V1 is known for its pre-processing capabilities of visual information; however, it is no longer considered the only perceptually effective gateway to the cortex. Motion information can reach V5 without passing through V1 and a return input from V5 to V1 is not required for seeing simple visual motion. Motion-related signals arrive at V1 (60–70 ms) and V5 (< 30 ms) at different times, with V5 acting independently of V1. Patients with blindsight have damage to V1, but because V5 is intact, they can still sense motion. Inactivating V1 limits motion vision, but does not stop it completely. Ventral and dorsal streams
Another thought on visual brain organization is the theory of streams for spatial vision, the ventral stream for perception and the dorsal stream for action. Since LM has impairment in both perception and action (such as grasping and catching actions), it has been suggested that V5 provides input to both perception and action processing streams. Case studies
Potzl and Redlichs patient
In 1911, Potzl and Redlich reported a 58-year-old female patient with bilateral damage to her posterior brain. She described motion as if the object remained stationary but appeared at different successive positions. Additionally, she also lost a significant amount of her visual field and had anomic aphasia. Goldstein and Gelbs patient
In 1918, Goldstein and Gelb reported a 24-year-old male who suffered a gunshot wound in the posterior brain. The patient reported no impression of movement. He could state the new position of the object (left, right, up, down), but saw "nothing in between".
Other intact functions include visual space perception and visual identification of shapes, objects, and faces. Besides simple perception, akinetopsia also disturbs visuomotor tasks, such as reaching for objects and catching objects. When doing tasks, feedback of ones own motion appears to be important. Causes
Brain lesions
Akinetopsia may be an acquired deficit from lesions in the posterior side of the visual cortex. Lesions more often cause gross akinetopsia. The neurons of the middle temporal cortex respond to moving stimuli and hence the middle temporal cortex is the motion-processing area of the cerebral cortex. In the case of LM, the brain lesion was bilateral and symmetrical, and at the same time small enough not to affect other visual functions. Some unilateral lesions have been reported to impair motion perception as well. Akinetopsia through lesions is rare, because damage to the occipital lobe usually disturbs more than one visual function. Akinetopsia has also been reported as a result of traumatic brain injury. Transcranial magnetic stimulation
Inconspicuous akinetopsia can be selectively and temporarily induced using transcranial magnetic stimulation (TMS) of area V5 of the visual cortex in healthy subjects. It is performed on a 1 cm² surface of the head, corresponding in position to area V5. With an 800-microsecond TMS pulse and a 28 ms stimulus at 11 degrees per second, V5 is incapacitated for about 20–30 ms. It is effective between −20 ms and +10 ms before and after onset of a moving visual stimulus.