Biomedical subjects

Alonso R Riestra

Publications and source records attributed to Alonso R Riestra.

3 recordsLinked to original sources

PubMed2004

Visual facial grasp.

Some patients with degenerative neurological diseases have a release of the vestibular-ocular reflex (VOR), as detected by passive head movement during visual fixation on a moving target ("doll's eyes"maneuver). However, a positive doll's eyes sign might be induced by other defects and the purpose of this article is to describe a new ocular sign of cortical dysfunction, the visual facial grasp. We observed three patients, one with progressive supranuclear palsy (PSP), another with probable Alzheimer's disease (AD) and a third with cortico-basal degeneration (CBD) all of whom appeared to demonstrate a release of the vestibulo-ocular reflex (VOR) with passive head movements. Whereas the patient with PSP, who was unable to inhibit the VOR regardless of the visual target used probably had a true release of the VOR, the patients with AD and CBD were able to inhibit this reflex when the visual target was the examiner's moving face. These two patients also exhibited spontaneous preference for visual fixation on the examiner's face and improvement in smooth pursuit when the examiner's face was the visual target. This clinical observation suggests that the deficits in these two patients with AD and CBD were related to the emergence of a primitive stimulus-bound behavior, the visual facial grasp.

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PubMed2003

Mental object rotation in Parkinson's disease.

Deficits in visual-spatial ability can be associated with Parkinson's disease (PD), and there are several possible reasons for these deficits. Dysfunction in frontal-striatal and/or frontal-parietal systems, associated with dopamine deficiency, might disrupt cognitive processes either supporting (e.g., working memory) or subserving visual-spatial computations. The goal of this study was to assess visual-spatial orientation ability in individuals with PD using the Mental Rotations Test (MRT), along with other measures of cognitive function. Non-demented men with PD were significantly less accurate on this test than matched control men. In contrast, women with PD performed similarly to matched control women, but both groups of women did not perform much better than chance. Further, mental rotation accuracy in men correlated with their executive skills involving mental processing and psychomotor speed. In women with PD, however, mental rotation accuracy correlated negatively with verbal memory, indicating that higher mental rotation performance was associated with lower ability in verbal memory. These results indicate that PD is associated with visual-spatial orientation deficits in men. Women with PD and control women both performed poorly on the MRT, possibly reflecting a floor effect. Although men and women with PD appear to engage different cognitive processes in this task, the reason for the sex difference remains to be elucidated.

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PubMed2002

Is the middle between both halves?: midpoint location and segment size estimation in neglect.

BACKGROUND: Line bisection errors in neglect are attributed to perceptual size distortions. In order to compare the two segments of the line to determine if they are equal, one might first estimate the location of a midpoint that defines the two line segments to be compared. OBJECTIVES: The authors attempted to determine whether estimating a line's midpoint can be dissociated from comparing the two segments of this line, and if so, what the relative contribution of each of these tasks is to the perceptual bias in neglect. METHODS: The authors studied two patients with hemispatial neglect from right hemisphere lesions by asking them where bisection marks were placed on prebisected lines and whether the two adjacent line segments were equal. RESULTS: There was a stronger bias judging the position of the bisecting marks ("where" determination) than comparing the size of two adjacent line segments. CONCLUSIONS: These results suggest that perceptual size distortion of line segments alone cannot explain the subjects' line bisection bias, but postperceptual deficits in "where" computations may better account for their errors locating the midpoint. "Where" determinations might require more attentional capacity, depend more heavily on viewer-centered allocation of attention, and be mediated by the right hemisphere's "where" dorsal stream. In contrast, comparing the length of two segments might be mediated by the left hemisphere's "what" ventral stream.

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