Table 2.
Spectroscopy studies in TRD.
| Article | Imaging modality | Aims | Experimental design | Summary of findings |
|---|---|---|---|---|
| Shah et al. (1998) | Voxel-based, whole brain, GM density analysis | To compare cortical GM density between patients with TRD, patients who recovered from depression, and HVs | TRD group: N = 20 (7 female, mean age = 48.9) Recovered group: N = 20 (7 female, mean age = 47.7) HV group: N = 20 (7 female, mean age = 49.3) |
Patients with TRD had reduced GM density in the left temporal cortex, including the left hippocampus. These changes could be associated with the duration of the illness and are linked with the cognitive difficulties that are linked to TRD. |
| Mervaala et al. (2000) | Voxel-based volumetric analysis | To examine amygdala and hippocampal volume in patients with TRD compared to HVs | TRD group: N = 34 (18 female, mean age = 42.2) HV group: N = 17 (11 female, mean age = 42.1) |
Reduced hippocampal volume and amygdala asymmetry (left smaller than right) were observed in the TRD group, highlighting the important role of those two brain areas in depression. |
| Shah et al. (2002) | Voxel-based volumetric analysis | To examine changes in fronto-striatal structures in TRD patients compared to patients who recovered from depression and HVs | TRD group: N = 20 (7 female, mean age = 48.9) Recovered group: N = 20 (7 female, mean age = 47.7) HV group: N = 20 (7 female, mean age = 49.3) |
Patients with TRD exhibited reduced volume in frontal and striatal brain structures. Changes were observed in the PFC as well as temporal structures, the right putamen, and the hippocampus. The degree of these changes was linked to illness duration. |
| Furtado et al. (2008) | Volumetric analysis | To examine possible abnormalities in the volume of the entorhinal cortex | TRD group: N = 45 (23 female, mean age = 37.5) HV group: N = 30 (17 female, mean age = 35.8) |
Compared to HV females, female TRD patients showed a significant reduction in total brain volume as well as volume of the left entorhinal cortex. |
| Sun et al. (2009) | Volumetric analysis | To identify differences in the whole and midsagittal CC in patients with TRD and TRS | TRD group: N = 45 (23 female, mean age = 40.8) TRS group: N = 42 (17 female, mean age = 39.6) HV group: N = 30 (18 female, mean age = 34.6) |
TRS and TRD patients did not significantly differ from HVs in the whole CC area. The CC4 area was significantly reduced in TRD patients compared to HVs. |
| Zhang et al. (2009) | Magnetization transfer imaging and voxel-based morphometry | To identify differences between the individuals with TRD and HVs in the limbic-cortical-striatal-pallidal-thalamic tract | TRD group: N = 15 (5 female, mean age = 33.5) HV group: N = 15 (5 female, mean age = 33.4) |
Reduced magnetization transfer ratio was observed in the TRD group in the ACC, insula, caudate tail, and amygdala-parahippocampal area. No VBM differences were observed between the TRD group and the HVs. |
| Guo et al. (2012) | DTI | To investigate the integrity of white matter tracts of different brain regions in patients with TRD compared to HVs | TRD group: N = 23 (12 female, mean age = 27.4) HV group: N = 19 (9 female, mean age = 24.4) |
Lower FA values were observed in the right anterior limb of the internal capsule, the body of the CC, and the bilateral external capsule in TRD patients compared to HVs. |
| Ma et al. (2012) | VBM and rs-fMRI | To identify GM differences in TRD and patients who responded to treatment and examine whether they are linked with altered functional connectivity | TRD group: N = 18 (7 female, mean age = 27.4) TRS group: N = 17 (7 female, mean age = 26.7) HV group: N = 17 (7 female, mean age = 24.2) |
Reduced GM volume was identified in the right middle temporal gyrus for individuals with TRD and those who had responded to treatment. Reduced GM volume was identified in the caudate of the TRD group. Both patient groups showed altered connectivity between these areas, the DMN, and frontal regions. |
