Directional Indicator on Neural Oscillations as a Measure of Synaptic Plasticity in Chronic Unpredictable Stress Rats

To examine whether the directionality index of neural information flow (NIF) over specific oscillatory bands is useful in measuring synaptic plasticity, we employed the IM approach to determine the direction of NIF between the cortex and thalamus in normal and stressed animals. The experiment was performed by inducing long-term potentiation (LTP) of the thalamocortical pathway after recording local field potential (LFP). Additionally, comparison of IM measurement between broad- and narrowbands was performed, while a numerical study was also carried out for assessing the number of data points. The results show that the instantaneous phases extracted from narrowband vary monotonically, while these phases are jagged in broadband. Our data show that there is a predominant driving effect (coupling directional index d >0) from the thalamus to the frontal cortex in normal animals; however, the value of d is significantly reduced in the chronic stressed group in both the delta and theta bands. Furthermore, the field LTP data show that chronic stress decreases medial prefrontal cortex synaptic plasticity, which is certainly in line with the LFP findings. Together, these data suggest that using an IM algorithm, the directionality index of NIF in specific oscillatory frequency bands will probably be used as a measure of synaptic plasticity.