Table 1.
The variance explained by and signal change attributed to different models of effects due to changes in the rates of respiration and cardiac pulsation (noise sources 3) and 4)) in the visual cortex (VC) and the total gray matter (GM) at the voxel and ROI level.
| VOXEL LEVEL | ROI LEVEL | |||
|---|---|---|---|---|
| VC | GM | VC | GM | |
| RVT⊗IRF1a) [7] |
7.0 (1.6) 1.0 (0.1) |
3.8 (0.5) 0.7 (0.1) |
19.4 (4.5) 1.0 (0.1) |
9.6 (2.5) 0.7 (0.1) |
| RVT⊗IRF2b) [15] |
3.5 (1.3) 0.8 (0.2) |
2.7 (0.9) 0.5 (0.1) |
9.8 (3.9) 0.7 (0.2) |
9.5 (4.3) 0.5 (0.1) |
| Dual-laggedc) RVT1d) |
6.8 (2.0) 1.1 (0.2) |
3.7 (1.0) 0.7 (0.1) |
17.4 (5.2) 1.0 (0.2) |
12.3 (4.4) 0.7 (0.1) |
| Dual-lagged Cardiac-rate2e) |
3.0 (1.3) 0.7 (1.1) |
1.7 (0.6) 0.5 (0.1) |
6.1 (2.7) 0.5 (0.1) |
2.5 (1.1) 0.3 (0.1) |
| Dual-lagged RVT2 |
5.1 (1.6) 0.9 (0.2) |
2.6 (0.8) 0.6 (0.1) |
14.3 (4.8) 0.8 (0.2) |
8.6 (3.9) 0.5 (0.1) |
| Dual-lagged Cardiac-rate1 |
4.7 (2.0) 0.9 (0.3) |
2.8 (0.9) 0.6 (0.1) |
9.2 (4.0) 0.6 (0.2) |
6.3 (2.2) 0.5 (0.1) |
| Multi-lagged f) RVT1 [9] |
12.3 (2.8) 1.1 (0.2) |
7.9 (1.6) 0.7 (0.1) |
31.2 (5.4) 1.0 (0.2) |
18.5 (6.6) 0.7 (0.1) |
| Multi-lagged Cardiac-rate2 [9] |
3.7 (1.0) 0.7 (0.2) |
2.4 (0.6) 0.5 (0.1) |
6.3 (2.1) 0.5 (0.1) |
4.1 (1.2) 0.3 (0.1) |
| Multi-lagged RVT2 [9] |
9.2 (1.9) 1.4 (0.2) |
5.9 (1.2) 1.0 (0.1) |
23.9 (5.0) 1.1 (0.2) |
14.1 (5.4) 0.8 (0.2) |
| Multi-lagged Cardiac-rate1 [9] |
6.7 (2.5) 1.2 (0.3) |
4.4 (1.3) 0.8 (0.2) |
13.6 (5.5) 0.7 (0.2) |
8.5 (3.4) 0.6 (0.2) |
Percentage of variance explained (% VE), average (s.e.) across subjects, is given in bold (upper row). Percentage signal change (% SC), average (s.e.) across subjects, is given in italic (lower row). Noise sources 1) and 2) were accounted for in all the regression models included in the table (for example, in the Birn model [15] in the top row, the matrix of regressors used was X = [ Xpol Xretroicor RVT⊗IRF1]).
IRF1 = respiration impulse response function used in [7] (see also Methods)
IRF2 = respiration response function described in [15] (Eq. (3))
The dual-lagged procedure corresponds to the model proposed in the present work, with RVT and cardiac-rate regressors shifted at two optimal time lags (lags = −9 s, +9 s and −3 s, +9 s respectively)
RVT1 means that VE = R2adj-1(Xrvt), see Eq. 2, and RVT2 means that VE = R2adj-2(Xrvt))
Cardiac-rate2 means that VE = R2adj-2(Xcard-rate), see Eq. 2 (analogous for Cardiac-rate1). Note that since the sum of values of RVT1 and Cardiac-rate2 is the same as that of RVT2 and Cardiac-rate1, in the table we grouped RVT1 with Cardiac-rate2 and RVT2 with Cardiac-rate1
The multi-lagged procedure corresponds to the model proposed in [9], with RVT and cardiac-rate regressors shifted at eight and five different time lags, respectively (lag range [−24 +18]s, and lag range [−12 +12]s, respectively, with step = 6 s)