MODULATION OF INFORMATION FLOW IN RAT AUDITORY THALAMOCORTICAL PATHWAYS BY VAGUS NERVE STIMULATION

Vagus nerve stimulation (VNS) is an established treatment for drug-resistant epilepsy. We previously reported that VNS selectively strengthens stimulus-evoked activity in superficial layers of the auditory cortex (A1), suggesting a modulation of feedforward (FF) and feedback (FB) balance. However, its impact on thalamocortical information flow remains unclear. We recorded multi-unit activity from the medial geniculate body (MGv) and A1 layers (L2, L4, L5) in 8 anesthetized rats using depth microelectrode arrays. Information flow was quantified via transfer entropy (TE). We analyzed TEs for MGv-to-L4 (FF) and L5-to-MGv (FB) connections during auditory-evoked and spontaneous activities. Two-way repeated measures ANOVA for evoked TEs showed significant main effects of direction (p < 0.01) and VNS (p < 0.05), with no interaction (p = 0.55). Spontaneous activities showed no significant effects. We further evaluated regional roles using the sender/receiver (SR) ratio (Ishizu et al., 2021), defined as the normalized difference between outgoing and incoming information flows. ANOVA revealed a significant main effect of region (p < 0.01) and a region × VNS interaction (p < 0.05). Post-hoc analysis indicated that VNS significantly decreased the SR ratio in the MGv (p < 0.05), while L2 remained unchanged (p = 0.104). These results suggest that VNS enhances bidirectional information flow across auditory thalamocortical pathways while shifting the MGv toward a more receptive state, potentially facilitating adaptive auditory processing within the circuit.