PROJECT SUMMARY
Modern neuroscience faces the challenge of bridging our understanding of single cell activity patterns to large
population dynamics. Brain oscillations evoked by sensory stimuli are fluctuations in field potentials reflecting
the combined activity of neural populations driven by a given stimulus. Oscillations have been observed in
many species from invertebrates to primates, and have been implicated in various processes like attention and
perceptual gating. Barn owls are specialists in sound localization studied for several decades. Their well-
described midbrain stimulus selection network, a circuit dedicated to localizing salient sounds, provides a
unique opportunity to evaluate the role of brain oscillations in coding. Previous in vivo recordings in the owl’s
optic tectum (OT), homolog of the mammalian superior colliculus, have shown that gamma oscillations (25-140
Hz) are tuned to both visual and auditory space. However, previous recordings in deep midbrain structures,
like OT, have relied on single electrodes and light tranquilization. These technical limitations impede our
understanding of how oscillations may spread across the space map at a given time, and underscores the
question of generalizability to awake processes like attention and perception. Our lab has pioneered population
recordings across the space map using multielectrode arrays, and has recently developed chronic microdrive
implants for recordings in awake owls. With these technical achievements, we will address several open
questions regarding the role of oscillations in perception of salient stimuli and stimulus selection. Aim 1 will
evaluate the spatial extent of gamma oscillations, and determine whether oscillations organize spike patterning
to preferred phases. Initial analyses show that sound stimulation with the preferred direction increases power
within the gamma range in a focal manner, supporting the hypothesis that spike patterning driven by brain
oscillations has a role in coding sound location. Aim 2 will compare oscillation properties across awake and
anesthetized states. Preliminary data and analysis suggest that while gamma power is higher in the awake
state, phase locking of spikes to gamma oscillations is consistent across states, suggesting significant
functional effects of gamma oscillations in organizing spike patterning are preserved during anesthesia. In Aim
3, we will conduct simultaneous recordings in the auditory thalamus and OT in awake behaving owls to test the
hypothesis that gamma oscillations play a role in perception of salient sounds and stimulus selection. We will
pair sound orienting behaviors, such as head turning and pupillary dilation responses, with electrophysiology to
elucidate the coding mechanisms underlying interregional signaling during perception. Understanding how the
owl’s midbrain stimulus selection circuit utilizes oscillations to conduct bottom-up relay and stimulus selection
can provide insight to similar processes in human audition where the most relevant auditory stream must be
prioritized in circumstances when the auditory scene is complex (cocktail party effect), and may inform novel
optimization strategies for hearing aids.
