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MEMP - Thesis Defense - Britni Crocker

Thursday, August 30, 2018 -- 2:30pm

Ether Dome - MGH Bullfinch Building - 55 Fruit Street, 4th Floor, Boston, MA 02114

Neurophysiological Properties of Cortico-Cortical Evoked Potentials in Humans
Invasive electrical brain stimulation has been increasingly used to treat an ever wide range of neuropsychiatric disorders from Parkinson’s disease to epilepsy and depression. In addition, single pulse electrical stimulation (SPES) is increasingly used to map connections between cortical areas using cortico-cortical evoked potentials (CCEPs).  However, the properties and mechanisms underlying brain stimulation remain mostly unknown, hindering the application of stimulation to new neurological disorders and the development of adaptive stimulation technologies that could improve clinical outcome. To improve understanding of SPES, we systematically explored the effects of cortical electrical stimulation in human epilepsy patients. 
Examining some fundamental properties of CCEPs, we show that the brain’s response to less than a millisecond pulse of stimulation can be detected up to one second post-stimulus.  This response has two peaks with distinct properties; the magnitude of the first peak is more variable and more diminished by distance, compared to the second.  Looking at the spatial distribution of CCEPs, we show that stimulation-derived networks are more closely related to structural connectivity than functional connectivity.  However, correcting for distance eliminates this difference.  Monitoring CCEPs across different brain states, we show that the second peak of the CCEP is significantly diminished during anesthesia. 
Taken together, these results provide important insight into the basic neurophysiological properties of CCEPs, their spatial distribution, and how they are modulated by the state of the brain itself.  These characteristics can inform experimental design, provide input parameters for modeling studies, and be applied towards the development of adaptive closed-loop stimulation paradigms.

Thesis Supervisor:
Sydney S. Cash, MD, PhD
Associate Professor of Neurology, HMS
Thesis Committee Chair:
Matthew P. Frosch, MD, PhD
Lawrence J. Henderson Associate Professor of Pathology and Health Sciences & Technology, HMS
Thesis Reader:
Patrick L. Purdon, PhD
Associate Professor of Anaesthesia, HMS
Date and Time: 
Thursday, August 30, 2018 - 2:30pm to 4:30pm

Ether Dome - MGH Bullfinch Building - 55 Fruit Street, 4th Floor, Boston, MA 02114