Ideational Apraxia - Pathophysiology

Pathophysiology

Ideational apraxia is characterized by the mechanism that the patient loses the “idea” of how they should interact with an object. Norman and Shallice came up with the dual-systems theory of the control of routine and willed behavior. According to this theory one system –contention scheduling is responsible for the control of routine action, while – supervisory attention is able to bias this system when willed control over the behavior is required.

Contention scheduling is a complicated set of processes that involve action schemas. These action schemas are what are used in the sequence of actions involved in making a cup of tea and situation specific factors such as whether a glass of lemonade is too bitter. Even simple tasks need the monitoring of goals: e.g., has sugar been added to a cup of coffee.

But as we learn new activities we are also learning new schemas. We all know how to open a jar of jelly or how to light a match. Schemas are needed in everyday life because they give purpose and goal to our behaviors. In each schema there are subgoals or components that make up the schema. An example would be the schema of lighting a match. There are three subgoals found in this schema: holding the match, holding the matchbox, and holding a lit match. More subgoals could be applied but those are the most obvious when the overall goal wanted is to light a match. That is why schemas form a hierarchy, with the more complicated and complex action sequences corresponding to high level schemas and low level schemas correlating with simple single object tasks.

As said earlier from Norman and Shallice the other component used in voluntary action is supervisory attention. Schemas cause the activation of behaviors; the greater the excitation of the activity the more easily it is to achieve the subgoals and complete the schema. Either top-down fashion activates schemas, where intentions are governed by some type of cognitive system, or by bottom-up fashion where features or an object in the environment trigger a schema to begin. The bottom-up feature is what is seen in ideational apraxia because an object appears to capture the attention of the patient. However, the schema that corresponds to the object cannot be fulfilled. For some reason there is a disconnect in the brain that does not allow the individual to produce the sequence of actions that they know should be happening with the object that is in their visual pathway. It is this area that is still an area of ambiguity to physicians and researchers alike. They are not sure where in the brain the action schema pathway is severed.