Chapter 14 Chapter 12 Brain Injury

"All the ruins of Babylon look far less terrible than the ruin of human thought." — Scrope Davies In recent years, neurologists have studied patients with brain injuries.These injuries can be caused in a variety of ways, such as stroke, blow to the head, gunshot wound, infection, etc. Many injuries alter some aspects of the patient's visual awareness, but some of the patient's other functions (such as speech or motor behavior) were largely unaffected, evidence of a remarkable functional differentiation of the cortex, often in rather surprising ways. In many cases, the damage to the brain is not single and specialized.A high-velocity bullet hits every cortical area equally. (Living cortical tissue is a fairly soft gel, and a small portion of it can be easily removed by sucking with a pipette.) Typically, the injury may involve several cortical areas, with simultaneous damage to corresponding areas on both sides of the head The most serious consequences, but this is very rare.

Many neurologists have only time to examine a patient briefly—just enough to make a reasonable guess about the likely location of the injury.Later, even this form of examination was largely replaced by brain scans.Recently, it has been considered unscientific to describe a single, isolated brain injury, so it is customary to report many similar conditions simultaneously.Unfortunately, this leads to conflating some actually different forms of injury. Current trends have somewhat corrected this practice.Special attention is now often paid to the rare cases in which a specific aspect of the patient's feelings or behavior is altered, while most others remain unharmed.These patients are likely to have had more limited and thus more specialized injuries.Efforts have also been made to locate these lesions on brain scans.If the patient cooperates, he will undergo a full battery of psychological and other tests in the awake state to discover what he can and cannot see or do.In some cases, this testing is carried out for several years.As theories about visual processing have become more sophisticated, experiments to test these ideas have become more extensive and sophisticated.Now, they can be combined with brain-scanning technology.The technique can record the behavior of the brain as it performs these various tasks.These results can be compared and controlled between patients with similar injuries or similar conditions (or both).

Lesions to area V1 (the striated cortex) are an obvious example, and we will start with that.If the V1 area on one side of the brain is completely destroyed, the patient appears to be unable to see the opposite half of the visual field. At the end of this chapter I will discuss in detail a strange phenomenon called "blindsight."Here let us first look at the results of the damage to the highest part of the visual hierarchy, and limit the damage to the right-hand side of the head.This is known as one-sided neglect.The area of ​​injury roughly corresponds to area 7a in macaques (see Figure 48).This is usually caused by disease in the arteries of the brain, such as a stroke.

In the early stages, symptoms can be severe—the patient's eyes and head turn to the right.In the most severe cases, the extent of the damage may be so extensive that the patient loses control and feeling on the left side, and he will deny that his own left leg is his.One man was so outraged that someone else's leg was on his bed that he threw it out of bed.He was surprised to find himself lying on the floor. Most cases are not that serious.Severe symptoms usually lessen or disappear after a few days.For example, the patient may not be able to pick up food on the left side of the plate at this time.If he is asked to draw a clock, or a face, he usually only draws the right side of it.After a few weeks, as the brain partially recovered, his neglect of one side decreased further, but he still seemed to pay less attention to the left than to the right.If asked to bisect a line, he would draw the midpoint to the right.He is not completely blind to the left side though.If there is an isolated object there, he will see it.But if there is also an obvious object on the right side, he cannot notice the object on the left side.In addition, he frequently denied that anything was oblique and did not admit to seeing an object-free space to the left of his field of vision.

One-sided neglect is not limited to visual perception.It also shows up in visual imagination.A typical example was reported by Edoardo Bisiach and colleagues in Italy [1].They asked patients to imagine themselves standing at one end of a main square in the city of Milan, facing the church, and to narrate what they recalled.They describe mainly the details of the building on the right as seen from this viewpoint.The patients were then asked to imagine standing on the opposite side of the square with the church behind them, and the process was repeated.Then they mainly narrate the details of the side they ignored when they narrated before, which is still the right side of the visual field at this time.

Another prominent form of brain injury results in partial or total loss of color vision.All objects seen by the patient are only shades of gray, which is known as "achromatopsia" - reported as early as 1688 by Robert Boyle, known as the "Father of Chemistry" . In 1987, Oliver Sacks (Oliver5acks) and Robert Wasserman (Robert Wasserman) described such a case in the "New York Review of Books". The patient was the New York abstract painter Jonathan I. (Jonathan I.).He had a special interest in color, so much so that when he listened to music he had "a burst of rich inner color."This is called synesthesia.After an accident his synaesthesia disappeared, and so did the music's appeal to him.

