Ideational apraxia

Cause

The cause of IA is still somewhat of a mystery to most researchers because there is no localized focal point in the brain that shows where this deficit will occur. Since 1905 Liepmann proposed a hypothesis of an action processing system that is found in the left hemisphere of the brain, which is dedicated to skilled, motor planning that guides the movement of the body. Yet, he still was never able to produce two patients with the same brain damage that showed ideational apraxia. The major ideas of where IA is found are in the left posterior temporal-parietal junction. Possibly damage to the lateral sulcus also known as Sylvian fissure may contribute to an individual’s deterioration of object recognition. Another possible area of damage leading to IA is the submarginal gyrus, which is located in the parietal lobe of the brain. Overall, IA is an autonomous syndrome, linked to damage in the left hemisphere involving semantic memory disorders rather than a defect in motor control.

Several severe injuries or diseases can cause IA in a wide range of patients. Alzheimer's patients are the largest cohort groups that express IA. Other groups that are often seen with this dysfunction are stroke victims, traumatic brain injuries, and dementia. The damage is almost always found in the dominant hemisphere (i.e. usually the left hemisphere) of the patient.

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.

Diagnosis

Ideational apraxia is difficult to diagnose. This is because the majority of patients who have this disorder also have some other type of dysfunction such as agnosia or aphasia. The tests used to make an IA diagnosis can range from easy single-object tasks to complex multiple-object tasks. When being tested, a patient may be asked to view twenty objects. They then have to demonstrate the use of each single object following three different ways of presenting the stimuli. The patient must then perform a complex test in which the examiner describes a task such as making coffee and the patient must show the sequential steps to make a cup of coffee. The patients are then scored on how many errors are seen by the examiner. The errors of the patients in performing the MOT were scored according to a set of criteria partly derived from De Renzi and Lucchelli.

Error classes

Two classes of errors are used to develop a diagnosis:

Class I: Sequence errors

• Action addition (AA) is a meaningful action step that is not necessary for accomplishing the goal of the MOT action (e.g., removing the filter of the orange squeezer in order to pour the liquid);
• Action anticipation (A) is an anticipation of an action that would normally be performed later in the action sequence (e.g., blowing the match out before using it);
• Step omission (SO) is an omission of a step of the multiple-actions sequence (e.g., inserting the filter in the coffee machine without pouring some water);
• Perseveration (P) is a repetition of an action step previously performed in the action sequence.

Class II: Conceptual errors

• Misuse (Mis) errors, which can be differentiated into two subtypes:

1. (Mis1) involves a well-performed action that is appropriate to an object different from the object target (e.g., hammering with a saw);
2. (Mis2) involves an action that is appropriate at a superordinate level to the object at hand but is inappropriately specified at the subordinate level (e.g., cutting an orange with a knife as if it were butter).

• Mislocation (Misl) errors, which can be differentiated into two subtypes:

1. (Misl1) is an action that is appropriate to the object in hand but is performed in completely the wrong place (e.g., pouring some liquid from the bottle onto the table rather than into the glass);
2. (Misl2) involves the correct general selection of the target object on which to operate with the source object or instrument in hand but with the exact location of the action being wrong (e.g., striking the match inside the matchbox).

• Tool omission (TO) is an omission in using an obligatory tool where the hand is used instead (e.g., opening a bottle without using a bottle opener);
• Pantomiming (Pant) is when the patient "pantomime shows" how the object should be used instead of using it;
• Perplexity (Perpl) is a delay or hesitation in starting an action or subcomponents of an action;
• Toying(T) consists of brief but repeated touching of an object or objects on the table.

As the examiner observes the patient for each task they mark off which errors were committed. From these criteria the examiner will be able to focus on severity of the dysfunction. It is important to express that the motor movement is not lost in patients with IA. Yet, at first glance their movements may appear to be awkward because they are unable to plan a sequence of movements with the given object.

Therapy

Since the underlying cause of the disorder is damage to the brain, at present ideational apraxia is not reversible. However, Occupational or Physical Therapy may be able to slow the progression and help patients regain some functional control, with the treatment approach being the same as that of ideomotor apraxia. Some recovery may occur in younger patients after stroke, because brain plasticity may allow the functions of these damaged regions to be remapped. As patients develop new behaviors to cope with their apraxia, their brain's functioning neurons may take on some of the functions of the dead or damaged regions.

In the context of dementia, apraxia is a major cause of morbidity, and progresses with the underlying disease sometimes to the extent that patients may be unable to feed themselves or use simple utensils. Patients often become highly dependent or require nursing home placement because of their inability to properly use objects.

Brain imaging techniques such as fMRI, EEG, and PET scans may help in understanding the neuroanatomical and computational basis of ideational apraxia. Understanding these mechanisms is likely to be crucial in developing new modes of therapy to help patients cope with their disorder.