The weakening of the mind has always been understood as a natural property of aging. The scientific study of this phenomenon began relatively recently. With improving living standards in the developed world has increased the number of older people and thus increased the amount of information about age-related changes of the psyche.

It was not difficult to find a term for intellectual decline. By the XVIII-XIX centuries, a huge number of suitable words had accumulated, one of them — dementia. So in Ancient Rome they called “madness”, what is now in Russian usage is designated with the help of the multi-faceted word “inadequacy”. The medicalization of the term was due to the French encyclopedists. In the” Encyclopedia ” (1765), dementia is a disease, one of the causes of which is old age. If dementia is caused by old age, then it is incurable, because, as we know, old age is not treated.

The “old man’s imbecility” (l’imbécillite de vieillard) was explained by the fact that with age, nerve fibers lose flexibility and as a result, old people become less susceptible to external stimuli, i.e. they process information slowly and with large errors.

At the beginning of the 19th century, dementia was spoken of as a condition typical of an aging body, but also found in young people. For example, it described chronic dementia due to systematic manual labor (one of the curious artifacts in the history of psychiatry).

Clinical manifestations of senile dementia were systematized in the first half of the XIX century, before there were technologies that help to study the brain. The only thing that could be observed at that time were anatomical defects, for example, a decrease in the mass of the brain, which in the middle of the XIX century was considered typical for almost all mental illnesses. Also, in the brain with dementia, signs of atrophy, an increase in the ventricles, and softening of tissues were found.

Until scientists began to compare the features of the brain identified with the help of a microscope, with certain symptoms, dementia was understood as a condition that ends almost all serious diseases, not only mental. Throughout the nineteenth century, there was a screening of symptoms atypical for dementia, and as a result of this work, the main and determining factor in dementia was recognized as a weakening of mental abilities, and not the accompanying delusions, hallucinations and mood disorders in some cases.

At the beginning of the XX century. The behavior of dementia patients is compared with a combination of three phenomena observed in the brain post mortem: vascular dysfunction, the accumulation of some, at that time poorly understood substances in the brain, and cellular changes.

Vascular problems attracted the most attention. Atherosclerosis has long been considered the main cause of decreased intelligence in the elderly. Due to a violation of the blood supply, the brain receives insufficient nutrition, and this affects memory, decision-making speed, etc. Vascular pathology was often explained not only by dementia, but also by many other mental disorders.

For brain research in dementia, the brains of patients with progressive paralysis caused by syphilis were often used. Due to syphilis, the diameter of the vessels decreases. This noticeable anomaly attracted the attention of scientists and determined the direction of research on dementia. Dementia has been linked to impaired blood circulation.

A decisive turn in the history of dementia is associated with the name of the German psychiatrist Alois Alzheimer. In 1907, he published a description of defects in the brain of a patient with symptoms of dementia. The symptoms appeared before she was 50 years old. Alzheimer’s monitored her condition, and after her death found plaques and tangles in her brain. Amyloid plaques are protein deposits between brain cells. Neurofibrillary tangles are clusters of protein in neurons.

Alzheimer did not say that he had discovered a new disease. Plaques and tangles were described before him. He just wanted to point out that senile dementia can occur in middle age, before old age. The name “Alzheimer’s disease” was coined by Kraepelin, which surprised many, including Alzheimer’s. Then, in the 1910s, the new term was seen as redundant in the presence of the well-established concept of “senile dementia”.

There is a version that Kraepelin introduced the concept of “Alzheimer’s disease” to annoy Freud and his students. Look, here is a mental illness that is absolutely dependent on organic defects! Where are your “unconscious conflicts”?

But this is not the case. First, Kraepelin and Freud, despite the unity of the theme, existed in different scientific and literary worlds and did not enter into personal competition. Secondly, Freud never denied that mental disorders have an organic substratum that will one day in the future receive an objective description.

Dementia, in fact, is more difficult to psychologize than many mental disorders. The theory of dementia has been reshaped over the past 100-150 years, but the main thesis has remained the same — dementia develops due to biological changes in the brain.

The current understanding of the nature of these changes does not completely coincide with the ideas of the time of Alois Alzheimer. We must not forget that at the beginning of the XX century, neuroscience was taking only the first steps. Questions about what a neuron is, whether it is separate from other neurons, whether it moves around the brain by absorbing neighboring cells, how to study a neuron, etc. have not yet been resolved. From a modern point of view, Alzheimer and his colleagues did not quite correctly describe “Alzheimer’s disease”. To its specific characteristics identify the things that do not belong to the markers of this disease.

