Amorphosynthesis

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Amorphosynthesis, also called a hemi-sensory deficit, is a neuropsychological condition in which a patient experiences unilateral inattention to sensory input. [1] This phenomenon is frequently associated with damage to the right cerebral hemisphere resulting in severe sensory deficits that are observed on the contralesional (left) side of the body. A right-sided deficit is less commonly observed and the effects are reported to be temporary and minor. [2] Evidence suggests that the right cerebral hemisphere has a dominant role in attention and awareness to somatic sensations through ipsilateral and contralateral stimulation. [3] [4] [5] In contrast, the left cerebral hemisphere is activated only by contralateral stimuli. [6] [7] [8] Thus, the left and right cerebral hemispheres exhibit redundant processing to the right-side of the body and a lesion to the left cerebral hemisphere can be compensated by the ipsiversive processes of the right cerebral hemisphere. [9] For this reason, right-sided amorphosynthesis is less often observed and is generally associated with bilateral lesions. [10]

Contents

Anatomy

Brain areas in the parietal lobes play an integral role in processing and interpreting somatic sensations from the body or environment. [11] The right parietal lobe is associated with sensory integration and perception whereas the left parietal lobe is believed to function at a more conceptual level involving speech, reading and writing. [10] The central sulcus divides the frontal lobe from the parietal lobe which is located superior to the occipital lobe and posterior to the frontal lobe. The primary somatosensory cortex- the main processing center for tactile sensations- is positioned posterior to the central sulcus, on the post-central gyrus. The somatosensory system is also associated with the perception of temperature, taste, vision, proprioception and kinesthesia. [12] Sensory receptors that are spread throughout the body [skin, organs, muscles, etc.] send sensory input signals to the cortex via sensory afferent neurons. [13] The parietal lobes then act as a main determinant for the summation of stimuli and spatial awareness. [14] In research by Denny-Brown and Banker, [15] a disturbance in the physiological process of perceiving somatic sensations was termed amorphosynthesis. This concept was associated with lesions of the parietal lobe leading to the ineffectual processing of sensory stimulus on the opposite side of the lesion. [15]

Causes

Amorphosynthesis is most closely related to damage of the right parietal lobe but instances of left parietal and bilateral damage have also been reported. [16] The inattention to or suppression of somatic sensations on the contralesional side of the body can manifest in the cerebral processing centers that produce the sensory modalities for touch, taste, vision, smell, and proprioception. [17] This phenomenon is frequently associated with other unilateral conditions such as hemispatial neglect, metamorphognosia, hemiplegia, hemisomatognosia, kinesthetic hallucination, anosognosia, balint optic ataxia, anaesthoagnosia and apraxia. [18] The causes of cerebral brain damage to either hemisphere can include traumatic brain injury, stroke, infection, surgery or a tumor. [19]

Causes of Amorphosynthesis are:

Types

The amorphosynthesis of sensory stimuli is associated with different perceptual and conceptual effects relative to the severity of damage to the parietal lobe. The degree of sensory suppression has been explored with bilateral and ipsilateral double stimulation methods in patients with either extensive or superficial parietal lesions. [22] [23] [24] [25] [26] Complete extinction is commonly observed in which patients with extensive right parietal damage show complete and constant inattention to tactile stimuli on the contralesional side of the body. [23] Incomplete extinction is frequently associated with lesions that are less extensive or superficial in nature. This phenomenon is supported by studies showing that if two stimuli are simultaneously applied to both sides of the body, the patient [with their eyes closed] will ignore the stimulus that is applied to the affected side and report a tactile sensation from the unaffected side alone. [24] [25] If each side of the body is separately stimulated, then each stimulus is correctly reported without delay. Incomplete sensory suppression has also been observed using ipsilateral double stimulation to one side of the body. [26] Results indicate that stimulation to a proximal and distal segment [for example, the face and hand] on one side of the body will result in a distal [hand] stimulus suppression, to which the patient will report feeling only the proximal [face] stimulation. [22] Further evidence suggests that the parietal lobe gives rise to the processing of attention and awareness that is necessary for sensory perception. In studies of double stimulation in which the patient has their eyes open, incomplete extinction is eliminated when attention is directed to the application of stimulus on the affected side. This phenomenon is not observed in patients with complete extinction in which there is extensive damage to the parietal lobe, suggesting that the subsequent sensory suppression is not affected by expectant attention [22] [26]

