  Alterations to structural and functional brain networks have been reported
across many neurological conditions. However, the relationship between
structure and function -- their coupling -- is relatively unexplored,
particularly in the context of an intervention. Epilepsy surgery alters the
brain structure and networks to control the functional abnormality of seizures.
Given that surgery is a structural modification aiming to alter the function,
we hypothesized that stronger structure-function coupling preoperatively is
associated with a greater chance of post-operative seizure control. We
constructed structural and functional brain networks in 39 subjects with
medication-resistant focal epilepsy using data from intracranial EEG
(pre-surgery), structural MRI (pre-and post-surgery), and diffusion MRI
(pre-surgery). We investigated pre-operative structure-function coupling at two
spatial scales a) at the global iEEG network level and b) at the resolution of
individual iEEG electrode contacts using virtual surgeries. At global network
level, seizure-free individuals had stronger structure-function coupling
pre-operatively than those that were not seizure-free regardless of the choice
of interictal segment or frequency band. At the resolution of individual iEEG
contacts, the virtual surgery approach provided complementary information to
localize epileptogenic tissues. In predicting seizure outcomes,
structure-function coupling measures were more important than clinical
attributes, and together they predicted seizure outcomes with an accuracy of
85% and sensitivity of 87%. The underlying assumption that the structural
changes induced by surgery translate to the functional level to control
seizures is valid when the structure-functional coupling is strong. Mapping the
regions that contribute to structure-functional coupling using virtual
surgeries may help aid surgical planning.
