Limits...
Detecting functional magnetic resonance imaging activation in white matter: interhemispheric transfer across the corpus callosum.

Mazerolle EL, D'Arcy RC, Beyea SD - BMC Neurosci (2008)

Bottom Line: This region connects the superior parietal cortices, which have been implicated previously in interhemispheric transfer.Consistent with the group results, the clusters of all five subjects were located in posterior callosal regions.Future work is needed to determine whether the detection of this activation can be improved by utilizing higher spatial resolution, optimizing acquisition parameters, and analyzing the data with tissue specific models of the hemodynamic response.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute for Biodiagnostics Atlantic, National Research Council, Halifax, Nova Scotia, Canada. emazerol@dal.ca

ABSTRACT

Background: It is generally believed that activation in functional magnetic resonance imaging (fMRI) is restricted to gray matter. Despite this, a number of studies have reported white matter activation, particularly when the corpus callosum is targeted using interhemispheric transfer tasks. These findings suggest that fMRI signals may not be neatly confined to gray matter tissue. In the current experiment, 4 T fMRI was employed to evaluate whether it is possible to detect white matter activation. We used an interhemispheric transfer task modelled after neurological studies of callosal disconnection. It was hypothesized that white matter activation could be detected using fMRI.

Results: Both group and individual data were considered. At liberal statistical thresholds (p < 0.005, uncorrected), group level activation was detected in the isthmus of the corpus callosum. This region connects the superior parietal cortices, which have been implicated previously in interhemispheric transfer. At the individual level, five of the 24 subjects (21%) had activation clusters that were located primarily within the corpus callosum. Consistent with the group results, the clusters of all five subjects were located in posterior callosal regions. The signal time courses for these clusters were comparable to those observed for task related gray matter activation.

Conclusion: The findings support the idea that, despite the inherent challenges, fMRI activation can be detected in the corpus callosum at the individual level. Future work is needed to determine whether the detection of this activation can be improved by utilizing higher spatial resolution, optimizing acquisition parameters, and analyzing the data with tissue specific models of the hemodynamic response. The ability to detect white matter fMRI activation expands the scope of basic and clinical brain mapping research, and provides a new approach for understanding brain connectivity.

Show MeSH
Activation clusters located primarily on the corpus callosum (individual level). The five subjects with clusters located primarily within the corpus callosum are presented (whole brain activation results are shown). The isthmus of the corpus callosum was activated in four subjects, with splenium activation for S02. Scale bars represent t-values. R: right, L: left.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2553800&req=5

Figure 2: Activation clusters located primarily on the corpus callosum (individual level). The five subjects with clusters located primarily within the corpus callosum are presented (whole brain activation results are shown). The isthmus of the corpus callosum was activated in four subjects, with splenium activation for S02. Scale bars represent t-values. R: right, L: left.

Mentions: In order to detect group level corpus callosum activation, liberal statistical thresholds were necessary. However, it was possible that reduced sensitivity at the group level was due to individual variance in corpus callosum activation. To explore this further, we investigated individual level activation results. Whole brain activation was examined to identify clusters located primarily in the corpus callosum. To reduce the potential contribution of partial volume effects, clusters located primarily in gray matter were excluded, even if they partially overlapped with the callosum. This analysis revealed white matter clusters for five subjects (21%). In four subjects, these clusters were located in the isthmus, while one subject (S02) had a cluster in the splenium (Figure 2).


Detecting functional magnetic resonance imaging activation in white matter: interhemispheric transfer across the corpus callosum.

Mazerolle EL, D'Arcy RC, Beyea SD - BMC Neurosci (2008)

Activation clusters located primarily on the corpus callosum (individual level). The five subjects with clusters located primarily within the corpus callosum are presented (whole brain activation results are shown). The isthmus of the corpus callosum was activated in four subjects, with splenium activation for S02. Scale bars represent t-values. R: right, L: left.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2553800&req=5

Figure 2: Activation clusters located primarily on the corpus callosum (individual level). The five subjects with clusters located primarily within the corpus callosum are presented (whole brain activation results are shown). The isthmus of the corpus callosum was activated in four subjects, with splenium activation for S02. Scale bars represent t-values. R: right, L: left.
Mentions: In order to detect group level corpus callosum activation, liberal statistical thresholds were necessary. However, it was possible that reduced sensitivity at the group level was due to individual variance in corpus callosum activation. To explore this further, we investigated individual level activation results. Whole brain activation was examined to identify clusters located primarily in the corpus callosum. To reduce the potential contribution of partial volume effects, clusters located primarily in gray matter were excluded, even if they partially overlapped with the callosum. This analysis revealed white matter clusters for five subjects (21%). In four subjects, these clusters were located in the isthmus, while one subject (S02) had a cluster in the splenium (Figure 2).

Bottom Line: This region connects the superior parietal cortices, which have been implicated previously in interhemispheric transfer.Consistent with the group results, the clusters of all five subjects were located in posterior callosal regions.Future work is needed to determine whether the detection of this activation can be improved by utilizing higher spatial resolution, optimizing acquisition parameters, and analyzing the data with tissue specific models of the hemodynamic response.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute for Biodiagnostics Atlantic, National Research Council, Halifax, Nova Scotia, Canada. emazerol@dal.ca

ABSTRACT

Background: It is generally believed that activation in functional magnetic resonance imaging (fMRI) is restricted to gray matter. Despite this, a number of studies have reported white matter activation, particularly when the corpus callosum is targeted using interhemispheric transfer tasks. These findings suggest that fMRI signals may not be neatly confined to gray matter tissue. In the current experiment, 4 T fMRI was employed to evaluate whether it is possible to detect white matter activation. We used an interhemispheric transfer task modelled after neurological studies of callosal disconnection. It was hypothesized that white matter activation could be detected using fMRI.

Results: Both group and individual data were considered. At liberal statistical thresholds (p < 0.005, uncorrected), group level activation was detected in the isthmus of the corpus callosum. This region connects the superior parietal cortices, which have been implicated previously in interhemispheric transfer. At the individual level, five of the 24 subjects (21%) had activation clusters that were located primarily within the corpus callosum. Consistent with the group results, the clusters of all five subjects were located in posterior callosal regions. The signal time courses for these clusters were comparable to those observed for task related gray matter activation.

Conclusion: The findings support the idea that, despite the inherent challenges, fMRI activation can be detected in the corpus callosum at the individual level. Future work is needed to determine whether the detection of this activation can be improved by utilizing higher spatial resolution, optimizing acquisition parameters, and analyzing the data with tissue specific models of the hemodynamic response. The ability to detect white matter fMRI activation expands the scope of basic and clinical brain mapping research, and provides a new approach for understanding brain connectivity.

Show MeSH