To achieve the objectives, we performed several experiments and performed new analyses on previously collected data.
In humans, resonance phenomena (increased amplitude response to certain rhythmic visual stimulation frequencies) have been studied exclusively at the cortical level. However, the primary visual cortex (V1) receives its primary input from dorsolateral geniculate nucleus of the thalamus (dLGN) and also sends back projections to dLGN, which highly outnumber feedforward connections. Thus, the resonance phenomena observed at the level of V1 could be a result of bidirectional interaction in corticothalamic networks. To address this possibility, we performed simultaneous recordings in the mouse V1 and dLGN by inserting laminar probe under an angle relative to the cortical surface to target both brain areas.
We found that resonance frequencies are highly preserved from humans to mice, with the same characteristic peaks with slight differences in the exact frequencies (in mice on average: 8 Hz, 15 Hz, 33 Hz; in humans we found on average: 10 Hz, 15 Hz, 45 Hz). These findings validate the use of mouse as a model for understanding mechanisms underlying generation of cortical oscillations and cross-frequency interactions. Additional resonance rhythm in the theta band (~5 Hz) has been also observed in mice. By combining animal motion and neural data analysis, we found that resonance in theta turned out to be related to whisking and breathing of the animal.
Although some studies have shown the effects of 40 Hz flicker stimulation in higher cortical regions (prefrontal cortex and CA1 of the hippocampus) in case of Alzheimer’s disease, it is generally assumed that rhythmic visual stimulation effects are constrained to visual system. In re-analysis of wide-field imaging data that I previously collected, we tested whether rhythmic visual stimulation effects are observable beyond the visual system. Comparison of spatial extent of responses across different flicker frequencies revealed that flicker frequencies below 11 Hz elicited responses beyond visual areas (auditory and somatosensory areas), thus providing some support for flicker effects outside V1. As part of the collaboration, I also led the project on resonance frequencies in the somatosensory cortex using EEG in humans, the results of which are published in high-impact factor journal (Journal of Neuroscience).
Recorded mouse electrophysiology data are currently analyzed and results from re-analyzed data are in the final stages of publication preparation for high-profile peer reviewed journal and have been presented at multiple international conferences and invited talks (Society for Neuroscience Meeting, International Conference of Cognitive Neuroscience, European Visual Cortex Meeting).
