Can you identify the difference between the two images of the houses below(Fig.1)? Isn’t it so obvious?  But a certain patient observes both these images to be completely identical. This patient has suffered from a stroke that damaged his right side of the brain, leaving everything on his left side unaware. But even though he couldn’t distinguish the difference between the two houses, when asked which house that he prefers to live in, he choose the house that is not burning. This complex and interesting condition is known as Hemispatial neglect.

Fig 1:Images of a burning house and a normal house

The brain of this patient is still processing information from his whole field of vision. He could see both images and tell the difference between them, but he just didn’t know it. If someone threw a stone at his left side, he might bend to avoid it. Yet he wouldn’t have any awareness of it or any idea why he bent. This is an important distinction between the processing of information of the brain and the experience of that information by an individual. This experience is called Consciousness.

What is Hemispatial Neglect?

Hemispatial neglect is due to a stroke in the parietal lobe of the brain. Parietal lobe is responsible in creating a 3D representation of the spatial layout of the world allowing a person to walk around without knocking on objects. Generally it is associated with lesions of the right posterior parietal cortex. When this occurs it makes the patient difficult to deal with the left side things.  They may write only on the right side of a page, shave or apply make up only on the right side and eat only from the right side of the plate.

Measuring Neglect

The gradient of neglect is not as sharp as in a primary visual field deficit and does not necessarily align with the vertical mid-line of vision. There are several neuropsychological tests to measure neglect. The most common methods are,

  1. Cancellation task
  2. Line bisection
  3. Copying task
Cancellation Task

The cancellation task includes to find out certain target characters in a cluster of other characters. The greater the number of non-target characters, there is a greater neglect of characters in the defective side(Fig.2).

Fig.2:Attempt to circle out the character “A” among varying cluster of non-target characters by a Hemispatial Neglect patient.

The figure below shows an attempt of a person with left-sided neglect to find the letter Ts among Ls. The Red dots show the correct findings and the yellow lines are the movements from one finding to another.(Fig.3)  

Fig.3:Eye movement to find the letters “T” by a left neglect person.
Line bisection

When the patient is asked to mark the midpoint of a horizontal line presented on a sheet of paper, the patient marks it on the midpoint of the right side of the bisected line(Fig.4).

Fig.4: Marking the mid-point of a line by a left neglect person
Copying Task

If asked to copy a drawing they will generally copy the right side of it including few details to the left. It is not only based on the neglect of the left side of the visuals of the world but also neglecting the left side of a mental image. When asked to draw a flower by memory, they often draw only the right side of it. The interesting fact is the patient thinks that his drawings are right, but when pointed out their mistakes the patient accepts it(Fig.5).

Fig.5: Drawings of left neglect patient.

These patients have no attention to sounds from their left side and they neglect their body parts on their left side. These patients do not suffer from any primary disorder of sensation of movement. They are not blind and they can walk normally since they have normal motor coordination.

Attempts to treat Hemispatial Neglect

Since different patients have different combinations of the deficit it is unlikely that a single treatment will be suitable for all. In the attempt to treat, several behavioral interventions and drug treatments have been followed but the results weren’t promising due to the heterogeneity of the patients.  Attempts to acknowledge the exploration of the neglected space by directing the attention to objects or tasks in that particular area minimizes the chances of neglect. Teaching patients to use an alerting device like the limb activation therapy which involves direct attention to the neglected limb had helped some individuals.

Further studies are necessary in order to combine behavioral and neuropharmacological aspects to build promising treatments.  The attempt to understand these neurological disorders needs the understanding of consciousness. It is strenuous but it is yet to be the next evolutionary step for mankind.

Image Credits

  1. Header Image-shorturl.at/wAOP3
  2. Fig.1: Capture- https://www.youtube.com/watch?v=MASBIB7zPo4
  3. Fig.2: shorturl.at/fiGQ5
  4. Fig.3: shorturl.at/pFMX2
  5. Fig.4: shorturl.at/mwRVW
  6. Fig.5: shorturl.at/hwB36

References

Tagged : / / /