Visuospatial working memory dysfunction from tapping span test as a diagnostic tool for patients with mild posterior cortical atrophy

Investigating the Link Between Subjective Depth Perception Deficits and Objective Stereoscopic Vision Deficits in Individuals With Acquired Brain Injury

Individuals with acquired brain injury have reported subjective complaints of depth perception deficits, but few have undergone objective assessments to confirm these deficits. As a result, the literature currently lacks reports detailing the correlation between subjective depth perception deficits and objective stereoscopic vision deficits in individuals with acquired brain injury, particularly those cases that are characterized by a clearly defined lesion. To investigate this relationship, we recruited three individuals with acquired brain injury who experienced depth perception deficits and related difficulties in their daily lives. We had them take neurologic, ophthalmological, and neuropsychological examinations. We also had them take two types of stereoscopic vision tests: a Howard-Dolman-type stereoscopic vision test and the Topcon New Objective Stereo Test. Then, we compared the results with those of two control groups: a group with damage to the right hemisphere of the brain and a group of healthy controls. Performance on the two stereoscopic vision tests was severely impaired in the three patients. One of the patients also presented with cerebral diplopia. We identified the potential neural basis of these deficits in the cuneus and the posterior section of the superior parietal lobule, which play a role in vergence fusion and are located in the caudal region of the dorso-dorsal visual pathway, which is known to be crucial not only for visual spatial perception, but also for reaching, grasping, and making hand postures in the further course of that pathway.

A Selective Hand Posture Apraxia in an Individual With Posterior Cortical Atrophy and Probable Corticobasal Syndrome

A selective impairment for making hand postures that are required to use specific tools has rarely been reported in individuals with acquired brain injury, and such an impairment has not been documented at all in individuals with degenerative disorders. We describe an individual with posterior cortical atrophy and probable corticobasal syndrome who was unable to use tools because of an inability to make the proper hand posture required for each tool. This individual was, however, able to use the tools properly once her hand postures were corrected, and her ability to manipulate the tools (ie, timing, arm posture, and amplitude) was intact. Also, she had no difficulty with a test of her manipulation knowledge. Areas of hypoperfusion observed by single-photon emission computerized tomography included the anterior intraparietal sulcus in the left parietal lobe, which is an area that has been proposed to control hand postures. This selective impairment might be explained by the reasoning-based hypothesis for apraxia, which attributes hand posture errors in the absence of manipulation errors to dysfunction in one of the three independent pathways that subserve tool use, rather than the manipulation-based hypothesis for apraxia, which attributes hand posture errors to impaired manipulation knowledge. This is the first case with a degenerative disorder that revealed a selective impairment for making hand postures for tool use, which might be explained mainly by apraxia of hand postures along with visuospatial dysfunction (simultanagnosia) and/or sensory disturbance.

Shadowing Behavior May Be Associated with an Inability to Recognize the External World: A Case Report of Shadowing in a Patient with Posterior Cortical Atrophy

Although shadowing behavior- when one individual closely follows another- is routinely documented among patients with dementia, its mechanisms have yet to be elucidated. In particular, there have been no detailed descriptions of patients with shadowing behavior. To propose its potential backgrounds, we describe a patient with posterior cortical atrophy who exhibited prominent shadowing behavior. He also experienced severe difficulties recognizing external stimuli, including visuospatial dysfunction, several types of agnosia, difficulties in verbal comprehension, disorientation, and its associated depression. This shadowing behavior may be adaptive relative to his extreme difficulty with recognizing the world around him.

What's "up"? Impaired Spatial Preposition Processing in Posterior Cortical Atrophy

This study seeks to confirm whether lesions in posterior regions of the brain involved in visuo-spatial processing are of functional relevance to the processing of words with spatial meaning. We investigated whether patients with Posterior Cortical Atrophy (PCA), an atypical form of Alzheimer’s Disease which predominantly affects parieto-occipital brain regions, is associated with deficits in working memory for spatial prepositions. Case series of patients with PCA and matched healthy controls performed tests of immediate and delayed serial recall on words from three lexico-semantic word categories: number words (twelve), spatial prepositions (behind) and function words (e.g., shall). The three word categories were closely matched for a number of psycholinguistic and semantic variables including length, bi-/tri-gram frequency, word frequency, valence and arousal. Relative to controls, memory performance of PCA patients on short word lists was significantly impaired on spatial prepositions in the delayed serial recall task. These results suggest that lesions in posterior parieto-occipital regions specifically impair the processing of spatial prepositions. Our findings point to a pertinent role of posterior cortical regions in the semantic processing of words with spatial meaning and provide strong support for modality-specific semantic theories that recognize the necessary contributions of sensorimotor regions to conceptual semantic processing.