Date of Award

January 2012

Document Type

Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Ramachandran Ramani

Subject Area(s)

Neurosciences

Abstract

The advent of functional neuroimaging techniques such as Positron Emission Tomography (PET) and Functional Magnetic Resonance Imaging (fMRI) has brought about a revolution in the field of neurophysiology. The assembly of a comprehensive structure/function map of the human brain has switched from an approach that examines static neural pathways to one that examines how cortical regions are functionally connected. Throughout the past decade, functional connectivity MRI (fc-MRI) studies on the resting and task-induced brain have made major contributions to this field. The study of connectivity under anesthesia has recently become an area of interest, both because of its ability to establish connectivity networks that define the state of consciousness, and because it might further elucidate the poorly understood mechanisms of anesthesia. Largely owing to the advancement of fc-MRI, it has become apparent that the underlying mechanism of general anesthesia may lie in its ability to unravel these functional connections that define consciousness, rather than act on any particular channel, or cortical "on/off" switch. Inhaled and intravenous anesthetic agents, in addition to their ability to alter cerebral blood flow, have been found to induce significant alterations in functional connectivity. This study examined the effects of 2µg/mL plasma propofol (equivalent to 0.5 MAC) on functional connectivity in 31 healthy volunteers. Our results demonstrated connectivity decreases primarily in higher-order association pathways (frontal lobe, hippocampus), as well as inducing connectivity alterations in the supplementary cortex (SMA) and posterior cingulate cortex (PCC).

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