Mental Retardation


Mental retardation (intellectual disability) is a disorder violating the process of development of a person’s intelligence and leading to social seclusion due to the lack of adaptive behavior. Despite its similarities with many other mental disorders, it has a set of features that allow distinguishing it from them. In particular, mental retardation manifests itself at very early age. It always occurs as a result of an organic diffuse damage to the cerebral cortex, which has severe and irreversible consequences. In addition, this disorder does not progress in the course of time. In accordance with the international classification, there are four levels of mental retardation (profound, severe, moderate, and mild), which are distinguished by the overall level of intellectual development (IQ), motor skills, perception, attention, vocabulary, and the ability to operate with generalized and abstract terms, as well as to analyze and synthesize the information. Depending on the person’s level of mental retardation, it is possible to define the set of skills he/she will be able to master, as well as select a training and education program for him/her. Thus, a comprehensive knowledge of this mental disorder is important as the correctness of such a diagnosis may determine the fate of many people that suffer from it.


The term mental retardation is always perceived as something negative. However, the knowledge of most people about this disorder is mostly based on the popular movies and TV shows, where reality is often distorted for the sake of entertainment. Still, one does not often see patients with severe mental retardation as they are usually isolated from the society (although in Europe and the United States these people are integrated into society and can be met in everyday life) (Baum & Lynggaard, 2006). As a result, many encounter mentally retarded people without knowing it, because it is often difficult to distinguish them from healthy ones. Nevertheless, the lack of knowledge of this disorder may result in the problems and conflicts while communicating with such people, as their perception and way of thinking are different from those of an average person. This knowledge is also important for psychiatrists as the correctness and clarity of the definition of mental retardation may determine the fate of many people that suffer from it. Therefore, the following work is dedicated to the study of mental retardation, namely its definition, mechanism of development, signs, and levels.

The Definition and Signs of Mental Retardation

Mental retardation, also known as intellectual disability (MR/ID), is a delayed or incomplete development of the mind, manifesting in an underdeveloped intelligence (an IQ level below 70) and leading to social seclusion due to the lack of adaptive behavior. It is either congenital or acquired at an early age. This pronounced irreversible systemic disorder of cognitive activity occurs as a result of organic diffuse damage of the brain.

In this definition, MR/ID has the three following signs (Baum & Lynggaard, 2006):
  1. An organic diffuse damage to the cerebral cortex;
  2. A systemic intellectual disability;
  3. The severity and irreversibility of the disorder.
The absence of even one of these signs indicates the presence of some other mental disorder, namely (Baum & Lynggaard, 2006):
  • The underdevelopment of mental activity in the absence of organic damage to the cerebral cortex is a sign of pedagogical neglect, which can be corrected;
  • A local brain damage can cause loss or disorder of some mental functions (impaired hearing, speech, spatial gnosis, and visual perception), but the overall level of intelligence remains unchanged, and it is possible to compensate the defect;
  • A functional damage of brain structures can lead to flaws in the cognitive activity of a temporary nature, which can be eliminated by appropriate treatment;
  • An inconspicuous intellectual impairment limits the ability to master complex cognitive activities, but does not affect the process of independent social adaptation of an individual;
  • The organic brain damage does not necessarily cause cognitive impairment and may lead to disorders of emotional and volitional spheres, as well as disharmonic development.

Thus, MR/ID occurs as a result of organic brain damage in the prenatal or natal period, as well as in the early years of life and is manifested in the total mental underdevelopment. It should be noted that MR/ID is determined not by etiological factors (i.e. the driving forces of the disorder), but their early influence on the brain. Thus, a wide array of hereditary and congenital hazards, as well as those acquired in the prenatal and early postnatal periods, determine the overall mental underdevelopment. Clinical manifestations of mental retardation are independent of its cause in contrast to dementia (which is often confused with MR/ID), when the structure of the defect is determined by certain etiologies. For example, pathogenesis and psychological characteristics of children with traumatic dementia and that, which has emerged as a result of the brain disease, are significantly different, whereas mental retardation always has the same symptoms (Baum & Lynggaard, 2006).

It is common knowledge that the brain of a newborn baby has yet to be formed. Its development, namely the establishment of connections between neurons of the cortex and myelination of nerve fibers are carried out parallel with the mental development of an individual and depend on the experiences of the child. As a result of a detrimental effect on the cerebral cortex in the early period of its development, the neurons either do not grow or become blocked and cannot fully perform their functions, which complicates the process of establishing connections between them. During MR/ID, the neurodynamics is characterized by a weakened obturator function of the cerebral cortex, unstable neural connections, inertia and weakness of the nervous processes, lack of the internal inhibition, excessive excitation, and difficulties in the performance of complex conditioned reflexes. Therefore, the child’s mental development is carried out on the anomalous basis. The early cerebral cortex damage results in a more expressive underdevelopment of functions that have a longer ripening period. In turn, it determines the hierarchy, at which the regulatory system and the highest level of the organization of any mental function become primarily affected by the disorder (Baum & Lynggaard, 2006).

It should be noted that mental retardation is a disorder of a residual nature, i.e. it does not progress with time. This fact, together with the relative preservation of motivational, emotional and volitional spheres of personality, purposeful activities, and the lack of psychotic disorders, provides an opportunity of satisfactory development dynamics and efficient pedagogical influence (Baum & Lynggaard, 2006).

