Here is a great article you should check out:
http://www.kristen-mcclure-therapist.com/bipolarandmemoryloss.html
Here is another one:
http://news.ucsf.edu/releases/study-suggests-bipolar-disorder-may-cause-progressive-brain-damage/
As far as hypomania goes, there is this study (written in journal format, not easy reading). It basically explains how the bipolar groups studied (manic, hypomanic, depressed) displayed a lower cognitive function than the group of people who have never had any type of psychiatric illness.
http://ajp.psychiatryonline.org/cgi/content/full/161/2/262
Sorry about the extra reading but I'm so cognitively impaired that I just can't explain it on my own lol.
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