areas, is entirely suspended 68 and characterized by closed-loop circuits. This characteristic feature of REM sleep perhaps promotes the continuous stream of perceptions with bizarre and fantastical elements reported during dreams. With waking hallucinations, by contrast, connectivity between anterior frontal and posterior sensory regions is generally retained, although typically abnormally modulated 83 , 84 and more precisely delineated. Similarly, connectivity of DMN with other networks may be unstable or weakly connected, but nonetheless functionally active. 85 In support, some level of top-down integration is necessary in hallucinations to account for appraisals and beliefs (row 7) and daytime dysfunctions (row 9);
- During hallucinations, the planum temporale is activated and correlated with the experience of a sensory signal originating in external space (row 8, table 1 ). 86 This activation may assist in amplifying signals to acquire external qualities, and is absent during sleep
The better we get at functional brain imaging, the better we will be able to differentiate the brain network states that are seen in normal waking, normal sleep, general anesthesia, disorders of brain functioning as seen in neurological and psychiatric conditions, and in ever subtler grades of alterations in any of the above.
The relationship between general anesthesia, brain function, and consciousness mechanisms is complex. As a matter of fact, anesthetic agents do not blunt out brain function globally but exert specific and dose-dependent effects on brain systems that sustain internal consciousness and perception of the environment. Each agent has its own mechanism of action, and dose-dependently induces distinct phenomenological altered consciousness states. Answering the questions that have recently emerged following recent discoveries on anesthetic brain effects will probably permit new insights into the specific diagnoses of anesthesia-induced altered states of consciousness, and into the understanding of the different aspects of consciousness itself. In that respect, general anesthesia can be considered as a flexible probe to explore consciousness.
These tools can do a lot of good as they are perfected. They can also be abused by unscrupulous persons and systems. Just be aware.
More: The female menstrual cycle involves ongoing reorganization of brain networks. This means that a woman’s brain will function differently at different stages of her monthly menstrual cycle. It is not politically correct to say that brain function can be different between men and women. How much less politically correct to say that a woman’s brain can function differently from itself, depending upon where in the monthly cycle it may be?
Human “consciousness” is a fascinating phenomenon. Learning more about the synchronous brain networks that modulate both the conscious and subconscious thought processes, would be a wonderful way to begin to understand our idiosyncrasies.