Constructional apraxia

Constructional apraxia is characterized by an inability or difficulty to build, assemble, or draw objects. Apraxia is a neurological disorder in which people are unable to perform tasks or movements even though they understand the task, are willing to complete it, and have the physical ability to perform the movements. Constructional apraxia may be caused by lesions in the parietal lobe following stroke or it may serve as an indicator for Alzheimer's disease. Constructional apraxia is characterized by an inability or difficulty to build, assemble, or draw objects. Apraxia is a neurological disorder in which people are unable to perform tasks or movements even though they understand the task, are willing to complete it, and have the physical ability to perform the movements. Constructional apraxia may be caused by lesions in the parietal lobe following stroke or it may serve as an indicator for Alzheimer's disease. A key deficit in constructional apraxia patients is the inability to correctly copy or draw an image. There are qualitative differences between patients with left hemisphere damage, right hemisphere damage, and Alzheimer's Disease. Patients with damage to their left hemisphere tend to preserve items, oversimplify drawing features and omit details when drawing from memory. In addition, left hemisphere patients are less likely to systematically arrange the parts of their drawing. Patients with damage to their right hemisphere have trouble correctly replicating spatial relationships of complex figures. Drawing elements are often piecemeal, transposed to different positions or orientations, or shown diagonally on the page. As a result, right hemisphere patients tend to produce asymmetric or distorted drawings characterized by hemispatial neglect, the omission of elements from one side of the model. It was once thought that right hemisphere patients were twice as likely to make mistakes in 3D construction tasks as left hemisphere patients but this inaccurate conclusion was attributable to participant selection bias in that researchers excluded from studies individuals with severe left hemisphere lesions due to the debilitating language impairments of those individuals. However, included in studies were individuals with severe right hemisphere lesions. Subsequent research has substantiated the absence of a marked difference in performance between left and right hemisphere patients on 3D construction tasks. Alzheimer's disease patients with constructional apraxia have unique symptoms. Their drawings contain fewer angles, spatial alterations, a lack of perspective and simplifications, which are uncharacteristic of left hemisphere or right hemisphere patients. Constructional disabilities are present early on in the disease and get progressively worse over time; however even patients with advanced Alzheimer's disease may be able to do some constructional tasks. Spontaneous drawing is affected early and is heavily dependent upon semantic memory; therefore simplifications in the drawing may be due to impaired access to semantic knowledge. As Alzheimer's disease progresses, the patient's ability to copy objects becomes increasingly impaired and they may lose the ability to correctly draw simple figures due to a motor loss in routine memories. Constructional apraxia cannot be localized to a specific hemisphere or cerebral area because drawing and constructional tasks require both perceptual and motor functioning. It has been linked to parietal lesions in the left and right hemisphere, stroke and Alzheimer's disease. Initially, researchers tried to isolate the cause to left hemisphere lesions in the parietal lobe because of its similarities to Gerstmann syndrome; however, lesions in the dorsal stream also result in visual agnosia and a piecemeal drawing. Although constructional apraxia can result from lesions in any part of the brain, it is most commonly associated with lesions in the parietal-occipital lobes. Constructional apraxia is common after right parietal stroke and it continues after visuospatial symptoms have subsided. Patients with posterior and parietal lobe lesions tend to have the most severe symptoms. In Alzheimer's disease research, the AT8 antibody has proven to be an early indicator of tau protein pathology. Constructional apraxia patients with the most AT8 pathology were least able to copy an image, while those best able to had the least neuritic pathology. Therefore, figure copying ability is highly correlated with Alzheimer's disease pathology.