The neural control of breathing in health and respiratory impairment

The inspiratory muscles, such as the diaphragm, receive descending neural inputs from the medulla and sensorimotor cortex. In response to increased respiratory demand or in the presence of respiratory impairment, the neural control of the inspiratory muscles adapts to meet ventilatory requirements. This thesis addresses the neural control of inspiration in health, healthy ageing and chronic tetraplegia. In the first two chapters of results, single motor unit electromyographic recordings of the costal diaphragm were performed in healthy people aged 23-80 years (Chapter 2) and in chronic tetraplegia (Chapter 3) during quiet breathing. The findings show that diaphragm motor unit discharge frequencies during quiet breathing do not change in healthy ageing but are increased in chronic tetraplegia. Diaphragm motor unit action potentials are larger in size in both healthy ageing and chronic tetraplegia, although more so in the latter group, which suggests motor unit remodelling. The difference between the two groups reflects the greater severity of respiratory motor impairment in chronic tetraplegia. Furthermore, ageing-related changes in diaphragm motor unit size were observed in middle age. The sensorimotor cortex is recruited during quiet breathing in certain conditions of respiratory impairment but not in healthy, younger people. In Chapter 4, electroencephalographic recordings were made from participants with chronic tetraplegia during quiet breathing. The results show that the sensorimotor cortex is not recruited which suggests that other sources of neural control, likely the medulla, generate the increase in diaphragm motor unit output during quiet breathing. In Chapter 5, electromyographic recordings were made from healthy people to investigate the simultaneous control of the costal and crural portions of the diaphragm with increased drive to breathe. Here, regardless of whether the source of increased drive is voluntary or involuntary, the costal portion of the diaphragm has greater relative activation compared to the crural portion, which is consistent with their mechanical actions during inspiration. Overall, various neural adaptations occur in healthy ageing and chronic tetraplegia, when respiratory impairment is present, and that the activation of the costal portion of the diaphragm is greater than the crural portion which reflects their relative contribution to inspiratory air flow

Negative motor phenomena in cortical stimulation: implications for inhibitory control of human action.

Electrical stimulation of the human cortex typically elicits positive sensorimotor effects. However, many neurosurgical studies have also reported negative motor areas (NMAs) in which stimulation produces inhibition of ongoing movement. The neurocognitive implications of these studies have not been systematically explored. Here we review the neurosurgical literature on NMAs and link this to cognitive mechanisms of inhibition and their role in voluntary control of action. In particular, we discuss the functional validity of NMAs. We contest the sceptical view that negative effects following stimulation merely reflect disruption of positive motor areas. Instead, we suggest that NMAs may produce an inhibitory mechanism under ecologically valid conditions

IFCN-endorsed practical guidelines for clinical magnetoencephalography (MEG)

Magnetoencephalography (MEG) records weak magnetic fields outside the human head and thereby provides millisecond-accurate information about neuronal currents supporting human brain function. MEG and electroencephalography (EEG) are closely related complementary methods and should be interpreted together whenever possible. This manuscript covers the basic physical and physiological principles of MEG and discusses the main aspects of state-of-the-art MEG data analysis. We provide guidelines for best practices of patient preparation, stimulus presentation, MEG data collection and analysis, as well as for MEG interpretation in routine clinical examinations. In 2017, about 200 whole-scalp MEG devices were in operation worldwide, many of them located in clinical environments. Yet, the established clinical indications for MEG examinations remain few, mainly restricted to the diagnostics of epilepsy and to preoperative functional evaluation of neurosurgical patients. We are confident that the extensive ongoing basic MEG research indicates potential for the evaluation of neurological and psychiatric syndromes, developmental disorders, and the integrity of cortical brain networks after stroke. Basic and clinical research is, thus, paving way for new clinical applications to be identified by an increasing number of practitioners of MEG. (C) 2018 International Federation of Clinical Neurophysiology. Published by Elsevier B.V.Peer reviewe

