Spatial Cognition Case File

Spatial Cognition Case File

EUGENE C.TOY, MD, RAHUL JANDIAL, MD, PhD, EVAN YALE SNYDER, MD, PhD, MARTIN T. PAUKERT, MD

CASE 43

A 67-year-old right-handed male returns to the neurology clinic with his wife for follow-up after a right middle cerebral artery (MCA) stroke. His wife says that he has been recovering well; however, he has some behaviors which are concerning to her. For example, she must be standing on his right side in order for him to acknowledge her. When he eats, he only eats food of the right side of his plate. Looking at the patient you realize he has only shaven the right side of his face.

Physical examination is notable for a left facial droop, 2+ strength of the left arm, and 3+ strength of the left leg. When you call his name while standing on the patient’s left, he turns his head to the right. The patient does not blink to threatening stimuli from the left side. The patient is asked to draw a clock and is only able to reproduce the right side.

• What is the reason for this patient’s behavior?
• What other symptoms are frequently seen with a right MCA stroke?
• What other tests can be used to elicit these symptoms?

ANSWERS TO CASE 43: SPATIAL COGNITION

Summary: A 67-year-old right-handed male presents with left-sided neglect following a right MCA stroke.

• Reason for the patient’s behavior: Hemineglect, which is more common in patients with cerebral lesions on the right (33%–85%) rather than the left side of the brain (0%–24%).
• Other symptoms seen with a right MCA stroke: The motor deficits including weakness of the face and arm more than the leg. As with 95% of the right-handed population, Broca and Wernicke areas appear to be on the left in this patient and are, therefore, not affected by the stroke. Other language deficits, include problems with prosody and nonverbal cues (see Case 46 for language disorders), behavior and attention (eg, extinction), autonomic dysfunction, and hemianopia.
• Tests to elicit the symptoms of neglect: When patients are asked to bisect a line, and they do so far to the right of center. If you were to show a photo or drawing to the patient and ask her to copy the image, she may copy only the right half of the image, or transfer the entire image to the right side of the paper. One may also ask the patient to verbally identify objects in the neglected field of vision. When asked to identify the rightsided limbs, a patient may not be able to recognize them as her own.

CLINICAL CORRELATION

Strokes provide important information about the function of the brain under normal as well as pathological circumstances. In this case, the stroke elucidated the importance of the right brain in global spatial cognition. Overall, for the majority of patients the poststroke visuospatial dysfunction will resolve. For the remaining 10%–20% of patients who have difficulties lasting greater than 3 months, rehabilitation and safety are the most concerning issues. The motor weakness secondary to stroke is compounded by the difficulties in rehab participation. For example, to have the patient practice strengthening their right arm muscles, he must first believe he has a right arm to move.

APPROACH TO SPATIAL COGNITION

Objectives

1. Know the neuroanatomy involved in spatial cognition.
2. Predict how injuries to these areas will lead to challenges in spatial cognition.
3. Be familiar with the terminology and disorders of spatial cognition.

Definitions

Extinction: Inattention to one stimulus when two stimuli are presented simultaneously.

Visual (hemi)neglect: Failure to give proper attention to the external environment.

Hemi-inattention: Failure to give proper attention to one side of the personal space.

Constructional apraxia: Inability to synthesize and comprehend discreet parts as a whole.

Dressing apraxia: Inability to manage spatial aspects of dressing oneself; a manifestation of hemi-inattention.

Prosopagnosia: Inability to identify a familiar face, without injury to visual nervous system.

Agnosia: Inability to recognize and identify objects or persons despite intact memory, knowledge of the objects or persons, and intact sensory function; generally limited to specific senses.

Allesthesia: Consistently attributing of sensory stimulation on one side to stimulation of the other side.

Ideational apraxia: Improper sequencing of events (eg, drinking from a cup and then filling it).

DISCUSSION

In the majority of the population the nondominant hemisphere is responsible for the composition and perception of spatial relations. This includes synthesizing individual parts of a visual image into a whole, as well as the perception of geometric designs and esthetic patterns. Constructional apraxia describes the inability to synthesize discrete parts into a whole image. A cortical or subcortical lesion of the forebrain may have this result.

The function of the nondominant hemisphere includes the interpretation of extrapersonal space. Self-awareness in terms of personal space and the concept of one’s own body lies in the dominant parietal lobe. A lesion to this area leads to confusion of left versus right, and an inability to identify body parts. This has to do with the posterior parietal lobe’s function in the spatial localization of stimuli, which allows for the recognition of spatial relationships from the individual to an object, or between objects. Without this essential analysis of visual-spatial information, the individual cannot orient herself or objects, nor can she navigate space appropriately, secondary to an inability to interpret spatial relationships. The superior colliculus is also involved in the perception of an object’s location. Split brain studies suggest the function of the superior colliculus to be bilateral.

