His research interests are on the neural mechanisms underlying human consciousness in health and disease. At present most work focuses on the neural correlates of particular types of conscious content, aiming to distinguish between conscious and unconscious representations in the human brain. As a considerable amount is already known about the anatomy and physiology of the visual system, much of the research in the laboratory focuses on visual awareness. However, his laboratory also studies the auditory and somatosensory systems. Most research involves functional MRI at high field, in combination with behavioral studies, transcranial magnetic stimulation and EEG/MEG. Previous work by Rees has suggested that subjective awareness of objects in the visual environment is associated not just with enhanced activation in visual areas of the occipital lobe, but also areas of parietal and prefrontal cortex often associated with attention. A major focus of this work is therefore in studying interactions between visual cortex and these areas, both in the context of attention, and with respect to eye movements. More recently, he has worked on neurodegeneration, collaborating with Sarah Tabrizi. His work on multivariate inference has led to collaborations with Parashkev Nachev and work in high-dimensional neurology and with DeepMind. He co-edited a large reference book entitled the Neurobiology of Attention with Laurent Itti and John Tsotsos, and is the author of numerous articles and invited reviews on the functional imaging of consciousness. He was a member of the board of the Association for the Scientific Study of Consciousness until stepping down in 2007, and with Patrick Wilken organised its tenth annual meeting that was held at St. Anne's College, Oxford in June 2006.
Teaching and training
Rees is currently Director of the UCL SLMS Academic Careers Office which delivers strategy and support to academics and clinical academics at UCL. He directs a Wellcome Trust Clinical PhD Programme and a large MRC Doctoral Training Programme associated with the ACO. Previously Rees was the elected Deputy Chair of the British Medical Association Medical Academic Staff Committee 2007-12, and led on policy development concerning medical academic training. He was a member of the Medical Programme Board for England 2007-2012 and chaired the MPB Recruitment Task and Finish Group overseeing recruitment of all trainee doctors in England. He served on the 'Walport' committee of the UK Clinical Research Collaboration developing Academic Clinical Fellow and Clinical Lecturer schemes, and leads the local ACF and CL schemes at University College London. He was also course director for over a decade for the Membership of the Royal College of Physicians Part 1 courses in London run by Pastest.
Enterprise and innovation
Rees is a Non-Executive Director of UCL Business PLC, the technology transfer company associated with UCL. He is also a Senior Scientific Advisor at Google DeepMind. Rees was Chair of the Knowledge Transfer and Enterprise Board, of the UCL School of Life and Medical Sciences between 2014-2017. He was a Director of Imanova Limited, a molecular imaging company until August 2017 when it was acquired by Invicro.