Allochyria is a neurological disorder in which patients respond to stimuli originating on one side of their body as if they had occurred on the opposite side. A disorder in which visual-perceptive and attentional alterations occur, resulting from lesions in the parietal lobe of the brain.
In this article we explain in more detail what this disorder consists of, what its possible causes are, what types of allochyria exist and what the indicated treatment is.
Allochyria is a neurological disease, described at the end of the 19th century by the Austrian neurologist Heinrich Obersteiner, who causes spatial transpositions in the patient ; That is, the stimuli that are presented on one side of the body (or space) are perceived as if they were presented on the opposite side.
For example, if the person’s right shoulder is touched, they will have the sensation that their left shoulder has been touched (somatosensory allochyria, when touch function is affected). In cases in which auditory or visual function is affected, patients report hearing sounds or voices on the opposite side to which they were actually presented; and with regard to the images or objects perceived, the affected people report the same thing, that they perceive them on the opposite side to the one presented.
Allokyria has also been considered as another sign of spatial hemineglect, an attention disorder characterized by the inability to orient and respond to stimuli or objects located in one of the halves of space (normally, the half opposite the hemisphere). damaged brain). The person would show “indifference” towards everything that happens to them on the left (or right) side of their reality
In the vast majority of disorders in which allokyria occurs, such as neglect syndromes or unilateral inattention syndrome, there is usually a lesion in the right parietal lobe.
There are multiple theories that would explain why a disorder like allochyria occurs. But the most current and widely accepted explanation is Hammond’s theory which states that an almost complete crossing or decussation of sensory fibers occurs within the cerebral gray matter.
This theory concludes that if a lesion occurs on one of the posterior sides, it can reach the center of the corresponding cerebral hemisphere and, therefore, the sensation is referred by this hemisphere to the opposite side of the body
Likewise, if another unilateral lesion is superimposed on a different level than the first, the sensation that was previously diverted to the wrong hemisphere could now be redirected upon encountering another obstacle, and thus could reach the correct hemisphere. The allochyria would occur equally with both unilateral and bilateral lesions, as long as they are asymmetrical
Another theory that would explain the causes of this neurological disorder would be that of Huber, which postulates that the appearance of a new lesion on the opposite side redirects the impulse towards its original destination.
Types of allochyria
Let’s see below how many types of allochyria there are and what each of them consists of.
electromotor allochyria
Electromotor allokyria occurs when there is a crossing of reflexes in muscle stimulation and has been observed on the face, lower extremities, and upper extremities
For example, when a stimulus is presented to the affected side, the opposite facial muscles contract, using a current so weak that not even the healthy part of the face reacts. There have also been cases in which applying pressure on one forearm causes movement in the opposite forearm.
The fact is that an electrical stimulus can manifest its effects in a distant area of the nervous system and that area can be on the same side of the body or on the opposite side, although it is generally more common for it to be the opposite side since the representation of the contralateral extremities of the spinal cord are closer to each other than the ipsilateral extremities ( of the same half of the body).
In this type of allochyria, If the patient is asked to perform a movement with the affected side of the body, he does so with the corresponding part of the opposite side and he has the impression (or the certainty for him) that he has executed it correctly.
2. Reflex allochyria
People who suffer from reflex allokyria respond to stimulation, for example, of the sole of their foot or the inner part of their thigh, evoking the corresponding reflex only on the opposite side.
3. Auditory allochyria
In cases of auditory allochyria, various investigations have been carried out and the observations made have recorded that when holding a tuning fork next to one of the ears, the patient responds with a series of symptoms, including pain and deafness in the opposite ear.
4. Visual allochyria
In visual allokyria, the patient perceives objects located on one side of the visual field on the contralateral side. In one of the studies carried out, the patient who received visual stimulation through his right eye regularly reported that it was his left eye that was stimulated (even though it remained closed).
In another study, one of the patients was presented with a colored object in front of his left eye, and the patient always maintained that the color was perceived with his right eye.
5. Gustatory allochyria
In cases of gustatory allochyria, the investigations carried out consisted of placing a specific substance on the side of the patients’ tongue, with the expected result that all of them reported that they had tasted it with the opposite side of their tongue
Furthermore, when a piece of their tongue was palpated on one side, they also reported that the opposite side to the one that actually corresponded had been touched.
Treatment
Although today there is no validated and effective treatment, this type of neurological disorders, such as allokyria, which affect attention capacity and visual-perceptive abilities, are usually addressed through the implementation of a neuropsychological rehabilitation program This intervention will depend on the etiology of the brain damage, the phase in which the patient is, as well as other variables and other types of deficits that may accompany the disorder.
Non-specific interventions can be carried out, in which the attentional function is treated as a unitary concept, working on aspects such as simple or complex reaction time, Stroop-type tasks, etc.; or, more specific interventions focused on rehabilitating certain attentional components, such as selective attention or arousal.
In cases where there is a neglect or hemineglect syndrome, accompanied by allokyria, techniques such as prism adaptation have been used, which enhances the lateralized reorganization of visual-motor mapping, facilitating perceptual changes in the patient; optokinetic stimulation, which induces changes in the patient’s attentional system through stimuli that capture their attention and redirect it towards the contralesional side; or behavioral techniques, such as positive reinforcement and reward, which exert a great influence and modulate the patient’s attentional processes.
On the other hand, in recent years more and more interventions that use technologies such as virtual reality or cognitive training software Various studies have shown that these techniques can be useful to improve the alertness performance and attentional aspects of patients.