The damage was the result of a fairly minor car accident.Jonathan Ai may have been hit, but otherwise appeared to be unhurt.He was able to clearly describe the cause of the accident to the police.But then he got a bad headache and often forgot about the accident.After falling asleep, he found himself unable to read the next morning.However, this obstacle disappeared after five days.Although his subjective perception of color has not changed, he has difficulty distinguishing colors. The situation developed further the next day.Even though he knew it was a sunny morning, the world seemed to be in fog as he drove to the studio.Only when he got there and saw that his brightly colored paintings were now "totally gray and devoid of color" did he startle at his own inadequacy.

This flaw is brutal.Sachs and Wasserman explained this psychological effect concretely.While one could judge his problem to be no worse than watching an old-fashioned black-and-white movie, Mr. Ai doesn't think so.Most foods disgust him - potatoes look black, for example.His wife's skin seemed to him the color of a white rat, and he couldn't stand making love to her.Even if he closes his eyes it doesn't help.His highly developed visual imagination has also become color blind.Even his dreams had lost their color. The gray scale felt by Mr. Ai is compressed, especially under strong light.Therefore he cannot discern subtle tonal gradations.It responds equally to all wavelengths of light, with an additional peak of sensitivity in the short-wavelength ("blue") region of the spectrum.This can explain why he can't see the white clouds in the blue sky.He also had trouble recognizing faces, unless they were in close proximity.But his vision was sharpened because the protruding objects were in striking contrast, so sharp, almost in silhouette.He is extremely sensitive to movement."I could see a worm wriggling about a block away," he reported. At night he claimed to be able to see so clearly that he could read a license plate four blocks away.Thus, in his own words, he became a "night crawler".When wandering at night, his vision is no worse than others.

Mr. Ai's loss of color awareness had little effect on other aspects of his vision, the loss merely altering his sensitivity to shades of gray and making him more aware of movement.The damage is apparently bilateral, since both sides of the field of vision are affected (in some cases achromatopsia affects only one side).This impairment is also a delayed process, as complete loss of color awareness develops within two days.If it weren't for his enhanced response to short-wavelength light (blue light), it would seem that the P system is defective (the P system is more sensitive to shape and color), while most visual tasks are performed by the unimpaired M system (which is more sensitive to motion. more sensitive, see Chapter 10) to complete.

Mr. Ai's brain was also scanned by MR1 and CAT (although the latter was at a coarser scale), but no damage was found, so it is not clear whether the damage is in the cortex.Regardless, the foregoing suggests that achromatopsia usually involves damage to a relatively high level of cortex in the human visual system (ventral median portion of the occipital lobe). Another type of injury that can be astonishingly flawed is prosopagnosia.A British prime minister in the last century encountered this difficulty.He didn't even recognize the face of his own eldest son.Prosopagnosia comes in many different forms, probably because the nature of the brain damage varies from patient to patient, and the problem is often not that they don't recognize a face, but that they don't recognize whose face it is, I don't know if it's his wife's face, his child's face, or an old friend's face.Often the patient does not recognize his own face in the photograph.He couldn't even recognize himself in the mirror, although he knew it must be his face, because when he blinked the mirror image blinked too.He can often recognize his wife by her voice or the way she walks, but not just by looking at her face.

