Descending Motor Pathways and Brainstem Reflexes in Cerebral Palsy

• Author / Creator

  Smith, Allison T

• This thesis discusses the organization of motor pathways in adults and children with cerebral palsy (CP). Individuals with CP experience impairments in the control of head and neck functions. The cranial nerves that innervate the head and neck pass through the brainstem. Thus, motor impairment could be indicative of dysfunction in brainstem circuitry. While brainstem reflexes are atypical in other neurological disorders in which there is known brainstem damage, the function and structure of brainstem circuitry in CP is less well known. In Chapter 2, we investigated the function of brainstem circuitry in CP by stimulating the trigeminal nerve to evoke a long latency, startle-like reflex in the sternocleidomastoid (SCM) muscle. We propose that this long-latency reflex is mediated by reticulospinal pathways. Individuals with CP showed facilitation of ongoing SCM EMG compared to age- and sex-matched controls, who showed suppression of ongoing SCM EMG. Additionally, injury to the sensorimotor system has shown to influence the development of cortico-reticulospinal circuits to mediate motor function. We also investigated if the modulation of cortically-evoked responses in the SCM was altered following the activation of brainstem circuits by trigeminal afferents. Some participants with CP had abnormally large, long-lasting responses in both the SCM and biceps brachii muscles when trigeminal nerve and cortical stimuli were combined. The enhanced excitatory responses evoked from trigeminal afferents in CP may be produced by heightened excitability of brainstem circuits, resulting in the augmented activation of reticulospinal pathways in response to early brain injury. Enhanced activation of reticulospinal pathways in CP may provide a compensated activation of the spinal cord and/or contribute to impairments in the precise control of head and neck functions. The sensorimotor regions of the brain are common sites of damage during development. Individuals with CP experience reorganization of sensorimotor pathways resulting in limited limb activity and motor impairment. Current therapies aimed at improving walking have shown promising functional results; however, the degree to which they influence underlying motor systems is unknown. In Chapter 3, we investigated the development of corticospinal pathways and the effects of intensive leg therapy to improve walking function in children with hemiplegic CP aged 8 months to 4 years of age. Motor pathway excitability was measured by applying transcranial magnetic stimulation over the leg representation of each motor cortex. We examined the onset latency and prevalence of motor-evoked potentials (MEPs) in lower limb muscles. Data is presented from an on-going, randomized, controlled trial. It remains unclear if and how intensive physiotherapy during infancy influences descending motor pathway development, as no consistent changes in MEP prevalence or correlation between MEP prevalence and functional improvements were seen throughout the study. However, we did observe several trends in the data whereby MEPs in leg muscles were more prevalent from the unaffected cortex in children older than 2 years of age, likely as a result of underlying maturation and refinement of corticospinal pathways. MEP onset latencies became progressively shorter with increases in age, suggesting myelination and increased synaptic efficacy of the motor system facilitate fast conduction of action potentials. Although we were unable to deduce the effect of training on MEP prevalence, we show that it is possible to characterize the development of descending motor pathways in children with CP under the age of 4 years.

• Subjects / Keywords

  • Hemiplegic
  • Corticospinal
  • Brainstem
  • Cererbral palsy

• Graduation date

  Spring 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3G15TS34

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.