MarsAtlas: A cortical parcellation atlas for functional mapping

Abstract

An open question in neuroimaging is how to develop anatomical brain atlases for the analysis of functional data. Here, we present a cortical parcellation model based on macroanatomical information and test its validity on visuomotor-related cortical functional networks. The parcellation model is based on a recently developed cortical parameterization method (Auzias et al., [2013]: IEEE Trans Med Imaging 32:873-887), called HIP-HOP. This method exploits a set of primary and secondary sulci to create an orthogonal coordinate system on the cortical surface. A natural parcellation scheme arises from the axes of the HIP-HOP model running along the fundus of selected sulci. The resulting parcellation scheme, called MarsAtlas, complies with dorsoventral/rostrocaudal direction fields and allows inter-subject matching. To test it for functional mapping, we analyzed a MEG dataset collected from human participants performing an arbitrary visuomotor mapping task. Single-trial high-gamma activity, HGA (60-120 Hz), was estimated using spectral analysis and beamforming techniques at cortical areas arising from a Talairach atlas (i.e., Brodmann areas) and MarsAtlas. Using both atlases, we confirmed that visuomotor associations involve an increase in HGA over the sensorimotor and fronto-parietal network, in addition to medial prefrontal areas. However, MarsAtlas provided: (1) crucial functional information along both the dorsolateral and rostrocaudal direction; (2) an increase in statistical significance. To conclude, our results suggest that the MarsAtlas is a valid anatomical atlas for functional mapping, and represents a potential anatomical framework for integration of functional data arising from multiple techniques such as MEG, intracranial EEG and fMRI.

Keywords: MEG; cortical parameterization; cortical parcellation; dorsoventral and rostrocaudal axes; functional segregation; gammaband neural activity; human brain atlas; visuomotor behaviors.

Figure 1

The HIP‐HOP parameterization model. A detailed description of all sulci involved can be found at the following link, with the same color code: http://brainvisa.info/doc/documents-4.4/nomenclature/BV_nomenclature.pdf.

Figure 2

From HIP‐HOP to the MarsAtlas parcellation model (top) and view on an inflated cortical surface (bottom). The atlas is represented on the HipHop138 average template (available at: http://www.meca-brain.org/softwares/hiphop138-cortical-surface-group-template/).

Figure 3

Arbitrary visuomotor mapping task. The relation between visual stimulus and motor response is deterministic and highly acquainted. Stimuli were digits from 1 to 5 and appeared at the center of the screen for 1 s. Participants were required to move the finger associated to the digit: “1” instructed thumb movement, “2” the index, etc. The maximum reaction time was 1 s (i.e., stimulus duration). After a fixed delay of 1 s, the feedback image instructed whether the executed motor response was correct, incorrect or late.

Figure 4

MarsAtlas parcellation of the white matter surface (left) and of the cortical volume (right) for a representative participant.

Figure 5

Cortical parcellation on the white matter surface of five participants.

Figure 6

Volume of each MarsAtlas region relative to the total gray matter volume for the left and right hemispheres for the first dataset (11 subjects). For each region, the average relative volume across subjects is shown, with standard deviation.

Figure 7

Single‐trial and single‐subject HGA. HGA for MarsAtlas regions shown in (d) for dorsomedial (a), dorsolateral (b), and ventral (c) motor cortex. HGA for BA 4L (e) depicted in (f).

Figure 8

The time course of activation of group‐level t‐values for motor (a) and premotor (b) areas. Black lines correspond to the time course at BAs, whereas colored lines correspond to MarsAtlas regions from ventral to dorsomedial.

Figure 9

Statistical map displaying the cortical regions in MarsAtlas associated with a significant increase in HGA (time‐point and cluster‐level threshold were set to q < 0.001 FDR‐corrected).

Figure 10

Percentage of significant time points at the group level over all BAs (bleu) and MarsAtlas cortical regions (green). The time‐point and cluster‐level threshold were set to q < 0.001 FDR‐corrected.