Apraxia

THE SENSORY GUIDANCE OF MOVEMENT - Parietal Lobe The parietal lobe is highly concerned with the mediation of movement.The primary motor cortex extends well beyond area 4 and includes portions of the somatosensory regions which in turn contribute almost one third of the fibers which make up the pyramidal tract. These areas are in fact richly interconnected. Together, the motor and somesthetic regions comprise a single functional unit, i.e. the sensorimotor cortex. Nevertheless, it is important to emphasize that in order for a movement to be correctly planned and carried out signals must be directed to the right muscle groups as based on efferent streams of visual, somesthetic, as well as auditory input. This includes information regarding the position of the body and limbs in space. Movement becomes extremely difficult without sensory feedback and guidance. Because of this, parietal lesions can result in unilateral paresis and even wasting (i.e. parietal wasting). Hence, the somesthetic cortex is very important in the guidence of movement, and in fact some neurons fire prior to making a movement.

Although the entire parietal lobule makes important contributions, the superior and inferior parietal lobule of the left hemisphere appears to be the central region of concern in regard to the performance of skilled temporal-sequential motor acts. This is because the motor engrams for performing these acts appear to be stored in the left angular and supramarginal gyri -a consequence, in part of its unique ability to guide, visually observe, and thus selectively learn hand movements, gestures, and complex temporal sequential actions such as involving tool construction. Related memories are therefore stored in this cortex.

Conversely, these hand movement related memories assist in the programing of the motor frontal cortex where the actions are actually executed. However, the inferior parietal lobule in turn is dependent on input from the primary and association somesthetic areas. There is some evidence of laterality: If the left inferior parietal region is destroyed the patient loses the ability to perform actions in an appropriate temporal-sequence or to even appreciate when they have been performed incorrectly. They may also be impaired in their ability to acquire or perform tasks involving sequential changes in the hand or upper musculature, including well learned, skilled, and even stereotyped motor tasks such as lighting a cigarette or using a key.
 * right hemisphere** of the brain: may be more concerned with movement of the trunk and the lower extremities. This would include navigational movement through space, running, certain types of dancing, and actions requiring analysis of depth and balance.
 * left hemisphere** exerts specialized influences on the upper extremities including the control of certain types of complex, sequenced motor acts such as those requiring alterations in the orientation and position of the upper limbs.
 * APRAXIA**

Apraxia is a disorder of skilled movement in the absence of impaired motor functioning or paralysis. Usually apraxic patients show the correct intent but perform the movements in a clumsy fashion. Like many other types of disturbances, patients and their families may not notice or complain of apraxic abnormalities. This is particularly true if they're aphasic or paralyzed on the right side. That is, clumsiness with either extremity may not seem significant. Hence, this is something that requires direct evaluation. Performance deteriorates the most when required to imitate or pantomime certain actions including the correct usage of some object.

In addition, patient's with apraxia may demonstrate difficulty properly sequencing their actions. Ex: May pretend to stir a cup of coffee, then pretend to pour the coffee into the cup, and then take a sip. The individual acts may be done accurately. Broadly speaking, there are several forms of apraxia, which like many of the disturbances already discussed may be due to a number of causes or anatomical lesions. These include, ideational apraxia, ideomotor apraxia, bucal facial apraxia, constructional apraxia and dressing apraxia. With the exception of dressing and constructional apraxia, apraxic abnormalities are usually secondary to left hemisphere damage, in particular, injuries involving the the **left frontal and inferior parietal lobes**. Frontal lesions were impaired on oral whereas those with parietal lesions had the most difficulty making hand postures or complex movements of the extremities. Thus, apraxic abnormalities secondary to left cerebral lesions tend to either involve destruction of the inferior parietal lobule (IFP) or lesions resulting in disconnection of the frontal motor areas (or the right cerebral hemisphere) from this more posterior region of the brain. If the inferior parietal region is destroyed the patient loses the ability to appreciate when they have performed an action incorrectly. If the motor region is destroyed, although the act is still performed inaccurately (due to disconnection from the IFP), the patient is able to recognize the difference.

Ideomotor apraxia is usually associated with lesions within the **inferior parietal lobe of the left hemisphere**. Rather than problems with temporal-sequencing of motor acts per se, these individuals: -Tend to be very clumsy when performing an act -May perseverate and erroneously perform a previous movement -Tend to be very deficient when attempting to perform an action via pantomime - Tend to be deficient when engaged in meaningful imitation, meaningless imitation, and the meaingful use or meaningless use of actual objects: presumably due to destruction of the engrams important in motor performance. Patients will demonstrate apraxic abnormalities in both the right and left hand. -Tend to have difficulty with simple versus complex movements, although elements within a complex action may be performed somewhat abnormal. Ex: Actions such as waving goodbye, throwing a kiss, making the "sign of the cross", may be performed deficiently. Moreover, many patients tend to uncontrollably comment on their actions; i.e. "verbal overflow". That is, when asked to "wave goodbye", they may say "goodbye" while waving even when instructed to say nothing. It has been suggested that ideomotor apraxia can occur in the absence of ideational apraxia, but that the converse is not true and thus may be a less severe form of ideational apraxia.
 * IDEOMOTOR APRAXIA**

Usually due to severe disturbances in the temporal sequencing of motor acts. That is, the separate chain of links which constitute an entire movement become dissociated, such that the overriding idea of the movement in it's entirety is lost. -Commit a number of temporal and spatial errors when making skilled movements, although the individual elements, in isolation, may be preserved and performed accurately Ex:a patient (via pantomime) may rotate their hand before inserting the key, drink from a cup before filling it from a pitcher of water, or puff from a cigarette and then lighting it. Thus they incorrectly sequence a series of acts. Both hands are effected. Because of conceptual, ideational abnormalities, they may also have difficulty using actual objects correctly. During pantomime they may use a body part as object such as an index finger for a key. Even so, their actions are out of temporal sequence. Hence, these patients seem to be unable to access the motor engrams (or "memories") which would allow them to perform appropriately.
 * IDEATIONAL APRAXIA**

Patients are sometimes hesitant to perform a task as they have difficulty understanding what has been asked of them. However, they can often describe verbally what they are unable to perform..

