Millisecond Timing in Sound: How Brains from Rats to Humans Decode Rapid Click Patterns

Every sound you have ever heard carries two kinds of information. The first is spectral: the mixture of frequencies that distinguishes a violin from a foghorn. The second is temporal: the precise way energy is distributed across time, down to intervals far shorter than a human can consciously measure. A new study published in PLOS Biology suggests that the auditory system is far more sensitive to that second kind of information than many researchers had assumed. A team led by Yuying Zhai and Xiongjie Yu, working with collaborators in China, Spain and the United Kingdom, showed that click trains with identical average rates but different millisecond-scale temporal patterns can be discriminated by human listeners, leave distinct traces in human brain recordings, and produce measurably different responses in the cortex of awake rats.

The experimental logic was elegantly simple. The researchers constructed sequences of clicks, brief broadband acoustic events lasting only a fraction of a millisecond, in which the average interval between clicks was held constant. What varied was the patterning of those intervals: some sequences were regular, while others interleaved short and long gaps in distinct arrangements. If the auditory system only tracked the mean rate of a sound, all of these patterns should sound alike and drive the brain identically. Instead, the team found that both behavior and neural activity betrayed the differences, demonstrating that temporal microstructure is encoded, not averaged away.

In human listeners, the behavioral evidence came first. Participants could reliably tell apart several of the click-train patterns despite their identical mean inter-click intervals, indicating that the human auditory system extracts features of temporal organization at a resolution of a few milliseconds. This is a demanding perceptual feat. The individual intervals involved sit near or below the limits traditionally associated with temporal resolution in hearing, yet listeners did not need to consciously time each gap; the patterns as wholes were discriminable, much as a listener can distinguish a galloping rhythm from a steady beat even when both contain the same number of notes per second.

Electroencephalography provided a window onto the neural machinery behind that perceptual ability. When the researchers occasionally switched the click-train pattern within a running sequence, the EEG recorded deviance-related responses whose character depended on the context in which the change occurred. In other words, the brain’s reaction to a sound was shaped not only by the sound itself but by the pattern that preceded it. This context dependence is a hallmark of predictive processing in sensory systems: neural circuits appear to build a model of what is coming next and respond vigorously when the temporal prediction is violated.

Crucially, the phenomenon was not unique to humans. The team recorded electrocorticographic signals, field potentials captured directly from the surface of the brain, from awake rats and found analogous differences in cortical responses to the same click-train patterns. The convergence across species is scientifically important. Rats and humans diverged tens of millions of years ago, yet both species’ auditory cortices distinguish temporal patterns that differ only in millisecond-scale structure. This suggests that sensitivity to fine-grained temporal patterning is a fundamental, conserved property of mammalian hearing rather than a specialization of the human speech and music perception system.

To locate where in the auditory pathway this sensitivity emerges, the researchers turned to single-unit recordings along the classical ascending route of auditory processing: from the inferior colliculus, a midbrain hub, to the medial geniculate body of the thalamus, and finally to the primary auditory cortex, known as A1. The results revealed a striking gradient. The inferior colliculus showed only weak sensitivity to oddball and context manipulations. The medial geniculate body displayed an intermediate level. The primary auditory cortex exhibited the strongest stimulus-specific adaptation, the phenomenon in which neurons reduce their firing to repeated stimuli while remaining responsive to novel ones.

That gradient tells a story about how the brain builds temporal representations. Early and mid-level stations appear to encode the acoustic waveform relatively faithfully, passing on information about the click sequence without much filtering. As signals ascend, however, circuits increasingly compare current input against recent history, sharpening responses to pattern changes. By the time activity reaches A1, the representation is no longer a passive copy of the sound but an actively shaped summary in which temporal context matters profoundly. This progression mirrors findings in other sensory domains, where higher cortical areas encode regularities and deviations rather than raw stimulus features.

One of the most intriguing findings concerned the conversation between cortex and thalamus. The auditory cortex is not merely a destination for thalamic signals; it also sends a massive projection back down to the medial geniculate body, forming a corticothalamic feedback loop whose function has been debated for decades. When the researchers reversibly inactivated the auditory cortex, the thalamus’s sensitivity to the click-train patterns dropped. This result indicates that part of the context sensitivity observed in the medial geniculate body is not generated locally but is imported from the cortex through these descending connections. The thalamus, in this view, is not a simple relay but a node in a loop in which cortical computations refine subcortical processing in real time.

Within the primary auditory cortex itself, the team probed deeper by examining responses across cortical layers. The neocortex is organized into layers with distinct input and output roles: granular layers receive thalamic input, supragranular layers are heavily involved in intracortical and feedback communication, and deep layers send projections to subcortical targets. The analyses showed stronger pattern-related effects in supragranular layers than in deep layers, hinting that the computations distinguishing temporal patterns may be concentrated in the superficial circuitry that integrates thalamic input with intracortical context and participates in the feedback loop back to the thalamus.

Taken together, the study reframes how scientists think about temporal coding in hearing. Natural sounds, from speech syllables to animal calls to the rhythmic textures of music, are defined not only by which frequencies they contain but by the exact millisecond choreography of their energy. The new results show that this choreography is differentially represented at every stage of the auditory system, with sensitivity to pattern and context growing stronger in higher structures and being actively maintained by cortical feedback. The work also offers a bridge between species, providing a rat model in which the neural basis of millisecond-scale temporal discrimination can be dissected with tools unavailable in humans. For conditions in which temporal processing is disrupted, such as developmental language disorders or age-related hearing decline, that animal model could prove invaluable, pointing toward the circuits where fine timing goes wrong and, potentially, where it might be restored.

Subject of Research: Millisecond-scale temporal pattern discrimination in the mammalian auditory system

Article Title: Distinct millisecond-scale click-train patterns evoke discriminable behavioral and neural responses in humans and rats

Article References: Zhai, Y., Song, P., Lao-Rodríguez, A. B., Du, X., Xu, H., Ye, H., Bao, X., Mehmood, I., Pandit, N. S., Chang, C., Dai, Z., Tu, Z., Chen, P., Zhang, T., Zhang, L., Zhao, X., Pérez-González, D., Malmierca, M. S., & Yu, X. (2026). Distinct millisecond-scale click-train patterns evoke discriminable behavioral and neural responses in humans and rats. PLOS Biology, 24(10), e3004046. https://doi.org/10.1371/journal.pbio.3004046

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3004046

Keywords: auditory neuroscience, temporal processing, click trains, EEG, electrocorticography, inferior colliculus, medial geniculate body, auditory cortex, corticothalamic feedback, stimulus-specific adaptation, rats, PLOS Biology