Hyperconnectivity and High Temporal Variability of the Primary Somatosensory Cortex in Low-Back-Related Leg Pain: An fMRI Study of Static and Dynamic Functional Connectivity

Figures & data

Table 1 Demographic Data and Clinical Characteristics of the LBLP and HCs Groups

Characteristics	LBLP Patients	Healthy Controls	P values
	Mean (SD)	Mean (SD)
Gender (M/F)	14/12	16/18	0.271 ^#
Age (y)	54.15 (7.83)	54.62 (5.62)	0.249
Duration of symptoms (months)	36.81 (49.40)	n/a (n/a)	n/a
VAS scores	5.65 (1.04)	n/a (n/a)	n/a
JOA scores	14.38(4.92)	n/a (n/a)	n/a
Fugl-Meyer scores	20.12 (1.90)	n/a (n/a)	n/a
Barthel index	86.15 (12.59)	n/a (n/a)	n/a
2PD of right hand	23.77(4.74)	n/a (n/a)	n/a
2PD of left hand	24.27(5.68)	n/a (n/a)	n/a
2PD of right foot	28.88(7.65)	n/a (n/a)	n/a
2PD of left foot	29.31(6.11)	n/a (n/a)	n/a

Note: ^# Chi-squared tests.

Abbreviations: LBLP, low-back-related leg pain; F, female; M, male; n/a, not available; SD, standard deviation; JOA, Japanese Orthopaedic Association; VAS, visual analog scale; 2PD, the two-point tactile discrimination; y, years.

Table 2 Differences in the Alterations of sFC of the S1 Cortex Between the LBLP and HCs Groups (Two-Sample t-Test, Two-Tailed, Voxel-Level P < 0.001, GRF Correction, Cluster-Level P < 0.005)

Brain Regions	BA	Peak T-Scores	MNI Coordinates			Cluster Size (Voxels)	zFC-values*(LBLP vs HCs)		Effect Size (Cohen’s d)
			x	y	z
Seed: left S1back (LBLP vs HCs)
Right superior and middle frontal gyrus (SFG/MFG)	9, 10	5.498	30	27	36	130		−0.008 ± 0.022 vs −0.175 ± 0.018	1.545
Seed: left S1chest (LBLP vs HCs)
Right SFG/MFG	8	4.345	30	24	39	109		0.005 ± 0.017 vs −0.146± 0.015	1.746
Seed: right S1chest (LBLP vs HCs)
Right SFG/MFG	10	4.707	36	48	27	99		0.070 ± 0.018 vs −0.083 ± 0.015	1.699
Seed: left S1face (LBLP vs HCs)
Right MFG	10	5.748	33	42	18	98		0.026 ± 0.019 vs −0.128 ± 0.019	1.519
Seed: right S1face (LBLP vs HCs)
Right Inferior parietal lobule (IPL)	40	5.487	60	−39	27	89		0.123 ± 0.036 vs −0.087 ± 0.024	1.275

Note: *mean ± standard error.

Abbreviations: LBLP, low-back-related leg pain; HCs, healthy controls; sFC, static functional connectivity; S1_back, representation of the back in the primary somatosensory cortex; BA, Brodmann’s area; MNI, Montreal Neurological Institute Coordinate System.

Figure 1 Static functional connectivity spatial distributions were observed at the group level for LBLP patients and healthy controls (the left somatotopic S1 subregions).

Abbreviations: sFC, static functional connectivity; S1, primary somatosensory cortex; LBLP, low-back-related leg pain; HCs, healthy controls.

Figure 2 Differences in the alterations of sFC between the LBLP patients and healthy controls (two-sample t-test, two-tailed, voxel-level P < 0.001, GRF correction, cluster-level P < 0.005).

Notes: (A–C) Patients with LBLP exhibited increased sFC to the right SFG/MFG. (D) Patients with LBLP exhibited increased sFC to the right MFG. Values of sFC are the mean ± SEM.

Abbreviations: sFC, static functional connectivity; LBLP, low-back-related leg pain; HCs, healthy controls; SFG, superior frontal gyrus; MFG, middle frontal gyrus; S1_{back_L}, representation of the left back in the primary somatosensory cortex.

Table 3 Differences in the Alterations of dFC of the S1 Cortex Between the LBLP and HCs Groups (Two-Sample t-Test, Two-Tailed, Voxel-Level P < 0.01, GRF Correction, Cluster-Level P < 0.05)

Brain Regions	BA	Peak T-Scores	MNI Coordinates			Cluster Size (Voxels)	zFC-values*(LBLP vs HCs)	Effect Size (Cohen’s d)
			x	y	z
dFC of the right S1hand (LBLP vs HCs)
Left precentral and postcentral gyrus (PRG/POG)	3,4	3.271	−24	−48	57	75	0.003 ± 0.001 vs −0.001 ± 0.007	1.004
dFC of the right S1finger (LBLP vs HCs)
Right PRG/POG	3, 4, 6	4.207	57	−18	36	129	0.004 ± 0.001 vs −0.001 ± 0.007	1.413

Note: *mean±standard error.

Abbreviations: LBLP, low-back-related leg pain; HCs, healthy controls; dFC, dynamic functional connectivity; S1_hand, representation of the hand in the primary somatosensory cortex; BA, Brodmann’s area; MNI, Montreal Neurological Institute Coordinate System.

Figure 3 Differences in the alterations of dFC between LBLP patients and healthy controls (two-sample t-test, two-tailed, voxel-level P < 0.01, GRF correction, cluster-level P < 0.05).

Notes: (A) Increased dFC between the right S1_hand cortex and the left PRG/POG in LBLP patients. (B) Increased dFC between the right S1_finger cortex and the right PRG/POG in LBLP patients.

Abbreviations: dFC, dynamic functional connectivity; LBLP, low-back-related leg pain; HCs, healthy controls; PRG, precentral gyrus; POG, postcentral gyrus; S1_{hand_R}, representation of the right hand in the primary somatosensory cortex; values of sFC are the mean ± SEM.

Figure 4 (A) Patients with LBLP exhibited increased sFC to the right IPL. Values are the mean ± SEM (two-sample t-test, two-tailed, voxel-level P < 0.001, GRF correction, cluster-level P < 0.005). (B) Partial correlational analysis between sFC alterations and the Barthel index in LBLP patients.

Abbreviations: sFC, static functional connectivity; LBLP, low-back-related leg pain; IPL, inferior parietal lobule; S1_{face_R}, representation of the right face in the primary somatosensory cortex.