Expertise:
Electromyography, bone strain,
3-d kinematics, biomechanics, digital videofluoroscopy comparative
anatomy.
I use in vivo studies of vertebrate feeding systems to
test hypotheses regarding the evolution of musculoskeletal
systems. Among these hypotheses are questions regarding the
relative evolutionary plasticity of muscular, skeletal and
motor systems. The primate feeding system presents practical
advantages for studies of these questions: all of the neurons
lie in or above the brainstem, making them accessible for
recording; masticatory muscles are large and superficially
placed, facilitating EMG recordings; the most important function
of the system—mastication—requires no specialized
training; the mandible is accessible for placement of strain
gauges that may be used to estimate the timing and magnitude
of bite force; and large areas of skull bone are accessible
for anchoring markers necessary for optically based or videofluoroscopic
kinematic analysis.
The masticatory system also exhibits characteristics making
it of theoretical interest in studies of motor control. Mastication
involves highly repetitive motions, consisting of relatively
rapid movements during “fast opening” and “fast
closing”, interspersed with relatively slow movements
during the power stroke. The former movements may be characterized
as nearly isotonic and the latter as nearly isometric. Thus,
the study of mastication may provide insight into whether
neuronal activity is related to the displacements or forces
involved in a movement, or both, but at different times during
a movement cycle. The functioning of the masticatory system
also requires coordination of bilateral muscles used to move
a structure that crosses the midline (the mandible), in comparison
with the forelimbs, which are bilaterally independent.
Research is currently focused on determining the importance
of food material properties on jaw kinematics; estimating
the relative timing of jaw muscle activity, mandibular corpus
bone strain, and jaw movements; quantifying movements of
the mandibular condyles; and establishing relationships between
dental microwear patterns and patterns of jaw movements.
Videofluoroscopy is being used to study the coordination
of jaw and hyoid monkeys during chewing and swallowing in
primates. Planned research projects include investigations
of cortical control of jaw movements in primates.
In addition to research on primates, I am comparing patterns
of bone strain in alligator and lizard mandibles with those
documented for mammals. Mammal data suggest that mammals
modulate bite force during rhythmic mastication primarily
by modulating the rate at which force is generated, rather
than the time over which it is generated. Comparative research
is aimed at determining whether other vertebrates modulate
bite force in a similar fashion.
In sum, comparative jaw kinematic, bone strain, and electromyographic
data are being collected in vivo in awake alert animals to
test hypotheses regarding the evolution of feeding systems
as a window into the evolution of vertebrate musculoskeletal
systems. |