In general, there are the following basic features of MR/ID:
  • The presence of intellectual defect, which is combined with impaired motor skills, perception, memory, attention, emotional sphere, and arbitrary behavior (Baum & Lynggaard, 2006);
  • The totality of mental disorders, i.e. the underdevelopment of all the neuropsychiatric features and violation of mobility of mental processes (Baum & Lynggaard, 2006);
  • A hierarchy of the intellectual defect, i.e. the overwhelming absence of the abstract forms of thinking on the background of the underdevelopment of nervous and mental processes. It is reflected in the course of all the mental processes, such as perception, memory, and attention. MR/ID mostly impairs all the functions of abstraction and generalization, the ability to compare and understand the metaphorical meaning of words. The components of mental activity associated with the analytic and synthetic activity of the brain are also damaged. Therefore, the higher mental functions, which are formed later and characterized by arbitrariness, are less developed than the elementary ones. In particular, in the emotional and volitional spheres, it is manifested in the underdevelopment of complex emotions and arbitrary behavior (Baum & Lynggaard, 2006).

Thus, MR/ID is characterized by non-progressiveness, totality, and the hierarchy of the disorders of mental development on the background of preservation of the personal aspect of cognitive activity, which allows distinguishing it from other similar disabilities, namely dementia.

The Levels of Mental Retardation

According to the current international classification of mental illnesses, there are four levels of mental retardation, which correspond to the indicators of the level of mental development (commonly known as IQ):
  1. Profound MR/ID (IQ is lower than 20) is the most expressive degree of mental retardation, which occurs as a result of damage to the depths of the cerebral cortex and subcortical part of the brain, leading to violation of physical and mental development. In this case, there are significant gaps in the formation of motor skills. In particular, among the people diagnosed with profound MR/ID, there are those who cannot walk or even sit. They are not able to worry about meeting their basic needs, and, therefore, require constant care. Most of them lack the self-help skills are completely that still can be acquired in their most elementary form as a result of a long-term special education. On the basis of the ability to form simple conditioned reflexes, some children with profound MR/ID can develop primitive visual-active thinking, understanding of primitive verbal instructions, and situational memory at the level of recognition. At the same time, on the background of the profound intellectual disability, the patients may possess striking mechanical memory as well as highly developed musical and other abilities (Switzky, 2004).
  2. Severe MR/ID (IQ ranges from 20 to 34) is accompanied with the underdevelopment of motor skills, which is manifested in low coordination, accuracy, and the rate of voluntary movements. Namely, the patients cannot run and jump, finding it difficult to switch from one movement to another. Severe violation of attention results in its instability and lack of its active form. In particular, children respond only to bright objects. However, even such a reaction is very brief. Perception is superficial and non-specific. As a result, there is observed an inability to analyze or compare. The memory of children with severe mental retardation is characterized by very low volume and significant distortion during the recreation of the memorized information. Their thinking is specific, chaotic, and haphazard. Sometimes, these children can carry out basic generalization, namely combine the objects into groups (furniture, clothing, animals). However, they cannot operate with abstract concepts to convey the content of even the simplest story pictures. The typical personality traits of children with severe MR/ID are the lack of motivation or a chaotic reaction to all the surrounding stimuli that attract their attention (Switzky, 2004).
  3. Moderate MR/ID (ІQ ranges from 35 to 49) is characterized by slow development of motor skills. The motions are often clumsy. Thus, people with moderate MR/ID cannot perform actions that require precision, arbitrary regulation, and coordinated movements. Their vocabulary is very limited and lacks general and abstract terms. The attention involuntary depends on the physical characteristics of the external objects and motivation. Their perceptual activity is characterized by randomness, and the capacity of memory is significantly narrowed. However, in adolescence, the memory is usually improved (Switzky, 2004). Children with moderate MR/ID can develop primitive visual-active and creative thinking, which, however, is characterized by specificity, as well as the lack of consistency and flexibility. They can be taught basic self-service skills, but the independent living is impossible for them. However, people with moderate MR/ID can be physically active, establish contacts, and participate in basic social classes organized by teachers. In adulthood, they are capable of simple practical work under the supervision (Foreman, 2009).
  4. Mild MR/ID (IQ ranges from 50 to 69) is the lowest degree of mental retardation, characterized by a lag in the development of motor skills. However, it can be identified only by means of a special survey. The children with Mild MR/ID have a relatively developed speech. They can learn to correctly pronounce the words, build sentences, and use general and abstract terms. The can also be taught to read and write, although with a large number of grammatical, stylistic, and logical errors. The volume of memory is narrowed, being further limited with inability to use the methods of mnemonics, and subordinate memory and thinking. People with mild MR/ID can develop voluntary attention, which, however, will be inferior in its properties to the attention of the child with normal mental and physical development. Under the conditions of the special studies, they can develop basic verbal and logical thinking. People with mild MR/ID are capable of purposeful activities. However, under the influence of immediate needs, they are prone to impulsive and reckless behavior. Children with mild MR/ID can study at the special auxiliary schools with the focus on labor studies, social and domestic orientation (Foreman, 2009).


Thus, mental retardation is an irreversible disorder of mental, primarily intellectual, development. Leading disorder in clinical and psychological picture of mental retardation is severe lack of cognitive activity. Mental disorders have a complex structure: they are diverse in their manifestations, mechanisms, and resistance and require a differentiated approach to their analysis. The education and training of mentally retarded people in special schools is a humane and noble approach. Without it, they could become helpless and useless members of the society. Training gives them the necessary knowledge and skills that help to overcome or compensate for impaired mental functions, further stimulating their mental development, and helping them to become full-fledged members of the family and society.

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