Table 1.
Overview of the main studies reviewed that related structural longitudinal brain imaging outcomes to manic episodes.
| Reference | Diagnosis and sample characteristics | Sample size | Follow-up time | Method; MRI metric | Main result | Brain area affected |
|---|---|---|---|---|---|---|
| Moorhead et al., 2007 | Bipolar type 1 (male and female adults). | 20 | 4 years (two timepoints) | VBM/TBM (region of interest); gray matter density | Number of manic/hypomanic episodes during follow-up correlated with gray matter loss in cerebellar and temporal lobe. | Temporal lobe (including hippocampus and fusiform) |
| Gogtay, 2007 | Heterogenous clinical picture with/without first manic episode, healthy controls (male children) | 8/9, 18 | 4–8 years (scanned every two years, incl. scans pre/post first manic episode) | Surface-based; gray matter density | Results suggestive for faster gray matter decreases in children who experienced first manic episode, but not in children that did not experience a manic episode. | Bilateral anterior (and sub genual) cingulate cortex |
| Abé et al., 2015 | Bipolar type 1 with/without manic episodes (male and female adults). | 18/21 | 6 years (two timepoints) | Surface based (region of interest): cortical thickness, surface area, volume | Patients who experienced mania decreased in cortical volume, whereas those without manic episodes did not. Patients who had no manic episodes displayed increases in cortical thickness and decreases in surface area. | Bilateral dlPFC, inferior frontal cortex |
| Zak et al., 2019 | Bipolar type 2 with few/many hypomanic episodes between time points, healthy controls (male and female adults). | 12/16, 35 | 2.4 years (two timepoints) | Surface based (vertex-wise, region of interest, and whole brain) | Patients with few (0–3) hypomanic episodes had greater temporal cortical thinning than patients with more (>3) hypomanic episodes. | left/right temporal cortex |
| Abé et al., 2020 | Bipolar type 1 with/without manic episodes between timepoints, bipolar type 2 with/without hypomanic episodes, healthy controls (male and female adults). | 35/21, 8/15, 46 | 6 years (two timepoints) | Surface based (vertex-wise, whole brain): cortical thickness | Bipolar disorder type 1 patients, who experienced mania, showed greater cortical thinning than controls and patients without manic episodes. The same pattern was observed in bipolar disorder type 2 with respect to hypomania. Cortical change rates did not differ between patients without manic episodes and controls, who displayed normal age-related thinning. | left inferior frontal cortex |
| Abé et al., 2021 | Bipolar type 1, type 2, NOS (male and female adults). | 230 | 0.5–9 years (two timepoints) | Surface based (region of interest, whole brain): cortical thickness, surface area; subcortical volumes | Negative correlation between yearly thickness change rates and the number of manic, hypomanic, and/or mixed episodes between time points. No correlation between the number of mood episodes and surface area or subcortical volumes. Follow-up tests: Patient who experienced manic, hypomanic, and/or mixed episodes showed cortical thinning, while those without showed no changes or increases in cortical thickness. Results remained when excluding patient included in Abé et al. 2015 and 2020, and when controlling for various potential confounders, incl. depressive episodes. | Frontal: left frontal pole, bilateral inferior frontal, right caudal anterior cingulate, left dm/dlPFC. Other brain areas: left lingual, right paracentral, left isthmus, left transverse temporal. |
| Cahn et al., 2021 (review) | Bipolar type 1 following first manic episode (male and female adults and children). | Sample sizes ranged from 8–41 patients and 17–70 controls | >1 year | Various methods; gray matter volume (cortical or subcortical), cortical thickness, or surface area. | Various findings. Most consistently reported finding was a faster gray matter volume decreases in patients that experienced a first manic episode compared with controls in anterior cingulate cortex. | Anterior cingulate cortex |
Sample characteristics, investigated MRI metrics, and main results are summarized.
dm dorsomedial, dlPFC dorsolateral prefrontal cortex, MRI magnetic resonance imaging, NOS not otherwise specified, TBM tensor-based morphometry, VBM voxel-based morphometry.