Akinetopsia is a condition that prevents patients from seeing motion in their visual field, following a lesion in the V5 portion of the brain. When light hits the retina, the optic nerve carries signals to the brain, which are interpreted into a series of images, perceived as motion. There are two reported types of akinetopsia: one is inconspicuous, where movement is perceived as a series of snapshots, and the other is gross, which is the invisibility of moving objects. The following review aims to describe the two types of akinetopsia from a neuropsychological standpoint by discussing two relevant cases and touching upon the future of motion blindness.
Akinetopsia can be separated into two different groups: inconspicuous and gross. Inconspicuous akinetopsia is the most common type, in which patients describe motion as a cinema reel, viewing the world as a series of snapshots. It usually occurs with palinopsia, meaning the images are static at every frame of motion . Gross akinetopsia is an extremely rare condition in which patients are unable to see motion. This results in a struggle to carry out everyday activities, negatively impacting one’s quality of life.
Several factors contribute to the development of akinetopsia. The condition could result from lesions, specifically in the posterior side of the visual cortex . This region is also known as the V5 area of the brain. In the middle temporal cortex, the motion-processing area of the brain, neurons respond to moving stimuli. Therefore, damage to this area results in motion blindness. Patients taking large doses of Nefazodone, an antidepressant, are usually subject to inconspicuous akinetopsia. When the dosage of the antidepressant is reduced, however, one’s vision returns back to normal .
The first recorded case of akinetopsia was identified in 1983 at the Max Planck Institute in Munich . It was discovered that patient M.P. had a loss of motion perception as a result of inconspicuous akinetopsia. For example, when pouring a cup of tea, she would see the empty cup and fail to notice the liquid rising, causing it to overflow. This is just one example of the debilitating life difficulties that patients with akinetopsia experience daily. Other issues they may face may be as simple as crossing the road, navigating through a store, playing sports, and walking with others. Patient M.P. was reluctant to cross the road. She stated: “when I'm looking at the car, first it seems far away. But then when I want to cross the road, the car is suddenly very near" .
Several tests were carried out on patient M.P. to determine her motion perception. One task required her to follow a wooden cube on a flat surface to and from her line of sight to determine her perception of motion depth. She was unable to recognize the movement in depth; however, she could distinguish that the cube's position had changed. She could also judge the cube's distance in relation to other objects. Another test required M.P. to follow the path of a wire using her finger. The patient found that she had difficulty following her finger as it moved, though she could follow the wire by feeling where it led .
Computed Tomography (CT) neuroimaging scans of the patient showed large bilateral lesions, encompassing temporoparietal cortices and the posterior and lateral portions of the middle temporal gyrus . These lesions also affected the areas of the brain that correlate with motion perception. The lesions were lateral in the area of the brain identified as V5; motion perception deficits are much more subtle, however, when unilateral to V5 . Motion is determined over a period of time; when the patient has more time to perceive motion, the signals have a chance to travel from the damaged part of the brain to the unimpaired hemisphere.
This case is of a patient who presented with gross akinetopsia. Unlike inconspicuous akinetopsia, patients with this type of motion blindness completely lose their ability to see motion. When objects began to move, the patient could not see them and his perception was that the objects had disappeared . This patient, a man in his 60s, developed akinetopsia after a unilateral right temporoparietal subcortical hemorrhage. After his positron emission tomography (PET) scan, it was found that he suffered from severe hypoperfusion in his right cerebral hemisphere. This means that there was reduced blood flow to the brain. As a result, he underwent cerebral artery bypass surgery.
One month after his surgery, he noticed that moving objects were entirely invisible to him. Consequently, he could not recognize when a cup was full, bumped into others while walking, and struggled to navigate his surroundings. Compared with his preoperative status, his left hemiparesis, left facial palsy, left hypoesthesia, and left hemispatial neglect were slightly improved on neurological examination . He was able to recognize and touch objects when they were still. However, when the object was moving, he could not see or touch it in any direction.
The patient's ability to view motion was assessed in both two-dimensional and three-dimensional tests. In the 2D motion assessment, dots moved around on a screen; some moved in the same direction while others moved randomly. When 75% of the dots moved in the same direction in parallel motion, the patient recognized their direction. This was far inferior to the score of 13-14% of normal subjects . During a three-dimensional motion assessment, the patient could not catch a ball when it was thrown to him. He could only determine the location of the ball by the sound of it hitting the ground.
Due to the rare nature of this condition, there is currently no effective treatment or cure for akinetopsia. Nonetheless, a doctoral student in Psychological and Brain Sciences at Dartmouth College, Zhengang Lu, revealed how the brain recognizes motion . He discovered that the brain interprets inanimate and animate motion differently. This shows that the brain categorizes objects into separate classes. This also indicates that the pathways interact with each other when processing motion. His findings have countless potential applications, including the development of a treatment for akinetopsia. Although their results may not provide direct treatment, they suggest that people with motion blindness should consider checking the functional interaction between these two pathways .
Akinetopsia is a rare neurological condition in which patients are unable to perceive motion. There are two known types of akinetopsia: inconspicuous, in which patients can see the world as a series of snapshots, and gross, in which patients cannot perceive motion. Though there is no specifically established cause for akinetopsia, a lesion in the V5 portion of the brain is a primary contributing factor to this condition. Akinetopsia has proven a vastly under-examined issue that can have severe implications on patients’ lives. Although recent research on the topic has opened up a path toward possible treatment options, a cure is yet to be found. This article emphasizes the nature of akinetopsia through a combination of the recent scientific literature and real-life patient stories, explicitly revealing the impact it has on patients’ quality of life. Understanding this rare condition will reveal insights into the perception of motion and how different brain structures work together to help navigate life, ultimately bringing scientists closer to understanding akinetopsia and how to treat it.
Nefazodone: an antidepressant that increases the amounts of certain natural substances in the brain that are critical for mood elevation .
Temporoparietal cortex: the region of the brain where the temporal and parietal lobes meet .
Brain hemorrhage: bleeding in the brain; can reduce oxygen delivery to the brain and create extra pressure, atrophying brain cells .
Hemiparesis: motor weakness on one side of the body; makes it difficult to perform activities of daily living (ADLs) .
Facial palsy: a condition in which the facial muscles are (usually temporarily) weakened .
Hypoesthesia: partial or total loss of sensation in a part of the body .
Hemispatial neglect: a disabling condition following brain trauma in which patients are not aware of items located on one side of the field of vision .
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