Tonotopy and inhibition in the midbrain inferior colliculus shape spectral resolution of sounds in neural critical bands.
Frequency resolution and spectral integration in acoustic perception is investigated psychacoustically by measuring critical bands (CBs) or equivalent quantities. In general, CB bandwidths increase with increasing sound frequency but remain constant over a large range of sound pressure levels (SPL; intensity independence). These CB properties have previously been found, on average, in responses of midbrain inferior colliculus neurons. Here, we use single-neuron recordings from the central nucleus of mouse inferior colliculus (ICC) to study neurons' excitatory and inhibitory frequency receptive fields together with neural critical bands (NCBs) measured in a narrowband noise-masking paradigm at SPLs up to 85 dB. We aim to clarify whether and how neurons with very different shapes of excitatory and inhibitory receptive fields express CB properties, whether and how inhibition contributes to set boundaries of NCBs, and where these boundaries are located in the excitatory-inhibitory receptive fields. The main results are: the above-mentioned general CB properties exist in neurons independent of the shapes of their receptive fields, that is, frequency filtering related to single tones (tuning curves) and frequency resolution related to complex sounds (NCBs) are different neuronal properties; NCB boundaries match the boundaries of an area devoid of inhibition around the characteristic frequencies in 67% of the neurons, that is, the inhibitory influence is adjusted to frequency resolution in part of the neurons; filter bandwidths of NCBs are, relative to their centre frequencies, about on average 1/3 octave wide, equaling the average frequency distance between frequency-band laminae as found in the cat ICC.
Egorova
Marina
M
Laboratory of Comparative Physiology of Sensory Systems, I.M. Sechenov Institute of Evolutionary Physiology and Biochemistry, RAS, St Petersburg, Russia.
Ehret
Günter
G
D000161:Acoustic Stimulation; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology*; D001931:Brain Mapping; D002415:Cats; D005260:Female; D006309:Hearing / Q000502:physiology; D007245:Inferior Colliculi / Q000033:anatomy & histology / Q000502:physiology; D051379:Mice; D012044:Regression Analysis; D013016:Sound