Digital Theses Archive


Tesi etd-04112017-122056

Type of thesis
Brain reorganization after stroke and cortical correlates in motor control
Scientific disciplinary sector
INGEGNERIA - Biorobotics
relatore Prof. MICERA, SILVESTRO
  • Clinical Neurophysiology
  • Motor Control
  • Neuronal Plasticity
  • Neurorehabilitation
  • Stroke
Exam session start date
The main interest of this project was to study how the brain and cortico-spinal tract functioning is involved in motor function. In detail the concern was to characterize the brain activity and excitability after a stroke injury and to describe plasticity mechanisms and their involvement in stroke motor recovery. <br>A cohort of stroke patients in subacute phase was subdivided on the basis of lesion location (cortico-subcortical and subcortical lesions) and assessed for brain electrical activity by means of 64ch EEG and motor functions. The results highlighted a characteristic bilateral cortical reorganization related to a specific clinical status. In detail, subcortical localization of the brain infarct was characterized by an higher Alpha power activity in the whole scalp and asymmetric distribution of Delta activity, higher in the affected hemisphere. This interhemispheric imbalance was related to the degree of clinical impairment: higher asymmetry corresponds to a better clinical status. Differently, cortical involvement determined a scattered increase of low-frequency Delta activity in both hemispheres.<br>Cortical-spinal tract was studied in post-stroke patients longitudinally by means of Motor Evoked Potential by Transcranial Magnetic Stimulation and Motor function evaluations were also performed between 10 and 45 days and 3 months post the acute event. The longitudinal study confirmed the relevant role of the unaffected hemisphere in mechanisms of brain reorganization. In detail we observed a reduction in contralateral Silent Period duration that was related to clinical improvement over time. This result was observed only in subcortical stroke patients.<br>The study of brain activity and brain excitability gave concordant information about different spontaneous cortical reorganization following two different lesions, highlighting a trend of normalization of cortical electrical activity of unaffected hemisphere in subcortical stroke type. <br>Furthermore our interest was to study the cortical reorganization induced by means of rehabilitation techniques able to boost the recovery-related brain plasticity. The improvement of motor function depends on ‘relearning’ of new patterns of activity, therefore an effective intervention could involve motor learning principles. Therefore we investigated the post-stroke neurophysiological correlates of the motor learning process induced by an intensive standardized rehabilitative protocol based on cognitive skill learning principles. In this regard we drew up a specific robotic-aided rehabilitation protocol for the upper limb incorporating many concepts from the motor learning literature in order to maximize retention and generalization of what is learned during the training. Our result showed that this specific rehabilitative protocol can induce an adaptive bilateral brain reorganization, reducing the brain asymmetry in post stroke patients. <br>Recapping cortical reorganization could have a different role in relation to the timing after the acute event and to the learning processes. In this regard the unaffected hemisphere could have a vicarial role for the subacute functional outcome but the asymmetry decrease could be necessary in acquisition of motor learning skills.<br>A better understanding of the central mechanisms underlying both spontaneous and training-guided recovery could give the possibility to design rehabilitative strategies able to maximize the brain capacity to reorganize its neural networks after a damage.<br>To date the role of the motor cortex in walking ability is not completely clarified. To this aim we developed an experimental setting to study the connectivity between motor cortex and major leg muscle activity during a stereotyped walking on a treadmill. An high brain to muscle connectivity was described between specific motor cortex areas and distal muscle. In detail we found unidirectional brain-to-muscle connectivity between contralateral Cingulate Motor and Supplementary Motor Areas and Tibialis Anterior muscle. The result determine for the first time the causal contributions of these cortical areas, particularly involved in planning of actions determined by internal drives, in controlling major leg muscles supporting stereotyped locomotion. <br>In conclusion a deeper knowledge of cortical function, an exact characterization of plasticity mechanisms and the identification of specific markers of recovery after stroke become crucial in order to design specific treatment and to provide the basis for a novel, more efficient and customized top-down rehabilitative intervention. Moreover the better knowledge of the physiological cortico-muscular connectivity during walking could be a starting point for more efficient gait training protocol.<br>