Biology subjects

Malone, B. J.

Publications and source records attributed to Malone, B. J..

3 recordsLinked to original sources

bioRxiv2025

Decoding of frequency modulated sweeps by core and belt neurons in the alert macaque auditory cortex.

Acoustic stimuli where the spectrum is time-varying are ubiquitous in natural sounds, including animal vocalizations, human speech, and music. Early studies of such stimuli involving frequency-modulated sweeps revealed that neurons in the primary auditory cortex of a variety of mammals show differences in firing rates depending on either the direction of the sweep and/or the sweep velocity. Psychophysical studies have also shown that the perception of such time-varying stimulus parameters is quite acute, underscoring the importance of such signals in normal acoustic perception. Surprisingly, the responses of auditory neurons in alert primates has been little studied, and we have limited information relating neural activity to the perception of these signals. In this study, we investigated the neural discriminability of sweep direction and velocity for frequency-modulated sweeps presented to alert rhesus macaque monkeys in both core and belt auditory cortical areas. We quantified how well these information-bearing parameters were encoded using spike train pattern discriminators, and compared decoder performance when neural responses were restricted to temporal patterns or firing rates. Decoding accuracy for firing rate alone exceeded chance, and rate-normalized, spike-timing information was essentially equivalent to the complete firing pattern. Although most belt areas showed small decreases in decoding accuracy relative to the primary field, all fields encoded and represented sweeps similarly. Thus, there was little evidence of hierarchical processing between core and belt fields for these stimuli, indicating that frequency modulation sweep direction and velocity are not specifically extracted in the early auditory cortical hierarchy. Significance StatementFrequency modulated (FM) stimuli are a key feature of many time-varying acoustic stimuli, including speech, vocalizations, music, and environmental sounds. The direction and velocity of FM stimuli are major information-bearing parameters that allow one to discriminate and perceive these sounds. We tested whether single neurons in core and belt auditory cortical fields in alert macaque monkeys preferentially process these features along the cortical hierarchy. We found that the timing of neural activity was much more important than the absolute amount of activity in all cortical areas, and did not observe any evidence of improved discriminability in core or belt fields beyond that seen in the primary auditory cortex (A1).

neuroscience↗

bioRxiv2024

Deep Neural Networks Explain Spiking Activity in Auditory Cortex

For static stimuli or at gross ([~]1-s) time scales, artificial neural networks (ANNs) that have been trained on challenging en gineering tasks, like image classification and automatic speech recognition, are now the best predictors of neural responses in primate visual and auditory cortex. It is, however, unknown whether this success can be extended to spiking activity at fine time scales, which are particularly relevant to audition. Here we address this question with ANNs trained on speech audio, and acute multi-electrode recordings from the auditory cortex of squirrel monkeys. We show that layers of trained ANNs can predict the spike counts of neurons responding to speech audio and to monkey vocalizations at bin widths of 50 ms and below. For some neurons, the ANNs explain close to all of the explain able variance--much more than traditional spectrotemporal- receptive-field models, and more than untrained networks. Non-primary neurons tend to be more predictable by deeper layers of the ANNs, but there is much variation by neuron, which would be invisible to coarser recording modalities.

neuroscience↗

bioRxiv2024

Hierarchical emergence of opponent coding in auditory belt cortex

We recorded from neurons in primary auditory cortex (A1) and middle-lateral belt area (ML) while rhesus macaques either discriminated amplitude-modulated noise (AM) from unmodulated noise or passively heard the same stimuli. We used several post-hoc pooling models to investigate the ability of auditory cortex to leverage population coding for AM detection. We find that pooled-response AM detection is better in the active condition than the passive condition, and better using rate-based coding than synchrony-based coding. Neurons can be segregated into two classes based on whether they increase (INC) or decrease (DEC) their firing rate in response to increasing modulation depth. In these samples, A1 had relatively fewer DEC neurons (26%) than ML (45%). When responses were pooled without segregating these classes, AM detection using rate-based coding was much better in A1 than in ML, but when pooling only INC neurons, AM detection in ML approached that found in A1. Pooling only DEC neurons resulted in impaired AM detection in both areas. To investigate the role of DEC neurons, we devised two pooling methods that opposed DEC and INC neurons - a direct subtractive method and a two-pool push-pull opponent method. Only the push-pull opponent method resulted in superior AM detection relative to indiscriminate pooling. In the active condition, the opponent method was superior to pooling only INC neurons during the late portion of the response in ML. These results suggest that the increasing prevalence of the DEC response type in ML can be leveraged by appropriate methods to improve AM detection.

neuroscience↗