title: Bottom-up Visual Integration in the Medial Parietal Lobe.
abstract: Largely based on findings from functional neuroimaging studies, the medial parietal lobe is known to contribute to internally directed cognitive processes such as visual imagery or episodic memory. Here, we present 2 patients with behavioral impairments that extend this view. Both had chronic unilateral lesions of nearly the entire medial parietal lobe, but in opposite hemispheres. Routine neuropsychological examination conducted >4 years after the onset of brain damage showed little deficits of minor severity. In contrast, both patients reported persistent unusual visual impairment. A comprehensive series of tachistoscopic experiments with lateralized stimulus presentation and comparison with healthy participants revealed partial visual hemiagnosia for stimuli presented to their contralesional hemifield, applying inferential single-case statistics to evaluate deficits and dissociations. Double dissociations were found in 4 experiments during which participants had to integrate more than one visual element, either through comparison or formation of a global gestalt. Against the background of recent neuroimaging findings, we conclude that of all medial parietal structures, the precuneus is the most likely candidate for a crucial involvement in such bottom-up visual integration.
authors.affiliation: Department of Neurology.|Center of Neurology and Neurorehabilitation, State Hospital Luzern, Luzern, Switzerland.
authors.forename: Tobias
authors.initials: T
authors.lastname: Pflugshaupt
authors.affiliation: Department of Neurology.
authors.forename: Myriam
authors.initials: M
authors.lastname: Nösberger
authors.affiliation: Department of Neurology, Inselspital, University Hospital Bern, Bern, Switzerland.
authors.forename: Klemens
authors.initials: K
authors.lastname: Gutbrod
authors.affiliation: Department of Neurology.|Department of Ophthalmology, University Hospital Zürich, Zürich, Switzerland.
authors.forename: Konrad P
authors.initials: KP
authors.lastname: Weber
authors.affiliation: Department of Neurology.
authors.forename: Michael
authors.initials: M
authors.lastname: Linnebank
authors.affiliation: Department of Neurology.
authors.forename: Peter
authors.initials: P
authors.lastname: Brugger
mesh_terms: D000328:Adult; D000377:Agnosia / Q000473:pathology / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009483:Neuropsychological Tests; D010296:Parietal Lobe / Q000473:pathology / Q000503:physiopathology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: double dissociation; hemiagnosia; neurovisual disorder; precuneus; tachistoscopic presentation