Constructional apraxia

[2][3] 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.

[6] 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.

[5] As a result, right hemisphere patients tend to produce asymmetric or distorted drawings[6] characterized by hemispatial neglect, the omission of elements from one side of the model.

[8] Subsequent research has substantiated the absence of a marked difference in performance between left and right hemisphere patients on 3D construction tasks.

[9] In Alzheimer's disease research, the AT8 antibody has proven to be an early indicator of tau protein pathology.

[10] As the study of constructional apraxia impairments narrows, research is concentrating on analyzing drawing abilities.

[5] There is an attentional subsystem responsible for moving the eyes, head, and body to focus on different images.

Damage at various levels of this system could lead to trouble localizing a stimulus or hemispatial neglect which manifests as perseverative errors on the drawing.

[7] The Van Sommers model describes two hierarchical systems for drawing: one for visual perception, another for graphic production.

This representation sends feedback to the other areas of the brain which encoded the spatial and physical properties of the object.

[2][13] In the graphic production model, the viewer begins by making a series of depiction decisions about the dimensions, amount of detail to include, etc.

If the drawing is familiar (e.g. a sun), then the drawer will reproduce the item line by lie regardless of the pictures organization due to automatic execution.

The fourth and final component of the model refers to the articulatory and economic constraints placed on the drawer by using a pencil.

A patient with trouble visually recognizing patterns or spatial relations may have difficulty correctly building a model.

[9] Modern attempts to understand constructional apraxia have moved away from anatomical functions towards a cognitive neuropsychological approach.

Gregory argues that ontogenetically and phylogenetically earlier behavioral traits are present in the brain, but inhibited.

Some researchers feel that neuronal mechanisms involved in drawing and copying differ, thus they should be tested individually.