The neurophysiology of sensorimotor integration in healthy aging and chronic stroke

ii Lay summary . iv Preface . v Table of contents . viii List of tables.xiv List of figures . xv List of abbreviations . xvii Acknowledgements . xix Chapter 1: General introduction . 1 1.1 Preamble . 1 1.2 Sensorimotor integration . 2 1.2.1 Neuroanatomy of sensorimotor integration . 3 1.2.2 Testing sensorimotor integration . 5 1.2.2.1 Transcranial magnetic stimulation . 7 1.2.2.2 Testing indirect sensorimotor integration . 9 1.2.2.3 Testing direct sensorimotor integration . 11 1.2.3 Aging and sensorimotor integration . 13 1.2.3.1 Aging: Somatosensory and motor function . 13 1.2.3.2 Aging: Somatosensory and motor neurophysiology . 14 1.2.3.3 Aging: Sensorimotor integration neurophysiology . 15 1.2.4 Chronic stroke and sensorimotor integration . 17 ix 1.2.4.1 Chronic stroke: Somatosensory and motor function . 17 1.2.4.2 Chronic stroke: Somatosensory and motor neurophysiology . 17 1.2.4.3 Chronic stroke: Sensorimotor integration neurophysiology . 20 1.3 Neuroplasticity . 22 1.3.1 Mechanisms of neuroplasticity . 22 1.3.2 Motor and somatosensory cortical plasticity . 24 1.3.3 Attention and neuroplasticity . 25 1.3.4 Plasticity of sensorimotor integration . 27 1.3.5 Plasticity and aging . 28 1.3. 6 Plasticity and chronic stroke . 30 1.4 Reliability of neurophysiological measures . 32 1.5 Thesis overview . 33 1.5. 1 Thesis impact . 34 1.5. 2 Research objectives . 35 Chapter 2: Exploring the influence of age and chronic stroke on the neurophysiology of indirect sensorimotor integration . 37 2.1 Introduction . 37 2.2 Methods. 40 2.2.1 Participants . 40 2.2.2 Experimental design. 40 2.2.3 Behavioural assessment . 41 2.2.4 Neurophysiological assessment . 41 2.2.4.1 Somatosensory evoked potentials . 42 x 2.2.4.2 Transcranial magnetic stimulation . 42 2.2.4.3 Sensorimotor integration . 43 2.2.4.4 Statistics . 44 2.3 Results . 44 2.3.1 Stroke and age-related changes in sensorimotor integration . 46 2.3.2 Association between neurophysiology, impairment, and function . 49 2.3.3 Somatosensory and motor cortical excitability . 50 2.4 Discussion . 51 2.4.1 Stroke and age-related changes in sensorimotor integration . 51 2.4.2 Relationship between neurophysiology, impairment, and function. 54 2.4.3 Somatosensory and motor cortical excitability . 56 2.4.4 Limitations . 57 2.5 Conclusions . 57 Chapter 3: Sensorimotor integration and aging: baseline differences and response to sensory training . 58 3.1 Introduction . 58 3.2 Methods. 61 3.2.1 Participants . 61 3.2.2 Experimental design. 62 3.2.3 Somatosensory functional tests . 62 3.2.4 Neurophysiological assessment . 62 3.2.4.1 Somatosensory evoked potentials . 63 3.2.4.2 Transcranial magnetic stimulation . 63 xi 3.2.4.3 Direct sensorimotor integration . 64 3.2.4.4 Indirect sensorimotor integration . 65 3.2.5 Sensory training . 65 3.2. 6 Statistical tests . 66 3.3 Results . 67 3.3.1 Baseline direct sensorimotor integration . 67 3.3.2 Influence of sensory training on sensorimotor integration . 69 3.3.3 Secondary measures – indirect sensorimotor integration . 71 3.3.4 Sensory training performance . 72 3.4 Discussion . 72 3.4.1 Baseline sensorimotor integration . 72 3.4.2 Neurophysiological response to sensory training . 74 3.4.3 Limitations . 77 3.5 Conclusions . 78 Chapter 4: Sensorimotor integration in chronic stroke: baseline differences and response to sensory training . 79 4.1 Introduction . 79 4.2 Methods. 83 4.2.1 Participants . 83 4.2.2 Experimental design. 84 4.2.3 Behavioural tests .