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

<p>Abstract</p> <p>Background</p> <p>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.</p> <p>Results</p> <p>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.</p> <p>Conclusion</p> <p>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.</p

Is extinction following parietal damage an interhemispheric disconnection phenomenon?

Experimental Brain Research serie

What is the role of the corpus callosum in intermanual transfer of motor skills? A study of three cases with callosal pathology

Intermanual transfer for a skilled motor task was studied in two patients with total callosal agenesis, and one with an acquired partial callosal lesion and clinical evidence for disturbed transfer of motor signals. Patients had to draw meaningless figures with one upper extremity (original learning, OL) and to reproduce their mirror-reversals thereafter with the other side (transfer learning, TL). Both directions of intermanual transfer were tested in two conditions, that is, between either proximal or distal muscle groups. Transfer was evaluated by comparing OL and TL performance at the same effector. The main variable of interest was movement time during the first eight trials of OL and TL. All three patients displayed a significant benefit for transfer from the dominant to the non-dominant hand but not vice versa during proximal motor activity. When compared with the performance of healthy subjects tested in almost identical conditions in a previously reported study, the proximal transfer behavior was found to be similar for all patients and the normal group. Although patients exhibited no significant benefit for distal transfer, their non-dominant-to-dominant distal transfer was above the normal range. The similar transfer pattern of the patients and healthy subjects when using proximal musculature suggests that proximal transfer may be subserved by identical extracallosal pathways, most probably by the ipsilaterally descending motor systems. Since non-dominant-to-dominant distal transfer was found to be disadvantageous in healthy subjects, the patients' relative superiority in this condition may reflect missing callosal influences of an inhibitory nature