Tactile perception refers to the passive sensation of touch, which together with haptic perception corresponds to the sense of touch. In tactile perception, stimulus molecules from the environment bind to mechanoreceptors and are conducted to the CNS. Neurological diseases disrupt tactile perception.
What is tactile perception?
Tactile perception refers to the passive sensation of touch, which together with haptic perception corresponds to the sense of touch. Under the term tactile sense, haptic and tactile perception are combined. Both types of perception are made possible by the human skin, which is the largest sensory organ in terms of surface area. Through haptics, humans are able to actively touch objects and subjects. At the same time, thanks to tactile perception, he also passively senses when objects or subjects touch him. With these two perceptual qualities, the sense of touch depends on the sensorimotor and somatosensory systems. Tactile perception refers predominantly to the detection of mechanical touch stimuli, as detected mainly by the so-called mechanoreceptors. Tactile perception corresponds to a large extent to exteroception, i.e. the perception of stimuli from the environment. To be distinguished from this is interoception, which allows humans to perceive stimuli from inside the body. In the field of interoception, tactile perception is closely interconnected with the kinesthetic system and thus influences the sense of position and the sense of the position of one’s own body in space. Protopathic sensitivity is the term used to describe all tactile perceptual qualities of gross perception. Epicritic sensitivity refers to the perceptual qualities of fine perception.
Function and task
Tactile perception makes humans feel. For this purpose, there are so-called mechanoreceptors in the human skin. Mechanoreception is the reception of mechanical stimuli from the environment, which are converted into electrical signals in the mechanoreceptors. The mechanoreceptors convert the stimuli into a form that the central nervous system can process. The respective stimuli correspond to a mechanical deformation of the tissue via pressure or stretching. Cation channels are located in the cell membrane of the receptors, which have a closed state when the cell is at rest. The channels are connected to the cytoskeleton of the receptors via microtubules. When stretched or compressed, the microtubules exert traction on the ion channels. In this way, the channels are opened and cations flow in, depolarizing the cell beyond its resting potential. The sensory cells then either generate action potentials at a frequency relative to the receptor potential or they release neurotransmitters relative to the receptor potential. The mechanoreceptors of the sense of touch are either SA receptors, RA receptors, or PC receptors. SA receptors are responsible for pressure sensation and include Merkel cells, Ruffini corpuscles, and pinkus Iggo tactile discs. RA receptors regulate touch sensation and correspond to either Meissner corpuscles, hair follicle sensors, or Krause end pistons. PC receptors control vibration sensation in humans. In this class, Vater-Pacini corpuscles are distinguished from Golgi-Mazzoni corpuscles. Tactile information is carried by nerves to the posterior roots of the spinal ganglion and travels through the structures of the spinal cord to higher centers, such as the thalamus and cerebral cortex. The spinal cord tracts involved, in addition to the funiculus posterior and the tractus spinothalamicus anterior, are primarily the tractus spinothalamicus lateralis, the tractus spinocerebellaris anterior and the tractus spinocerebellaris posterior. Stimuli received by mechanoreceptors do not enter consciousness until they reach the brain. There, sensory integration of different stimuli takes place to give the person an impression of the concrete touch situation. Touch sensation is equipped with its own memory, which helps in the classification and interpretation of touch.
Diseases and complaints
Neurology is primarily responsible for classifying tactile perception disorders. A variety of neurologic diseases can be associated with tactile perception disorders.A tactile-kinesthetic perception disorder, for example, is often the result of congenital defects or a sensory integration disorder. Touching, touching and grasping objects does not help the affected person to recognize objects, so that the patients often make a clumsy impression. Basically, tactile-kinesthetic are distinguished from intermodal or serial perceptual disorders. In tactile hypofunction, tactile sensations are hardly perceived. Often, there is also a partial insensitivity to pain. Patients with tactile hypofunction can train tactile perception with occupational therapy if necessary. Tactile hypersensitivity, on the other hand, usually manifests itself in pain hypersensitivity and can have far-reaching consequences on the behavior of the affected person. Typically, patients react to physical contact with tactile defensiveness up to aggression. In addition to congenital deficits, a tactile perception disorder can also be caused by a lesion in the brain or spinal cord. Such lesions occur, for example, in the autoimmune disease multiple sclerosis, in which the immune system attacks the body’s own nerve tissue and causes inflammation in it. Compression of various cranial nerves or trauma-induced injury to the conducting pathways in the spinal cord can also cause tactile perception disorders. The same is true for tumors, cerebral infarcts, or spinal cord infarcts. Often, tactile perception disorders caused by diseases such as MS, tumor diseases, and other nerve damage are localized and thus affect only a limited part of the body. If, on the other hand, a sensory integration disorder or a congenital deficit of tactile perception is present, the perceptual disorder is usually not of local limitation but affects the entire body. In the case of a tactile perception disorder, MRI usually serves as a basic workup because imaging can clarify any brain and spinal cord lesions. In rare cases, a tactile perception disorder is preceded by damage to the mechanoreceptors. Receptor damage can occur, for example, in the setting of poisoning.
