Pure optic ataxia and visual hemiagnosia – extending the dual visual hypothesis

Abstract

Goodale and Milner's two visual system hypothesis is an influential model for the understanding of the primate visual system. Lesions of either the ventral (occipito-temporal) or the dorsal (occipito-parietal) stream produce distinct and dissociated syndromes in humans: visual agnosia is typical for ventral damage, whereas optic ataxia (OA) for dorsal damage. We studied the case of a 59-year-old left-handed woman with a circumscribed lesion around the left posterior occipital sulcus, extending to the underlying white matter. Initially, she presented with a central visual field OA, which regressed to an OA to the right visual hemifield during the 3 months observation period. In addition, tachistoscopic experiments showed visual hemiagnosia to the right visual hemifield. In line with the findings of the neuropsychological experiments, the analysis of the structural MR data by means of a trackwise hodologic probabilistic approach revealed damage to the left superior longitudinal fasciculus and to the left inferior longitudinal fasciculus, indicating an impairment of both the dorsal and the ventral stream. The combination of OA and visual hemiagnosia in the same patient has never been previously described. The present case study thus provides further insights for the understanding of visual processing.

Functional Anatomy of the Inferior Longitudinal Fasciculus: From Historical Reports to Current Hypotheses

“…In view of the ILF’s cortical endpoints in visual occipital and inferior temporal associative areas, this tract is topographically well located to subserve the so-called ventral visual stream (as opposed to the dorsal visual stream) thought to be critical for object recognition ( Ungerleider and Haxby, 1994 ; Milner and Goodale, 1995 ). In support of this hypothesis, unilateral or (more frequently) bilateral disruption of the ILF following infarction of the posterior cerebral artery ( Benson et al, 1974 ; Albert et al, 1979 ; Feinberg et al, 1994 ) or occipital-temporal hematoma ( Kawahata and Nagata, 1989 ; Meichtry et al, 2017 ) has been linked to visual agnosia (i.e., the inability to recognize objects, despite the absence of primary visual defects). These neuropsychological findings concur with the results of neuromodulation studies in which “virtual” disruption of the ILF (using direct electrostimulation) in patients undergoing “awake” craniotomy for low-grade glioma caused transient visual hemi-agnosia ( Mandonnet et al, 2009 ; Coello et al, 2013 ; Gil-Robles et al, 2013 ).…”

Visual Object Agnosia in Acute Ischemic Stroke: A First Neuroimaging Biomarker

“…Например, у пациентки J.R. Meichtry и соавт. (2018) отмечалась зрительная гемиагнозия при небольшом кровоизлиянии в проек ции левой затылочно-теменной борозды [5].…”

“…Нарушение зрительного узнавания, согласно теории двух путей зрительной информации [4], патогенетически связано с поражением структур вентрального пути, следующего из затылочной коры в височную кору головного мозга [5]. Особую роль в идентификации объектов, сцен и лиц в системе этого пути играют так называемые объект-избирательные (objectselective), место-избирательные (place-selective) и лице-избирательные (face-selective) функциональные нейро нальные комплексы: их повреждение с высокой вероятностью приводит к развитию зрительной агнозии [6].…”

A taxonomy of the brain’s white matter: Twenty-one major tracts for the twenty-first century

“…Functions of the ILF map to known functions of the ventral visual stream (Herbet et al, 2018). For example, lesions or degeneration of the ILF lead to deficits in object recognition (Benson et al, 1974;Meichtry et al, 2018), alexia (Gaillard et al, 2006;Epelbaum et al, 2008), and visual memory (Shinoura et al, 2007). The ILF is likely also involved in face recognition, which depends upon intact connections between the occipital face area and the fusiform face area (Herbet et al, 2018).…”