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More instructive are two types of clinical evidence: One is to apply electrical stimulation to the cortical tissue, and the other is for patients who are injured or ill in a specific brain area. the study. For example, before removing brain tumors or epilepsy lesions, neurosurgeons directly apply electrical stimulation to nearby cortical tissues to detect their functions. Stimulating the hot zone on the back will cause a series of sensations and feelings, such as flashes, geometric figures, deformed faces, auditory or visual hallucinations, familiarity or unreality, the urge to move certain parts of the body, and so on. These phenomena do not appear when the anterior cortex is stimulated: roughly speaking, the anterior cortex does not induce direct sensation.
Other clues come from patients with neurological diseases in the early 20th century. In order to remove tumors or treat epilepsy, surgeons sometimes had to cut off a large area of the prefrontal cortex of patients. It is amazing that after the operation, the lives of these patients have not changed much. Although the lack of a part of the prefrontal lobe has caused some adverse effects on patients: they cannot suppress some bad emotions or behaviors, they have movement disorders, and they cannot repeat some actions or words without self-control. But after a period of time, their personality and IQ have slowly recovered, and they have lived safely for many years. There is no sign that the lack of prefrontal tissue has a significant impact on their conscious experience. On the contrary, if the back side hot zone is removed, even if the area is small, it will cause the patient to lose some consciousness functions, such as the inability to recognize the face, or the inability to perceive movement, color or space.
So, it seems that subjective sensations and experiences such as vision and hearing are produced by the posterior cortex. In fact, as far as we know, all conscious experiences are produced in the posterior cortex. So, what is the difference between this area and the prefrontal cortex? We don’t know the answer yet. But what is exciting is that a recent discovery seems to suggest that neuroscientists are close to the answer.
consciousness measuring instrument
The medical field needs an instrument that can reliably detect whether an injured or incapacitated patient has consciousness. For example, during surgery, it is necessary to administer anesthesia to patients so that they cannot exercise, keep their blood pressure stable, and have no pain and related memories. Unfortunately, this goal is not always achieved. In the United States, hundreds of patients each year still have a certain level of consciousness during anesthesia. (perturbational complexity index, PCI) can give an estimate of the overall complexity of brain activity. Studies have found that the perturbation complexity index of subjects in the waking state is generally between 0.31 and 0.70, but in Under deep sleep or anesthesia, it will drop below 0.31. Massimini and Tononi did the same test on 48 patients with brain damage but conscious and able to respond to the outside world, and found that each patient’s The scores are all within the range of waking state, consistent with behavioral observation.
The researchers then measured 81 patients in a minimally conscious state or a vegetative state. This group of patients in the minimally conscious state still has some unconditioned behaviors. Studies have shown that 36 of the 38 minimally conscious patients were conscious and the other 2 were misdiagnosed as unconscious. For 43 patients in a vegetative state, previous clinical observations have confirmed that it is impossible to establish communication with them, but the test results showed that only 34 were unconscious and the other 9 patients were conscious. Their brain’s response pattern to the perturbation stimulus is similar to that of the awake control group, which may indicate that they are still conscious but unable to communicate with their loved ones.
Researchers are working hard to improve this set of equipment so that it can be applied to the clinic and can be extended to patients with mental illness and children. Sooner or later, scientists will be able to find the specific neural mechanisms corresponding to all subjective experiences. Although these developments have important clinical significance and may help the patient’s family and friends, it cannot answer some more fundamental questions: Why do these neurons and not others generate consciousness? Why the discharge frequency is this value and not other values? In fact, the real mystery lies in why organizations with complex structures can produce consciousness and how does it do it? After all, the brain, like the heart and liver, is also governed by the laws of physics. What is special about the brain? What biophysical process does the brain use to make a pile of gray matter produce beautiful melody and colorful images?
A satisfactory theory of ultimate consciousness needs to point out that any physical system (can be a complex circuit composed of neurons, or it can be on a chip Circuit) Under what conditions can consciousness be generated. You have to be able to answer, why are there differences between different feelings? Why does a blue sky and an inaccurate violin feel different? Does the difference between different feelings make sense? If so, what is the significance? The ultimate consciousness theory should be able to infer what kind of system can have feelings. If the theory cannot give verifiable predictions, then any machine