Conscientious of the Conscious: Interactive Capacity as a Threshold Marker for Consciousness

Abstract

Along with their potential benefits, recent technological advances in neuroimaging and electroencephalographic assessment of brain-injured patients have brought to light uncertainty in diagnosing disorders of consciousness. Such technologies highlight the difficulty in determining the presence or absence of consciousness, and in particular the distinction between the minimally conscious state (MCS) and the vegetative state (VS). We describe the ethical importance of this diagnostic distinction, discuss how these delineations have been affected by recent technological advances, and explore the resulting ethical challenges. We then propose a potential means of addressing these diagnostic dilemmas—namely, by stipulating demonstrable interactive capacity as a standard threshold for assessing consciousness—in order to guide the ethical management of patients whose state of consciousness remains uncertain.

Keywords:

• Consciousness
• brain injury
• neuroimaging
• decision making
• minimal consciousness
• permanent vegetative state

Notes

1. It should be noted that the VS has been alternatively defined elsewhere. For example, Jennett and Plum (1972) propose a behavioral definition and Shewmon (2004b) has suggested that the definition must consider conceptual (i.e., the existence of consciousness), behavioral, and anatomical features in tandem. Because the conceptual definition proposed by the Multi-Society Task Force on PVS has been widely accepted in the study of VS, this definition is the one assumed for the purposes of this essay.Thank you to David Silbersweig, MD, for his guidance and support in navigating disorders of consciousness. Thank you also to Joseph Fins, MD, Alan Shewmon, MD, and Thomas Cochrane, MD, for lending their insights and perspectives to the construction of this essay.

It should be noted that these technologies also implied the possibility of discovering severely “locked-in” patients, or patients whose brain damage prevents them from offering any behavioral evidence of consciousness. However, these patients can be conceptually distinguished from MCS patients, in that the former retain full consciousness, but the latter only partial, or intermittent, consciousness. Because this essay focuses on detecting the mere presence of consciousness—and not a fully normal state of consciousness as implied by the locked-in syndrome—the MCS serves as a more appropriate contrast to the VS. Thus, the possibility of these locked-in patients is not further discussed, although many of the same principles of detecting consciousness technologically will apply.