Quantifying Consciousness: Sensory and Sonic PCI

INSTITUTE: UCLA, Department of Psychology

PROJECT LEADERS: Martin Monti, Alessandra Dallavecchia, Micah Johnson

PROJECT DURATION: 3 years

LAB WEBSITE: Monti Lab

One key difficulty in assessing whether someone (other than ourselves) is conscious is the fact that this judgment typically relies on subjective reports. In the clinic, for example, distinguishing a patient who is unconscious from a patient who is (minimally) conscious relies on the patient’s ability to perform some manifestly voluntary behavior that can be taken to imply the presence of consciousness. For example, a patient might be asked to open their mouth, move a hand, or gesture in response to a verbal question. But what if the patient had a cognitive dysfunction (e.g., aphasia; that is, the inability to understand language), or motor impairment, that prevented them from responding to such a request? The patient might appear as unconscious. 

Recently, a new technique has been devised to measure, in a quantitative and objective manner, whether the brain possesses the degree of complex network dynamics that is typical of states of consciousness. This approach, known as the Perturbational Complexity Index, is based on assessing quantitatively the electrophysiological signature of the brain’s response to an electromagnetic pulse. In particular, complex responses are typical of states of consciousness whereas simpler, more stereotyped responses are characteristics of states of unconsciousness. This technique has now been extensively validated across several models (e.g., sleep, anesthesia) and has been shown to be sensitive to the presence of consciousness in patients with a Disorder of Consciousness. Nonetheless, this technique poses several challenges (e.g., the need for advanced and expensive instrumentation, requirement for extensive training, and possible confounds tied to the use of transcranial magnetic pulses) which limit its broad deployment.

The present project is aimed at evaluating two alternative approaches which dispense with the need for electromagnetic pulses and replaces them with either sensory (e.g., auditory, somatosensory) or ultrasonic stimulation (e.g., Figure 1). If either of these approaches revealed a similar sensitivity to the state of consciousness, they might provide for a simpler and more broadly deployable technique to objectively assess, in the clinic, a patient’s level of consciousness.

Figure 1. Example brain dynamics response to an ultrasound pulse (top) compared to a sham pulse (bottom). Ultrasound Evoked Potential (top) and the sham session (bottom). Approximately 200 ms after the sonic pulse, a suppression in the brain signal is visible after ultrasound (top) but not after sham (bottom).

Broader Impact:

This project has the potential for providing a simpler and more broadly deployable (and portable) technique for assessing someone’s level of consciousness in an objective and quantitative manner.