Bipolar disorder is a psychiatric illness that is characterized by episodes of “mania.” Symptoms include euphoria, distractibility, irritability, and grandiosity. During a manic episode, people often have remarkable energy and move, think, and talk rapidly. They sleep little but do not appear to be tired. They may also experience delusions such as the belief that they are able to fly or are Jesus or another famous person. They may be suspicious that people are out to harm them. During a manic episode, some people hear voices or see visions. Severe depressive episodes are also often part of bipolar disorder.
Schizophrenia is an illness characterized by a group of so-called “positive” symptoms that may include hallucinations (hearing voices, seeing visions), delusions (fixed false beliefs), and/or a thought disorder (speech that makes little sense). Words are spoken, but the connections between sentences or paragraphs are illogical. (This is called a formal thought disorder.) Also, people with schizophrenia often exhibit “negative” symptoms where they become uninterested in interacting with others, lose the ability to take pleasure in previously enjoyed activities, talk less, and exhibit a demeanor that is rather flat or without much expressiveness.
Psychiatrists often see patients with a mixture of the above symptoms, and it may be difficult to determine whether a patient has schizophrenia or bipolar disorder even after following him or her for many years. Such patients may receive a diagnostic label of schizoaffective disorder, bipolar type.
Genes and environment both contribute to the causes of bipolar disorder and schizophrenia. In terms of genetic factors, it appears that small changes in a large number of genes can add up and increase the risk of someone developing one of these disorders. Some genes are more related to the development of schizophrenia, and other genes are more related to bipolar disorder. However, some genes seem to be related to both disorders. In other words, some abnormalities in the same genes may be shared by schizophrenia and bipolar disorder.
S. A. Meda and colleagues recently published a study in Biological Psychiatry that compared the interactions between specific brain systems in several groups of people: persons without psychiatric illness, persons with clear-cut bipolar disorder, and persons with clear-cut schizophrenia. This research team used functional brain imaging to examine the interrelationships among 5 brain networks. A brain network is composed of brain regions that function together and are responsible for activities of the mind such as motivation, emotion, and cognition (memory, attention, planning, etc). Networks interact with each other, and various behaviors are likely related to these interactions. The 5 networks that were examined in this study involved 1) visual processing, 2) social awareness, 3) recognizing and interpreting emotions, 4) integrating language with emotions and planning, and 5) control and regulation of movement and timing of responses. Each of these networks involves a number of specific brain structures that are increasingly well understood.
How do these 5 networks interact in persons with schizophrenia or bipolar disorder compared to healthy controls? It turns out that patients with schizophrenia had a diminished interaction between two of these specific networks when compared to either controls or persons with bipolar disorder. Patients with bipolar disorder demonstrated increased interactions between a different pair of networks when compared to patients with schizophrenia or controls. However, there were two networks that showed diminished interactions in both schizophrenia and bipolar disorder when compared to controls.
Meda and colleagues interpret these results as indicating that there are certain brain network interactions that are uniquely out of balance in schizophrenia. Other network interactions are uniquely out of balance in bipolar disorder. However, there are some interactions that are similarly out of balance in both schizophrenia and bipolar disorder. They suggest that the networks that are similarly out of balance in both illnesses may be related to certain psychotic symptoms, such as delusions. Furthermore, they suggest that the pattern of connections specific to schizophrenia involves brain regions that may be related to the negative symptoms described above and that the pattern of abnormal interactions unique to bipolar disorder may be related to brain regions involved in mood regulation.
Interestingly, these authors also examined brain network interactions in psychiatrically healthy, first-degree relatives of persons with these two illnesses. Healthy relatives of persons with bipolar disorder exhibited some of the same out-of-balance network interactions as their symptomatic relatives.
What should we make of this type of research? The bottom line is that we are beginning to be able to relate symptoms of illnesses to abnormalities in the interactions between specific brain networks. The more we understand symptoms at a brain level, the better our chances of pinpointing the cause(s) of abnormal brain system interactions. It is likely that this sort of work will help us develop imaging procedures to recognize patterns of connections that might predict risk for developing specific psychiatric illness. Eventually, as we elucidate causes, we should be more equipped to develop increasingly specific forms of treatment.
Years ago, this would be considered science fiction. Now, it is a matter of “when” not “if.”
This column was co-written by Eugene Rubin MD, PhD and Charles Zorumski MD