Unless the damage is severe, he can describe the features of a face (such as eyes, nose, mouth, etc.) and their relative positions.In addition, his visual scanning mechanism is also normal.In some cases, he was able to distinguish between these different faces when asked to identify certain unfamiliar photographs taken under different lighting conditions.But even if he knew them well, he couldn't tell whose face was in which photo. People with bilateral achromatopsia often also suffer from prosopagnosia.But it should be kept in mind that there is no reason to think that damage (often caused by a stroke) affects only a single cortical area.In fact, prosopagnosia can appear alongside several other deficits. Neurologist Antonio Damasio has made several important contributions to the study of prosopagnosia.The situation was not limited to face recognition difficulties; in one case, a farmer could no longer identify his cattle, although he had previously been able to name each of them.But Damasio's research goes a step further.He and colleagues have shown that in many cases patients are unable to identify individual members of a group of similar objects; for example, a patient may easily recognize a car but be unable to tell whether it is a Ford or a Rolls-Royce · Royce sedan; however he can identify ambulances or fire trucks, probably because they differ significantly from typical automobiles.He could recognize a shirt, but didn't know if it was a dress shirt. Damasio and colleagues also found that although some patients could not distinguish faces, they could identify the meaning of facial expressions and estimate age and gender.People with other prosopagnosias don't have this ability, and these results suggest that recognition of different aspects of faces is done in different parts of the brain. How to accurately describe prosopagnosia and its internal mechanism is still controversial.Damasio stresses that this is not an ordinary memory disorder, as the memory can be triggered through other sensory channels, such as hearing.The precise mechanism in each case remains to be discovered. Psychologist Joseph Zihl and colleagues reported a startling case [5] of a patient who was unconscious of most forms of movement.The patient's lesions were bilateral and located in multiple areas of the cortex.It is not surprising that the patient was in a state of great fright when she was first examined, for she saw persons and objects in one place suddenly appear in another, without her feeling their movement.She was especially frustrated when she wanted to cross the street because a car that was far away would suddenly be very close to her.When she tried to pour the tea into the cup, she saw only the reflection of an arc of frozen liquid.Because she doesn't notice the tea rising in the cup, the tea often overflows.The world she experiences is similar to the dancefloor floors some of us see in disco nightclubs under strobe lights. We also encountered this problem on extremely slow timescales.The hour hand of the clock does not appear to be moving, but when we look at it after a while, it is in another position.We're familiar with the idea that an object can move even if we don't directly feel its motion.But on the usual timescales of everyday life we ​​usually don't have this difficulty.Obviously we must have a special system that detects motion by itself, without having to logically infer it from two different observations separated by time. Careful testing has shown that the patient can detect certain forms of movement, possibly the result of the action of a short-term mechanism that survives a severe impairment, while the more global associations that form about movement have been disrupted.She has a few other defects in her vision, most of which are related to movement.But she could see colors and recognize faces, and she showed no signs of the types of neglect described earlier in this chapter. There are many other kinds of visual deficits caused by brain injuries.In two reported cases, the patients lost their depth perception and saw everything and people as completely flat, so that "since the human body is represented only by outlines, even the fattest people appear to be nothing more than moving cardboard figures ".Other patients recognize the object only when it is viewed from the usual straight-on direction, but not from unconventional angles, such as looking at a pan from directly above. Two British psychologists, Glyn Humphreys and Jane Riddoch, spent five years studying a patient.He had multiple visual deficits, eg, he lost color vision and could not recognize faces [7].They showed that his main visual problem was that when he saw partial features of an object, he could not put them together.Thus, although he could reproduce a map well, pronounce words clearly, and verbally describe things he knew before his stroke fluently, he could not recognize objects for what they were.These cases are important because they show that a person who has lost part of his high-level vision can still have low-level visual awareness.It supports the claim that no single cortical area labels everything we can see. There is one visual defect so marvelous that those who know it doubt its existence.This is Anton's syndrome (Anton's syndrome), or "blindness denial".The patient is clearly blind, but is unaware of this fact [8].When asked to describe the doctor's tie, the patient will say that it is a blue tie with red spots, but in fact the doctor does not wear a tie at all. If you ask the patient further, he will take the initiative to tell you that the lights in the room seem a little dark. At first, this scenario seemed unlikely to be true.The medical diagnosis was hysteria, but that didn't help much.However, consider the following possibility.I often find that when I talk on the phone with someone I've never met in person, I automatically form a rough image of his (or her) appearance in my mind.I once had many long phone conversations with a man who I pictured as being in his fifties, rather thin, and wearing very dark glasses.When he finally came to see me I found he was in his