Subtypes of amorphosynthesis, depending on the type of deficit, have been referred to as tactile amorphosynthesis, visual amorphosynthesis, and amorphosynthetic apraxia of speech or writing [18] [22]

Treatment

Treatment of amorphosynthesis is often carried out by a variety of clinicians, neuropsychologists, physical therapists, occupational therapists, caretakers, speech-language pathologists and optometrists, depending on the severity and type of sensory suppression. [27] Rehabilitation consists of developing an individualized treatment plan that is designed to help the person address the deficits that are affecting them. Trained professions can help to improve communication and are primarily advised to direct attention to the contralesional [affected] side of the body. Although not all deficits have seen improvements after therapy, evidence suggests that many patients are able to live independently following treatment implementation [28] [29]

Signs and Symptoms

S. Fazlullah, in his article Tactile Perceptual and Tactile-Amorphosynthesis in the Localization of Cerebral Lesions (1956), provides a detailed explanation of the specific signs and symptoms in amorphosynthesis caused by left and right parietal lobe lesions.

Left Parietal Lobe Lesion

Gerstmann syndrome :

Parietal apraxia:

Constructional apraxia :

Right Parietal Lobe Lesion

Anosognosia

Hemiasomatognosia

Metamorphognosia

Corporeal agnosia

Phantom Sensations

Transposition of Parts of the Body

Constructional apraxia

Disorientation of space:

Agnosia of left portion of space:

Anaesthoagnosia:

Balint optic ataxia:

Primary Research

Denny-Brown and Banker

According to Denny-Brown's 1954 article [31] lesions of the parieto-occipital region cause disturbance of recognition in a patient – left-sided lesions usually cause agnosia, while right-sided lesions usually cause lack of recognition of the person's left side and extrapersonal space. Denny-Brown defines agnosia as a disorder in formation or use of symbolic concepts, such as recognizing body parts; in naming objects; in understanding numbers; or in understanding geographic and/or spatial location. It applies to both sides of a person, even though a lesion in only one side of the parietal lobe – the dominant one – causes it. He argues that amorphosynthesis, on the other hand, is usually caused by a lesion in the non-dominant parieto-occipital lobe and results in lack of awareness on the opposite side of the body.

Before Denny-Brown, researchers such as Lange, [32] Dide, [33] Lenz, [34] and McFie and associates [35] proposed that the brain's right hemisphere controls a specific function in spatial perception, explaining why damage to the parieto-occipital lobe of the right hemisphere results in the loss of spatial perception. In his article, Denny-Brown alternately proposes that lesions of the parieto-occipital lobe cause errors in spatial summation, not spatial perception. By using a case study, he argues that amorphosynthesis actually may result from lesions of either side of the parietal lobe, depending on the patient's dominant hemisphere. He further argues that lesions in the dominant lobe cause both amorphosynthesis and agnosia – the agnosia just obscures the amorphosynthesis.

Fazlullah

According to Fazlullah's article [30] bilateral simultaneous and ipsilateral double stimuli in testing cutaneous (skin) sensations can help study the sensory suppression phenomenon called Tactile-Amorphosynthesis.

Cherington and Yarnell

According to Cherington and Yarnell's article [21] The game of chess can be used as a tool to study the visual perception of subjects who have a dominant hemisphere infarction, for that reason, it is useful to the understanding of the evolution of amorphosynthesis.

Case Studies

Denny-Brown: Amorphosynthesis From Left Parietal Lesion

A 36 yr. old white married boilermaker named W.F. was admitted to the Boston City Hospital on March 23, 1953, after a week of general weakness and malaise. Three days before his admission, he developed a throbbing bilateral headache, and on the day of admission, he was unable to walk or support himself due to right-sided weakness. On the first day, his symptoms were severe – while he could perform simple movements of his right limbs, he did not feel pain, temperature, or touch on his right side and refused to acknowledge that his right limbs were his. In fact, he repeatedly threw his right arm from the hospital bed, believing that the arm did not belong to him.

On the second day, W.F. was transferred to a neurological division for further examination. Even though he had been right handed his entire life, he ate, wrote, and held a cigarette in his left hand. When asked to extend his arms or grab an object with his right hand, he repeatedly hyperextended the fingers on his right hand without being conscious of doing so. He also shaved with his left hand and only on the left half of his face, not realizing there was anything wrong with his actions.

