Biomedical subjects
Olaf Blanke
Publications and source records attributed to Olaf Blanke.
Direction-selective motion blindness after unilateral posterior brain damage.
Motion blindness (MB) is defined as the selective disturbance of visual motion perception despite intact perception of other features of the visual scene. MB is characterized by a pandirectional deficit of motion direction discrimination and is assumed to result from damage to the visual motion pathway, especially area MT/V5. However, the most characteristic feature of primate MT/V5 neurons is not their motion selectivity but their preference for one direction of motion (direction selectivity), which changes incrementally at neighbouring columns. In addition to this microscopic directional organization, studies in nonhuman and human primates suggest that single directions of motion are also coded at a more macroscopic level. We thus hypothesized that if MB in humans results from damage to direction-selective neurons in the visual motion pathway, posterior brain damage might cause MB which is direction selective, not pandirectional. The present study investigated motion direction discrimination in patients with posterior unilateral brain damage and determined separate psychophysical thresholds for the four cardinal directions. In addition, we analysed whether the direction of erroneous motion perception (i.e. the perception of right motion for upward motion) was random or showed a directional bias. We report three principal findings. First, motion direction discrimination was severely impaired in one or two directions while it was normal in the other directions. This constituted direction-selective MB. Second, MB was characterized not only by a quantitative direction-selective increase in psychophysical thresholds but also by a qualitative impairment of perceiving motion direction systematically in wrong directions. Both findings suggest that the cortical modules specialized for the perception of a single direction of motion might be larger than previously thought. Third, lesion analysis showed that unilateral damage, not only the human homologue of MT/V5 but also to parieto-occipital cortex, leads to MB.
Hearing of a presence.
Here we describe a patient with epilepsy (secondary to left parieto-temporal brain damage) suffering from the paroxysmal unilateral experience of hearing a person in her near extrapersonal space. The paroxysmal auditory experience was associated with a deficit in spatial auditory perception and other paroxysmal disorders of somatognosia. Based on these findings, it is suggested that the paroxysmal hearing of a person nearby corresponds to an auditory disorder of somatognosia.
The metaphysical art of Giorgio de Chirico. Migraine or epilepsy?
It has been suggested that the great Italian painter Giorgio de Chirico (1888-1978), who developed the unique style of 'metaphysical art', suffered from migraine and used some of his morbid manifestations as a source of inspiration for his paintings. Yet, whereas many of the symptoms that de Chirico described are rare in migraine, they are frequently encountered in patients with temporal lobe epilepsy. Here we rediscuss de Chirico's symptoms critically and suggest that, if his symptoms were of neurological origin, they rather relate to temporal lobe epilepsy than migraine.
Stimulating illusory own-body perceptions.
'Out-of-body' experiences (OBEs) are curious, usually brief sensations in which a person's consciousness seems to become detached from the body and take up a remote viewing position. Here we describe the repeated induction of this experience by focal electrical stimulation of the brain's right angular gyrus in a patient who was undergoing evaluation for epilepsy treatment. Stimulation at this site also elicited illusory transformations of the patient's arm and legs (complex somatosensory responses) and whole-body displacements (vestibular responses), indicating that out-of-body experiences may reflect a failure by the brain to integrate complex somatosensory and vestibular information.