Left world neglected

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Posted by Sanya Naware MSIV, Drexel University College of Medicine

What would it feel like to only perceive one half of the world around you?

For patients with hemispatial neglect, this is an everyday reality.  Hemispatial neglect or hemineglect is a condition in which damage to one hemisphere of the brain causes a lack of awareness of one contralateral side of space.  It is most often a lesion of the right posterior parietal cortex affecting the contralateral side of the body.  The person is unable to recognize stimuli or process them on the affected side.  Left neglect is more common than right neglect because the right hemisphere is able to compensate for the loss of left hemispheric function.

Because these patients only perceive one side, they only draw what we know to be half of an image as seen in the video and image below:

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Lisa Genova, a neuroscientist, expertly describes the daily challenges of living with neglect in her book Left Neglected. It is a difficult condition to imagine and this book does a wonderful job of explaining the realities and frustrations of the patient and her family.

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The main character, Sarah Nickerson, suffers a traumatic brain injury in a car crash.  When she wakes up, everyone around her realizes that she ignores the left side of everything.  Whether it is a clock, a painting, or a room around her, she is not able to recognize the left side of anything.  While she is able to feel the left side of her body, she has to focus on the fact that she has a left side in order to control her left leg and walk.  In fact, when she first sees her left arm, she states that it feels like it belongs to another person, a problem called somatoparaphrenia.  While eating, she only eats the food on the right side of her tray.  She frequently bumps into objects on the left side of her body because she is unaware of their presence.

Sarah’s story is optimistic as her therapist and family use certain tricks to help her adjust.  Some of these methods include placing bright orange tape on the left side of things around their home, using a ruler to guide her to the left side of the page, and wearing shiny jewelry on her left hand to attract attention to it.

Genova ends her book by endorsing the New England Handicapped Sports Association (NEHSA), an organization of volunteers who help people like Sarah find some independence and confidence.

Click here to find out more about right hemispheric brain damage from NEHSA.

References

  1. Genova, Lisa. Left Neglected: A Novel. New York: Gallery, 2011.
  2. Waxman SG. Chapter 21. Higher Cortical Functions. In: Waxman SG, ed.Clinical Neuroanatomy. 26th ed. New York: McGraw-Hill; 2010.
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Synesthesia: Boy that word tastes good, huh?

Posted by Deepak H. Singh, MS IV Drexel University College of Medicine

Putting my intense desire to describe the mauve affect of a patient, or the loud shirt that a colleague is wearing aside, synesthesia is a fascinating phenomenon in which two or more senses in certain individuals are overlapped, meaning that the experience of both senses is connected in someway.

This has been described in terms of various different senses including forms such as grapheme-color synesthesia in which letters and numbers are perceived as colors, chromesthesia in which sounds are perceived as color, or lexical-gustatory synesthesia in which individual words are perceived as taste sensations in the mouth as alluded to in the title of this blog post.

Click here to find out more about word-taste synesthesia from the BBC.

Some notable supposed synesthetes to perhaps pique your interest are inventor Nikola Tesla, Muscians Eddie Van Halen, Billy Joel, Pharell Williams, and Actor Geoffrey Rush, among others.

This condition has long perplexed neuroscientists who are only touching the surface of the unique neural pathways that may account for the various experiences described by synesthetes.

One school of thought that has gained some traction is the concept of cross-activation, which is made possible by a failure of the physiological process of “synaptic pruning” that occurs in all of our brains during the initial developmental stages.  Synaptic pruning refers to a series of regulatory processes during which various axonal networks that were functional in one stage of development are outcompeted and subsequently eliminated as other synaptic connections become more frequently used as maturation occurs. In synesthetes  it is hypothesized that certain of these connections fail to regress leading to atypical connections between two sensory regions of the brain, thereby opening the door for some pretty vivid sensorial experiences. This, however, has only really held up for sensory regions directly adjacent to one another, as was demonstrated by fMRI studies showing significant brain activity in both the auditory cortex and the fusiform gyrus (responsible for color perception) in synesthetes while no such congruous activity was seen in age-matched controls. Similarly, in one study on lexical-gustatory synesthesia, the lateral sulcus (responsible for taste processing) was activated simultaneously with the auditory cortex in synesthetes.

Another prevailing hypothesis is the concept of “disinhibited feedback“. Normally, signals are travelling in both directions between the primary sensory regions of the brain and those that are involved in organizing that information, and feedback (both positive and negative) is constantly occurring to reconcile all of the different sensory input. If this balance were disrupted, however, it would be possible for signals encountered in the later stage of processing to influence those that were encountered earlier, resulting in the overlapping sensations that are perceived by synesthetes. This, too, may make more sense of the case reports in which individuals with temporal lobe epilepsy or individuals who have just experienced head trauma or stroke to “acquire” a synesthesia-like experience due to some disruption in those pathways, though no concrete studies have been done to test that theory.

Perhaps we’ll never know what is truly occurring at a neuroanatomical level that causes such a curious phenotype. In the meantime, looking at the accomplished list of puported “sufferers” of this condition, it may be worthwhile to pose the following question: which came first the synesthesia or the visionary?