Mouse vocal communication system: are ultrasounds learned or innate?

Abstract

Mouse ultrasonic vocalizations (USVs) are often used as behavioral readouts of internal states, to measure effects of social and pharmacological manipulations, and for behavioral phenotyping of mouse models for neuropsychiatric and neurodegenerative disorders. However, little is known about the neurobiological mechanisms of rodent USV production. Here we discuss the available data to assess whether male mouse song behavior and the supporting brain circuits resemble those of known vocal non-learning or vocal learning species. Recent neurobiology studies have demonstrated that the mouse USV brain system includes motor cortex and striatal regions, and that the vocal motor cortex sends a direct sparse projection to the brainstem vocal motor nucleus ambiguous, a projection previously thought be unique to humans among mammals. Recent behavioral studies have reported opposing conclusions on mouse vocal plasticity, including vocal ontogeny changes in USVs over early development that might not be explained by innate maturation processes, evidence for and against a role for auditory feedback in developing and maintaining normal mouse USVs, and evidence for and against limited vocal imitation of song pitch. To reconcile these findings, we suggest that the trait of vocal learning may not be dichotomous but encompass a broad spectrum of behavioral and neural traits we call the continuum hypothesis, and that mice possess some of the traits associated with a capacity for limited vocal learning.

Figure 1

Sonograms of species-typical vocalizations produced by (a) humans (Doupe & Kuhl, 1999), (b) vervet monkeys (Seyfarth & Cheney, 1986) (the cited study uses the older species name of Cercopithecus aethiops), (c) ringdoves (Nottebohm & Nottebohm, 1971), (d) zebra finches (Scharff & Nottebohm, 1991), (e) canaries (Nottebohm et al., 1976), and (f) mice (Arriaga, Zhou, & Jarvis, 2012). The mouse song sonogram was generated from Supplementary Audio 2. All images used with permission.

Figure 2

Examples of syllables categories from courtship vocalizations of adult male BxD mice. Eight major syllable classes (A-H) and several minor (I-K) can be distinguished by the series of notes (boundaries marked by colored dots) and the corresponding sequence of upward or downward instantaneous jumps (>10 kHz) in the dominant pitch (Holy & Guo, 2005). The simplest syllables (Type A) are characterized by a single note with no pitch jumps. Two-note syllables (Types B & C) can be classified by a single ‘Down’ or ‘Up’ pitch jump. Common three-note syllables (Types D-F) follow one of the following sequences: ‘Down-Down’, ‘Down-Up’, or ‘Up-Down’; the fourth possible pitch jump combination ‘Up-Up’ is rarely observed. Commonly observed four- and five-note syllables (Types G & H) follow ‘Down, Down, Up’ and ‘Up, Down, Up, Down’ pitch jump sequences, respectively. Since a jump is defined based on the instantaneous peak frequency, the harmonics present in some notes are not considered for classification purposes. Blue dots mark ‘Up’ jumps, and red lines mark ‘Down’ jumps. Scale bar: 20 ms.

Figure 3

Examples of syllables from courtship vocalizations of adult male mice as classified by Scattoni et al. (2008). This alternative 10 syllable classification splits syllable Type A from Figure 2 into 6 different sub-types (Complex, Upward, Downward, Chevron, Shorts, Flat) and groups syllable types B & C into a super-category (Two-Syllable).

Figure 4

Song bout of an adult BxD male lasting 47 seconds and containing 264 syllables.

Figure 5

Summary diagrams of brain systems for vocalization in mice, and classical vocal learning and vocal non-learning species for comparison. All vocalizing species including monkeys and chickens have a midbrain/brainstem vocal motor pathway. Monkeys have a premotor cortex region in Area 6V that makes an indirect projection to vocal motor neurons, but is not required for vocalizing. The vocal learning species (Human and Songbird) possess additional forebrain premotor circuits that are critical for producing and learning vocalizations, including cortico-striatal-thalamic loops (dotted lines) and a direct primary motor cortical projection to vocal motoneurons in the brainstem (red arrows: RA to XIIts in songbirds; Face motor cortex (FMC) to Amb in humans) (Jarvis, 2004; Jürgens, 2009; Kuypers, 1958c; Simonyan & Horwitz, 2011). Mice have a similar direct cortico-bulbar projection (Arriaga et al., 2012). Red arrows, the direct forebrain projection to vocal motor neurons in the brainstem (RA to XIIts in song learning birds; Laryngeal motor cortex [LMC] to Amb in human and mouse) (Jarvis, 2004; Jürgens, 2002b; Kuypers, 1958b; Wild, 1997). White lines, anterior forebrain premotor circuits, including cortico-striatal-thalamic loops. Dashed lines, connections between the anterior forebrain and posterior vocal motor circuits. Yellow lines, proposed connections for cortico-striatal-thalamic loop that need to be tested. Auditory input is not shown. All diagrams show the sagittal view. Figure used with permission from Arriaga et al. (Arriaga et al., 2012).