The dynamism and inconstancy of views in psychiatry leads some to think about the scientific failure of this medical specialty. The source of such doubts is in the model of perception of medicine. The evolution of nosology is often described as the work of a garden botanist who comes up with descriptions of new plants. Carl Linnaeus, the author of the famous botanical system “Species Plantarum”, also created a medical classification — “Genera Morborum” (1759). An important idea of Linnaeus — all the species described by him are static and not subject to change. God created the world exactly in the order in which it is revealed to the observer, laying down the principle of hierarchy in nature. A person is able to identify the natural order by studying the external signs of phenomena. These are the principles of Linnean classification: immutability, hierarchy, description by external features.

Linnaeus failed to fully translate these principles into the Genera Morborum. But at least the third principle he considered quite applicable in medicine: “The symptoms of a disease are the leaves of a plant.” In psychiatry, the Linnean approach remains relevant to this day. Diseases, with rare exceptions, are classified according to the clinical picture.

Despite the emergence of alternatives to the Linnean system, the prototype for nosologies by the end of the XIX century. there was still botany. It is significant that Kraepelin in his youth was fond of botany and in particular he liked to understand the classification of plants.

A key component of the Kraepelin system is the belief that disease is a natural phenomenon with boundaries that the scientist must find and define. If you look closely at the ICD and DSM, you can see their botanical prototypes. First, it is assumed that each disease is a separate natural phenomenon. Secondly, the main thing in the classification of diseases is recognized as the observed properties. Third, a hierarchical structure with chapters, sections, codes, used. The botanical metaphor is still the most popular when compiling classifications of diseases.

In reality, diseases in psychiatry have never received an unambiguous description, as clear as drawings for botanical taxonomy. The description of the disease always depends on the historical moment. The features of the descriptive language reflect specific socio-cultural circumstances, so there can be no final and complete description of the disease in psychiatry, at least with the scientific apparatus that is used in the XX-XXI centuries.

In the future, the development of knowledge about dementia will follow the improvement of technology. It is easy to see how in the last century, the development of new research methods raised neuroscience to a higher level. At the initial stage, the main technology was histological analysis. In the 1930s and 1960s, its capabilities grew with the modernization of microscopes.

The second half of the XX century was marked by the development of methods of neuroimaging, which made it possible to create a more accurate systematics of dementia. First, it became clear that dementia is only a syndrome inherent in a variety of heterogeneous diseases of the brain. Secondly, the diagnosis is no longer based only on clinical symptoms, because it is now possible to study what is happening in the patient’s brain from MRI images, and not from his answers to questions that test cognitive functions (for example, knowledge of historical dates). The undeniable “advantage” of dementia is that, unlike most other mental disorders, neuroimaging methods are used by doctors in practice and effectively help in the diagnosis and determination of treatment tactics. Third, the comparison of neuroimaging data with the results of cognitive testing has allowed neuropsychologists and psychiatrists to develop quite effective scales and diagnostic tools for determining the types of dementia [50].

Neuropsychology has made a major conceptual contribution to the development of the science of dementia. Instead of the term “intelligence”, which mainly referred to memory, specialists began to use the broader concept of “cognitive functions”, which includes, in addition to memory, attention, executive functions (planning and control processes), speech, perception (gnosis) and purposeful motor acts (praxis).

Improved understanding of how memory works. In a healthy brain, memory is the process by which information about the world is encoded, stored, and then reproduced. Memory can be short-term and long-term. Short-term memory (or working memory) functions only from a few seconds to a minute and has a certain capacity. Long-term memory stores an almost unlimited amount of information throughout a person’s life. Long-term memory can be divided into explicit (conscious) and implicit (unconscious) memory. Unconscious memory can be divided into conditioned reflex, priming (improved recognition of objects and words) and procedural (cognitive and motor skills). Conscious memory is divided into semantic (facts and general knowledge) and episodic (personal experience). Semantic memory is regulated by the part of the brain responsible for a certain semantic concept, for example, the concept of “tools” is located in the motor zone. Episodic memory is modulated by the entorhinal cortex and the hippocampus. In Alzheimer’s disease, both types of conscious memory are affected: semantic and episodic. As the disease progresses, the unconscious types of memory are also affected.

