Biology subjects

Walker, K. M. M.

Publications and source records attributed to Walker, K. M. M..

5 recordsLinked to original sources

bioRxiv2025

Pitch selectivity in ferret auditory cortex

Our perception of pitch - the tonal quality of a sound at a fundamental frequency (F0) - is essential for musical melody, vocal communication, and attending to a voice in a crowded room. Pitch is distinct from simple frequency tuning. Although pitch perception can arise from either harmonic spectral structure or temporal regularity, it remains unclear how individual neurons represent these distinct cues. We recorded spiking activity in hundreds of ferret auditory cortical neurons while systematically varying harmonic and temporal pitch cues. A subset of neurons represented F0 based on harmonic content, another subset on temporal periodicity, and a third population exhibited invariant pitch tuning across both cue classes. These findings provide the first evidence for specialized pitch neurons in non-primates, and demonstrate that mammalian auditory cortex employs dual spectral-temporal mechanisms for extracting F0. Significance statementPitch allows us to enjoy music, understand speech, and follow voices in noisy settings, yet how the brain represents pitch remains a long-standing question. Pitch selective neurons have been identified previously only in primates, limiting our ability to investigate the neural of pitch. Here, we show that ferret auditory cortex also contains such neurons, which extract pitch from both harmonic structure and temporal periodicity. This discovery reveals that the brain uses dual, complementary strategies for encoding pitch.

neuroscience↗

bioRxiv2023

Auditory training alters the cortical representation of both learned and task irrelevant sound features

Auditory learning is supported by long-term changes in the neural processing of sound. We examined these task-depend changes in auditory cortex by mapping neural sensitivity to timbre, pitch and location cues in trained ferrets (n = 5), and untrained control ferrets (n = 5). Trained animals either identified vowels in a two-alternative forced choice task (n = 3) or discriminated when a repeating vowel changed in identity or pitch (n = 2). Neural responses were recorded under anesthesia in two primary auditory cortical fields and two tonotopically organized non-primary fields. In trained animals, the overall sensitivity to sound timbre was reduced across three cortical fields compared to control animals, but maintained in a non-primary field (the posterior pseudosylvian field). While training did not increase sensitivity to timbre across auditory cortex, it did change the way in which neurons integrated spectral information with neural responses in trained animals increasing their sensitivity to first and second formant frequencies,, whereas in control animals cortical sensitivity to spectral timbre depends mostly on the second formant. Animals trained on timbre identification were required to generalize across pitch when discriminating timbre and their neurons became less modulated by fundamental frequency relative to control animals. Finally, both trained groups showed increased spatial sensitivity and an enhanced response to sound source locations close to the midline, where the loudspeaker was located in the training chamber. These results demonstrate that training elicited widespread alterations in the cortical representation of complex sounds.

neuroscience↗

bioRxiv2021

Cortical adaptation to sound reverberation

In almost every natural environment, sounds are reflected by nearby objects, producing many delayed and distorted copies of the original sound, known as reverberation. Our brains usually cope well with reverberation, allowing us to recognize sound sources regardless of their environments. In contrast, reverberation can cause severe difficulties for speech recognition algorithms and hearing-impaired people. The present study examines how the auditory system copes with reverberation. We trained a linear model to recover a rich set of natural, anechoic sounds from their simulated reverberant counterparts. The model neurons achieved this by extending the inhibitory component of their receptive filters for more reverberant spaces, and did so in a frequency-dependent manner. These predicted effects were observed in the responses of auditory cortical neurons of ferrets in the same simulated reverberant environments. Together, these results suggest that auditory cortical neurons adapt to reverberation by adjusting their filtering properties in a manner consistent with dereverberation.

neuroscience↗

bioRxiv2019

Complexity of frequency receptive fields predicts tonotopic variability across species

Primary cortical areas contain maps of sensory features, including sound frequency in primary auditory cortex (A1). Two-photon calcium imaging in mice has confirmed the presence of these large-scale maps, while uncovering an unexpected local variability in the stimulus preferences of individual neurons in A1 and other primary regions. Here we show that fractured tonotopy is not unique to rodents. Using two-photon imaging, we found that local variance in frequency preferences is equivalent in ferrets and mice. Much of this heterogeneity was due to neurons with complex frequency tuning, which are less spatially organized than those tuned to a single frequency. Finally, we show that microelectrode recordings may describe a smoother tonotopic arrangement due to a bias towards neurons with simple frequency tuning. These results show that local variability in the tonotopic map is not restricted to rodents and help explain inconsistencies in cortical topography across species and recording techniques.

neuroscience↗

bioRxiv2018

Pitch perception is adapted to species-specific cochlear filtering

Pitch perception is critical for recognizing speech, music and animal vocalizations, but its neurobiological basis remains unsettled, in part because of divergent results from different species. We used a combination of behavioural measurements and cochlear modelling to investigate whether species-specific differences exist in the cues used to perceive pitch and whether these can be accounted for by differences in the auditory periphery. Ferrets performed a pitch discrimination task well whenever temporal envelope cues were robust, but not when resolved harmonics only were available. By contrast, human listeners exhibited the opposite pattern of results on an analogous task, consistent with previous studies. Simulated cochlear responses in the two species suggest that the relative salience of the two types of pitch cues can be attributed to differences in cochlear filter bandwidths. Cross-species variation in pitch perception may therefore reflect the constraints of estimating a sounds fundamental frequency given species-specific cochlear tuning.

neuroscience↗