Alcoholic Korsakov psychosis: causes and consequences

What is Korsakoff's syndrome

Few people understand what Korsakoff syndrome is. The condition, which includes a number of symptoms, is a mental disorder accompanied by various types of amnesia - memory loss. For this reason, the pathology is also called amnestic syndrome. A feature of the disease is the replacement of past memories with false ones that surfaced in a dream, during delirium, or hallucinations.

Memory loss for a short time - a person suffering from amnesia is not able to remember recently occurring events, but can perfectly, down to the smallest detail, retell what happened many years ago.

Korsakoff's syndrome often involves a person's disorientation in both space and time.

The disease was first described by Dr. Sergei Korsakov in 1887. The symptoms have been proven to be related to disorders of the peripheral nervous system, and not to moral problems.

Korsakov's syndrome has a number of names: amnestic, amnestic-paramnestic, Korsakov's psychosis, amnestic syndrome of a patient with alcoholism, Gaines-Wernicke syndrome in encephalopathy. It is worth understanding that the term “syndrome” includes a series, that is, a complex of symptoms that accompany a certain disease.

Korsakoff psychosis is determined by the presence of certain symptoms manifested through the following types of pathologies:

1. Amnestic disorders:

• Fixation amnesia - the patient cannot remember a moment that happened 10-15 minutes ago.
• Amnestic disorientation - a person cannot navigate the area and time. The situation is related to the factor of inability to remember recent events.
• Retrograde - loss of information about events that occurred before the development of Korsakoff's syndrome.
• Anterograde - there is no ability to remember everything that happened after the development of the disease.

2. Paramnestic disorders:

• Confabulation - the patient talks about events that did not happen.
• Pseudo-reminiscence - events told to patients are displaced in time space.
• Cryptomnesia – a person suffering from memory loss cannot remember where the memories and information that surfaced in his consciousness came from.

History of Korsakov's psychosis

Korsakov's psychosis is a disease of chronic alcoholics, which is associated with damage and manifests itself as a mental disorder that occurs mainly in the third stage of alcoholism.

The disorder got its name from the name of the Russian psychiatrist who described it in 1877. Sergei Korsakov proved that alcoholism is a disease that needs to be fought. He found that this psychological condition is preceded by alcoholic encephalopathy. Initially, the doctor called it “polyneuretic psychosis,” since polyneuritis is the destruction of the peripheral nervous system.

Causes of Korsakov's syndrome

The main factor due to which the disease develops is a deficiency of vitamin B1 in the human body. The following causes of Korsakoff syndrome:

• brain hypoxia;
• eating disorders, poor diets;
• tumors;
• brain surgery for the treatment of epilepsy;
• head injuries, concussion;
• limbic encephalitis, herpetic;
• senile dementia;
• diabetes;
• regular and excessive consumption of alcohol.

Experts also pay attention to such factors as insufficiency of vitamins and microelements during pregnancy, bulimia, Beri-Beri disease, frequent and repeated vomiting.

As for alcoholism, alcohol causes a lack of thiamine, which is involved in the absorption of an important element. And in the absence of treatment for a long time, a person risks acquiring not only physiological and irreversible damage to internal organs, but also Korsakoff’s syndrome.

So, a lack of vitamin B arises, and for still unexplored reasons, processes of metabolic disorders develop, necrosis of tissues, cells in the brain structure, demyelination, vascular proliferation, microhemorrhage, etc. As a result, a person develops Wernicke encephalopathy, gait becomes upset, and delirium tremens and other equally dangerous mental disorders. Korsakov's syndrome, according to doctors, occurs in at least 85% of people suffering from alcoholism.

Diagnosis and difference from other ailments

Here is what Dr. Oliver Sacks wrote in the mentioned book about a case of unfavorable development of the disease: “...Mr. Thompson’s memory is completely destroyed, but the true essence of the catastrophe that befell him lies elsewhere. Along with his memory, the fundamental ability to experience was lost, and it was in this sense that he lost his soul.”

The diagnosis is made based on signs indicating vitamin B1 deficiency. To do this, a blood test is taken, as well as a liver function test. Diagnosis also includes a general examination, after which intravenous administration of vitamin B1 is prescribed. But still, the main symptom of Korsakoff's syndrome when making a diagnosis is memory problems against the background of chronic alcoholism. To identify them, medical psychologists or psychiatrists use a word memory test, as well as other psychological tests for mechanical and voluntary memorization.