Figure 6

Molecular mapping and some connectivity of mouse song system forebrain areas. a-b, Dark-field images of cresyl violet stained (red) coronal brain sections at the level of motor cortex, approximately 0.2 mm rostral to Bregma, showing singing-induced egr1 expression (white) in the forebrain of a male mouse (a) relative to a non-vocalizing control that moved around the cage in a similar amount (b). c, Pyramidal neurons expressing enhanced green fluorescent protein in cortical layer V of the singing activated region of M1 following injection of pseudorabies virus (PRV-Bartha) into the cricothyroid and lateral cricoarytenoid laryngeal muscles. Labeled cells were not observed in the adjacent M2 and cingulate cortex (Cg) or subjacent anterodorsal striatum (adSt). d, Higher magnification of the labeled cells in (c). e, Fine caliber M1 axons (black arrows) contact CTb-labeled laryngeal Amb motor neurons (MN; brown) from an injection in the M1 singing activated region of cortex. f, Backfilled layer III cells in secondary auditory cortex (A2) from the same animal. Scale bar = 1mm for a-c; 0.5mm for d and f; 10 um for e. Figures used with permission from Arriaga et al. (Arriaga et al., 2012). Figure panels c and d are from an additional animal not shown in that paper.

Figure 7

Example results of deafening experiments in mice. a Sonograms representing 1 second of ultrasonic song from an adult mouse 1 month before deafening. b-c, Same mouse 8 months after deafening (bilateral cochlear removal) showing the smaller (b) and larger (c) effects seen. d, Sonogram of wild-type B6 mouse; e-f, Same mouse strain but congenitally deaf due to knock out of the CASP3 gene, showing the smaller (e) and larger (f) effects seen on song. Red dots represent the average pitch over the entire recording session for that individual animal. g, Sonogram of wild type ola1/B6 male USVs. h, Same mouse strain but congenitally deaf due to knock out of the otoferlin gene. i, Standard deviation of the pitch of Type A syllables (expressed as a log-ratio) over 8 postoperative months (** = p<0.01; repeated measures ANOVA with the Bonferroni-Dunn post-hoc test comparing within-group means across recording months). Data are plotted as means ± s.e.m. j, P values for comparisons of syllable features of three major category types (CT1—CT3) between hearing-intact and otoferlin knockout mice. Panels a-f and i used with permission from Arriaga et al. (2012), and g, h, and j from Hammerschmidt et al. (2012).

Figure 8

Example results of vocal development and social experience on vocal behavior in mice. a, No change in repertoire composition of syllable types (colors) of the cross fostered animals from Kikusui et al. (2011). b, No change in mean peak frequency of biological sons and cross fostered sons of B6 and BALB mice from Kikusui et al. (2011). c, Changes in repertoire composition (y-axis is syllable types) over development (x-axis is proportion and age) from Grimsley et al. (2011). d, Changes in frequency (pitch) of different syllable types in different directions over development from Grimsley et al. (2011). e, Changes repertoire composition as a result of social experience in adult mice from Chabout et al. (2012). f, Changes in mean peak frequency as a result of social experience in adult mice from Chabout et al. (2012). g, Convergence of pitch of Type A syllables from the songs of B6 and BxD males before and over 8 weeks of cross-strain paired housing from Arriaga, et al. (2012). Box plots show the median, 1^st and 3^rd quartile, and full range. h, The average change in difference in pitch of Type A syllables between the two males in each B6-BxD pair from before to after 8 weeks of cross-strain paired housing (paired Student's t-test) from Arriaga, et al. (2012). i, The change in difference in pitch of each individual specific pair from Arriaga, et al. (2012); 0 is no difference. Figures used with permission.