Recent findings from a team of American researchers point toward a telltale shrinkage in brain size in women who have late-stage bipolar I disorder. Current evidence indicates that the effects of various bipolar illnesses can grow substantially worse over time, and researchers note clear differences between early-stage cases of these illnesses and late-stage cases. In a study published in January 2015 in the journal Acta Psychiatrica Scandinavica, researchers from the University of Texas Health Science Center at Houston assessed the brain changes in women that distinguish early-stage bipolar I disorder from late-stage cases of this disorder. The researchers concluded that women with late-stage bipolar I disorder experience significant shrinkage in the corpus callosum, a part of the brain responsible for maintaining communication between the left and right hemispheres. Bipolar I Disorder There are several distinct forms of bipolar disorder, including bipolar I disorder, bipolar II disorder, cyclothymic disorder and substance\/medication-induced bipolar and related disorder. All of these conditions center on periods of unusually \u201cup\u201d or agitated mental states (i.e., mania) and periods of the unusually \u201cdown\u201d mental states that characterize depression. Bipolar I disorder is the most severe form of bipolar illness. People affected by this condition experience periods of full-blown mania that seriously impair their ability to function; they also typically experience periods of depression severe enough to qualify for a diagnosis of major depression. In addition, some people with the disorder experience overlapping symptoms of mania and depression during \u201cmixed\u201d episodes of illness, or severe symptoms that rapidly cycle through mania and depression. In order to qualify for a bipolar I disorder diagnosis, a man or woman must experience bouts of mania or mixed mania and depression that last for a week or longer. Severe but shorter-term bouts of mania or mania\/depression may also qualify an individual for a diagnosis. Separate bouts of major depression associated with the disorder usually last for a minimum of 14 days. Late-Stage Bipolar Disorder Current evidence points toward the existence of two groups of people affected by bipolar illness. People in the first group experience relatively few bouts of mania and depression in any given year, develop their first bipolar symptoms relatively late in life and have a fairly short history of illness exposure. People in the second group experience relatively frequent bouts of mania and depression, develop their first bipolar symptoms at a relatively early age and have a fairly long history of illness exposure. Researchers sometimes refer to the characteristics found in the first group as early-stage bipolar illness; conversely, they refer to the characteristics found in the second group as late-stage bipolar illness. Crucially, individuals with late-stage bipolar illness appear to undergo a substantial decline in their ability to lead functional daily lives. Women and Late-Stage Bipolar Illness In the study published in Acta Psychiatrica Scandinavica, the University of Texas researchers used information gathered from 66 women to compare the brain effects of early-stage bipolar I disorder to the brain effects of late-stage bipolar I disorder. Twenty of the women involved in the project had an early-stage form of the illness, while 21 had a late-stage form. The remaining 25 women acted as a generally healthy comparison group unaffected by any form of bipolar illness. All of the women filled out questionnaires designed to reveal any bipolar disorder-related issues. In addition, each woman underwent an MRI (magnetic resonance imaging) brain scan. The researchers focused their MRI testing on various parts of the corpus callosum, which plays a critical role in maintaining healthy brain function. After completing their comparisons between the three groups of women, the researchers concluded that women with late-stage bipolar I disorder experience unusual shrinkage in the size of the rear portion of the corpus callosum, an area responsible for maintaining communication between the brain\u2019s left and right occipital lobes. (These lobes give humans the ability to make sense of visual and spatial information, as well as distinguish between different colors.) This fact holds true even when a number of intervening factors\u2014including age of the individual, medication intake and co-occurring mental illness\u2014are taken into account. Based on their findings, the study\u2019s authors believe that, at least in women, reduction of the size of the brain\u2019s corpus callosum may be a reliable telltale sign of advancing bipolar I disorder.