Rapid Recovery From Cortical Blindness Caused by an Old Cerebral Infarction

Abstract

When the primary visual cortex (V1) is damaged, cortical blindness results. However, visual information obtained from the superior colliculus (SC) or direct thalamic afferents to higher visual cortices produces unconscious visual functions called blindsight. Alarming visual stimuli suggesting the approach of a predator are known to trigger escape behaviors via visual information mediated by the SC and amygdala in small animals, and salient and dynamic visual stimuli also produce some conscious visual experience even in patients with blindsight. Fresh cortical blindness sometimes recovers spontaneously in patients with fresh cerebral damages, and recovery can be accelerated by early rehabilitation. However, the mechanisms underlying recovery are not well-known. We analyzed a patient with cortical blindness caused by an old cerebral infarction. After repeated presentation of alarming visual stimuli, the ability to detect visual stimuli in the impaired visual field showed behavioral short-term improvement (STI) within a few minutes. Repeated behavioral STI induction was followed by behavioral long-term improvement (LTI) lasting more than several days. After behavioral LTI, the patient partially recovered the ability to read letters presented in the impaired visual field. The behavioral STI experiment, which can be performed within 10 min, may serve as a clinical screening test for anticipating recovery from cortical blindness.

Visual Field Test With Gaze Check Tasks: Application in a Homonymous Hemianopic Patient Unaware of the Visual Defects

“…We planned self-training using the visual field test to improve the visual defects, since repeated presentation of appropriate visual stimuli may ameliorate visual defects in hemianopic patients ( 12 ). However, if an extra examiner is required to operate the visual field test, self-training is not possible.…”

“…The increased stimulus detection after repeated presentation of visual stimuli ( Figure 4 ) suggested that some form of neural plasticity might be induced in the visual system ( 12 ). We further investigated the patient's visual functions in detail.…”

“…However, he could not detect any of the visual stimuli in the left visual field, when tested using the visual field test with gaze check tasks again ( Figure 6B ). For confirmation, the examiner directly checked the gaze during the test using visual inspection ( 12 ), and it was clear that the left visual field of the patient was not visible ( Figure 6C ).…”

“…Generally, neurons in higher visual cortices have larger and more complex receptive fields as compared to those in the retina and primary visual cortex ( 13 – 15 ); therefore, the test in this study could be applied to evaluate the function of higher visual cortices. Some patients with cortical visual impairment can sense dynamic visual stimuli presented in the impaired visual field ( 28 , 29 ), and training of these rudimentary visual functions may improve symptoms of cortical visual impairment ( 12 ). The visual field test of this study may be useful as a means of analyzing the properties of cortical visual impairment and self-rehabilitating the impaired visual functions.…”

“…Transient dysfunction in the cortical areas surrounding the infarct may recover spontaneously (6) or with compensatory neuronal plasticity in the remaining cortical areas (9)(10)(11). Recovery can be observed even in patients who have had a cortical infarction over 5 years ago (12). The recovery process should be monitored by a visual field test in which various visual stimuli are applied to a particular part of the visual field.…”