As Ch. Darwin (1859, 1907) wrote, it is necessary to study expressive movements of mentally sick people. In his opinion, phylogenetically expressive movements were developed in different ways. Some of them were initially useful to the body, but had a special, different meaning; other movements were kept according to the principle of antithesis (e.g., the dog's readiness to attack when it sees a stranger and a down-grade position of its torso when it recognised its owner in the stranger). Special movements depend on the constitution type of nervous system (e.g., trembling after fright). According to V.M. Bekhterev (1918), the principle of the utility of movements has the greatest phylogenetic meaning.
DISORDERS OF PSYCHOMOTOR SYSTEMS
According to M.O. Gurevich (1949), the psychomotor system is defined as a combination of consciously controlled motor actions under one's volitional control. Symptoms of psychomotor disorders can be expressed in difficulty, retardation of performance of motor acts (hypokinesia), in complete immobility (akinesia), and can also be characterised by directly opposed manifestations - motor agitation or inadequate movements and actions.
The most typical example of pathology of effector volitional activity is catatonic disorders, which are diverse in their form. Catatonic movement disorders differ essentially from phenomenologically similar organic movement disorders, which are permanent, have a certain pathological cerebral substrate with corresponding cerebral cortex motor areas affection.
K. Kahlbaum (1874) was the first to have summarised observations of patients with catatonia in his classic work "Catatonia, or Psychosis of Tension". The description of disease given by Kahlbaum is clinically reliable and is valid at present: uniformity of posture, stereotyped movements, negativism; epileptiform seizures are described by him so brightly, and precisely that further observers added almost nothing.