Pathomorphologically (at autopsy), damage to the deep parts of the brain is determined: a structural deficit in the brainstem and diencephalic regions, as well as bilateral damage to at least one limbic structure.

Since Korsakoff's disease occurs not only with alcohol consumption, it should be distinguished from other alcohol-induced syndromes of damage to the nervous system (dementia, delirium), as well as from amnestic mental disorders not caused by alcohol intake (memory impairment in dementia or delirium, in organic lesions or diseases non-alcoholic brain; dissociative amnesia; memory dysfunction in depressive disorders).

Symptoms of Korsakov's syndrome

Recognizing the disease is not difficult if you pay attention to the symptoms of Korsakoff syndrome. Memory impairment, disorientation in space and time, inability to recognize family and friends - this is not the whole picture. Symptoms also include:

• dysphoria;
• attacks of anger, irritability;
• mood swings;
• anxiety, excessive worry;
• panic attacks;
• impaired concentration in actions and conversations.

With Korsakoff syndrome, the body is severely depleted, strength dries up, and weakness accompanies it. At the same time, the alcoholic categorically denies his addiction and the resulting mental disorders. But without the help of a qualified doctor and the support of loved ones, it is impossible to recover.

As described earlier, confabulation is possible, in which the patient replaces events with false ones. And one cannot say that he is composing; in fact, it could have seemed, been imagined, or dreamed of.

What is especially dangerous is that in advanced cases, one syndrome can overlap another. Such dynamics lead to deterioration of treatment, but experts note cases in which cognitive, motivational, affective, motor, etc. were restored.

Diagnosis of mental disorder

Diagnosing Korsakoff psychosis is quite simple, judging by the symptoms. It is better to examine such patients and discuss treatment tactics in the presence of relatives. When making a diagnosis, it is very important to exclude other causes of the disease. If the disease did not occur through alcohol addiction, then the treatment will be different.

To make a diagnosis, first of all, the patient must be completely examined, blood taken, and in addition to general tests, the thiamine level must be examined. It is also necessary to check the functioning of the liver (do an enzyme test), possible disturbances in coordination during movement, and the correct functioning of the brain. Specialists are required to conduct tests that can help determine memory disorders and the ability to process information, as well as determine the level of memorization of new information. Tests are carried out on the oldest area of ​​the brain - the limbic system. It is responsible for converting short-term memory into long-term memory. If during the tests damage to at least one part of the system was detected, then a diagnosis can be made.

Often, patients do not realize their disorder and, accordingly, do not seek help themselves. Therefore, it is very important to do all the necessary examinations and study the clinical picture in detail in order to prescribe the most effective treatment.

Treatment of Korsakov's syndrome

The course and duration depend on a number of factors, and primarily on the severity of the disease. But you need to remember when treating Korsakov's syndrome - it is persistent. In rare cases, there has been a sudden disappearance of symptoms, which was facilitated by stress, a strong blow to the head, etc. But if the amnestic state was developed as a result of alcohol abuse, then the symptoms arise quickly, layer on top of each other, and it is quite difficult to get rid of them. Sometimes this takes decades, and it is not always possible to fully recover.

The age of the patient is also an important factor. With the development of Korsakoff's syndrome in older people, the prognosis is more unfavorable. This is due to inhibition of human brain activity, general health, and concomitant age-related pathologies of a physiological, mental and psychological nature.

Before treatment, it is mandatory to diagnose the disease, in which an experienced specialist differentiates the symptoms from other pathologies. After diagnosis, the patient is registered. The therapy is complex and aimed at specific symptoms:

• To restore thinking abilities and memory, nootropic substances, vitamin and mineral complexes are prescribed. Thiamine, vitamin B1, is injected separately intramuscularly.
• The patient is prescribed a special diet, high in protein and capable of cleansing the body of toxins.
• To eliminate mental disorders, excessive restlessness, anxiety, antipsychotics, sedatives and sedatives are used.

It is important that the patient completely abstains from drinking any alcoholic beverages – light and strong. Without this there will be no positive result.

Treatment involves detoxifying the body by administering special medications. To avoid relapse, the psychotherapist, in turn, conducts sessions and consultations with the patient to adapt to society.

