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Searching for the Mechanisms of Cognition

Neuroimaging (e.g. fMRI) data are increasingly used to attempt to
identify not only brain regions of interest (ROIs) that are especially
active during perception, cognition, and action, but also the
qualitative causal relations among activity in these regions (known as
effective connectivity; Friston, 1994). Previous investigations and
anatomical and physiological knowledge may somewhat constrain the
possible hypotheses, but there often remains a vast space of possible
causal structures. To find actual effective connectivity relations,
search methods must accommodate indirect measurements of nonlinear time
series dependencies, feedback, multiple subjects possibly varying in
identified regions of interest, and unknown possible location-dependent
variations in BOLD response delays. We describe combinations of
procedures that under these conditions find feed-forward sub-structure
characteristic of a group of subjects. The method is illustrated with an
empirical data set and confirmed with simulations of time series of
non-linear, randomly generated, effective connectivities, with feedback,
subject to random differences of BOLD delays, with regions of interest
missing at random for some subjects, measured with noise approximating
the signal to noise ratio of the empirical data. This talk is based on
work (forthcoming in NeuroImage) with Ramsey, Hanson, Hanson, Halchenko
and Poldrack.