| Maller et al. (2012) | Volumetric analysis | To investigate hippocampal volume changes in individuals with TRD, those with schizophrenia, and HVs | TRD group: N = 182 (88 female, mean age = 42.2) Schizophrenia group: N = 52 (20 female, mean age = 41.0) HV group: N = 76 (35 female, mean age = 35.0) |
Reduced hippocampal volume was identified in the tail section of patients with TRD and schizophrenia. This finding was most pronounced in the schizophrenia group. |
| Peng et al. (2013) | Voxel-based analysis of DTI data | To investigate white matter changes in TRD with specific interest in cortical-limbic, cortical-subcortical, and emotion regulation brain areas | TRD group: N = 30 (11 female, mean age = 26.8) HV group: N = 25 (11 female, mean age = 28.2) |
Decreased FA was identified in the left middle frontal gyrus, left limbic lobe uncus, and right cerebellum posterior lobe of patients with TRD. |
| Serra-Blasco et al. (2013) | VBM | To investigate GM volume in depression | TRD group: N = 22 (18 female, mean age = 49) Remitted, recurrent group: N = 22 (20 female, mean age = 48) First episode depressed group: N = 22 (15 female, mean age = 44) HV group: N = 32 (23 female, mean age = 46) |
In the TRD group, reduced brain volume was observed in frontolimbic areas. This group also showed smaller volumes in the left insula and right medial frontal gyrus compared to the first episode group. The remitted, recurrent group showed increased volume in the bilateral medial frontal gyrus compared to the TRD group. |
| Young (2013) | VBM | To examine differences in fronto-limbic GM volume and the connecting tracts | TRD group: N = 22 (14 female, mean age = 52.1) HV group: N = 21 (no additional information provided) |
Patients with TRD had increased GM volume in the left medial orbitofrontal cortex and bilateral hippocampus. Increased FA was also identified for the left angular bundle and right uncinate fasciculus in patients with TRD. |
| De Diego-Adeliño et al. (2014) | DTI | To investigate whole brain, white matter microstructure abnormalities in TRD | TRD group: N = 18 (15 female, mean age = 48.5) Remitted, recurrent group: N = 15 (14 female, mean age = 47) First episode depressed group: N = 19 (11 female, mean age = 44.2) HV group: N = 17 (12 female, mean age = 43.4) |
Compared to the first episode depressed and HV groups, the TRD group had reduced FA at the cingulum, CC, and superior and inferior longitudinal fascicule. Reduced FA was also observed in the TRD group at the ventromedial PFC compared to the remitted recurrent depressed group. |
| Machino et al. (2014) | VBM | To investigate the relationship between GM volume and rumination | TRD group: N = 29 (13 female, mean age = 39.6) HV group: N = 29 (13 female, mean age = 38.7) |
For the TRD group, decreased GM volume was identified in the left dorsal ACC, right ventral cingulate cortex, right superior frontal gyrus, right cerebellum, and cerebellar vermis. GM volume in the right superior temporal gyrus correlated with rumination. |
| Lan et al. (2016) | VBM | To identify structural brain changes in TRD and how these might change in response to TMS | TRD group: N = 45 (27 female, mean age = 41.5) HV group: N = 42 (27 female, mean age = 39.2) |
Patients with TRD had lower GM volume in several brain areas including the ACC and frontal and temporal cortical areas. TMS increased brain volume in a cluster including the ACC, left medial frontal gyrus and frontal medial orbital gyrus. |
ACC: anterior cingulate cortex; CC: corpus callosum; DMN: default mode network; DTI: diffusion tensor imaging; FA: fractional anisotropy; GM: grey matter; HV: healthy volunteer; PFC: prefrontal cortex; rs-fMRI: resting-state functional magnetic resonance imaging; TRD: treatment-resistant depression; TRS: treatment-resistant schizophrenia; VBM: voxel-based morphometry.