Lamina-dependent calibrated BOLD response in human primary motor cortex
Section snippets
Mathematical symbols
- [X]:
concentration of compound X;
- .0:
index indicating a baseline (‘rest’) level;
- .t:
index indicating the total blood compartment;
- .v:
index indicating the venous compartment;
- CBF:
cerebral blood flow;
- CBV:
cerebral blood volume;
- CMRO2:
cerebral metabolic rate of oxygen consumption;
- f:
relative CBF;
- M:
calibration constant, i.e., maximal BOLD signal change;
- n:
metabolic-vascular coupling factor;
- R2:
(irreversible) transverse relaxation rate;
- R2′:
effective transverse relaxation rate induced by external fields;
- r:
Calculation of CMRO2 and scaled profiles
The Davis model assumes the following relationship (Davis et al., 1998, Hoge et al., 1999):
where δSact = (Sact − S0)/S0 is the relative BOLD signal change (induced either by a task or a gas manipulation) from the baseline value, S0, and β is a constant describing the coupling between the effective transverse relaxation rate induced by external fields, R2′, and the dHb concentration according to.
κ is a proportionality constant that varies with magnetic field
Results
Robust BOLD and VASO activations were found in all participants within the hand-knob area (Fig. 4).
The average temporal SNR (tSNR) was (20.7 ± 2.2) for BOLD and (15.2 ± 2.4) for VASO. The functional CNR (defined as (∆ S/S) ∙ tSNR) for the finger-tapping contrast was (0.9 ± 0.3) for BOLD and (− 0.4 ± 0.2) for VASO; the functional CNR for the pure hypercapnia challenge (i.e., without concomitant tapping) was (1.1 ± 0.2) for BOLD and (− 0.4 ± 0.1) for VASO. The statistical activation maps show the responses under
Discussion
The data from our study suggest that sufficient CNR was obtained to investigate simultaneously recorded BOLD and CBV responses during finger tapping and hypercapnia, as well as for high-resolution estimation of CMRO2. Fig. 3 demonstrates that significant changes in BOLD and VASO signals are consistently detected across participants. Independent of this consistent detectability, however, there is relatively large variability in the amplitude of the functional responses across participants,
Conclusion
We have demonstrated that it is possible to measure CBV and BOLD signal changes during finger tapping and hypercapnia on a submillimeter laminar level. By application of a modified Davis model, this data can be used to estimate changes of CMRO2 and the value of the calibration parameter M across the cortical thickness on this laminar scale. We have shown that there are differences in depth-dependent activation profiles of the BOLD signal and CBV and that these features are consistent across
Acknowledgements
This study was supported by the Initial Training Network, HiMR, funded by the FP7 Marie Curie Actions of the European Commission (FP7-PEOPLE-2012-ITN-316716). We thank Enrico Reimer for IT support regarding MRI data conversion and developing a 3D MRI data projection viewer for planning slice orientation. We also thank Riccardo Metere for fruitful discussions and Domenica Wilfling and Elisabeth Wladimirow for radiographic assistance. Parts of the this work have been presented at the 23rd Annual
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Cited by (0)
- 1
Present address: Laurentius Huber, Ph.D. Section on Functional Imaging Methods Laboratory of Brain and Cognition, National Institute of Mental Health, Building 10, Room 1D80 10, Center Dr. MSC 1148 Bethesda, MD 20892-1148, USA.
- 2
Present address: Claudine J. Gauthier, Ph.D., Richard J. Renaud Science Complex, 7141 Sherbrooke W. Concordia University, Montréal, Québec, Canada.