When stimulated with pain, temperature, touch, and vibration, W.F. reported feeling these sensations on his right side but described them as “not as clear” as on the left. When both sides of his body were simultaneously stimulated, he was unable to distinguish sensation on his right side. Denny-Brown terms this phenomenon extinction, and for the first week, the patient's left side remained dominant over his right side. In addition, when stimulated by two points simultaneously on his right side, W.F. could not distinguish between them – the right side of his face was dominant over his right arm and leg, and his right leg over his right arm, throughout the first week.

Importantly, W.F. gave no evidence of agnosia. He expressed himself clearly, named objects well, had no trouble finding his way about the hospital, and could even draw maps of Boston, Massachusetts, and the USA fairly well. He was able to identify all the parts of his body and distinguish right from left on his own body, and his initial belief that his right arm belonged to somebody else ceased after the second day of hospitalization. But he still had difficulty perceiving the right side of his body – even on the 12th day, he would properly put his left hand into the sleeve of his shirt when dressing but simply drape the shirt around his right side, not realizing he had done so.

Even though left-sided lesions of the parieto-occipital lobe usually cause agnosia, W.F. appeared to have a left-sided lesion causing amorphosynthesis. Electroencephalograms, obtained on admission and a week later, showed focal slow waves in the left parietal and occipital leads, and the clinical diagnosis was a left anterior parietal lesion, most likely caused by a small hemorrhage in the brain.

In analyzing W.F., Denny-Brown raises the question of why the patient's left-sided lesion caused amorphosynthesis rather than agnosia. In general, as Denny-Brown explains in his introduction, left-sided lesions cause agnosia while right-sided lesions cause amorphosynthesis. He gives two possible explanations – first, that the right hemisphere might be dominant in the patient, not the left. This would suggest that just as right-handed and left-handedness differ among the population, so too does the dominance of the parieto-occipital lobe. While Denny-Brown notes that he cannot refute this explanation, he sees it as more likely that the patient's lesion simply did not extend posteriorly to produce agnosia. Therefore, he argues that the difference between causes of amorphosynthesis and agnosia is directly related to the size and extension of the parieto-occipital lesion. As a whole, he concludes that amorphosynthesis of the opposite side of the body from a parieto-occipital lesion can occur on as a result of either left or right-sided lesion, even though amorphosynthesis from right parietal lesion is more commonly observed. [31]

Fazlullah:Tactile Perception Rivalry And Tactile-Amorphosynthesis In The Localization Of Cerebral Lesions

At the time of Fazlullah's writing, neurologists were interested in the clinical value of using bilateral simultaneous and ipsilateral double stimuli in testing sensations of the skin. This testing is applied simultaneously on two sides of the body. In such studies, patients are required to announce whether or not they can feel any type of sensation on either side of their body. Such procedures are meant to study the sensory suppression phenomenon present in tactile-amorphosynthesis. In Fazlullah's study, patients with parietal lesions were blindfolded and tested for tactile-amorphosynthesis by applying simultaneous stimulation on both sides of the body. Patients were then asked to report on the size, shape and nature of the presented object. Results determined that patients with a right parietal lobe lesions presented symptoms such as anosognosia, hemiasomatognosia, metamorphognosia, corporeal agnosia, phantom sensations, transposition of parts of the body, constructional apraxia, disorientation of space, agnosia of the left portion of space, anaesthoagnosia, and Balint optic ataxia, while patients with left parietal lobe lesions presented symptoms such as Gerstmann syndrome, parietal apraxia and construction apraxia. Other patients with symptoms of Tactile-Amorphosynthesis showed signs of lobe lesions in the sensory tract and the spinal cord glioma. For this reason, such studies as Fazlullah's suggest that patients with lesions in other regions of the brain or spinal cord can also develop tactile-amorphosynthesis. [30]

Cherington: Amorphosynthesis on the Chess Board

A 23-year-old college student who collapsed the day after a party due to the consumption of heroin showed signs of arterial branch disease in the interior, middle and left parietal veins through bilateral carotid angiography. Further testing, radio isotope scintigraphy, revealed the spread of a left parietal occipital tumor a week after. Once fully conscious, the patient showed signs of hemiparesis and deficit in right visual field. However, the patient was still able to speak with no sign of disturbance in language. By the 11th day, double simultaneous stimulation showed rare mistakes being made on the right side of his visual field as well as unawareness of the right side of his body. These symptoms caused a diagnosis of Amorphosynthesis.

