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An “ecological” action-based synthesis

Behavioral and Brain Sciences; New York Vol. 39,  (2016). DOI:10.1017/S0140525X15002046

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Why do we experience such a rich visual world all of the time our eyes are open, but seem to be aware of smells only when they first occur? There do seem to be more than incidental and irrelevant differences between the olfactory system and the other four major sensory systems. Morsella et al. suggest that we study the olfactory system for clues as to the neural correlates of conscious perceptual content. However, the olfactory system is admittedly a very primitive, albeit highly conserved, sensory system. The olfactory cortex is paleocortex, only three layers deep. Moreover, as Morsella et al. emphasize, olfactory information does not pass through a thalamic “relay” nucleus on its way to the olfactory cortex, but rather goes directly there from the olfactory bulb, only informing the mediodorsal nucleus of the thalamus after paleocortical processing. Even that pathway is minor, as olfactory input is mainly directed to the orbitofrontal cortex, from where it also projects to the mediodorsal thalamus. Although some insights about consciousness can surely be gained by taking the olfactory system as a model, we believe that it is sufficiently different from the other sensory/perceptual systems that those insights will not be sufficient to explain much about the more sophisticated, and recently evolved, systems that subserve mammalian consciousness. Indeed, there might even be two separate types of consciousness: paleoconsciousness (paleoC), arising from a phylogenetically old system like the olfactory system, and neoconsciousness (neoC), arising from a more recent adaptation involving thalamic relay nuclei and extensive neocortical processing.

In the service of describing the newer type of consciousness, we offer the following observation: neoC has many properties that paleoC does not have. Most compelling to us is the fact that as long as we are awake and have our eyes open, we experience a rich visual scene....