Risks and forecasts

It is almost impossible to completely get rid of a disease such as Korsakoff syndrome, since brain damage is often irreversible. But with timely treatment, it is possible to stop the development of the disease, as well as significantly improve the patient’s condition.

Recently, the number of patients with Korsakoff's syndrome has decreased markedly, since thiamine is used in the treatment of alcoholism at all its stages. As a result, it is possible to prevent the development of vitamin B1 deficiency, which is the main cause of amnestic syndrome.

In addition to people leading an antisocial lifestyle and abusing alcohol, people who may be exposed to the following factors are also at risk:

• treatment of cancer using chemotherapy;
• dialysis;
• radical dietary restrictions caused by the desire to lose weight or religious beliefs;
• advanced age;
• genetic predisposition.

Since the disease is based on a certain pattern of behavior, for example, alcoholism or poor nutrition, Korsakoff's syndrome is highly preventable. First of all, it is necessary to limit the consumption of alcoholic beverages, as well as introduce foods containing B vitamins into the diet. The latter is important for all people, since thiamine is necessary for vital processes, but it is not synthesized in the body.

Korsakoff syndrome in alcoholism

Unfortunately, no matter what measures are taken to treat society from alcoholism and other addictions, the opposite effect occurs. This is especially true for young people. They started drinking more and that’s a fact! For this reason, a number of life-threatening diseases for the dependent and the public have become “younger,” including Korsakoff syndrome in alcoholism. A harmful passion manifests itself through quite tangible signs:

• cramps and pain in the legs at night;
• sparkles in the eyes darkening;
• impaired speech;
• broken connection between thoughts and actions;
• hand shaking (tremor);
• visual and auditory hallucinations;
• sleep disturbance, nightmares;
• excessive anxiety, unreasonable anger, irritability, panic and fear attacks.

A particular difficulty arises due to the fact that the alcoholic categorically does not want to admit his illness, which is alcoholism. And everyone is sure that they can stop drinking at any moment, at the first desire. Therefore, his relatives and friends play a big role in the treatment of the disease. They must pay attention to the following obvious signs:

• the patient loses interest in previous hobbies;
• behaves inappropriately;
• says strange things;
• constantly confused in thoughts;
• gait becomes unsteady;
• gets confused about time and location;
• does not recognize his relatives - wife, children, parents, etc.

He suffers from frequent depression, screams for no reason, makes scandals out of the blue, and constantly argues. May forget recent events - when to say hello again, re-read the newspaper. This is the behavior of a person suffering from addiction. As a rule, most try to avoid his company. Therefore, it is important to pay attention to the condition of a loved one in time and convince him to undergo treatment. Not only the patient, but also his relatives and friends do not always understand that alcoholism is a serious illness that causes mental disorders. Correct diagnosis and complex therapy with a diet rich in proteins and useful elements will restore the body and psyche. And loved ones should remember that there is no alcohol dependent person who does not dream of getting rid of his harmful addiction. All you need to do is help him take the main step - give up alcohol and seek adequate treatment.

Prevention of Korsakov's psychosis

It is much easier to prevent any disease than to cure it. The most important thing is to lead a healthy lifestyle that excludes the use, and most importantly, the abuse of alcohol.

essential into your diet . It doesn’t hurt to undergo regular medical examinations in order to promptly identify and prevent the development of various diseases.

It is very important to seek medical help in a timely manner, and even better not to abuse alcohol.

results

In all patients, the development of CRS occurred acutely, while in 3 - against the background of acute pancreatitis with severe intoxication, abdominal pain syndrome, repeated vomiting and diarrhea, in 1 - chronic pancreatitis with malabsorption, in 1 - exacerbation of chronic ulcerative colitis, in 1 - after operations for gastric ulcers, in 2 - after surgery on the upper gastrointestinal tract for malignant diseases of the stomach and pancreas. 4 patients had long-term alcohol abuse, but the diagnosis of chronic alcoholism was not established. The demographic and clinical characteristics of the patients are shown in Table. 1.

Table 1. Demographic and clinical characteristics of patients with CRS included in the study Note. GDN - oculomotor disorders, ZR - impaired pupillary reactions, CS - Korsakov's syndrome, MA - cerebellar ataxia, TCS - tonic-clonic seizures; MCI is a moderately severe cognitive disorder.

