Expertise:
fMRI,
ERP, TMS, Computer modeling
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.
Our laboratory uses functional magnetic resonance imaging
(fMRI) and transcranial magnetic stimulation (TMS) to study
the organization of the normal human cerebral cortex and
the changes that it undergoes after neurological injury,
particularly stroke. Cortical damage has profound effects
on such functions as learning, memory, language, motor function,
and affect. Damage to structures that must communicate with
the cortex and/or damage to the communication channels themselves
also cause serious impairments. We believe that by studying
the neuroanatomical substrate of recovery from injury, we
will be able to construct a theory of neurological rehabilitation
that is grounded in basic neuroscience.
Our current projects are in the areas of language and motor
function, and are concerned with both the normal anatomy
of these functions and their recovery after stroke. In the
study of normal adults, we have found that the language areas
of the brain are more widely distributed than previously
thought, extending to brain regions that are anatomically
removed from those originally postulated by Broca, Wernicke,
and Déjérine, and extending to both cerebral
hemispheres. Furthermore, different language functions have
overlapping neuroanatomical substrates, such as the shared
representations for speech comprehension and production in
the ventral premotor cortex. In the motor system, we have
also demonstrated the presence of distributed circuits, with
hand motor execution and kinetic imagery overlapping considerably,
but with regions differing in their effective connectivity.
In the primary sensory and motor cortices, the brain seems
to encode finger movements as a graded overlapping somatotopy,
further elaborating in normal subjects the motor maps previously
studied in the surgical epilepsy patients of Penfield.
Motor and language recovery from stroke can proceed quite
slowly after the initial effects of emergency “brain
attack” treatment have been fully appreciated. This
is a time when patients receive various behavioral interventions,
such as physical therapy and speech therapy, and a time when
such concomitants of stroke as major depression are prominent.
We have begun to investigate the neurobiological changes
that take place in patients during this period of recovery.
People who have recently had a stroke are invited to undergo
functional testing and brain imaging (with fMRI) at regular
intervals during the course of recovery. During each fMRI,
they are asked to perform tasks that were affected by the
stroke, and over time, their performance improves and their
pattern of brain activity changes. In motor function, we
have shown that the cerebellum plays an active role in such
recovery, but that the side of the brain “opposite” to
the stroke doesn’t.
If such neurobiological recovery can be influenced by particular
types of behavioral tasks, by pharmacological intervention,
and/or by surgical intervention, then the basic results can
have important clinical implications. We are exploring all
of these approaches. In one study of a stroke patient with
a reading impairment, we showed that learning a particular
reading strategy (mapping letters onto sounds) both improved
reading skill and also changed the brain to emphasize certain
regions (occipital/temporal) over others (inferior parietal).
We have recently begun the study of action observation and
imitation to see if these specialized motor systems can be
exploited for use in therapy, both with and without concomitant
pharmacological or surgical intervention.
Specific research projects:
--Functional Neuroanatomy of Normal and Impaired
Language
The major goals of this project are to determine the functional
neuroanatomy of ecological language comprehension in the
syntactic, semantic, social, and emotional context that occurs
in the actual environment.
--Neurophysiological Measurement in Aphasia Treatment
The goal of the project is to use neurophysiological (functional
imaging) measures to assess treatment effects in patients
with aphasia.
--Environmental and Biological Variations in Language
Growth
The major goal of this project is to examine reorganization
of language systems after neonatal, perinatal, and early
postnatal injury.
--Prevention of Post-Stroke Depression Treatment
Strategy
This project aims to determine the efficacy of pharmacological
treatment in the prevention of depression after stroke.
-- Effect of Bromocriptine on Aphasia Treatment
Outcome
The major goals of this project are to develop the methods
and protocols for a potential clinical trial that will evaluate
the effectiveness of the pharmacological agent, bromocriptine,
on the language outcome of patients with nonfluent aphasia.
Laboratory personnel:
Uri Hasson, Ph.D., Postdoctoral Fellow
uhasson@uchicago.edu
Goulven Josse, Ph.D., Postdoctoral Fellow
goulven@uchicago.edu
Ryan Walsh, M.D., Ph.D. Neurology Resident
ryan.walsh@uchospitals.edu
Jeremy Skipper, M.A., Graduate Student
skipper@uchicago.edu
Charles Gaylord, B.A., Graduate Student
cgaylord@uchicago.edu
Jing Liang, M.A., Graduate Student
liang@uchicago.edu
Peter Zhi, Undergraduate Student
zhi@uchicago.edu
Emily Cooper, Undergraduate Student
ecooper@uchicago.edu
Tara McCrimmon, Undergraduate Student
trm16@uchicago.edu
Sonja Swanson, Undergraduate Student
sonja@uchicago.edu
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