Size of the spatial correlation between ECoG and fMRI activity
Electrocorticography (ECoG) is typically employed to accurately identify the seizure focus as well as the location of brain functions to be spared during surgical resection in participants with drug-resistant epilepsy. Increasingly, this technique has become a powerful tool to map cognitive function...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Elsevier
2021-11-01
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| Series: | NeuroImage |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S1053811921007333 |
| _version_ | 1818670278236962816 |
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| author | Giovanni Piantoni Dora Hermes Nick Ramsey Natalia Petridou |
| author_facet | Giovanni Piantoni Dora Hermes Nick Ramsey Natalia Petridou |
| author_sort | Giovanni Piantoni |
| collection | DOAJ |
| description | Electrocorticography (ECoG) is typically employed to accurately identify the seizure focus as well as the location of brain functions to be spared during surgical resection in participants with drug-resistant epilepsy. Increasingly, this technique has become a powerful tool to map cognitive functions onto brain regions. Cortical mapping is more commonly investigated with functional MRI (fMRI), which measures blood-oxygen level dependent (BOLD) changes induced by neuronal activity. The multimodal integration between typical 3T fMRI activity maps and ECoG measurements can provide unique insight into the spatiotemporal aspects of cognition. However, the optimal integration of fMRI and ECoG requires fundamental insight into the spatial smoothness of the BOLD signal under each electrode.Here we use ECoG as ground truth for the extent of activity, as each electrode is thought to record from the cortical tissue directly underneath the contact, to estimate the spatial smoothness of the associated BOLD response at 3T fMRI. We compared the high-frequency broadband (HFB) activity recorded with ECoG while participants performed a motor task. Activity maps were obtained with fMRI at 3T for the same task in the same participant prior to surgery. We then correlated HFB power with the fMRI BOLD signal change in the area around each electrode. This latter measure was quantified by applying a 3D Gaussian kernel of varying width (sigma between 1 mm and 20 mm) to the fMRI maps including only gray-matter.We found that the correlation between HFB and BOLD activity increased sharply up to the point when the kernel width was set to 4 mm, which we defined as the kernel width of maximal spatial specificity. After this point, as the kernel width increased, the highest level of explained variance was reached at a kernel width of 9 mm for most participants. Intriguingly, maximal specificity was also limited to 4 mm for low-frequency bands, such as alpha and beta, but the kernel width with the highest explained variance was less spatially limited than the HFB.In summary, spatial specificity is limited to a kernel width of 4 mm but explained variance keeps on increasing as you average over more and more voxels containing the relatively noisy BOLD signal. Future multimodal studies should choose the kernel width based on their research goal. For maximal spatial specificity, ECoG electrodes are best compared to 3T fMRI with a kernel width of 4 mm. When optimizing the correlation between modalities, highest explained variance can be obtained at larger kernel widths of 9 mm, at the expense of spatial specificity. Finally, we release the complete pipeline so that researchers can estimate the most appropriate kernel width from their multimodal datasets. |
| first_indexed | 2024-12-17T07:05:34Z |
| format | Article |
| id | doaj.art-79efae7319354815837baa44efcc9de9 |
| institution | Directory Open Access Journal |
| issn | 1095-9572 |
| language | English |
| last_indexed | 2024-12-17T07:05:34Z |
| publishDate | 2021-11-01 |
| publisher | Elsevier |
| record_format | Article |
| series | NeuroImage |
| spelling | doaj.art-79efae7319354815837baa44efcc9de92022-12-21T21:59:10ZengElsevierNeuroImage1095-95722021-11-01242118459Size of the spatial correlation between ECoG and fMRI activityGiovanni Piantoni0Dora Hermes1Nick Ramsey2Natalia Petridou3Dept Neurology & Neurosurgery, UMC Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands; Corresponding author.Dept Physiology & Biomedical Engineering, Mayo Clinic, Rochester, MN, United States; Dept Neurology, Mayo Clinic, Rochester, MN, United States; Dept Radiology, Mayo Clinic, Rochester, MN, United StatesDept Neurology & Neurosurgery, UMC Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the NetherlandsDept Radiology, UMC Utrecht, Heidelberglaan 100, Utrecht, the NetherlandsElectrocorticography (ECoG) is typically employed to accurately identify the seizure focus as well as the location of brain functions to be spared during surgical resection in participants with drug-resistant epilepsy. Increasingly, this technique has become a powerful tool to map cognitive functions onto brain regions. Cortical mapping is more commonly investigated with functional MRI (fMRI), which measures blood-oxygen level dependent (BOLD) changes induced by neuronal activity. The multimodal integration between typical 3T fMRI activity maps and ECoG measurements can provide unique insight into the spatiotemporal aspects of cognition. However, the optimal integration of fMRI and ECoG requires fundamental insight into the spatial smoothness of the BOLD signal under each electrode.Here we use ECoG as ground truth for the extent of activity, as each electrode is thought to record from the cortical tissue directly underneath the contact, to estimate the spatial smoothness of the associated BOLD response at 3T fMRI. We compared the high-frequency broadband (HFB) activity recorded with ECoG while participants performed a motor task. Activity maps were obtained with fMRI at 3T for the same task in the same participant prior to surgery. We then correlated HFB power with the fMRI BOLD signal change in the area around each electrode. This latter measure was quantified by applying a 3D Gaussian kernel of varying width (sigma between 1 mm and 20 mm) to the fMRI maps including only gray-matter.We found that the correlation between HFB and BOLD activity increased sharply up to the point when the kernel width was set to 4 mm, which we defined as the kernel width of maximal spatial specificity. After this point, as the kernel width increased, the highest level of explained variance was reached at a kernel width of 9 mm for most participants. Intriguingly, maximal specificity was also limited to 4 mm for low-frequency bands, such as alpha and beta, but the kernel width with the highest explained variance was less spatially limited than the HFB.In summary, spatial specificity is limited to a kernel width of 4 mm but explained variance keeps on increasing as you average over more and more voxels containing the relatively noisy BOLD signal. Future multimodal studies should choose the kernel width based on their research goal. For maximal spatial specificity, ECoG electrodes are best compared to 3T fMRI with a kernel width of 4 mm. When optimizing the correlation between modalities, highest explained variance can be obtained at larger kernel widths of 9 mm, at the expense of spatial specificity. Finally, we release the complete pipeline so that researchers can estimate the most appropriate kernel width from their multimodal datasets.http://www.sciencedirect.com/science/article/pii/S1053811921007333Motor cortexElectrocorticographyFunctional MRIFunctional neuroimaging |
| spellingShingle | Giovanni Piantoni Dora Hermes Nick Ramsey Natalia Petridou Size of the spatial correlation between ECoG and fMRI activity NeuroImage Motor cortex Electrocorticography Functional MRI Functional neuroimaging |
| title | Size of the spatial correlation between ECoG and fMRI activity |
| title_full | Size of the spatial correlation between ECoG and fMRI activity |
| title_fullStr | Size of the spatial correlation between ECoG and fMRI activity |
| title_full_unstemmed | Size of the spatial correlation between ECoG and fMRI activity |
| title_short | Size of the spatial correlation between ECoG and fMRI activity |
| title_sort | size of the spatial correlation between ecog and fmri activity |
| topic | Motor cortex Electrocorticography Functional MRI Functional neuroimaging |
| url | http://www.sciencedirect.com/science/article/pii/S1053811921007333 |
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