Aberrant topology of the default mode network is associated with phosphatidylcholine and triglyceride levels in major depressive disorder

Table 1 Introduction of nodal metrics and their meaning in the brain structural network

Nodal metrics	Meaning
Betweenness centrality	The extent to which a node controls information flow by lying on shortest paths between other node pairs in the network
Degree centrality	The number of edges directly connected to a node
Clustering coefficient	The density of connections among a node’s immediate neighbors
Efficiency	The ability of a node to propagate information with the other nodes in a network
Local efficiency	The robustness of information transfer within the immediate neighborhood of a node upon its removal
Shortest path length	The minimum number of edges required to traverse between two nodes

Table 2 Default mode network nodes in prior research

Node name	Left	Right
SFGmed	SFGmed.L	SFGmed.R
ORBsupmed	ORBsupmed.L	ORBsupmed.R
PCG	PCG.L	PCG.R
PHG	PHG.L	PHG.R
SMG	SMG.L	SMG.R
ANG	ANG.L	ANG.R
PCUN	PCUN.L	PCUN.R
MTG	MTG.L	MTG.R

SFGmed: Superior medial frontal gyrus; SFGmed.L: Left medial superior frontal gyrus; SFGmed.R: Right medial superior frontal gyrus; ORBsupmed: Superior orbital frontal gyrus; ORBsupmed L: Left superior orbital frontal gyrus; ORBsupmed R: Right superior orbital frontal gyrus; PCG: Posterior cingulate gyrus; PCG.L: Left posterior cingulate gyrus; PCG.R: Right posterior cingulate gyrus; PHG: Parahippocampal gyrus; PHG.L: Left parahippocampal gyrus; PHG.R: Right parahippocampal gyrus; SMG: Supramarginal gyrus; SMG.L: Left supramarginal gyrus; SMG.R: Right supramarginal gyrus; ANG: Angular gyrus; ANG.L: Left angular gyrus; ANG.R: Right angular gyrus; PCUN.L: Left precuneus; PCUN: Precuneus; PCUN.R: Right precuneus; MTG: Middle temporal gyrus; MTG.L: Left middle temporal gyrus; MTG.R: Right middle temporal gyrus.

Table 3 Demographic characteristics, mean ± SD

	MDD (n = 71)	HC (n = 76)	t/χ2	P value
Age	31.52 ± 11.63	30.68 ± 8.71	0.496	0.621
Education (years)	13.07 ± 3.15	15.62 ± 3.07	-4.960	< 0.001c
Sex (male/female)	27/44	35/41	0.969	0.325
BMI (kg/m2)	22.56 ± 4.21	22.81 ± 4.55	-0.345	0.730
HAMA	19.69 ± 5.69	-	-	-
HAMD-17	21.59 ± 5.62	-	-	-
Total disease duration (months)	52.44 ± 53.0	-	-	-
Average daily dose (mg)	21.12 ± 12.92	-	-	-
SSRI/SNRI/NaSSA/SARI	34/21/9/7	-	-	-

^cP < 0.001.

Antidepressants were converted into fluoxetine equivalents. MDD: Major depressive disorder group; HC: Health control group; BMI: Body mass index; HAMA: Hamilton Anxiety Rating Scale; HAMD-17: 17-item Hamilton Depression Rating Scale; SSRI: Selective serotonin reuptake inhibitor; SNRI: Serotonin-norepinephrine reuptake inhibitor; NaSSA: Noradrenergic and specific serotonergic antidepressant; SARI: Serotonin receptor antagonist and reuptake inhibitor.

Table 4 Abnormal topological properties of the default mode network nodes in patients with major depressive disorder

Nodal metrics	Node	P value	FDR q value
Betweenness centrality	SFGmed.R	0.002	0.019a
	PCG.R	< 0.001c	0.011a
	SMG.L	0.016	0.049a
	SMG.R	0.012	0.049a
	ANG.L	0.004	0.021a
Degree centrality	SFGmed.R	< 0.001c	0.005a
	SMG.L	0.019	0.153
Clustering coefficient	PCG.R	0.002	0.029a
	SMG.L	0.034	0.108
	SMG.R	0.020	0.108
	ANG.L	0.025	0.108
	ANG.R	0.029	0.108
Efficiency	SFGmed.R	< 0.001c	0.005a
	SMG.L	0.014	0.114
Local efficiency	PCG.R	0.002	0.029a
	SMG.L	0.034	0.108
	SMG.R	0.020	0.108
	ANG.L	0.025	0.108
	ANG.R	0.029	0.108
Shortest path	SFGmed.R	< 0.001c	0.005a
	SMG.L	0.014	0.109

^aq < 0.05.

^cP < 0.001.

Only uncorrected P values with a threshold of < 0.05 are presented. False discovery rate correction was performed solely on the P values of the 16 default mode network nodes. FDR: False discovery rate; SFGmed.R: Right medial superior frontal gyrus; PCG.R: Right posterior cingulate gyrus; SMG.L: Left supramarginal gyrus; SMG.R: Right supramarginal gyrus; ANG.L: Left angular gyrus; ANG.R: Right angular gyrus.