Imagine we are with a friend who is having coffee. We observe how he takes the cup, takes it to his mouth and takes a sip. Then, we ask you to repeat the action, but to our surprise you are unable to do so. Given this, we take another cup and tell him to imitate us. Nor is he able to imitate us. How is it possible that he cannot perform an action he has done for himself? The answer is that our friend suffers an ideomotor apraxia. Throughout the article we will describe what this type of apraxia consists of and which brain areas are altered. Let's get started!
In clinical practice, ideomotor apraxia is the most prevalent type of apraxia. But what does this type of apraxia consist of? It is an alteration in the ability to perform voluntary movements learned in response to a verbal order. That is, his diagnosis requires that he who suffers this apraxia be unable to obey an order whether he is asked to make a move or if he is asked to imitate it.
A striking aspect is that the person can carry out movements automatically that through an order is unable to do them. For example, the subject is able to drink a glass of water but may be unable to take the glass at the examiner's request. As Alfredo Ardila (2016) states, "The ideomotor apraxia can go unnoticed since the movements carried out spontaneously can be almost normal, and the difficulties only manifest when the movement is carried out in a consciously directed way, under the verbal order".
Ideomotor apraxia affects simple movements, although through automatic movements it is observed that preserved motor sequences are possessed. The movements are usually improved when done with objects. A task may be favored if the experimenter orders the subject to take a brush and comb, than if he only orders him to make the gesture of combing without a brush.
It is important to rule out another type of problem before the diagnosis of ideomotor apraxia. It is therefore important to rule out other causes such as attention deficits, inability to initiate an action or frontal perseverations. Patients with this type of apraxia also usually show alterations when they place their hands spatially when making a movement or they also tend to show little coordination movements with their fingers and hands.
Anatomy of the ideomotor apraxia
Ideomotor apraxia can be caused by alteration of different pathways involved. On the one hand, when an examiner gives an order to the patient and he is unable to carry it out, the altered route is the one that comes from the Wernicke area and goes to the left parietal cortex. On the other hand, in movements altered by imitation, it is an alteration of the visual areas with the left parietal cortex. In this way, it is ensured that the failure is not due to an alteration in visual perception or understanding. The main alteration is found in the connection of the left parietal cortex and the premotor area - in the frontal cortex - of both hemispheres.
The linguistic functions of the dominant hemisphere are fundamental to make movements at will. Before evaluating the patient, check that your verbal comprehension is intact.. When the information leaves Wernicke's area towards the supramarginal gyrus, verbal instruction is associated in the parietal cortex with previously learned movement patterns. Finally, this information is transferred to the motor planning areas in the frontal cortex and to the primary motor area. An injury to the parietal cortex or any part of this pathway can produce ideomotor apraxia.
Importance of the parietal cortex
Dynamic body representation is possible thanks to the superior parietal cortex. Various studies indicate that some lower areas of the parietal cortex are responsible for storing the characteristics of the movements that define the most common motor patterns. On the other hand, it has also been observed that this area is activated by performing movements in which the use of objects is present.
The role of the parietal cortex in the storage and generation of motor patterns related to actions is fundamental. This importance lies in the differences between the type of apraxia of patients with parietal cortex injury and that of patients in whom the lesion affects the connection between the parietal and frontal cortex. When we do motor learning, they determine the creation of space-time motor representations associated with them.. In this way, when we want to make a movement, stored representations are recovered and transformed into the movement we want to carry out.
Patients with parietal lesions are unable to differentiate whether the movements they perform are correct or incorrect. due to its involvement in movement patterns. However, when the parietal cortex is preserved and the lesion is located in more anterior areas, they are unable to perform the movement, but they try several times because they realize they are not able to perform it. So that, the dominant hemisphere in language is also the dominant one to perform this type of movement.
The corpus callosum
The anterior corpus callosum also takes center stage in a special form of apraxia. The injury in this area disconnects the motor information of a particular movement contained in the left hemisphere of the motor areas of the right frontal cortex. Thus, the information of the movement pattern to be performed does not reach these areas. In this case, a unilateral apraxia or callous apraxia. In this type of apraxia, the patient can only successfully imitate the movements with his right hand, but is not able to do them with the left hand.
Ardila, A. (2016). Kinetic, ideomotor, ideational and conceptual apraxia. Journal of Neuropsychology, Neuropsychiatry and Neurosciences, 15, (1), 119-139.