thirties and visibly fatter.I was so surprised by his appearance that I realized that I had imagined him to be something else. I suspect that the blind deniers produced this image.Perhaps due to brain damage these images don't have to compete with normal visual input from the eye.In addition, there may be important functions in normal people's brains that remind them that certain images are wrong, and these patients lost these functions due to damage elsewhere.Whether this explanation is correct remains to be seen, but it at least makes the situation not seem completely incomprehensible. Are there trends in the responses of different cortical areas to injury?Damasio noted that brain lesions in the human temporal region (both sides of the head) that are closer to the back of the head are characterized differently than lesions that are closer to the front [9].Lesions near the posterior temporal lobe (or the occipital lobe behind it, see Fig. 27) are related to conceptual stuff.If the lesion is closer to the front, the impact on concepts becomes progressively smaller until near the hippocampus, where the major loss is related to specific events.Thus, the distinction between conceptual and episodic memory is striking.There may be a gradual shift between areas dealing with objects and events in general and areas dealing with only one of them. Damasio's suggestion is consistent with my description of the function of individual cortical areas.For each cortical area, other (usually lower-level) areas have inputs to its intermediate layers; this cortical area combines the features extracted by these areas to construct new features. For example, when you go up the visual hierarchy, you start in cortical area V1. Area v1 processes fairly simple visual features (such as oriented straight lines).These characteristics appear all the time.Then you get to areas that process less frequently occurring complex objects like faces, up to the cortex that connects to the hippocampus (top of Figure 52), where the combined signals detected (both visual and otherwise) mostly correspond to unique events . So far, our previous discussion has sufficed to establish two general points: These damaged visual systems work in a strange and mysterious way, and its behavior is consistent with what scientists have discovered about how macaque monkeys and our own visual systems are connected. Behavior is not contradictory. Our task, however, is to understand visual consciousness.It is the result of the many complex processes necessary to construct a visual imagery.Are there certain forms of brain injury that have a more direct effect on consciousness itself?It has been found that there are indeed some. The first is often referred to as "split-brain".In its most radical form, the corpus callosum (a large bundle of nerve fibers that connects cortical areas on both sides of the brain) and a small bundle of fibers called the "anterior commissure" are completely removed.This surgical procedure is performed in patients with epilepsy to alleviate their symptoms after conventional treatment has failed.Other forms of brain injury also cause the patient to lose the corpus callosum, but at this time there is usually additional damage elsewhere in the brain, so the results cannot be interpreted as straightforwardly as this.There are also some people born without the corpus callosum, but the brain often compensates for the early deficit to some degree during development, so the results are not as pronounced as in the case of surgery. The history of this subject is so curious that it deserves a brief account.A prominent American neurosurgeon reported in 1936 that the corpus callosum was removed without symptoms. In the mid-1950s, another expert, reviewing the experimental results, wrote: "The corpus callosum can hardly be linked to psychological function." Karl Lashley (Karl Lashley, a brilliant and influential American neuroscientist. Weird Yes, he's almost always wrong) went even further, joking that the only function of the corpus callosum is to keep the two hemispheres from collapsing together. (The corpus callosum appears hard, hence the name. Callus means hard skin.) We now know that these ideas were completely false.This error is partly due to incomplete resection of the corpus callosum, but mainly due to insensitive or inappropriate detection methods. The work of Roger Sperry and colleagues in the 1950s and 1960s brought about a marked improvement.For this work Sperry won the 1981 Nobel Prize.Through carefully designed experiments, they clearly showed that when a cat or monkey's brain is divided in half, it can be taught one hemisphere to learn one response and the other to learn another, or even to Totally contradictory responses to the same situation.As Sperry puts it, "It's as if the animal had two separate brains."① Why is this so?For most right-handed people, only the left hemisphere can speak or communicate by writing.The same is true for most abilities related to language, although the right hemisphere understands spoken language to a very limited extent and may also process the phonology of speech.When the corpus callosum is removed, the left hemisphere can only see the right half of the visual field, and the right hemisphere can only see the left half.Each hand is controlled primarily by the opposite hemisphere, but the ipsilateral hemisphere can control the hand or arm for some coarser movements.Speech can be heard in each hemisphere, except in exceptional cases. Patients who have just undergone surgery may experience various transient effects.For example, his hands do the exact opposite, buttoning a shirt with one hand and then undoing it with the other.The behavior usually subsides and the patient appears more normal.But closer inspection revealed something more. In the experiments, patients were asked to fixate their gaze on a screen.An image will flash on the screen to the left or right of his gaze point.This ensures that visual information only reaches one of the two hemispheres.There are more elaborate ways to do this now. When a flashing picture reaches the verbal left hemisphere, he