Area of Research

Neural Degeneration & Repair, Motor Systems

Specialization

Development of motor pathways and motor behavior; recovery after spinal cord injury and CNS axon regeneration.

RESEARCH THEME

Skilled motor behavior, such as reaching to grasp an object, is the expression of complex interactions between multiple motor pathways in the brain and spinal cord. Several factors are important for producing skilled movements, including the specificity of connections between axons of the motor pathways and spinal cord neurons as well as the presence of internal movement representations in the cerebral cortex.

Research in this laboratory examines postnatal development of the motor systems and skilled motor behavior in animals. Development of motor skills occurs over a prolonged postnatal period. During this period, specific connections are being formed between the brain and spinal cord and motor maps are becoming elaborated. We study how neural activity in the developing motor pathways and an animal's early postnatal behavioral experiences shape the anatomical and functional organization of motor circuits later in development and in maturity.

In addition, we have recently begun to apply principles learned from the study of motor system development to examine recovery of motor function after spinal cord injury. Like in development, after spinal cord injury new connections form and skilled motor behaviors are relearned. In one set of experiments, we have developed a novel approach in which a healthy nerve is used to "bypass" the injury. Here, motor axons in the nerve regenerate novel connections with the injured portion of the spinal cord. In another set of experiments, we are using immuno-blockade of myelin-associated growth inhibitory proteins to help re-establish connections between the cortex and spinal cord.

SELECTED PUBLICATIONS

Martin JH, Friel K, Salimi I, Chakrabarty S. Corticospinal Development. In: Encyclopedia of Neuroscience, volume 3, pp. 302-214. (Ed) L. Squire. Oxford: Academic Press. (2009).

Chakrabarty S, Friel K, Martin JH. Activity-dependent plasticity of the M1 motor map and corticospinal tract connectivity. J. Neurophysiology (2009) 101:1203-1293

Campos L, Chakrabarty S, Haque R, Martin JH. Regenerating motor bridge axons refine connections and synapse on lumbar motoneurons to bypass chronic spinal Cord Injury. J. Comp. Neurology (2008) 506:838-850.

Salimi I, Friel K, Martin JH. Pyramidal tract stimulation restores normal corticospinal tract connections and visuomotor skill after early postnatal motor cortex activity blockade. J Neurosci (2008) 28:7426-7434.

Friel K, Martin JH. Rebalancing corticospinal activity promotes recovery of motor skill and anatomical integrity after inactivation during a critical period. J. Neuroscience (2007) 27:11083-11090.

Brus M, Carmel JB, Chakrabarty S, Martin JH. Electrical Stimulation of Spared Corticospinal Axons Augments Connections with Ipsilateral Spinal Motor Circuits After Injury. J. Neuroscience (2007) 27:13793-13801.

Beg AA, Sommer JE, Martin JH, Scheiffele P. Alpha2-chimaerin is an essential EphA4 adapter in the assembly of neuronal locomotor circuits. Neuron (2007) 55:768-778.