Central nervous system physiology

This is the second chapter of the series on the use of clinical neurophysiology for the study of movement disorders. It focusses on methods that can be used to probe neural circuits in brain and spinal cord. These include use of spinal and supraspinal reflexes to probe the integrity of transmission in specific pathways; transcranial methods of brain stimulation such as transcranial magnetic stimulation and transcranial direct current stimulation, which activate or modulate (respectively) the activity of populations of central neurones; EEG methods, both in conjunction with brain stimulation or with behavioural measures that record the activity of populations of central neurones; and pure behavioural measures that allow us to build conceptual models of motor control. The methods are discussed mainly in relation to work on healthy individuals. Later chapters will focus specifically on changes caused by pathology

Brain signal analysis in space-time-frequency domain: an application to brain computer interfacing

In this dissertation, advanced methods for electroencephalogram (EEG) signal analysis in the space-time-frequency (STF) domain with applications to eye-blink (EB) artifact removal and brain computer interfacing (BCI) are developed. The two methods for EB artifact removal from EEGs are presented which respectively include the estimated spatial signatures of the EB artifacts into the signal extraction and the robust beamforming frameworks. In the developed signal extraction algorithm, the EB artifacts are extracted as uncorrelated signals from EEGs. The algorithm utilizes the spatial signatures of the EB artifacts as priori knowledge in the signal extraction stage. The spatial distributions are identified using the STF model of EEGs. In the robust beamforming approach, first a novel space-time-frequency/time-segment (STF-TS) model for EEGs is introduced. The estimated spatial signatures of the EBs are then taken into account in order to restore the artifact contaminated EEG measurements. Both algorithms are evaluated by using the simulated and real EEGs and shown to produce comparable results to that of conventional approaches. Finally, an effective paradigm for BCI is introduced. In this approach prior physiological knowledge of spectrally band limited steady-state movement related potentials is exploited. The results consolidate the method

Brain signal analysis in space-time-frequency domain : an application to brain computer interfacing

In this dissertation, advanced methods for electroencephalogram (EEG) signal analysis in the space-time-frequency (STF) domain with applications to eye-blink (EB) artifact removal and brain computer interfacing (BCI) are developed. The two methods for EB artifact removal from EEGs are presented which respectively include the estimated spatial signatures of the EB artifacts into the signal extraction and the robust beamforming frameworks. In the developed signal extraction algorithm, the EB artifacts are extracted as uncorrelated signals from EEGs. The algorithm utilizes the spatial signatures of the EB artifacts as priori knowledge in the signal extraction stage. The spatial distributions are identified using the STF model of EEGs. In the robust beamforming approach, first a novel space-time-frequency/time-segment (STF-TS) model for EEGs is introduced. The estimated spatial signatures of the EBs are then taken into account in order to restore the artifact contaminated EEG measurements. Both algorithms are evaluated by using the simulated and real EEGs and shown to produce comparable results to that of conventional approaches. Finally, an effective paradigm for BCI is introduced. In this approach prior physiological knowledge of spectrally band limited steady-state movement related potentials is exploited. The results consolidate the method.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Sensory information to motor cortices: Effects of motor execution in the upper-limb contralateral to sensory input.

Performance of efficient and precise motor output requires proper planning of movement parameters as well as integration of sensory feedback. Peripheral sensory information is projected not only to parietal somatosensory areas but also to cortical motor areas, particularly the supplementary motor area (SMA). These afferent sensory pathways to the frontal cortices are likely involved in the integration of sensory information for assistance in motor program planning and execution. It is not well understood how and where sensory information from the limb contralateral to motor output is modulated, but the SMA is a potential cortical source as it is active both before and during motor output and is particularly involved in movements that require coordination and bilateral upper-limb selection and use. A promising physiological index of sensory inflow to the SMA is the frontal N30 component of the median nerve (MN) somatosensory-evoked potential (SEP), which is generated in the SMA. The SMA has strong connections with ipsilateral areas 2, 5 and secondary somatosensory cortex (S2) as well as ipsilateral primary motor cortex (M1). As such, the SMA proves a fruitful candidate to assess how sensory information is modulated across the upper-limbs during the various stages of motor output. This thesis inquires into how somatosensory information is modulated in both the SMA and primary somatosensory cortical areas (S1) during the planning and execution of a motor output contralateral to sensory input across the upper-limbs, and further, how and what effect ipsilateral primary motor cortex (iM1) has upon modulation of sensory inputs to the SMA