Nina S. Bradley


Associate Professor

Biokinesiology & Physical Therapy, Cell & Neurobiology
Keck School of Medicine
School of Dentistry

Nina S. Bradley

Research Topics

  • Behavioral Neurobiology
  • Developmental Psychobiology
  • Sensorimotor physiology

Research Images

Chicks are precocious walkers. They can walk, run and negotiate obstacles in the environment within hours after hatching. The presence of this precocious skill indicates that the neural substrates for walking must be established during embryogenesis. Studies in our lab are investigating the emergence of neural control for precocious locomotion and whether environmental factors contribute to its emergence.In the chick, control of leg movements for locomotion emerges during embryonic development. The muscle activity and limb excursions for these coordinated movements can be recorded during spontaneous activity (motility) in the egg. This figure is a typical example of EMG and joint kinematic recordings during spontaneous repetitive leg movements in a chick at embryonic day 20. Upward excursions in the kinematic traces indicate extension of the hip, knee and ankle joints during the EMG traces for muscle activity in the same leg.Here we show a higher resolution example of the alternating muscle activity in flexors (red) and extensors (blue) during spontaneous leg movements in the egg. Note all 4 muscles are active in this 10 sec segment. The SA is a hip flexor and TA is an ankle dorsi flexor. The FT is a knee extensor and the LG is an ankle plantar flexor. The average TA burst frequency is 1.8 Hz over 10 TA bursts, a frequency range common during locomotor behaviors in hatchlings. A force probe (F) was placed in contact with the hip to track body displacements, and is an indicator of limb movements concurrent with muscle bursts.

Research Overview

Development and control of repetitive leg movements during embryonic development

Our long-term objectives are to determine if fetal movements and the environment in which they are generated contribute to adaptive postnatal motor behavior. New imaging technologies are revealing ever greater details of motor behavior in the fetus for clinical diagnosis and treatment. Understanding the form, mechanisms and significance of fetal behavior will be important for maximizing clinical application of these tools. Evidence indicates fetal movement is essential for differentiating musculoskeletal structures, and may also be useful in identifying a potential medical crisis, but it is not known if specific complex movements reliably distinguish states of neurodevelopment or if they shape the neonatal motor repertoire. Results of our studies will provide fundamental information relevant to questions of prenatal experience, environmental impact on the control of prenatal limb movements during both normal development in utero and when environmental forces are altered by extremely premature birth.

Our model for prenatal motor development is the chick embryo. Like the human fetus, the chick embryo begins generating complex movements such as kicking and stepping early in development. The chick embryo is a valuable model of fetal behavior because it is amenable to combinations of behavioral, physiological, pharmacological and neuroanatomical study throughout embryonic development. Our recent studies provide evidence that leg stepping in the last 3 days before hatching is produced by neural circuits that control leg movements during locomotion. Our current studies are exploring the impact of muscle proprioception and light-induced acceleration of development during embryogenesis on control of stepping movements prior to hatching and bipedal locomotion. Our studies will provide fundamental insights into the impact of gravity and intense light exposure on motor control when the infant is born prematurely and is exposed to conditions commonly associated with neonatal intensive care.

Contact Information

Mailing Address 9006 HSC
Office Location CHP G10H
Office Phone (323) 442-2910
Lab Location
Lab Phone
Fax (323) 442-1515
Office Location CHP G10H



  • BS 1975 Physical Therapy - University of Southern California
  • MS 1983 Kinesiology - University of California, Los Angeles
  • PhD 1986 Kinesiology - University of California, Los Angeles

Selected Publications

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  • Sindhurakar A, Bradley NS (2012) Light Accelerates Morphogenesis and Acquisition of Interlimb Stepping in Chick Embryos. PLoS ONE 7(12): e51348. doi:10.1371/journal.pone.0051348.

    PubMed Link
  • Sindhurakar A, Bradley NS (2010) Kinematic analysis of overground locomotion in chicks incubated under different light conditions. Developmental Psychobiology, 52: 802-812.  PubMed
  • Ryu YU, Bradley NS (2009) Precocious locomotor behavior begins in the egg: development of leg muscle patterns for stepping in the chick. PLoS One 4: e6111. PubMed
  • Bradley NS, Ryu YU, Lin J (2008) Fast locomotor burst generation in late stage embryonic motility. Journal of Neurophysiology 99: 1733-1742. PubMed
  • Bradley NS, Solanki D, Zhao D (2005) Limb movements during embryonic development in the chick: evidence for a continuum in limb motor control antecedent to locomotion. Journal of Neurophysiology 94: 4401-4411. PubMed
  • Oztop E, Bradley NS, Arbib MA (2004) Infant grasp learning: A computational model. Experimental Brain Research, 158: 480-503. PubMed
  • Bradley NS, Jahng DY (2003) Selective effects of light exposure on distribution of motility in the chick embryo at E18. Journal of Neurophysiology 90: 1408-1417. PubMed
  • Bradley NS - Connecting the dots between animal and human studies of locomotion. Focus on "Infants adapt their stepping to repeated trip-inducing stimuli". - J Neurophysiol [2003] Oct;90(4):2088-9 PubMed
  • Bradley NS (2001) Age-related changes and condition-dependent modifications in distribution of limb movements during embryonic motility. Journal of Neurophysiology 86: 1511-1522. PubMed Link
  • Bradley NS, Sebelski C (2000) Ankle restraint alters motility at E12 in chick embryos. Journal of Neurophysiology 83: 431-440. PubMed Link