RT Journal Article
SR Electronic
T1 Faster repetition rate sharpens the cortical representation of echo streams in echolocating bats
JF eneuro
JO eNeuro
FD Society for Neuroscience
SP ENEURO.0410-21.2021
DO 10.1523/ENEURO.0410-21.2021
A1 Silvio Macias
A1 Kushal Bakshi
A1 Michael Smotherman
YR 2021
UL http://www.eneuro.org/content/early/2021/12/06/ENEURO.0410-21.2021.abstract
AB There is consensus that primary auditory cortex utilizes a combination of rate codes and temporally precise population codes to represent discreet auditory objects. During the response to auditory streams, forward suppression constrains cortical rate coding strategies, but it may also be well-positioned to enhance temporal coding strategies that rely upon synchronized firing across neural ensembles. Here, we exploited the rapid temporal dynamics of bat echolocation to investigate how forward suppression modulates the cortical ensemble representation of complex acoustic signals embedded in echo streams. We recorded from auditory cortex of anesthetized free-tailed bats while stimulating the auditory system with naturalistic biosonar pulse-echo sequences covering a range of pulse emission rates. As expected, increasing pulse repetition rate significantly reduced the number of spikes per echo stimulus, but it also increased spike timing precision and doubled the information gain. This increased spike-timing precision translated into more robust inter-neuronal synchronization patterns with >10dB higher signal-to-noise ratios at the ensemble level. We propose that forward suppression dynamically mediates a trade-off between the sensitive detection of isolated sounds versus precise spatiotemporal encoding of ongoing sound sequences in auditory cortex.Significance StatementAuditory cortical neurons are unable to follow trains of sounds with repetition rates higher than roughly 15 Hz. The dynamics and synaptic mechanisms responsible for this forward suppression are well known. However, their functional consequences on the representation of sounds remain unknown. We evaluated the effects of forward suppression on both rate and temporal coding of complex sounds in auditory cortex. We show that forward suppression can greatly facilitate synchronization-based time codes and thereby enhance the cortical spatiotemporal representation of natural sounds at ecologically relevant rates. Such increases in neuronal synchrony are consistent with emerging theories of how sound spectral envelopes are encoded, with important implications for music and speech processing.