Pitch can be coded by neuron firing rate matching the repetition frequency

Evidence

Abstract The basic nature of pitch is much debated. A robust code for pitch exists in the auditory nerve in the form of an across-fiber pooled interspike interval (ISI) distribution, which resembles the stimulus autocorrelation. An unsolved question is how this representation can be “read out” by the brain. A new view is proposed in which a known brain-stem property plays a key role in the coding of periodicity, which I refer to as “entracking”, a contraction of “entrained phase-locking”. It is proposed that a scalar rather than vector code of periodicity exists by virtue of coincidence detectors that code the dominant ISI directly into spike rate through entracking. Perfect entracking means that a neuron fires one spike per stimulus-waveform repetition period, so that firing rate equals the repetition frequency. Key properties are invariance with SPL and generalization across stimuli. The main limitation in this code is the upper limit of firing (~ 500 Hz). It is proposed that entracking provides a periodicity tag which is superimposed on a tonotopic analysis: at low SPLs and fundamental frequencies > 500 Hz, a spectral or place mechanism codes for pitch. With increasing SPL the place code degrades but entracking improves and first occurs in neurons with low thresholds for the spectral components present. The prediction is that populations of entracking neurons, extended across characteristic frequency, form plateaus (“buttes”) of firing rate tied to periodicity. — Dijk, Pim van, Physiology, Psychoacoustics and…, 4491

Categorization

Category: Causal Relationships

• DEFINE: Defines ‘entracking’ as entrained phase-locking, a contraction introduced here.
• QUESTION: The butte hypothesis is novel and the abstract poses the open problem of how the AN autocorrelation-like ISI distribution is read out by the brain.

Related

• Pitch is coded by firing rate constancy, not spike phase (similarity 0.93)
• Brainstem entracking produces horizontal ‘butte’ rate-place profiles encoding pitch (similarity 0.90)
• Entracking codes pitch through constant firing rate while spike phase stays irrelevant (similarity 0.89)
• Entracking codes low-frequency pitch through uniform firing across neurons while high-frequency firing varies (similarity 0.89)
• Entracking generates horizontally flattened rate profiles that encode pitch as firing rate (similarity 0.88)
• Pitch may be encoded by entrained phase-locking producing a rate code (similarity 0.87)
• Pitch can be coded by monotonic firing rate instead of tuned delay circuits (similarity 0.87)
• No neural evidence supports autocorrelation models of pitch at the brainstem (similarity 0.87)
• Pitch coding shifts between place and entracking mechanisms depending on stimulus level (similarity 0.86)
• The dominant interspike interval may be coded as predominant neural firing rate. (similarity 0.86)
• Temporal pitch coding via entracking gives way to place coding above 500 Hz (similarity 0.86)
• Neural pitch coding produces a butte of equal-rate activity centered on the stimulus frequency (similarity 0.85)
• The brainstem may convert interspike intervals directly into firing rates (similarity 0.85)
• Neurons can convert stimulus frequency directly into firing rate at the brainstem (similarity 0.84)
• Pitch-period codes divide into delay-based vector codes and rate-based scalar codes (similarity 0.84)

Broader Connections

• Neural pitch coding produces a butte of equal-rate activity centered on the stimulus frequency #corroborates (0.80) — Dijk, Pim van, Physiology, Psychoacoustics and…, 4507
• Pitch can be encoded by scalar firing rate rather than tuned vector codes #corroborates (0.80) — Dijk, Pim van, Physiology, Psychoacoustics and…, 4494
• Neurons can convert stimulus frequency directly into firing rate at the brainstem #expands (0.80) — Dijk, Pim van, Physiology, Psychoacoustics and…, 4494
• Pitch perception is encoded by the timing of neural firing in the cochlea #responds-to (0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 897