Frequency response areas of mouse inferior colliculus neurons: II. Critical bands

Abstract

Critical bands are perceptual filters that detect and separate spectral peaks in complex sounds. Here, we show that the main properties of psychophysically defined critical bands, as measured in narrow-band noise masking tests (species-specific frequency dependence and intensity independence of the bandwidths), are present in single neurons of the mouse's central nucleus of the inferior colliculus. Bandwidths of critical bands amount to, on average, 3/8-1/3 octave related to the neurons' characteristic frequencies. They are not determined by the shapes of the neurons' excitatory receptive fields. The results support the view that frequency resolution in the auditory system is shaped to its perceptual level in the main nucleus of the auditory midbrain.

A Discontinuous Tonotopic Organization in the Inferior Colliculus of the Rat

“…Interestingly, our data in the IC suggest that there may be 8 -12 laminae, each covering 0.29 -0.36 octaves. This separation is similar to critical bands of 0.333-0.375 octaves suggested for the mouse (Egorova et al, 2006). Moreover, this grouping is also compatible with studies on the frequency separation needed to activate independent neuronal populations in the IC (Yang et al, 2003(Yang et al, , 2004Oliver, 2005).…”

High concentrations of divalent cations isolate monosynaptic inputs from local circuits in the auditory midbrain

“…The head of the animal was positioned so that the IC was flat with respect to the horizontal and combined with a 90° fixed electrode impalement angle, allowing us to reach almost the whole range (~60 kHz) of characteristic frequencies in the IC (Egorova et al, 2006). Recordings on the same animal were performed for four consecutive days in two 2-h sessions each day, with a rest period of at least an hour between sessions.…”

Rodent auditory perception: Critical band limitations and plasticity

“…Tones within the frequency range of a critical band are thought to activate the same location of the basilar membrane (Schreiner et al, 2000). Critical bands contribute to the ability to discriminate sounds (Ehret and Merzenich, 1988; Schreiner and Langner, 1997; Egorova et al, 2006; Egorova and Ehret, 2008) and to detect sounds in background noise (Watson, 1963). Critical band filtering and integration are basic components of mammalian sound perception (Plomp, 1968; Scharf, 1970; Plomp, 1971; Greenwood, 1991; Roederer, 2008) and are active for any sound composed of complex frequencies, which is almost every natural sound (Scharf, 1970).…”

“…This is especially challenging in young animals, as some early postnatal developmental processes occur more rapidly than the duration required for training (Dorrn et al, 2010; Froemke and Jones, 2011). Additionally, tone-evoked responses may not generalize to more complex stimuli that make up vocalizations and other natural sounds; conventional tuning curves reflect single tone measurements, while critical bands filter the interactions of two or more spectrally complex sounds (Ehret and Merzenich, 1988; Egorova et al, 2006). Single-tone tuning curve shapes differ significantly from those derived for complex sounds (Ehret and Schreiner, 1997).…”

“…Neural critical bandwidths are 3/8 to 1/3 of an octave around the respective excitatory characteristic frequency, and are asymmetrically centered closer to the high-frequency boundary. However, neural critical bandwidth boundaries are not the same as the extents of excitatory receptive fields, but are instead defined by lateral inhibition (Ehret and Merzenich, 1988; Egorova et al, 2006). The organization of excitation and inhibition in the inferior colliculus also contributes to the balance of spectral and temporal modulation sensitivity at this central relay; as sensitivity to one increases, sensitivity to the other decreases, across the collicular tonotopic gradient (Rodriguez et al, 2010).…”