The posterior parietal lobe fixes visual attention on a particular stimulus of interest. Right-sided neglect, secondary to an assault to the left side of the brain is generally accompanied by an aphasia and, therefore, may be difficult to detect. Neglect, while generally thought to be secondary to a lesion of the parietal lobe, can also result from injury to the frontal lobe, thalamus, or caudate. The hemineglect syndrome embodied by the above example has multiple forms, but can consist of hemineglect, hemi-inattention, visual extinction, allesthesia, anosognosia, anosodiaphoria, nonbelonging, visual-field defects, and gaze paresis.

Motor neglect refers to the under use of the side of the body contralateral to the cerebral insult. This may be mistaken for hemiparesis. With extraordinary care by the diagnostician, the patient may be encouraged to demonstrate function. Regardless, on examination the affected side shows decreased withdrawal, and a lack of routine movements, such as repositioning a limb when in an uncomfortable position. Likewise, when the patient falls toward the affected side, there is no reflexive effort to protect against injury. Attempts at rehabilitation may be successful, and a recent study indicated that limb activation and cueing may lead to a reduction in unilateral visual neglect (Bailey, 2002).

Bilateral occipital temporal lesions result in visual agnosia. As the primary visual cortex is intact, the patient has normal visual fields and acuity; however, when a known object is presented visually, it cannot be named. The object can be verbalized when presented via other sensory modalities such as tactile, auditory, or olfactory. Occipitotemporal lesions may also lead to environmental agnosia.

COMPREHENSION QUESTIONS

[43.1] A 67-year-old woman is brought into the clinic because she has recently begun behaving very strangely. Most notably, she has become very clumsy recently, dropping objects when trying to set them down, and running into objects that have been in their location for years while walking around her house. On examination you further note that when asked to perform an action with her left hand, she unpredictably uses her right hand instead, and the same occurs when asked to use her right. Given this conglomeration of symptoms, in what part of her brain would you expect to find a lesion?

A. Nondominant parietal lobe

B. Dominant parietal lobe

C. Nondominant temporal lobe

D. Dominant temporal lobe

[43.2] A 57-year-old man is brought into the emergency room because of acute onset of weakness and sensory loss over the left side of his body. On examination, he can move the right side of his body without difficulty to command, but cannot move anything on the left, and denies feeling anything to touch or pain stimuli on the left. Additionally, when presented with his own left hand, he denies that it is his, and also denies that there is anything wrong with him. He will also not respond to you unless you are standing on his right side. You suspect that he has had an acute stroke, which is confirmed by emergent neuroimaging. A lesion to what area of his brain most likely accounts for his inability to recognize his own hand?

A. Nondominant parietal lobe

B. Dominant parietal lobe

C. Nondominant frontal lobe

D. Dominant frontal lobe

[43.3] A 54-year-old man presents to your clinic because he feels like he is “losing his mind.” Recently, he has become less and less able to identify objects while looking at them, although he has no difficulty seeing and describing what objects look like. On examination you find that he is in fact not able to name objects based on visual stimulus alone, but when he is able to touch the object as well, he has no difficulty in naming the object. A lesion to what part of the brain would best account for these symptoms?

A. Dominant hemisphere occipital-temporal region

B. Nondominant hemisphere occipital-temporal region

C. Bilateral occipital-temporal region

D. Bilateral occipital lobe

Answers

[43.1] B. Deficits in visuospatial perception are attributed to lesions in the dominant parietal lobe. Lesions to the nondominant parietal lobe are more commonly associated with a contralateral hemineglect syndrome.

[43.2] A. Hemineglect syndromes (when the patient cannot recognize nor respond to stimuli that are coming from either the right or the left half of his body or visual field) occur from lesions in the contralateral parietal lobe, and occur more commonly with lesions in the nondominant parietal lobe than in the dominant parietal lobe. This patient may additionally have some left-sided paresis and anesthesia, although it is very difficult to diagnose that in the face of a neglect syndrome.

[43.3] C. This man is presenting with visual agnosia, an inability to recognize objects based on vision, which is caused by a lesion to the bilateral occipital-temporal region that interrupts the communication between the visual cortex and the association cortex where objects are identified. If the lesion is unilateral, the object can still be identified if it is viewed in the ipsilateral visual field (which projects to the contralateral brain, where there is no lesion). Vision remains intact, but no information is getting to the association cortex, so identifying the object becomes impossible. Communication between other sensory cortices and the association area are intact, however, so when presented with stimuli of a different modality, the object can be recognized.

NEUROSCIENCE PEARLS ❖ Spatial perception and composition is generally the complex work of the the nondominant hemisphere. ❖ Disruptions in spatial processing leads to significant disability with varied manifestations. ❖ Attention is an important part of spatial cognition, and is for the most part controlled by the posterior parietal lobe.

REFERENCES

Bailey MJ, Riddoch MJ, Crome P. Treatment of visual neglect in elderly patients with stroke: a single-subject series using either a scanning and cueing strategy or a left-limb activation strategy. Phys Ther. August 2002;82(8):782-797. 

Mort DJ, Malhotra P, Mannan SK, et al. The anatomy of visual neglect. Brain. September 2003;126(9);1986-1997.

HomeNeuroscience Case FileSpatial Cognition Case File