Although the patient made rare mistakes on the right side of his visual field, he also showed improvement when playing chess by correctly using his pieces, making more passive moves and blunts on the right side on the chessboard. Double simultaneous testing revealed a fully intact right visual field as well as movement. Stereognosis determined that the patient was capable of localizing touch on his right hand.

In general, games can become useful when evaluating spatial perception problems such as those found in patients with amorphosynthesis. The improvements recorded from this patient are in relation with Denny-Brown and Welman's observations of patients with disordered visual spatial summations with dominant hemisphere lesions. [21]

History

Related Research Articles

Agnosia communication disorder that is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss.

Agnosia is the inability to process sensory information. Often there is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss. It is usually associated with brain injury or neurological illness, particularly after damage to the occipitotemporal border, which is part of the ventral stream. Agnosia only affects a single modality, such as vision or hearing. More recently, a top-down interruption is considered to cause the disturbance of handling perceptual information.

Alien hand syndrome (AHS) or Dr. Strangelove syndrome is a category of conditions in which a person experiences their limbs acting seemingly on their own, without conscious control over the actions. There are a variety of clinical conditions that fall under this category, which most commonly affects the left hand. There are many similar terms for the various forms of the condition, but they are often used inappropriately. The afflicted person may sometimes reach for objects and manipulate them without wanting to do so, even to the point of having to use the controllable hand to restrain the alien hand. While under normal circumstances, thought, as intent, and action can be assumed to be deeply mutually entangled, the occurrence of alien hand syndrome can be usefully conceptualized as a phenomenon reflecting a functional "disentanglement" between thought and action.

Parietal lobe part of the brain

The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus.

Occipital lobe part of the brain

The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1. Human V1 is located on the medial side of the occipital lobe within the calcarine sulcus; the full extent of V1 often continues onto the occipital pole. V1 is often also called striate cortex because it can be identified by a large stripe of myelin, the Stria of Gennari. Visually driven regions outside V1 are called extrastriate cortex. There are many extrastriate regions, and these are specialized for different visual tasks, such as visuospatial processing, color differentiation, and motion perception. The name derives from the overlying occipital bone, which is named from the Latin ob, behind, and caput, the head. Bilateral lesions of the occipital lobe can lead to cortical blindness.

Astereognosis is the inability to identify an object by active touch of the hands without other sensory input, such as visual or sensory information. An individual with astereognosis is unable to identify objects by handling them, despite intact elementary tactile, proprioceptive, and thermal sensation. With the absence of vision, an individual with astereognosis is unable to identify what is placed in their hand based on cues such as texture, size, spatial properties, and temperature. As opposed to agnosia, when the object is observed visually, one should be able to successfully identify the object.

Hemispatial neglect neuropsychological condition in which, after damage to one hemisphere of the brain is sustained, a deficit in attention to and awareness of one side of space is observed

Hemispatial neglect is a neuropsychological condition in which, after damage to one hemisphere of the brain is sustained, a deficit in attention to and awareness of one side of the field of vision is observed. It is defined by the inability of a person to process and perceive stimuli on one side of the body or environment, where that inability is not due to a lack of sensation. Hemispatial neglect is very commonly contralateral to the damaged hemisphere, but instances of ipsilesional neglect have been reported.

Supramarginal gyrus It’s the part of the brain that shows that Elon musk was born in Detroit

The supramarginal gyrus is a portion of the parietal lobe. This area of the brain is also known as Brodmann area 40 based on the universally used brain map created by Korbinian Brodmann to define the structures in the cerebral cortex. It is probably involved with language perception and processing, and lesions in it may cause receptive aphasia.

Stereognosis is the ability to perceive and recognize the form of an object in the absence of visual and auditory information, by using tactile information to provide cues from texture, size, spatial properties, and temperature, etc. In humans, this sense, along with tactile spatial acuity, vibration perception, texture discrimination and proprioception, is mediated by the dorsal column-medial lemniscus pathway of the central nervous system. Stereognosis tests determine whether or not the parietal lobe of the brain is intact. Typically, these tests involved having the patient identify common objects placed in their hand without any visual cues. Stereognosis is a higher cerebral associative cortical function.

