Neuroimaging Shows Increased Activity in Bipolar Mania

In a recent study looking at the difference in neural activity between persons with bipolar I disorder who were experiencing mania, those with bipolar I disorder who were experiencing euthymia or a normal, non-depressed mood, and persons who did not have any psychiatric disorders and were considered “healthy controls,” researchers found some significant differences in two brain networks.

The first was in the Dorsal Attention Network (DAN), which is a group of regions in the brain that plays a large role in our internally motivated goals using our visual attention and short-term memory processes. In other studies, increased activity is evident in the DAN after the presentation of cues indicating where, when, or to what participants should direct their attention.

In this study, those individuals who were manic had significantly higher levels of activity in their DAN compared to the euthymic group and the healthy control group, possibly explaining the often apparent hyperattention, arousal and emotional response of those experiencing mania to external stimuli.

gr1_lrg

This figure shows the increase of connectivity in mania (A) versus euthymia (B)

The second brain area assessed was the Default Mode Network (DMN), which is a group of brain regions that shows a lower level of activity when we are working on a particular mental task like paying attention, but higher levels of activity when we are doing more generic thinking tasks such as daydreaming, recalling memories, guessing about the future, monitoring the environment, speculating on the intentions of others – just thinking without any task-oriented goal in mind. Recent research has begun to find connections between the DMN and mental illnesses like anxiety and depression. Also, meditation is thought to be related to the DMN, which may be why its influence in well-being is significant.

Of particular note in this study, was the fact that those with bipolar disorder in a euthymic state showed hypo-connectivity in the dorsal nodes of their DMN compared to the mania group and healthy control group. The mania and healthy control groups showed the same connectivity.

Does this mean that the euthymic group was more relaxed, less worried about the past and future, less concerned about their surroundings and the behaviors of others than the other groups? Even the “healthy” group? I don’t know. The researchers didn’t comment on what this particular finding suggested other than the fact that this dorsal node is the exact location that corresponds to the target for transcranial magnetic stimulation (TMS) for the treatment of depression, even though they made sure to reiterate the fact that the euthymic group was not depressed.

The researchers pointed out the fact that their study’s results contribute to a body of growing evidence that points to bipolar mania as a behavioral pathology due not to circuit disruption but rather increased coherence (connectivity).

As far as the hypo-connectivity of the dorsal nodes of the DMN in the euthymic group goes, the researchers were not sure if this was due to a compensatory mechanism of the disorder trying to right itself or if it was in fact still part of the diseased state.

Of note:
– Diagnosis was determined using the Structured Clinical Interview for the DSM-IV (SCID)
– Limitations of the study included a small sample size of 23 manic, 24 euthymic, and 23 healthy controls.
– There were no significant differences in participant age, sex, and medications

Resources:

Differential brain network activity across mood states in bipolar disorder
Dorsal Attention Network
Dorsal and Ventral Attention Systems
Know Your Brain: Default mode network

Advertisements