Neurological and mental disorders arose in patients 24-72 hours after the onset of an acute gastroenterological disorder, manifested by epigastric pain, nausea, repeated vomiting with dysmetabolic disorders and dehydration, or after recovery from surgical anesthesia. CRS debuted with a disturbance of consciousness from somnolence to coma; 4 patients developed delirium, manifested by a disturbance in the level of consciousness, orientation in person, place and time, visual and/or tactile hallucinations. Ataxia, oculomotor disorders, and bulbar syndrome appeared 24-48 hours later. In 1 patient, generalized epileptic tonic-clonic seizures acutely developed, which turned into status epilepticus, resistant to antiepileptic therapy and resulting in death.

During the examination in the acute period of CRS, all patients were found to have disturbances of consciousness: in 5 - a decrease in the level of wakefulness from somnolence to coma, in 3 - psychomotor agitation, in 4 - meningeal syndrome, in 1 - bilateral ptosis, in 4 - impaired pupillary reactions, 3 had oculomotor disorders, 3 had nystagmus, 8 had cerebellar ataxia, 4 had bilateral pyramidal disorders.

A CT scan of the brain in 1 patient with a fatal course of CRS revealed a picture of cerebral edema with the presence of small hyperdense foci in the hemispheres and brain stem. At autopsy, multiple petechial hemorrhages were found in the brain. MRI revealed hyperintense lesions in the hypothalamus, mammillary bodies, brain stem, and cerebellum in 2 patients.

2 patients were treated in the neurological department, the rest were treated in intensive care. Along with treatment of the underlying disease, patients received symptomatic therapy with neuroleptics and bezodiazepines (6), antiepileptic drugs (2), and massive infusion therapy with solutions of colloids and crystalloids. In only 4 patients, the diagnosis of CRS was made in the acute period of the disease and they were prescribed pathogenetic therapy with thiamine; the remaining patients also included vitamin B1 preparations in suboptimal doses in the treatment complex, which may have prevented further development of the disease. Here is one of our observations.

Patient N.

, 23 years old. Diagnosis: Wernicke-Korsakoff encephalopathy, cerebellar ataxia, moderate cognitive impairment, lower mixed paraparesis, severe neurodynamic disorders, subcortical dysarthria.

Concomitant diagnosis: acute destructive pancreatitis, edematous form. Exacerbation of chronic calculous cholecystitis.

Upon admission, complaints of non-systemic dizziness, double vision, general weakness, memory impairment.

Entered the Department of Gastroenterology of the Moscow Regional Research Clinical Institute named after. M.F. Vladimirsky on September 25, 2015 with a diagnosis of chronic biliary pancreatitis in the acute stage. Chronic calculous cholecystitis." Due to the ineffectiveness of conservative therapy, he was transferred to the abdominal surgery department, where on 10/07/15 an operation was performed: diagnostic laparoscopy, cholecystostomy, drainage of the abdominal cavity. In the postoperative period, conservative, antibacterial and symptomatic therapy was carried out.

CT scan of the abdominal organs a week after surgery (10/14/15): showed that the patient has ongoing total-subtotal pancreatic necrosis with infiltrative changes in the surrounding soft tissues and the presence of collectors with dense contents; thickening of the walls of the gallbladder and the likelihood of a small amount of fluid in its bed were noted, as well as infiltrative changes at the level of surgery and the hepatic flexure of the colon.

On 10/21/15, the patient began to experience severe weakness associated with changes in body position, vomiting of eaten food, non-systemic dizziness and headache.

On 10/22/15, the patient was examined by a neurologist, who presumably diagnosed an acute stroke in the vertebrobasilar system and recommended MRI of the brain and MR angiography. But during MRI on 10.22.15, no data on the volumetric process and focal lesions of the brain substance were obtained; only asymmetry of the lumens of the vertebral arteries was revealed (hypoplasia of the left was not excluded).

On 10/28/15, the patient’s condition worsened: the patient was disoriented, drowsy, forgetful, dizziness increased and vision deteriorated. The ophthalmologist noted the presence of phenomena of initial stagnation of the optic discs. The patient was also consulted by an otorhinolaryngologist: no damage to the labyrinth was identified, but it was suggested that there was central vestibular ischemia and hemorrhage in the quadrigeminal region of the midbrain. A dynamic MRI of the brain was recommended.

