The olfactory system as the gateway to the neural correlates of consciousness

Abstract

How consciousness is generated by the nervous system remains one of the greatest mysteries in science. Investigators from diverse fields have begun to unravel this puzzle by contrasting conscious and unconscious processes. In this way, it has been revealed that the two kinds of processes differ in terms of the underlying neural events and associated cognitive mechanisms. We propose that, for several reasons, the olfactory system provides a unique portal through which to examine this contrast. For this purpose, the olfactory system is beneficial in terms of its (a) neuroanatomical aspects, (b) phenomenological and cognitive/mechanistic properties, and (c) neurodynamic (e.g., brain oscillations) properties. In this review, we discuss how each of these properties and aspects of the olfactory system can illuminate the contrast between conscious and unconscious processing in the brain. We conclude by delineating the most fruitful avenues of research and by entertaining hypotheses that, in order for an olfactory content to be conscious, that content must participate in a network that is large-scale, both in terms of the neural systems involved and the scope of information integration.

A Model of Early Motivational States and Their Uses

“…Neural facilitators are traditionally thought of as neural or synaptic structures that amplify signals (Kandel, 1991). Here, the facilitator's definition is extended to compensation for transmission delays and neural mechanisms that speed up and accelerate the arrival of danger signals to consciousness where danger is perceived and appropriate action is taken (Smith, 1958;Merrick et al, 2013).…”

“…The issue of physiological reflexes in general are treated in reference (McMahon, 1984) and higher reflexes such as in fighting or competition in reference (Ischlondsky, 1952). Concentration, physical fitness, and strength (Shaffer, 1928;Murphy & Murphy, 1962;Merrick et al, 2013) are attributes of human performance (Rasch & Burke, 1978). Response to pain (Eichenbaum, 2002, Chapters 1 and 11) and to flight or fight are other examples.…”

Can skeletomotor action integration occur without consciousness? Evidence from unconscious action inhibition

“…It is clear that isolating the neuroanatomical substrate of a visual conscious content remains controversial. From an EASE perspective, and based on previous research (Merrick et al 2014;Morsella & Bargh 2007), we focus our attention instead on olfaction (see also Keller 2011), a phylogenetically old system whose circuitry appears to be more tractable and less widespread in the brain than that of vision or higherlevel processing such as music perception. As Shepherd (2007) concludes, "the basic architecture of the neural basis of consciousness in mammals, including primates, should be sought in the olfactory system, with adaptations for the other sensory pathways reflecting their relative importance in the different species" (p. 93).…”

Olfactory Consciousness across Disciplines

“…Quilty-Dunn's article explores Reid's account of odors as secondary qualities and argues for the relevance of Reid's theory for contemporary debates (Quilty-Dunn, 2013). The simplicity of the olfactory system is also what prompts Merrick and her colleagues to suggest in their review article that olfaction can be used as "the gateway to the neural correlates of consciousness" (Merrick et al, 2014).…”

“…The many unique features that distinguish olfactory consciousness from other forms of perceptual consciousness are reviewed here with a focus on cognition by Stevenson and Attuquayefio (2013), and with a focus on neuroanatomy and neurodynamics by Merrick et al (2014).…”