Allochria 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. It is a disorder in which visually perceptive and attentional disturbances occur as a result of 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 alochia exist and what the indicated treatment is.
What is alochia?
Aloqueria is a neurological disease, described at the end of the 19th century by the Austrian neurologist Heinrich Obersteiner, which causes the patient to have spatial transpositions ; that is to say, the stimuli presented to him on one side of the body (or of space) are perceived as if they were presented on the opposite side.
For example, if the person is touched on the right shoulder, he or she will have the feeling that the left shoulder has been touched (somatosensory alochia, when tactile function is affected). In cases where auditory or visual function is affected, patients report hearing sounds or voices on the side opposite to that which was actually presented; and with regard to perceived images or objects, affected persons report the same, which they perceive on the side opposite to that presented.
Allochria has also been considered a sign of spatial hemineglect, an attention disorder characterized by the inability to orient oneself and respond to stimuli or objects located in one of the halves of space (usually the opposite half of the damaged brain hemisphere). The person would present “indifference” towards everything that happens on the left (or right) side of his/her reality .
In the vast majority of disorders in which alochia occurs, such as neglect syndromes or unilateral inattention syndrome, there is usually an injury to the right parietal lobe.
Possible causes of this disorder
There are multiple theories that would explain why a disorder like alochia occurs. But the most current and widely accepted explanation is Hammond’s theory , which states that there is an almost complete crossing or decusation of sensory fibers within the brain’s 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 .
Also, if another unilateral injury is superimposed at a different level from the first, the sensation that was previously diverted to the wrong hemisphere, could now be redirected when encountering another obstacle, and thus could reach the appropriate hemisphere. Alochria would occur equally with both unilateral and bilateral lesions, provided that they are asymmetrical .
Another theory that would explain the causes of this neurological disorder would be that of Huber, who postulates that the appearance of a new lesion on the opposite side redirects the impulse towards its original destination.
Types of alochia
Let’s see below how many types of alochia there are and what each one consists of.
Electromotor alochia occurs when there is a crossing of reflexes in muscle stimulation and has been observed in the face, lower extremities and upper extremities .
For example, when a stimulus is presented on the affected side, the opposite facial muscles contract, using a current so weak that even the healthy part of the face does not react. There have also been cases where 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 frequent for it to be on the opposite side since the contralateral limbs of the spinal cord are represented closer together than the homolateral limbs (from the same half of the body).
1. Motor alochyria
In this type of alochia, 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 has the impression (or the certainty for him) that he has performed it correctly.
2. Alochyria reflex
People suffering from reflex alochia respond to stimulation of, for example, the sole of the foot or the inner thigh, evoking the corresponding reflex only on the opposite side.
3. Auditory alochia
In cases of auditory alochia, various investigations have been carried out and 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 alochia
In visual alochia, 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 referred 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. Alokiria of taste
In the cases of gustatory alochia, the investigations carried out consisted of placing the patients, on one side of their tongue, a specific substance, with the expected result that all of them referred that they had tasted it with the opposite side of their tongue .
In addition, when a piece of their tongue was touched on one side, they also referred to the fact that they had been touched on the side opposite the one that really belonged.
Although at present there is no effective and validated treatment, this type of neurological disorder, such as alochia, which affects attention span and visceral skills, is 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.
Unspecific interventions can be performed, 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 syndrome of negligence or heminegligence , accompanied by alochia, techniques have been used such as the adaptation of prisms, which promotes the lateralized reorganization of visomotor mapping, facilitating perceptual changes in the patient; optokinetic stimulation, which induces changes in the patient’s attentional system by means of stimuli that capture their attention and redirect it to the opposite side; or behavioural 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 there has been an increasing use of interventions in which technologies such as virtual reality or cognitive training software are used . Various studies have shown that these techniques can be useful in improving the performance of the alert state and the attentional aspects of patients.
- Arnedo, M, Bembibre, J. and Triviño, M. (2013). Neuropsychology through clinical cases. Madrid: Editorial Médica Panamericana.
- Halligan PW, Marshall JC, Wade DT. Left on the Right – Allochiria in a case of left visuospatial neglect. J Neurol Neurosurg Psychiatry 1992;55:717-9