Effective connectivity between precuneus and supramarginal gyrus in healthy subjects and temporal lobe epileptic patients.

The effective connectivity (EC) when the brain is resting and how a neuronal system exerts influence over other regions of the brain, in different groups of subjects are still being investigated. Limited information was seen about the relationship between precuneus (PRE) which is a wellknown resting state hub with supramarginal gyrus (SMG) in healthy subjects (HS) and temporal lobe epilepsy (TLE) participants.Fourteen HS and 14 TLE patients with age and gender matched underwent resting state functional magnetic resonance imaging (rsfMRI) scanning using a 3-Tesla MRI machine to investigate the EC and percentage of amplitude fluctuation (PerAF) involving SMG and PRE. The rsfMRI data were analysed using Statistical Parametric Mapping (SPM12) and Spectral Dynamic Causal Modelling (spDCM) from which causal models were specified, estimated and inferred.Model with bidirectional connections between PRE and SMG was chosen as the winning model. The EC from PRE to SMG is positive but the EC from SMG to PRE is negative in both hemispheres and in HS and TLE. Based on the findings from the EC analysis, there is an excitatory effect shown by PRE to SMG connection indicating a dominant role of PRE over SMG in both groups.There is important evidence showing that PRE might also have influence on areas outside resting state network and the influence changes in the presence of brain abnormality.