Wednesday, December 1, 2010

ADHD and Vision Meets the Brain

Superficial dissection of brain-stem. Lateral ...Image via Wikipedia Two areas interest me:  the link between adhd and convergence insufficiency (the ability to pull your eyes together ) and the link between peripheral vision and adhd.  I have problems in both areas and I am starting to wonder whether these hot these areas are related to attention.

Link Between Vision Problems and ADHD Distractibility 

Children diagnosed with ADHD have a three fold increase in the incidence of Convergence Insufficiency as compared to controls and a two fold increase in the incidence of visual tracking problems. This may be related to a hyper responsive superior colliculus. The superior colliculus (SC) is a brain structure which is involved in the control of distractibility and of eye and head movements. Some researchers have proposed that in ADHD, the colliculus is hyper-responsive, which causes inattention and distractibility. Could the hyper-responsive SC also be causing the problems with convergence and tracking??

Peripheral Vision Meets the Attention System

Another interesting intersection of attention and vision lies in peripheral vision.   Peripheral vision lies in the magnocellular visual system -- magnocellular or "parasol" cells in the retina.  These cells have high contrast sensitivity, fast response times and transient responses.  The magnocellular system has a short latency pathway from the visual cortex to the superior colliculus.  It is thought that this may result in a reflexive saccadic movements (rapid movements of the eyes between fixation points) that bring peripheral stimulus into focus.    The interaction between the posterior attention network and the magnocellur visual system controlling peripheral vision localization may explain distractability (lack of attention) or non distractibilty.  The posterior attention network has inhibitory control over the superior colliculus via the substantia nigra.   The superior colliculus control over peripheral eye movements  is inhibited during focal visual attention (when you focus with the eyes).  When you are focused on something, you are relatively undistracted from things on the periphery. 

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