Since the 1970s, scientists have described different types of dementia, differing in the degree of cognitive impairment and the type of disorders of the brain structure: vascular dementia, dementia with Levi bodies, frontotemporal degeneration. There are many factors that lead to a strong cognitive decline (tumors, metabolic disorders, toxins, etc.). However, Alzheimer’s disease is still a reference example of diseases of this group.

Neuroimaging revealed a characteristic feature of Alzheimer’s disease-brain atrophy, mainly in the median temporal structures (especially in the hippocampus) and parietal lobes. Vascular dementia is indicated by the presence of lesions of the brain substance that occur due to impaired blood flow. In dementia from the group of frontotemporal degenerations, neuroimaging shows atrophy of the frontal regions with the involvement of the temporal lobes. In Alzheimer’s disease, the activity of the enzyme that synthesizes the neurotransmitter acetylcholine is significantly reduced. The effect of three of the four currently registered drugs for the treatment of Alzheimer’s disease is aimed at strengthening the work of this neurotransmitter. The fourth drug (and the most famous — memantine) targets the excessive activity of the neurotransmitter glutamate, which destroys the nerve tissue in the areas of the brain involved in cognitive processes. A decrease in the activity of the dopamine system is observed in dementia with Lewy bodies or dementia due to Parkinson’s disease.

No mental disorder has received such a detailed description and comprehensive explanation as Alzheimer’s disease. Recently, neurologists, rather than psychiatrists, have become increasingly involved in dementia. About the same thing happened with epilepsy, when the famous “falling” completely moved from the field of psychiatry to the field of neurology. This transition became possible after mastering the methods of studying the electrical activity of the brain (EEG) and describing the symptoms of epilepsy in the language of brain science, rather than in the language of psychopathology.

Unfortunately, there is no effective treatment for dementia right now. In the final stage, the disease affects the parts of the brain responsible for basic body functions, such as walking and swallowing. Patients remain bedridden and require round-the-clock care.

Despite numerous scientific developments, accurate methods for diagnosing dementia have also not yet been invented. Neither hippocampal atrophy, nor lack of the neurotransmitter acetylcholine, nor the plaques and glomeruli described by Alois Alzheimer are reliable biological markers of dementia. Currently, a reliable diagnosis of Alzheimer’s disease can only be made after a post-mortem examination of the brain.

The disease begins approximately 15 years before clinical manifestation and proceeds in a prodromal form [51] (moderate cognitive decline). First of all, the entorhinal cortex is affected, which is manifested by a decrease in episodic memory. As the disease progresses and other areas of the cortex become involved in the disease process, other forms of cognitive deficits appear, which eventually leads to dementia.

Recent discoveries in the field of neuroscience bring the solution to the problem of diagnosis closer. The fact is that amyloid plaques (or rather the protein beta-amyloid, which makes up plaques) are not used as a biological marker of Alzheimer’s disease, because they often “stick together”, forming conglomerates of various sizes, sometimes capturing other molecules. Accurate calculation of the number of plaques is often difficult. Even more complex is the fact that plaque levels are not directly related to Alzheimer’s disease. Many adults with an increased number of such plaques do not have problems with mental activity, while others develop Alzheimer’s disease with a small number of plaques.

It turns out that the concentration of amyloid plaques in the blood is not so critical for Alzheimer’s disease. Much more important is how “sticky” the amyloid itself is-it forms small fragments or large conglomerates. By examining the stickiness of amyloid plaques, the researchers were able to identify patients with Alzheimer’s disease with more than 90% accuracy.

In addition, the researchers found a possible correlation between the indicator of “stickiness” and the progression of the disease. Patients with a higher rate of “stickiness” (which corresponds to larger conglomerates of beta-amyloid) tend to have a more pronounced decrease in cognitive function.

If the accuracy and practical applicability of the new technique is confirmed in further, larger studies, we will have a tool for detecting Alzheimer’s disease and tracking the development of the disease. Perhaps this will also affect the creation of a new more effective therapy.

However, the study of Alzheimer’s disease is the focus of most of the monetary and, therefore, scientific resources. Other types of dementia remain in the shadows, although most of them are more aggressive than Alzheimer’s disease. The population of developed countries is rapidly aging, and the decline in the birth rate leads to an age imbalance. WHO officials call dementia, along with mood disorders, the plague of the XXI century. The issue of preventing and effectively treating dementia is not just a matter for scientists and doctors, but for politicians of the highest ranks.