Oscillatory waveform shape and temporal spike correlations differ across bat frontal and auditory cortex

Abstract

Neural oscillations are associated with diverse computations in the mammalian brain. The waveform shape of oscillatory activity measured in cortex relates to local physiology, and can be informative about aberrant or dynamically changing states. However, how waveform shape differs across distant yet functionally and anatomically related cortical regions is largely unknown. In this study, we capitalize on simultaneous recordings of local field potentials (LFPs) in the auditory and frontal cortices of awake, male Carollia perspicillata bats to examine, on a cycle-by-cycle basis, waveform shape differences across cortical regions. We find that waveform shape differs markedly in the fronto-auditory circuit even for temporally correlated rhythmic activity in comparable frequency ranges (i.e. in the delta and gamma bands) during spontaneous activity. In addition, we report consistent differences between areas in the variability of waveform shape across individual cycles. A conceptual model predicts higher spike-spike and spike-LFP correlations in regions with more asymmetric shape, a phenomenon that was observed in the data: spike-spike and spike-LFP correlations were higher in frontal cortex. The model suggests a relationship between waveform shape differences and differences in spike correlations across cortical areas. Altogether, these results indicate that oscillatory activity in frontal and auditory cortex possess distinct dynamics related to the anatomical and functional diversity of the fronto-auditory circuit. Significance statementThe brain activity of many animals displays intricate oscillations, which are usually characterized in terms of their frequency and amplitude. Here, we study oscillations from the bat frontal and auditory cortices on a cycle-by-cycle basis, additionally focusing on their characteristic waveform shape. The study reveals clear differences across regions in waveform shape and oscillatory regularity, even when the frequency of the oscillations is similar. A conceptual model predicts that more asymmetric waveforms result from stronger correlations between neural spikes and electrical field activity. Such predictions were supported by the data. The findings shed light onto the unique properties of different cortical areas, providing key insights into the distinctive physiology and functional diversity within the fronto-auditory circuit.