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Consciousness level is known by propagating signals to the prefrontal cortex and parietal lobe.

Updated: May 29, 2022

Studying the "Study of Consciousness" (Stanislas Duanne) can further deepen your understanding of coaching theory.

I am studying to add a unique flavour to "unconscious rewriting".


This series of blog posts are my study notes. This time, the theme that follows the unconscious and conscious

I will write a "sign of consciousness".


 

There are many cases of patients who did not pass the local/global test mentioned in yesterday's article but recovered from coma and regained consciousness.

We expect the local/global test to indicate consciousness, but it is not perfect yet.


They can make further improvements by applying advanced. Google-like tools, or machine learning algorithms, to the acquired data.

You can search for any brain response to global novelty, including the unique ones that are exceptionally found in a particular patient.


However, even with this method, about half of the patients with minimal consciousness and those who regained communication ability could not detect the reaction to the rare global deviation.


In statistics, such a condition is considered a case with high specificity but low sensitivity.


If you get a positive result, you can ensure that the patient is conscious. But with negative results, we cannot conclude that the patient is unconscious. There are several reasons for this insensitivity.


One of them is that there is a lot of noise in EEG recording.

It is tough to detect a clear signal in a hospital bed surrounded by a pile of electronic devices, sometimes with a patient who is not still or unable to fix their line of sight.

There are quite a few patients who are conscious but do not understand the meaning of the test.

If the obstacle is severe, it may lack the ability to count and detect strange sounds.

Or, in the first place, some patients may not be able to focus on the beep for more than a few seconds.


Yet these patients maintain their inner world.

It means that their brains still retain the ability to communicate information between cortical areas far apart from each other.


In the late 2000s, Marcello Massimini of the University of Milan proposed the use of internal stimuli.

He thought that electrical activity should be directly in the cortex.





Sonar ping is the process of sending a signal and confirming some state by its echo.


Strong stimuli are transmitted to the cortex and thalamus, and the intensity and duration of their echoes should indicate the degree of integration of the area where the stimulus propagated.

If the activity reaches a remote area and echoes for a long time, the patient is probably conscious.

With this method, you don't need to pay attention to or understand the stimulus.

Electric pulses allow the condition of long-distance pathways in the cortex to be scrutinized, even if the patient is unaware.


Massimini used a clever combination of two technologies, TMS and EEG, to realize this idea.


TMS is a technology that stimulates the cortex by causing magnetic induction by passing an electric current through a coil placed near the head.


EEG is an EEG recording method that has been used for a long time. Massimini's trick is to "ping the cortex" with TMS and record magnetic pulse-induced brain activity propagation with EEG.


Experimenting with this combination requires a unique amplifier capable of quickly recovering from the effects of solid currents from TMS and accurately depicting brain activity after just a few milliseconds.


Massimini first conducted a test on healthy individuals who were awake, sleeping, and anaesthetized.

When the subject was unconscious, the TMS pulse produced only short, focused activity, limited to the first approximately 200 milliseconds.

When the subject was conscious, the same pulse caused a complex, long-lasting sequence of activities in the brain.


At that time, the accuracy of the vital part did not seem to matter. No matter where the pulse stimulus was applied in the cortex, the complexity and duration of the subsequent response provided a valuable indicator of consciousness.


This result is also consistent with the results of experiments conducted by the Duanne team using sensory stimuli.

Thus, the transmission of signals to the network covering the entire brain occurs after 300 milliseconds. Therefore, it is an indicator of the presence of consciousness.


Massimini tested five patients in a vegetative state and five in a minimally conscious state. He is also testing two patients with Locked-in Syndrome.


The number of subjects was small, but the test was 100 per cent accurate.

All conscious patients had a complex and long-lasting response to pulse stimuli to the cortex.


A multi-month study was also conducted on five vegetative patients. Three of them regained their "minimum state of consciousness" during the study period. They recovered to some extent in their communication skills, but the signals in their brains showed a return of complexity.


They found the transmission of signals to the prefrontal cortex and parietal lobe to be a reliable indicator of the patient's level of consciousness.

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