HOW PURE IS PURE ALEXIA? A NEUROPSYCHOLOGICAL ANALYSIS OF A CASE SERIES OF PATIENTS WITH ALEXIA DUE TO LEFT HEMISPHERIC STROKES

The aim of this study was to analyze a case series with acquired alexia after stroke within the posterior areas of the left hemisphere, in the context of the current criteria for pure alexia and their relevance to the set of symptoms observable in clinical practice. Seven patients with ischemic strokes and an initial diagnosis of pure alexia were enrolled for detailed analysis. The evaluation consisted of neuropsychological assessment in the form of standardized tests and non-standardized reading tasks, while oculomotor activity during reading was measured. Language functions, visual object and space perception, verbal and nonverbal memory, and visuospatial constructional ability were among the domains assessed. In five of the participants, pure alexia was recognized based on sig- nificant and specific discrepancies between test scores, indicating primary abnormalities in the visual processing of letter strings as a basic mechanism of the disorder. In most of the patients, coexisting cognitive deficits were revealed; however, these were dispropor- tionately milder and less functionally significant than reading disturbances. Pure alexia is a relatively rare disorder after a stroke, but it considerably affects the quality of everyday independent functioning. Its clinical characteristics in practice rarely meet all the criteria proposed in the subject literature. The differential diagnosis of this form of alexia and other reading disorders requires detailed clinical analysis

Emotionally negative stimuli can overcome attentional deficits in patients with visuo-spatial hemineglect.

Left unilateral spatial neglect resulting from right brain damage is characterized by loss of awareness for stimuli in the contralesional side of space, despite intact visual pathways. We examined using fMRI whether patients with neglect are more likely to consciously detect in the neglected hemifield, emotionally negative complex scenes rather than visually similar neutral pictures and if so, what neural mechanisms mediate this effect. Photographs of emotional and neutral scenes taken from the IAPS were presented in a divided visual field paradigm. As expected, the detection rate for emotional stimuli presented in the neglected field was higher than for neutral ones. Successful detection of emotional scenes as opposed to neutral stimuli in the left visual field (LVF) produced activations in the parahippocampal and anterior cingulate areas in the right hemisphere. Detection of emotional stimuli presented in the intact right visual field (RVF) activated a distributed network of structures in the left hemisphere, including anterior and posterior cingulate cortex, insula, as well as visual striate and extrastriate areas. LVF-RVF contrasts for emotional stimuli revealed activations in right and left attention related prefrontal areas whereas RVF-LVF comparison showed activations in the posterior cingulate and extrastriate visual cortex in the left hemisphere. An additional analysis contrasting detected vs. undetected emotional LVF stimuli showed involvement of left anterior cingulate, right frontal and extrastriate areas. We hypothesize that beneficial role of emotion in overcoming neglect is achieved by activation of frontal and limbic lobe networks, which provide a privileged access of emotional stimuli to attention by top-down modulation of processing in the higher-order extrastriate visual areas. Our results point to the importance of top-down regulatory role of the frontal attentional systems, which might enhance visual activations and lead to greater salience of emotional stimuli for perceptual awareness