Resting State Effective Connectivity between Inferior Parietal Lobe (IPL) and Inferior Temporal Gyrus (ITG) in the Left and Right Hemispheres / Jurnal Sains Kesihatan Malaysia

ABSTRACT

Inferior parietal lobule (IPL) and inferior temporal gyrus (ITG) are two important brain regions for the default modenetwork (DMN). IPL has been known to be involved in the control of attention and responding to given information whileITG is involved in the processing and perception awakened by visual stimuli. These two key DMN regions are highlyinterconnected as determined from white matter and fiber tracking studies. However, little is known about their natureof connectivity while the brain is at rest, whether it is linear, bilinear or nonlinear and whether it is of mono- or bidirection.Resting state functional magnetic resonance imaging (rsfMRI) data were obtained from 7 healthy male andfemale participants (average age = 20.7 ± 4.5 years) and were concatenated. Data were analyzed using statisticalparametric mapping (SPM12). Endogenous brain signals were modelled by Fourier series at 0.01 – 0.08 Hz. IPL-ITGconnected linear, bilinear and non-linear causal models in both hemispheres were constructed and estimated by means ofstochastic dynamic causal modelling (sDCM) and were compared using Bayesian Model Selection (BMS) for group studies.Group fixed-effects results indicated that bilateral IPL and ITG exhibited high neural activity at a corrected significantlevel (pFWE 1000) which has the best balance betweenmodel accuracy and difficulty. The minimum free energy (F) = -4.41 × 104 and -4.09 × 104 for left and right hemispherebilinear models respectively. From BMS and DCM results, it was found that IPL and ITG do have a dynamic collaborationbetween each other, a connectivity that belongs to a greater network when the brain is at rest. The intrinsic connectionsbetween them are negative in both directions i.e. IPL and ITG mutually inhibited each other. The effective connectivitywas modulated by the endogenous fluctuation of the brain signal.