Biology subjects

Vellema, M.

Publications and source records attributed to Vellema, M..

4 recordsLinked to original sources

bioRxiv2020

Singing-related reorganization of the song motor circuit is accompanied by a shift in hormonal modulation of song

Sex hormones are essential modulators of birdsong. Testosterone, and its active androgenic and estrogenic metabolites, 5-dihydrotestosterone (DHT) and estradiol, can re-shape the brain circuits responsible for song learning and production. The differential mechanisms of action of these different hormones during song development and song maintenance are, nonetheless, not fully understood. Here we demonstrate that unlike testosterone, DHT treatment does not induce singing behavior in naive adult female canaries that have never previously produced song. However, in birds with previous testosterone-induced singing experience, DHT alone is enough to promote the re-acquisition of high quality songs, even after months of silence. In addition, we show that the synaptic reorganization that accompanies vocal motor skill development requires more than DHT-induced androgen receptor activation. These results indicate that vocal motor practice will persistently modify the hormone-sensitive brain circuit responsible for song production, suggesting a mechanistic differentiation in the hormone-dependent regulation of the initial vocal motor skill acquisition and later re-acquisition.

neuroscience↗

bioRxiv2020

One-to-one innervation of vocal muscles allows precise control of birdsong

The motor control resolution of any animal behavior is limited to the minimal force step available when activating muscles, which is set by the number and size distribution of motor units (MUs) and muscle specific force [1, 2]. Birdsong is an excellent model system for understanding sequence learning of complex fine motor skills [3], but we know surprisingly little how the motor pool controlling the syrinx is organized [4] and how MU recruitment drives changes in vocal output [5]. Here we combine measurements of syringeal muscle innervation ratios with muscle stress and an in vitro syrinx preparation to estimate MU size distribution and the control resolution of fundamental frequency (fo), a key vocal parameter, in zebra finches. We show that syringeal muscles have extremely small MUs, with 50% innervating [≤] 3, and 13 - 17% innervating a single muscle fiber. Combined with the lowest specific stress (5 mN/mm2) known to skeletal vertebrate muscle, small force steps by the major fo controlling muscle provide control of 50 mHz to 4.2 Hz steps per MU. We show that the song system has the highest motor control resolution possible in the vertebrate nervous system and suggest this evolved due to strong selection on fine gradation of vocal output. Furthermore, we propose that high-resolution motor control was a key feature contributing to the radiation of songbirds that allowed diversification of song and speciation by vocal space expansion.

neuroscience↗

bioRxiv2018

Vocal motor experiences consolidate the vocal motor circuitry and accelerate future vocal skill development

Complex motor skills take considerable time and practice to learn. Without continued practice the level of skill performance quickly degrades, posing a problem for the timely utilization of skilled motor responses. Here we quantified the recurring development of vocal motor skills and the accompanying changes in synaptic connectivity in the brain of a songbird, while manipulating skill performance by consecutively administrating and withdrawing testosterone. We demonstrate that a songbird with prior singing experience can significantly accelerate the re-acquisition of vocal performance. We further demonstrate that an increase in vocal performance is accompanied by a pronounced synaptic pruning in the forebrain vocal motor area HVC, a reduction that is not reversed when birds stop singing. These results provide evidence that lasting synaptic changes in the motor circuitry are associated with the savings of motor skills, enabling a rapid recovery of motor performance under environmental time constraints.

animal behavior and cognition↗

bioRxiv2017

Fundamental Constraints In Synchronous Muscle Limit Superfast Motor Control In Vertebrates

Superfast muscles (SFM) are extremely fast synchronous muscles capable of contraction rates up to 250 Hz, enabling precise motor execution at the millisecond time scale. To allow such speed, the archetypal SFM, found in the toadfish swimbladder, has hallmark structural and kinetic adaptations at each step of the conserved excitation-contraction coupling (ECC) pathway. More recently SFM phenotypes have been discovered in most major vertebrate lineages, but it remains unknown whether all SFM share ECC adaptations for speed, and if SFM arose once, or from independent evolutionary events. Here we use genomic analysis to identify the myosin heavy chain genes expressed in bat and songbird SFM to achieve rapid actomyosin crossbridge kinetics and demonstrate that these are evolutionarily and ontologically distinct. Furthermore, by quantifying cellular morphometry and calcium signal transduction combined with force measurements we show that all known SFM share multiple functional adaptations that minimize ECC transduction times. Our results suggest that SFM evolved independently in sound producing organs in ray-finned fish, birds, and mammals, and that SFM phenotypes operate at a maximum operational speed set by fundamental constraints in synchronous muscle. Consequentially, these constraints set a fundamental limit to the maximum speed of fine motor control.

physiology↗