Sensory processing is the process that organizes sensation from one’s own body and the environment, thus making it possible to use the body effectively within the environment. Specifically, it deals with how the brain processes multiple sensory modality inputs, such as proprioception, vision, auditory system, tactile, olfactory, vestibular system, interoception, and taste into usable functional outputs.

Lobes of the brain part of the cerebral cortex

The lobes of the brain were originally a purely anatomical classification, but have been shown also to be related to different brain functions. The cerebrum, the largest portion of the human brain, is divided into lobes, but so is the cerebellum. If not specified, the expression "lobes of the brain" refers to the cerebrum.

Posterior cerebral artery

The posterior cerebral artery (PCA) is one of a pair of arteries that supply oxygenated blood to the occipital lobe, part of the back of the human brain. It begins near where the posterior communicating artery and the basilar artery join, and connects with the middle cerebral artery of the same side and internal carotid artery via the posterior communicating artery.

Parieto-occipital sulcus

Only a small part of the parieto-occipital sulcus, or parietooccipital fissure is seen on the lateral surface of the hemisphere, its chief part being on the medial surface.

Focal neurologic signs also known as focal neurological deficits or focal CNS signs are impairments of nerve, spinal cord, or brain function that affects a specific region of the body, e.g. weakness in the left arm, the right leg, paresis, or plegia.

Autotopagnosia from the Greek a and gnosis, meaning "without knowledge", topos meaning "place", and auto meaning "oneself", autotopagnosia virtually translates to the "lack of knowledge about one's own space," and is clinically described as such.

Apperceptive agnosia is a failure in recognition that is due to a failure of perception. In contrast, associative agnosia is a type of agnosia where perception occurs but recognition still does not occur. When referring to apperceptive agnosia, visual and object agnosia are most commonly discussed; This occurs because apperceptive agnosia is most likely to present visual impairments. However, in addition to visual apperceptive agnosia there are also cases of apperceptive agnosia in other sensory areas.

The neuroanatomy of memory encompasses a wide variety of anatomical structures in the brain.

Extinction is a neurological disorder that impairs the ability to perceive multiple stimuli of the same type simultaneously. Extinction is usually caused by damage resulting in lesions on one side of the brain. Those who are affected by extinction have a lack of awareness in the contralesional side of space and a loss of exploratory search and other actions normally directed toward that side.

Allochiria

Allochiria is a neurological disorder in which the patient responds to stimuli presented to one side of their body as if the stimuli had been presented at the opposite side. It is associated with spatial transpositions, usually symmetrical, of stimuli from one side of the body to the opposite one. Thus a touch to the left side of the body will be reported as a touch to the right side, which is also known as somatosensory allochiria. If the auditory or visual senses are affected, sounds will be reported as being heard on the opposite side to that on which they occur and objects presented visually will be reported as having been presented on the opposite side. Often patients may express allochiria in their drawing while copying an image. Allochiria often co-occurs with unilateral neglect and, like hemispatial neglect, the disorder arises commonly from damage to the right parietal lobe.

Constructional apraxia is characterized by an inability or difficulty to build, assemble, or draw objects. Apraxia is a neurological disorder in which people are unable to perform tasks or movements even though they understand the task, are willing to complete it, and have the physical ability to perform the movements. Constructional apraxia may be caused by lesions in the parietal lobe following stroke or it may serve as an indicator for Alzheimer's disease.

Disconnection syndrome

Disconnection syndrome is a general term for a number of neurological symptoms caused by damage to the white matter axons of communication pathways—via lesions to association fibers or commissural fibers—in the cerebrum, independent of any lesions to the cortex. The behavioral effects of such disconnections are relatively predictable in adults. Disconnection syndromes usually reflect circumstances where regions A and B still have their functional specializations except in domains that depend on the interconnections between the two regions.

References

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  21. 1 2 3 4 Cherington, Michael, and Philip Yarnell. "Amorphosynthesis on the Chess Board." Scandinavian Journal of Rehabilitation Medecine 7, no. 4 (February 1975): 176-78. .
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  31. 1 2 Denny-Brown, D., and Betty Q. Banker. "Amorphosynthesis from Left Parietal Lesion." A.M.A. Archives of Neurology and Psychiatry 71, no. 3 (March 1954): 302-13.
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