Unable to imitate or perform certain movements with their left (but not right) hand and are clumsy in their use of objects. Sometimes due to a lesion of the **anterior corpus callosum or left frontal motor cortex**. This is because lesions of the corpus callosum or premotor and motor region of the **left hemisphere** can result in a disconnection syndrome; i.e. the motor areas of the right hemisphere cannot gain access to the motor engrams stored within the left inferior parietal lobe. Thus, with a left frontal lesion there results an apraxia of the left hand and paralysis of the right. Often this is //secondary to strokes within the distribution of the anterior cerebral arter//y such that the anterior portion of the corpus callsom is destroyed. It is noteworthy that patients also may show deficient finger tapping performance in the left hand due to apraxic abnormalities secondary to left hemisphere injury. In these instances, reduced finger tapping is bilateral.
 * LEFT SIDED OR UNILATERAL APRAXIA (also called Callosal & frontal apraxia)**

**Dressing Apraxia** Dressing apraxia is usually secondary to lesions involving **right hemisphere inferior parietal region**, and as the name implies, the patient has difficulty putting on their clothes. Severe spatial-perceptual abnormalities as well as body image disturbances are usually contributing factors. Ex: May attempt to put a shirt on upside down, then inside-out, and then backwards.

Many patients who are aphasic also appear apraxic because they have severe difficulty comprehending language and understanding motor commands. That is, a patient may fail to perform a particular action because he doesn't comprehend what is being asked. To distinguish between receptive aphasic abnormalities and apraxia one must ask "yes" and "no" questions ("are you in a hospital?"); require them to perform certain actions via pantomime ("show me how you would throw a ball" or "show me how a soldier salutes"); as well require pointing response ("point to the lamp"). If they can answer appropriately "yes" or "no" or point to objects named but cannot execute commands they have apraxia. It is important to note that in severe cases apraxic patients may have difficulty even with pointing.
 * Aphasia & Apraxia**

Individuals with damage involving the **left parietal lobule** not only make errors when performing motor acts but comprehending, recognizing and discriminating between different types of motor acts such as demonstrated via pantomime. Moreover, individuals with lesions in the left inferior occipital lobe have also been shown to have difficulty verbally understanding, describing or differentiating between pantomime. That is, in the extreme, if one were to pantomime the pouring of water into a glass vs. lighting and smoking a cigarette, these indviduals have problems describing what they have viewed or in choosing which was which. Deficits in pantomime recognition occur frequently among indviduals with aphasia. Moreover, this disturbance is also significantly correlated with reading comprehension. In this regard, individuals with alexia frequently suffer from pantomime recognition deficits as well. Because of this relationship it has been suggested that the ability to read may be based on or derived from the ability to understand gestural communication, i.e. the reading of signs. By contrast to left anterior lesions which may impair motor functioning and the capacity to imitate the ability to comprehend pantomime is retained. As noted, the inferior and superior parietal lobule receives considerable visual input, particularly from the periphery and lower visual field -the area in which the hands are most likely to be viewed. Hence, this area of the brain views, manipulates, guides and mediates hand-object coordination and reaching movements, including the comprehension of hand movements; i.e. gestures. Hence, when the left superior and inferior parietal lobule is destroyed gestural comprehension, including the understanding of (as well as the capacity to execute) complex gestures, including ASL and the capacity to engage in complex temporal sequential acts is significantly impacted. If the **right parietal area** is destroyed, these deficits may also include constructional apraxia.
 * PANTOMIME RECOGNITION**

Constructional apraxia may be expressed in a number of ways.
 * CONSTRUCTIONAL APRAXIA**

On a drawing or copying task this may include: -Addition of unncessary/non-existant details or parts -Misalignment or inattention to details -Disruptions of the horizontal and verticle axis with reversals or slight rotations in reproduction -Scattering of parts.

Although constructional deficits are //more severe// after **right hemisphere damage**, disturbances involving constructional and manipulo-spatial functioning can occur with lesions to **either half of the brain**. Depending on the laterality and extent and site of the lesion, the deficit may also take different forms.

Ex: following posterior right cerebral lesions - patient is spatially-agnosic (constructional agnosia and a failure to perceive and recognize visual-spatial and object interrelationships). vs, following left cerebral injury, the disturbance may be secondary to a loss of control over motor programming

Although visual motor deficits can result from lesions in either hemisphere, visual-perceptual disturbances are more likely to result from right hemisphere damage.

Right hemisphere - In general, the size and sometimes the location has little or no correlation with the extent of the visual-spatial or constructional deficits demonstrated, although right parietal lesions tend to be worst of all. With right parietal involvement patients tend to have: -Trouble with the general shape and overall organization -Correct alignment and closure of details -May be a variable tendency to ignore the left half of the figure or to not fully attend to all details -Ability to perceive (or care) that errors have been made is usually compromised.

Left Hemisphere - Constructional disturbances are positively correlated with lesion size, and left anterior lesions are worse than left posterior. This is because the capacity to control and program the motor system has been compromised. The larger the lesion, the more extensive the deficit. -oversimplification and a lack of detail although the general outline or shape may be retained (left hemisphere is concerned with the analysis of parts or details and engages in temporal- sequential motor manipulations) -In some cases, when drawing, there may be a tendency to more greatly distort the right half of the figure with some preservation of left sided details.