General anesthesia (GA) is a pharmacologically-induced state of unresponsiveness and unconsciousness which millions of people experience every year. Despite its ubiquity, a clear and consistent picture of the brain circuits mediating consciousness and responsiveness has not emerged. Assertions from non-invasive human studies (i.e. EEG and brain imaging), modeling and animal studies implicate key cortical and subcortical brain areas (including cortex, thalamus, and basal ganglia (BG)) during anesthesia. However, studies to date are limited by the lack of direct recordings in humans from both cortical and subcortical regions with sufficient spatial, temporal, and spectral resolution during pharmacologically-induced anesthesia. Our overall hypothesis is that the mesocircuit model of consciousness, which was original proposed to characterize recovery after brain injury, can be generalized to understand mechanisms of consciousness more broadly. The current research proposal focuses on experimentally probing the mesocircuit in neurosurgical patients, taking advantage of differences in patient populations with respect to basal ganglia disease (e.g., Parkinson disease [PD] vs essential tremor [ET]), the ability to synchronously acquire high resolution BG and cortical neurophysiology, and the opportunity to modulate the circuit in a targeted fashion with deep brain stimulation (DBS) to interrogate brain-behavior relationships. We pursue three specific aims:
Aim 1 : To demonstrate that patients with underlying basal ganglia pathology are more sensitive to propofol than other patients. Specifically, we will use target-controlled infusion of propofol to characterize pharmacokinetic-pharmacodynamic parameters in patients with PD and ET to gain insights into the potential role of BG circuitry in regulating consciousness, bearing on our more generalized model of mesocircuit mediation of consciousness.
Aim 2 : To correlate temporal evolution of basal ganglia-frontoparietal cortical circuit dynamics with behavioral correlates of induction and emergence from propofol anesthesia. We will use high spatial, temporal, and spectral resolution recordings in human subjects to provide direct evidence of circuit function, temporal evolution, causal circuit flow, and brain-behavior correlates.
Aim 3 : To evaluate the effects of targeted mesocircuit DBS (including both globus pallidus internus and externus) on propofol induced loss and recovery of consciousness and responsiveness. The research is innovative in its use of natural variations in neurological disease and concurrent invasive recording and stimulation in humans with a mechanistic and causal study design. The proposed research is significant because it will demonstrate a complex interplay of cortical and subcortical networks with partially separable effects of anesthesia, contrary to the most common clinical approach of measuring a single, continuously scaled metric for depth of anesthesia. This program will provide important human data to shed light on the generalizability of the mesocircuit model of regulating consciousness as well as validate a human experimental model for further investigation and characterization of anesthetic effects on the human brain.
Although general anesthesia is used everyday to enable surgical care, brain mechanisms for inducing loss of consciousness are not well understood. The goal of this proposal is to use neurosurgical opportunities in humans to gain insight into the systems-level neurophysiological basis of anesthesia and consciousness, with greater spatial, temporal, and spectral resolution and confidence than can be achieved in animal or computational models. This work will explicitly test the mesocircuit theory of consciousness in humans to better characterize the complex interplay and causal relationships between cortical and subcortical networks, expanding the knowledgebase that is critical for developing, optimizing, and monitoring anesthetics.