On October 28, 2015, the patient also underwent a CT scan of the abdominal organs to exclude an increase in the underlying pathology. The preservation of infiltrative changes at the level of the parapancreatic region, porta hepatis, and subhepatic space was noted, although there was a slight decrease in comparison with the previous study. Infiltrative changes in fiber also became less pronounced. A catheter was visible in the lumen of the gallbladder. Otherwise, the condition of the parenchymal organs was without pronounced dynamics. Increased pneumatization of the transverse colon and sigmoid colon is determined. The lumen of the colon contains dense contents. In general, positive dynamics were noted.

On 10/30/15 the patient was consulted by Prof. S.V. Kotov, at the time of examination the patient complained of non-systemic dizziness, double vision and instability when walking. His general condition was assessed as serious. The patient was euphoric, disoriented in place and time, had amnesia for the events of the previous day, and did not control the functions of the pelvic organs. He complied with the doctor’s commands, but quickly became exhausted; answered questions. The level of consciousness was determined to be mildly stunned.

Neurological status: no meningeal syndrome. Cranial nerves: bilateral symmetrical ptosis to the lower third of the pupil. The pupils are symmetrical, reactions to light are lively. Internuclear ophthalmoplegia - when looking to the side, a horizontal medium-wide monocular nystagmus occurs in the extreme abduction in combination with the contralateral eye not reaching the inner corner of the orbit, vertical nystagmus when looking up. The face is symmetrical. Swallowing and breathing are not impaired. Tongue in the midline. Muscle strength in the limbs is diffusely reduced to 4 points. Tendon reflexes are symmetrical, low in the arms, lively in the knees, and absent in the Achilles. The finger-nose test is performed with intention tremor and misses. In the Romberg test it is unstable. No sensory disorders were detected at the time of examination.

Diagnosis: Wernicke-Korsakoff encephalopathy. Ataxia, internuclear ophthalmoplegia, cognitive impairment. Therapy with thiamine 200 mg intravenously twice daily was started.

Lumbar puncture at the time of examination of the patient by a neurologist is contraindicated due to the presence of brainstem symptoms, swelling of the optic discs and the threat of complications.

An MRI of the brain on 10/30/15 revealed damage to the gray matter of the midbrain tegmentum, mammillary bodies, hippocampus and hypothalamus with a slight accumulation of contrast in these areas, characteristic of CRS (Fig. 1).

Rice. 1. MRI of patient N. 10.30.15. 1, 2, 3, 4 — FLAIR, axial sections; 5 — T1-weighted image with gadolinium contrast, sagittal section; 6 — T1-weighted image with gadolinium contrast, coronal section. Symmetrical zones of pathological signal are visible in the tegmentum of the pons (1), midbrain (2), in the hypothalamus region (3), in the medial parts of the visual thalamus (4) on both sides. Accumulation of contrast in the area of ​​the mammillary bodies (5) and periaqueductal gray matter (6).

Metabolic therapy was added to the treatment: a complex of vitamins B1, B6 and B12 (neurobion), choline alfoscerate, alpha-lipoic acid, dexamethasone. The daily infusion volume is 1200 ml.

On 11/03/15 the patient was transferred to the neurological department. His general condition at the time of transfer was moderate.

Respiratory rate 16/min, blood pressure 130/80 mm Hg, pulse 76 beats. per minute, the abdomen is soft, painless, peristalsis is clear, the liver measures 11×8×7 cm, the gallbladder is not palpable, urination is not impaired.

Neurological status: the patient is conscious, there are no meningeal symptoms. The palpebral fissures are symmetrical. Full movement of the eyeballs. The pupils are symmetrical, 6 mm, round. Direct and friendly reactions of the pupils to light are symmetrical and lively. The reaction to convergence with accommodation is reduced. Nystagmus is horizontal, medium-wide, vertical when looking up. Corneal and conjunctival reflexes are symmetrical. The face is symmetrical. There are no vestibular disorders. Phonation and swallowing are not impaired. Reflexes from the soft palate and posterior pharyngeal wall were preserved. Shoulder lift and head rotation are not impaired. Tongue in the midline. The volume of active and passive movements is not limited. Arm muscle strength D=S is characterized by 4 points, leg muscle strength D=S - 3 points proximally and 4 points distally. The tone in the limbs is reduced. Tendon and periosteal reflexes: from the hands D=S, live. Knees and Achilles are missing. Abdominal reflexes are low. There are no pathological reflexes. Performs finger-nose test and heel-knee test with missed hits and dysmetria. No clear sensory disturbances were identified. Mental state: the patient is euphoric, self-oriented, but orientation in place and time is difficult. Memory for current events is reduced. MOCA test - 12 points. There is a positive trend in the state of cognitive functions compared to the results of previous studies.

