Barognosia: What is this ability and how does it work?

The human body is a complex machine. He often performs seemingly simple tasks; but which require the coordination of a very precise interlocking of organs, muscles, nerves and ligaments.

The review is particularly relevant in the process which exists from the perception of a stimulus (in any sensory modality) until its arrival at the port of the brain where it is to be processed.

In this article, we will discuss one of these phenomena: barognosis. The truth is, we all use it in our daily activities, but … did you know that?

    What is barognosis?

    The term barognosia can be dissected for a more precise etymological analysis, offering originality and about its meaning. The elements that compose it, “baro” and “gnosia”, come from classical Greek. The first refers to weight or pressure (hence the word barometer to measure this atmospheric condition) and the second refers to the ability to recognize an aspect of reality after its reception through the senses.

    Therefore, barognosis is the ability we humans have to recognize the weight of the objects with which we interact on a daily basis., Independently from other visual or acoustic parameters which could suggest such a property thereof. The use of this ability, included in the sensitive recognition functions, would be done when an object is held with one hand and its weight is calculated as opposed to another.

    In fact, it is one of the essential mechanisms by which the preservation of barognosis in any neurological examination is explored, which is very common, as it is a function that can be affected due to certain pathologies of the nervous system. central or peripheral. . More precisely, objects of similar morphology (balls, for example) are placed in each of the two hands, in order to estimate which of them is the one which has more or less relative weight (by varying the magnitude of this variable to be exhausted in the precision of the measurement).

    It is an ability included in the general category of stereognosies, a mode of perceptual recognition that is related to the sense of touch (haptic), and from which the physical properties of objects are extracted without the need to resort to the rest of the senses. . . Although aspects such as texture or temperature can be included here, with which one obtains a more precise knowledge of the stimulus with which one is interacting, for barognosia is alluded to the evident deep sensitivity of receptors of another nature ( superficial).

    How does barognosis occur?

    Barognosis is possible thanks to a group of mechanoreceptors located in the skin, periosteum, joint capsule, ligaments and menisci; called Pacini corpuscles.

    At the anatomical level, they can be described as nerve endings originating from the cell axon. and the end takes on the appearance of an encapsulated cone, which surrounds the central space. This cone is formed by the succession of about 40 to 80 leaves, made up of connective tissue cells and separated by collagen. They are receptors sensitive to vibrations and tissue deformation.

    It is precisely this same capsule, which deforms when pressure is exerted on the tissues, that informs the nervous system of the magnitude of such an external force so that it can be interpreted in terms of weight. Since their distribution is concentrated in the deep layers of the skin (dermis), as well as in the hypodermis of the fingers and palms (hairless areas), it is usually the parts of the body that are used most frequently to assess preservation of barognosis.

    The detection of alterations in barognosis has an essential clinical component, as they are discriminatory tasks that only the subject can report and for which objective evidence is lacking. However, once this symptom is detected, attention should be paid to a thorough examination of the skin tissue and the central and peripheral nervous system, with the aim of affiliating an organic cause susceptible of intervention.

    How is barognosis assessed?

    Tests to assess barognosis are included in the neurological examination protocol for tactile discrimination, as well as a variety of procedures to assess deep sensitivity. In all cases, the person is asked to close their eyes, in order to minimize interference from any adjuvant perception. After that, you are asked to recognize which object remains on your hand, the intensity of your vibration, or the location of different points when stimulated by pressure.

    In the particular case of the barognosis assessment, the assessor is asked to remain in a seated position while placing the palms of the hands on the thighs (without contact) and positioned upwards. Two pieces with different weights are placed on it, the size and shape being comparable, and you are asked to distinguish which of them has a higher weight. The sweep begins with a major dissonance and the parameter is gradually adjusted until a differential threshold is detected.

    The differential threshold refers to the minimum weight, expressed in grams, from which one is able to recognize a difference between two objects.. So, it is not always a function of absolute commitment, but sometimes there are different degrees in a spectrum from normal assignment to full assignment. It is informative to explore the lower and upper limits, so they should consider all possible alternatives to both limbs.

    It may be useful to further explore sensitivity, stereognosis (recognition of objects such as coins, balls or dice), tactile pressure (not painful), graphesthesia (recognition of signs drawn on the palm of the hand), textures, kinesthesia (movement), proprioception (location of the body in relation to the space around it) and vibrations; because all depend (like weight discrimination) on the dorsal lemniscal-medial pathway.

    If the subject is able to respond appropriately, his barognosis is considered perfectly preserved. Otherwise, the presence of a problem can be inferred at any of the points at which sensitive information passes from receptors to areas of the brain in which it is processed. Detecting the cause is essential for developing the treatment and differential diagnosis of any underlying pathology.

    In the event that the scan detects an alteration limited to a deep sensitivity and with conservation of the surface, a dorsal tabes may be suspected. It would be a degeneration of the spinal cord of the spinal cord, which would disrupt the capacity of sensory discrimination by maintaining the action of nociceptors (widely distributed in the skin) and thermoreceptors (Ruffini’s corpuscles).

    How does barognosis express itself when it is compromised?

    Barognosis is a specific form of recognition that requires the participation of Pacini corpuscles and many other structures located in the nervous system.

    When an object is picked up in the hand, said cells send information to the spinal cord through sensory nerves, ascending afferently to the medulla oblongata and finally to the thalamus (from which much of the sensory information is managed). It is from there that the signal can be processed and interpreted, all mediated by the parietal cortex (which integrates the sensation into a perception).

    Any point in the path can be changed by different circumstances, so that abarognosis would occur. This results in serious difficulty in estimating, recognizing and discriminating the weight of objects located in areas of the body likely to be assessed. Very often this occurs as a result of injury to the parietal cortex, the clinic manifests itself at the contralateral level (if it is in the right hemisphere, the left hand would be affected, for example).

    It is proven that lesions of the postcentral gyrus are most frequently detected in people with abarognosis., Who also exhibit tactile / haptic agnosia (inability to recognize textures and forms), staesthesia (inability to interpret numbers or letters drawn on the affected surface) and atopognosia (difficulty recognizing contact with one or more stimuli on the skin).

    When abarognosis is present without apparent damage to tissues, joints or bones (burns, fractures, etc.), diagnostic procedures must be available, among which neuroimaging techniques play an essential role (especially structural). Thanks to these, it will be possible to complete the initial examination carried out by the specialist in neurology, determining the condition of the spinal cord and the brain regions potentially involved.

    Bibliographical references:

    • Biber, U. Visual stability and the posterior effect of movement: a psychophysical study that reveals a spatial update. PLoS One, 6 (1), e16265.
    • Cássia, M., Meireles, V., Lalone, E., Claro, N., Barbosa, R., Marcolino, AM … Pessoni, F. (2018). Instruments for functional, motor and sensory assessment in nerve repair in adults: systematic review of psychometric properties. Systematic reviews, 7, 175-186.

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