Top-down functions (e.g., attention and working memory) go hand-in-hand with consciousness. Yet we know more about the former, because it is hard to define consciousness in most contexts. There is, however, a way in. General anesthesia (GA) provides transition through different stages of consciousness.
We aim to determine which aspects of cortical processing are critical for these changes by using a surgical anesthetic, propofol, in monkeys. Propofol increases cortical-wide delta oscillations and alpha in frontal cortex. One hypothesis posits that the increased frontal alpha disrupts top-down cortical feedback from frontal cortex. Another points to the widespread delta oscillations that, unlike sleep, are decoupled across cortex. This could fragment long-range communication across cortex or, as some suggest, loss of consciousness (LOC) could be due to frontal-parietal cortex disconnectivity per se. The thalamus is likely to play a major role. Mounting evidence suggests it controls top-down cortical processing, perhaps by modulating cortical oscillations. Abnormal thalamic oscillations could entrain different cortical areas or the changed dynamics could be largely a cortical phenomenon. Previous primate studies of GA lack the combination of wide scope and single-neuron precision to directly test these hypotheses. We will use chronic intracranial multiple electrodes in monkeys to record simultaneously from a wide range of critical brain structures (prefrontal cortex, posterior parietal cortex, auditory cortex, and thalamus). We will also test if thalamic stimulation can restore consciousness and wakeful cortical dynamics.
This project aims to uncover the neural correlates of consciousness by using many-electrode recording in monkeys being induced into unconsciousness by general anesthesia. We will test the hypothesis that anesthesia disrupts cortical communication by causing abnormal rhythms in thalamocortical circuits.