Biology subjects

Fritzinger, J. B.

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

3 recordsLinked to original sources

bioRxiv2026

Representations of Pitch and Timbre of Instrument Sounds in the Inferior Colliculus

PurposeThe neural representation of pitch and timbre in complex sounds has previously been studied using synthetic, controlled stimuli to investigate underlying encoding mechanisms. These studies provide information about how single attributes of sound are represented in the inferior colliculus (IC), a critical hub of the auditory pathway where neurons are sensitive to stimulus periodicity and spectral shape, giving rise to representations of pitch and timbre, respectively. However, there is a gap in understanding how natural sounds with both pitch and timbre attributes, such as instrument sounds, are represented in the IC. MethodsIn this study, extracellular recordings were made in the IC of awake rabbits in response to natural instrument stimuli varying in fundamental frequency (F0) to determine how instrument identity (timbre) and F0 (pitch) are represented in IC neurons. ResultsUsing decoding models for instrument identification, we found that instrument identity was redundantly encoded in a population of neurons with diverse rate and timing characteristics. F0 identification using decoding models trained on single-neuron rate responses was poor, but the population of rate responses contained enough information to identify F0 reliably. F0 information was also encoded in single-neuron temporal responses up to 196 Hz. F0 identification from a population of temporal responses was accurate up to approximately 900 Hz, but accuracy decreased at high F0s. For the task in which F0 was identified based on responses to both oboe and bassoon stimuli that had overlapping F0s, performance decreased compared to F0 identification based on responses to a single instrument. ConclusionThis result supports the hypothesis that pitch and timbre information are encoded jointly in the IC.

neuroscience↗

bioRxiv2025

Mechanisms of Tone-in-Noise Encoding in the Inferior Colliculus

Extracellular single-unit responses to tone-in-noise (TIN) stimuli were recorded in the inferior colliculus (IC) of awake female Dutch-belted rabbits. Stimuli consisted of wideband and narrowband tone-in-noise (TIN) with on-and off-characteristic frequency tones. Neural responses to wideband TIN showed a pattern of rates that increased when the tone matched CF and decreased (with respect to noise-alone responses) when the tone was above or below CF. This result differed from narrowband TIN IC responses that depended on envelope fluctuations in the stimulus, consistent with neural-fluctuation sensitivity. The WB-TIN responses could be fit with a difference-of-gaussians model that had narrow excitation and broad inhibition; responses to TIN could not be predicted by response-maps or spectrotemporal receptive fields. Responses to diotic and contralateral presentations of WB-TIN did not differ due to presentation ear. A single-CF computational model of the IC could not predict responses to wideband TIN. However, adding local off-CF inhibitory inputs to an on-CF IC model improved accuracy. These results suggest that broad inhibition could explain encoding of wideband TIN at suprathreshold signal-to-noise ratios, whereas neural fluctuation sensitivity is more important for narrowband sounds.

neuroscience↗

bioRxiv2021

Carbon Fiber Electrodes for Intracellular Recording and Stimulation

To understand neural circuit dynamics, it is critical to manipulate and record from many neurons, ideally at the single neuron level. Traditional recording methods, such as glass microelectrodes, can only control a small number of neurons. More recently, devices with high electrode density have been developed, but few of them can be used for intracellular recording or stimulation in intact nervous systems, rather than on neuronal cultures. Carbon fiber electrodes (CFEs) are 8 micron-diameter electrodes that can be organized into arrays with pitches as low as 80 {micro}m. They have been shown to have good signal-to-noise ratios (SNRs) and are capable of stable extracellular recording during both acute and chronic implantation in vivo in neural tissue such as rat motor cortex. Given the small fiber size, it is possible that they could be used in arrays for intracellular stimulation. We tested this using the large identified and electrically compact neurons of the marine mollusk Aplysia californica. The cell bodies of neurons in Aplysia range in size from 30 to over 250 {micro}m. We compared the efficacy of CFEs to glass microelectrodes by impaling the same neurons cell body with both electrodes and connecting them to a DC coupled amplifier. We observed that intracellular waveforms were essentially identical, but the amplitude and SNR in the CFE were lower than in the glass microelectrode. CFE arrays could record from 3 to 8 neurons simultaneously for many hours, and many of these recordings were intracellular as shown by recording from the same neuron using a glass microelectrode. Stimulating through CFEs coated with platinum-iridium had stable impedances over many hours. CFEs not within neurons could record local extracellular activity. Despite the lower SNR, the CFEs could record synaptic potentials. Thus, the stability for multi-channel recording and the ability to stimulate and record intracellularly make CFEs a powerful new technology for studying neural circuit dynamics.

neuroscience↗