Surgical Neurophysiology and Neurostimulation
Surgical Neurophysiology
The concept of Surgical or Interventional Neurophysiology emerges from two main phenomena in recent years: Firstly, an increasingly large number of neurosurgical procedures involving brain, cranial nerves, spinal cord and the peripheral nervous system needs the neurophysiological expertise to achieve efficacy and attain safety. Traditional ‘Clinical Neurophysiology’ has consequently extended its diagnostic roles to more interventional roles to assist surgical procedures with more and more neurophysiological procedures being applied in the operating room.
Secondly, some neurophysiological techniques have gradually become therapeutic in themselves, as represented by the terms of ‘Neurostimulation’ and ‘Neuromodulation’. These terms imply that the therapeutic alteration of activity in the nervous systems is achieved not by surgical ablation or medication but electrophysiological means via the implanted or non-implanted devices. As a result, new areas of clinical research have been created for investigating pathophysiological mechanisms of neurological disorders, evaluating and validating new therapeutic methods. For the above reasons, Surgical or Interventional Neurophysiology have been recognised as a new clinical sub-specialty by the Joint Committee on Higher Medical Training (JCHMT) of Royal Colleges and the Specialist Training Authority (STA).
Current research interests include assisting target localisation using micro- or macro-electrode recording, detecting capsular responses using surface EMGs. Great efforts have also been made to develop effective on-line and off-line signal processing techniques.
This project is currently funded by the Hammersmith Hospitals NHS Trust.
Neurostimulation
The last decade has seen a resurgence of interest in functional neurosurgery, particularly the therapeutic deep brain stimulation (DBS) in various movement and other neurological disorders. Nevertheless, its mechanisms are still unclear. A fuller understanding of the role of modulating brain activity by electrical current will provide a rational basis for the optimisation of therapeutic effects. A multi-disciplinary approach to study the mecahnisms of neurostimulation: (1) neurophysiological recording, (2) test stimulation combined with sensitive quantification on its effects, and (3) computation modelling.
Recent work on the electrode/brain interface in the therapeutic DBS has been funded by the Medical Research Council (MRC). The novelty of this study is to model the distribution of stimulating current around the electrode with consideration of the dynamic interaction with the local field potentials generated by the brain volume around the implanted electrode. This study has direct clinical implication that the optimal effects of therapeutic DBS can be achieved by adjusting the stimulation parameters based on the understanding of the dynamic interaction at the electrode/brain interface.
Sensorimotor Control in Health and Disease
Sensorimotor control in health and movement disorders is a research area shared with other clinicians in the unit. Combining psychophysic and neurophysiological techniques, voluntary and involuntary are quantified before and after medical or surgical treatment.
This project is currently funded by the National Tremor Foundation.
References
X Liu, S Wang, J Yianni, D Nandi, PG Bain, R Gregory, JF Stein and TZ Aziz. The sensory and motor representation of synchronised oscillations in the globus pallidus in patients with primary dystonia. Brain, 2008, in press.
P Feys, W Helsen, A Lavrysen, S Swinnen, B Nuttin, P Ketelaer, X Liu. The unsteady visual fixation enhances the amplitude of intention tremor during visually-guided manual tracking. Neurology, 70:106-113; 2008.
N Yousif, R Bayford, S Wang and X Liu. Quantifying the effects of the electrode-brain interface on the crossing electric currents in deep brain recording and stimulation. Neuroscience, 152: 683-691; 2008.
X Liu and A Forster. Interventional neurophysiology: A new frontier in investigation, treatment and research. Frontiers in Bioscience 13:1691-1697; 2008.
N Yousif and X Liu. Modelling the current distribution across the depth electrode-brain interface in deep brain stimulation. Expert Review of Medical Devices. 4:623-631; 2007.
S Wang, TZ Aziz, JF Stein, PG Bain and X Liu. The physiological and harmonic components in neural and muscular coherence in Parkinsonian tremor. Clinical Neurophysiology, 117:1487-1498; 2006.
Prof Tipu Aziz (Collaborator)