Consultation with a speech therapist (11.11.15): severe neurodynamic disorders, subcortical dysarthria.

Consultation with an ophthalmologist (11/19/15): the optic discs are pale pink, the borders on the upper and nasal sides are somewhat blurred. The excavation is normal. The retina is without features. Arteries and veins are not changed.

Recommended: diet No. 5; care of a cholecystostomy by a surgeon. Repeated K.T. abdominal cavity after 3 months.

The condition at discharge was satisfactory with positive dynamics during observation: absence of dizziness and diplopia, improvement of cognitive functions, reduction of coordination disorders, increase in strength in the limbs. The clinical picture, however, remained mild cognitive impairment, nystagmus, general weakness and severe weakness in the legs (the patient can move only with assistance).

Observation by a neurologist and an abdominal surgeon is recommended; general regimen, diet No. 5. Considering the impaired absorption of vitamins from the gastrointestinal tract, Neurobion 1 ampoule intramuscularly 2 times a week for a long time was prescribed, choline alfoscerate 0.4 g three times a day orally for 1 month. Exercise therapy, cognitive rehabilitation. Observation by a surgeon. Care for cholecystostomy at the place of residence. CT scan of the abdomen after 3 months.

The patient was examined 3 months after discharge: a general improvement in well-being and regression of neurological disorders were noted, although the patient still had complaints of weakness in the legs and forgetfulness. The neurological status revealed horizontal nystagmus when looking to the sides, bilateral increased tendon reflexes, a slight symmetrical decrease in strength in the legs (up to 4 points), MOCA test - 20 points. It is recommended to continue therapy with Neurobion and metabolic drugs.

Clinical signs

The primary clinical signs of this pathology are aching pain in the lower extremities. Spontaneously occurring disorders . They are accompanied by tingling, burning and crawling sensations. It should be noted that these signs of Korsakov’s psychosis occur long before the full clinical picture appears.

If we talk about the symptoms of Korsakoff psychosis, it should be noted that this pathology is often accompanied by:

• unsteadiness of gait;
• sleep disorders;
• the emergence of causeless feelings of anxiety and fear;
• loss of interest in family and work.

Prolonged binge drinking can contribute to a deterioration in mental state, hallucinations and disturbances of consciousness.

Untimely treatment of this pathology can lead to severe amnesia, the appearance of fictitious memories and problems with time orientation. It is worth noting that the patient may not remember current information, but at the same time he will retain old memories .

Severe disorientation in polyneuritic psychosis is accompanied by the inability of patients to name the current date and even the year. They may forget what they said a few seconds ago and not realize where they are at the current moment in time. Gaps in memories are usually replaced by paramnesias. As a result, patients may confuse fictitious and real events. Situations often arise when a person suffering from Korsakov psychosis believes that an event from the distant past occurred relatively recently.

It should be noted that alcohol dependent people suffering from this pathology are often well aware of their problems and try to hide them from others. They retain the ability to operate with situational phenomena. Moreover, in the first minutes of a conversation, patients can give the impression of intelligent and well-mannered people. However, further acquaintance with these people makes it clear that they have mental disorders. Such conclusions can be drawn on the basis of narrow thinking, stereotyping and the introduction of fictitious facts into the conversation.

This disorder is accompanied by affective and asthenic disorders. Alcohol addicts show lethargy, passivity and fussiness. Demonstration of increased excitability and depressive symptoms is also possible.

Other clinical signs of polyneuritic psychosis include:

• confusion;
• carelessness;
• impaired pupil reaction;
• involuntary oscillatory eye movements;
• gaze paralysis;
• paresis of the limbs;
• violations of coordination of movements.

This pathology is presented in two forms - regressive and stationary. In the first case, the severity of clinical manifestations begins to decrease significantly over time, in the second, the intensity of disturbances in the functioning of the central nervous system does not change.