The Lingering Echo: Neural Activity After Sound

Published on September 6, 2022

Imagine you’re at a concert, and the band finishes their last note. But even after the music has ended, there’s an echo – a faint, lingering trace of sound that stays with you. Well, it turns out our brains do something similar! Scientists have discovered that neural activity in the auditory cortex continues even after a sound has stopped. This activity, known as OFF response plasticity, serves a unique purpose. It acts as a mnemonic signature, holding onto the memory of specific and impactful sounds. Just like an echo helps us remember the music we heard, this lingering brain activity helps us remember important auditory information. Researchers are still uncovering the intricacies of how and why this happens, but they believe it plays a role in guiding our behavioral decisions. To learn more about this fascinating phenomenon and how our brains hold onto sound memories, be sure to check out the underlying research!

In studying how neural populations in sensory cortex code dynamically varying stimuli to guide behavior, the role of spiking after stimuli have ended has been underappreciated. This is despite growing evidence that such activity can be tuned, experience-and context-dependent and necessary for sensory decisions that play out on a slower timescale. Here we review recent studies, focusing on the auditory modality, demonstrating that this so-called OFF activity can have a more complex temporal structure than the purely phasic firing that has often been interpreted as just marking the end of stimuli. While diverse and still incompletely understood mechanisms are likely involved in generating phasic and tonic OFF firing, more studies point to the continuing post-stimulus activity serving a short-term, stimulus-specific mnemonic function that is enhanced when the stimuli are particularly salient. We summarize these results with a conceptual model highlighting how more neurons within the auditory cortical population fire for longer duration after a sound’s termination during an active behavior and can continue to do so even while passively listening to behaviorally salient stimuli. Overall, these studies increasingly suggest that tonic auditory cortical OFF activity holds an echoic memory of specific, salient sounds to guide behavioral decisions.

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