can describe it like a normal person.This function is not limited to verbal expressions.The patient is also able to point to objects with the right hand (the right hand is primarily controlled by the left hemisphere) without speaking, on request.He can also identify an object with his right hand without looking at it. However, if the flashes reached the right hemisphere, where language cannot be used, the results were very different.The left hand, mainly controlled by this nonverbal hemisphere, can point to objects and recognize unseen objects by touch, just as the right hand can do.But when the patient was asked why his left hand was behaving in this particular way, he would invent an explanation based on what he could verbally see in the left hemisphere, but not what the right hemisphere saw.The experimenters knew what it was that actually flashed into the speechless hemisphere to produce the behavior, and could see that these interpretations were wrong.This is a good example of "fiction disease". Simply put, it appears that one half of the brain almost completely ignores what the other half sees.Only minimal information sometimes leaks to the opposite side.While flashing a series of photos of a woman's right hemisphere, Michael Gazzaniga added a nude photo.This made the patient blush a little.Her left hemisphere couldn't perceive the content of the pictures, but knew it made her blush, so she said, "Did you show me some funny pictures, doctor?" After a while the patient learned to tell the other The lateral hemisphere provides some cross-cues; for example, the left hand signals in such a way that the verbal hemisphere can recognize the signal.For normal people, the detailed visual awareness of the right hemisphere can be easily transmitted to the left hemisphere, so that it can be described in words. After the corpus callosum is completely removed, this information cannot be transmitted to the language hemisphere.This information cannot be transmitted to the opposite side through various low-level connections in the brain. Note that I haven't touched on any differences between the two halves of the brain other than mentioning that language is usually in the left hemisphere.I don't care whether the right side has some special ability, for example, it is very good at recognizing faces.I also don't have to take into account the extreme view of some people that the left side has "human" properties and the right side is just an automaton.Clearly the right side lacks a well-developed language system and is therefore less "human" in a sense - because language is the only ability that marks a human being.Actually we need to answer the question of whether the right side is higher than the automaton, but I think we should wait a little until we better understand the neural mechanism of consciousness, otherwise we can't answer it very well, let alone the question of free will .The eclectic occupational view emphasizes that, in addition to language, the perceptual and motor abilities of the two sides are not identical, but the general characteristics are consistent. Most brain incisions do not cut the intertectal commissures of the superior colliculi (described in Chapter 10).The brain cannot use this untouched pathway to transmit visual awareness information from one side to the other.So although the superior colliculus is involved in the visual attentional process, it does not appear to be the seat of consciousness. Another striking phenomenon is called "blindsight".Oxford psychologist Larry Wriskrantz has done extensive research in this area.Blindsighted patients can point out and distinguish certain very simple objects, but at the same time deny seeing them. ① Blindsight is usually caused by extensive damage to the primary visual V1 area (striate cortex), in many cases on only one side of the head.In the experiment, a row of small lights was arranged horizontally so that when the patient gazed at one end of these lights, they all fell into the blind spot of the visual field.A light comes on briefly after a warning beep while the patient cannot move their eyes or head.Ask the patient to indicate which light was turned on.The patient usually disputes this, saying that since he cannot see what is there, there is no need for the experiment.After a short persuasion, he will try and "guess".The experiment is repeated multiple times, sometimes with this lamp being turned on, sometimes with another.To the astonishment of the patient, although he denied seeing anything, he was able to pinpoint the lit lamp with considerable accuracy, usually within five or ten degrees. ② Some patients can also distinguish simple shapes, such as Xs and Os, as long as they are large enough.Some people can also identify the orientation and flickering of straight lines.Two patients were claimed to be able to adjust the shape of the hand to match the shape and size of an object about to be touched, while denying seeing the object.In some cases the patient's eyes can track moving streaks, but this task may be performed by other parts of the brain, such as the superior colliculus.The patient's pupils also respond to light intensity because the size of the pupils is not voluntary but controlled by another small brain area. Thus, although the V1 area is severely damaged and the patient vehemently denies noticing these stimuli, the brain can still detect and act on certain fairly simple visual stimuli. The neural pathways involved are still unclear.It was initially suspected that information was transmitted through a part of the "Oldbrain" known as the superior colliculus, but it now appears to be much more than that, as new experiments show that eye cones are involved in blindsight's response to light wavelengths.Their response to different wavelengths is similar to that of normal people, but the light required is brighter.No color-sensitive neurons were found in the superior colliculus, so it would not be the only channel. This problem is complicated because damage to the Vl area of ​​the cortex will eventually lead to massive cell death in the corresponding part of the lateral geniculate body (the relay station of the thalamus), which in turn will kill a large number of retinal P-type ganglion cells, because like hermits, They have no one to talk to.However, some P-type neurons were preserved, like some neurons in the associated area of ​​the lateral geniculate body, probably because they projected to some uninjured sites.There are direct but weak pathways from the lateral geniculate body to cortical areas above area V1, such as area V4.These pathways may remain intact enough to generate motor output (for example, being able to point to objects), but not enough to generate visual awareness (see Libet's work discussed in Chapter 15).There is some suggestive evidence that there are islands of untouched tissue in sites of V1 injury, and that V1 may still play a role in these areas, although this role may be minor or ultimately found to be due to other factors. A full V1 area is necessary for consciousness for many reasons, not just because it normally generates input to higher visual areas.Whatever the reason, the patient does make use of some visual information while denying seeing anything. Another intriguing form of behavior has been found in some prosopagnosia patients.When patients were hooked up to a polygraph and presented with a set of familiar and unfamiliar faces, they were unable to tell which faces were familiar to them, but the polygraph clearly showed that the brain was making this discrimination. I don't know.Here again we have the situation where the brain can respond without being aware of a visual feature. The hippocampus is a part of the brain that is actually not limited to vision, but is associated with a type of memory.It is at the top of Figure 52, marked HC①.Also shown is its connection to a part of the cortex called the "entorhinal cortex" (labeled ER in the diagram).It has fewer layers than most neocortex.Because of its location near the top of the sensory-processing hierarchy, one can't help but suspect that this is finally the true seat of visual (and other) consciousness.It receives input from and projects back to many higher cortical areas.This complex one-way pathway is re-entrant - that is, it returns very close to the starting point - which may also imply that it is the seat of consciousness, since the brain may use this pathway to reflect itself . This hypothesis seems attractive, but has been strongly contradicted by experimental evidence.Damage to the hippocampus can be caused by a viral herpetic encephalitis infection, which causes considerable but sometimes limited damage.It appears that the virus tends to attack the hippocampus and its associated cortex.The boundaries of the injury will be clear.Because the lesions can be located on scans and do not progress, patients can be reexamined years after the severe stage of infection has passed. If you happen to meet someone who's lost both hippocampi and adjacent areas of cortex, you don't immediately realize there's something wrong with him.You will be amazed after watching such a tape.It tells about a person who can talk, smile, drink coffee, play chess, etc.He pretty much only has one problem, which is that he can't remember any events that happened about a minute ago.He shakes your hand during introductions, repeats your name, and strikes up a conversation.But if you temporarily leave the room and return after a few minutes, he will deny ever seeing you.His motor skills are preserved and he can learn new techniques, often for years or more, although he can't remember when he learned them.His memory for categorization was intact, but his memory for new objects lasted only a very short time before it was almost completely lost.He also had trouble recalling events that occurred before his brain injury.In short, he knew what the word breakfast meant and how to eat it, but he had hardly any recollection of what he had eaten.If you ask him, he'll probably tell you he doesn't remember, or gossip and describe what he thinks he might have eaten. Although in a sense he lost all human "consciousness", his short-term visual awareness does not appear to have changed.If it's damaged, it's only in a subtle way that experiments haven't yet revealed.The hippocampus and its closely related cortical regions are therefore not required for visual awareness.However, information flowing in and out often has the potential to reach the conscious state, so it is reasonable to pay attention to the neural areas and pathways in it.This may help to find out the location of consciousness in the brain. Research on brain injury can yield results that cannot be achieved otherwise.Unfortunately, due to the complex nature of most injuries, this knowledge is often fraught with ambiguity.Despite these limitations, in the smooth case the message is unambiguous.The results of brain damage can at least provide hints about the workings of the brain, which can be detected in humans or animals by other methods.In some cases, it confirmed that some of the results obtained in monkeys were also valid in humans. ①These results in animals led to a more careful examination of split-brain patients.This work was notably directed by Sperry, Joseph Bogen. Michael Gazzaniga, Eran, Dahlia Zaldel, and their colleagues carried out. ①A great deal of parallel work has been done on monkeys, but I do not intend to describe them here. ② In fact, this result met doubts.One objection, for example, is that this behavior is caused by the eye scattering light to other locations on the retina corresponding to the patient's visible field of view.But that doesn't seem to be the case, especially now that it's been shown that light shining into the blind spot can't have this effect. (Recall that there are no photoreceptors in the blind spot and therefore do not respond to light. On the other hand, the photoreceptors of blindsighted patients are intact and detect signals. It is the visual cortex that is initially damaged.) Further experiments have answered With all these objections, there is now little doubt that blindsight is a real phenomenon. ① If all the output of a neuron goes only to the dead neuron, it tends to die itself too.