Nestor Israel Zaragoza Jimenez1, Tomas Goucha1, Alfred Anwander1, Angela Friederici1
1Department of Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
One question in neuroscience that remains unclear is the relation between structural connectivity and functional connectivity of a certain brain region. A region of high interest and descriptions is Broca's area, because it has been identified functionally as one of the core regions for language processing. Cytoarchitectonically, Broca's area encompasses Brodmann area (BA) 44 (in the pars opercularis of the inferior frontal gyrus, IFG) and BA 45 (in the more anterior pars triangularis of the IFG). Based on multiple receptor mapping (Amunts et al., 2010) both areas were further subdivided into two areas, and a transition zone in the ventral precentral gyrus was characterized, more posteriorly to Broca's area proper. While recent evidence offers new insights into the specificity of Broca's area in different aspects of language computations (Goucha & Friederici., 2015), the nature of the relationship between its structural pattern and its function is still unknown. This area was also parcellated using diffusion MRI tractography (Anwander et al., 2007) and functional connectivity (Kelly et al., 2010, Jakobsen et al., 2016a,b) with contrasting results. Here we investigated how both the structural and the functional connectivity based parcellations of Broca's area are related to the macroanatomical features of the IFG and analyzed the different features which are revealed by the functional and structural parcellation in relation to its function.
We collected diffusion and functional MRI data from 27 healthy adult volunteers. The parcellation of Broca's area was constructed in three steps. A tractography based parcellation of Broca's area employing dMRI as described by Anwander et al. (2007) was initially created. Secondly, a functional parcellation pipeline was implemented based on the functional parcellation approach used by Jakobsen et al. (2016b). The degree of correspondence between parcellations, determined by calculating cross-correlations between the different parcellation results, and the correspondence to the gyrification and the cytoarchitectonic maps was computed for each parcel.
The results from diffusion MRI tractography suggest a subdivision of Broca's area (pars triangularis and pars opercularis) into three sub-regions in anterior-posterior order. The middle area partially overlaps with the posterior part of pars triangularis and the anterior part of the pars opercularis reaching until the diagonal sulcus, if present. The functional connectivity based parcellation revealed a less clear differentiation between the pars opercularis and the pars triangularis of the IFG. However, the posterior part of pars opercularis in the ventral precentral sulcus (BA 6) could be clearly separated. This area differs clearly in functional connectivity from the somato-motor/premotor areas around the central sulcus and overlaps with the BA6-BA44 transition zone defined by receptor mapping (Amunts et al., 2010).
Our results allowed us to improve our understanding of Broca's structural and functional organization. This new topological characterization has the potential to help new investigations about the involvement of Broca's region in cognitive computations, and specifically during language processing. Thus, our description of Broca's area could allow us to investigate neural mechanisms of language processing to a new degree of functional specialization. In a similar fashion the parcellation has granted us new insights about the relationship between SC and FC.
Modeling and Analysis Methods:
Segmentation and Parcellation 2
Anatomy and Functional Systems
Cortical Anatomy and Brain Mapping 1
WHITE MATTER IMAGING - DTI, HARDI, DSI, ETC
Other - parcellation
1|2Indicates the priority used for review