Spike Analysis of the Neural Activities Across the Rats’ Auditory Brain Structure

Abstract

Abstract Tinnitus has been a health condition that affects a large population. Clinical diagnosis and treatment have been developed for tinnitus for years. However, there are still limitations because researchers have yet to find an underlying mechanism for how it develops in the brain structure. Abnormal neural interactions among the brain areas are considered to play an important role in tinnitus generation. From bottom to top, researchers have been working on the analysis of neural activities in the auditory brain structures, including the dorsal cochlear nucleus (DCN), inferior colliculus (IC), and auditory cortex (AC), to seek a better understanding of the information flow among these areas, especially in comparison of both health and tinnitus conditions. In the project, a collection of multiple animals’ neural activities from DCN, IC, and AC, on conditions of before and after noise exposure and before and after Auditory Cortex Electrical Stimulation (ACES) were processed and analyzed. These conditions in rats were used to estimate healthy animals, noise-trauma-induced tinnitus, and after ACES treatment. The signal processing algorithms started with the raw measurement data and focused on the local field potentials (LFPs) and spikes in the time domain. First, conventional ways of evaluation were applied to the signals. Based on the signals of each channel inserted in the different structures, the firing rate was calculated by counting the total number of spikes for the given period of time in each channel. Meanwhile, the Hilbert transform was used to obtain the phase-frequency information. Phase-phase correlation analysis was applied to test any relations between channels, especially for those from different auditory brain structures. Second, the shape of spikes was investigated to find the changes in neural activities in auditory brain areas under various conditions, therefore determining if tinnitus-related abnormal neural activities have a specialized pattern. In this procedure, spikes above the threshold were extracted with the rectangular window on the time domain. Spike shapes were quantified in terms of amplitude and width of peak and compared across channels. Averaged spike shapes from different areas/channels were plotted synchronized for comparison. The above-mentioned information could present the difference in neural activities among the DCN, IC, and AC in the auditory pathway. Last, the time difference of arrival of spikes among areas was calculated to help further understand the information transfer in the auditory pathway. This was a preliminary test to see if it could help observe abnormal time delays in tinnitus conditions compared to healthy ones. All the above numerical analysis results were summarized in plots and color maps and also used to compare animal conditions and discussed.