1. Modelling, Analysis and Visualization of Brain Connectivity
Jos Roerdink
Institute for Mathematics and Computing Science, University of Groningen

2. Outline
Anatomical Connectivity
Functional Connectivity
Effective Connectivity

3. Brain Connectivity Special issue on Functional Connectivity
E. Bullmore,L. Harrison,
L. Lee, A. Mechelli, K. Friston
(eds.)
Vol. 2, No. 2, 2004

4. Central questions
How is integrated human brain function constrained anatomically?
How is it organized dynamically?
How can it best be modeled mathematically?

5. Diffusion-tensor imaging

6. Themes
Graph theoretical analysis of brain networks measured by fMRI, EEG, PET
Statistical analysis of functional and effective connectivity
Dynamic causal modeling:
path analytic methods for effective connectivity analysis
Brain dynamics (nonlinear dynamical systems, stochastic systems)

7. The CoCoMac (“Collations of Connectivity data on the Macaque brain”) Database
literature database of tracing data on the macaque monkey brain
full transparency from published data to final output
integration of redundant or contradictory published data
transformation of integrated primary data into coherent brain maps

8. On-line interface http://www.cocomac.org
Keywords searches in three data categories:
literature
partitioning schemes (brain maps) e.g.
- Felleman & Van Essen, 1991: visual cortex
- Pandya and Seltzer, 1982: parietal cortex
- Hackett et al., 1998: auditory cortex
Connectivity
Query construction and display of results (XML output) can be automated

9. Connectivity Viewer Data shown for light green selected areas
Existing connections:
light grey
Absent connections:
dark blue

10. Problems & Perspectives
omissions in published data
confusing number of brain maps and varying nomenclature
optimization of interfaces needs software engineering
cross-species comparisons
link to ontology of macaque brain structures

11. Functional connectivity MRI (fcMRI)
Does not rely on a comparison of experimental and baseline conditions as in usual fMRI
But, it detects interregional temporal correlations of blood oxygen level-dependent (BOLD) signal fluctuations
Greicius et al. , Functional connectivity in the resting brain:
A network analysis of the default mode hypothesis
PNAS, 2003, vol. 100, no. 1, 253–258

12. Approach
Identify regions of interest (ROIs) with increased or decreased activity during a cognitive (working memory) task
For each ROI, compute an averaged times series
Use the resulting time series as covariate in whole-brain statistical parametric analysis

13. Results
posterior cingulate cortex (PCC) connectivity patterns during visual task and resting-state

14. Conclusions
deactivation : certain regions show greater activity during rest and passive visual processing than during cognitive tasks
these regions support a default mode network of brain function
precise mental processes supported by the default mode network remain to be elucidated

15. Whole brain connectivity
no-task or “resting” state fMRI
volumes parcellated using anatomical template
regional mean time series for 90 regions (major cortical gyri and subcortical nuclei)
Statistical correlation analysis, hierarchical clustering and multidimensional scaling
Salvador, Suckling, Menon & Bullmore, Neurophysiological architecture of human brain images. Submission to Cerebral Cortex, July 2004

16. Multidimensional Scaling
Regions color-coded by membership of 6 main systems identified by hierarchical cluster analysis
Lines indicate statistically significant inter-regional partial correlation

17. Dynamical Connectivity
dynamical measures of interdependence
role of nonlinear (de)synchronization
alternative to statistical approaches based on covariance data
dynamical systems theory (differential equations, chaotic systems, control theory)