Lecture by Julio Hechavarria: Theta oscillations and the coding
of rhythmic acoustic sequences in the bat brain

How does the mammalian brain represent temporally complex acoustic structures? This is a question that has haunted neuroscientists for several decades. In this talk, I will present data on how the bat brain represents information from artificial and natural acoustic sequences. I will argue that bats, as animal model, represent a valuable tool for studying neuronal activity in response to complex acoustic streams that occur in the context of echolocation and distress calling. The talk will focus on findings from my group related to three main topics. (i) The coding of echolocation sequences in the auditory midbrain and cortex, where we have shown a trade-off between periodicity coding and information extraction by means of “tuning” along the colliculo-cortical axis. (ii) The relationship between spiking and local field potential (LFP) oscillations in response to amplitude modulated sounds. We have collected data indicating that in the bat cortex, the occurrence of spiking events is coupled to LFP fluctuations in the theta-alpha range, and that such coupling appears to be a marker for periodicity coding. (iii) The coding of multiple temporal scales present in distress sequences by separate cortical neuronal groups. These neuronal groups represent “independent” information and are differently linked to ongoing LFP oscillations. All these findings point towards a job parcellation in the bat brain, which allows these animals to extract information from temporally complex acoustic stimuli.