Most of the neural activity in our brains does not produce conscious sensations: it simply takes place without leaving any trace of conscious sentience.
This unconsciousness might seem an alien and unknown territory, but it is actually one of the most common facts of our lives. Every morning we can collect evidence of how this non-conscious neural activity operates: the neural mechanisms that literally wake us up after a good night of sleep are in fact completely unconscious to us — we cannot wake ourselves up, our brain (or the neural activity within it) wakes “us” up. By definition, those mechanisms lack consciousness.*
Similarly, even when we are conscious and attentive to the world that surrounds us, the neural activity related to most of our cognitive processes does not correlate with conscious sensations. Think, for example, of episodic memory. How do we retrieve a single piece of memory? If we want to remember an event (say, what we had for dinner the previous day) we ask ourselves a specific question (what did I eat yesterday?), wait for approximately a second or so, and then see the answer in our “minds eye” (a pizza). The initiation of the process of retrieving a memory is under our voluntary control (we exert that command) but the intermediate cognitive steps needed to retrieve a memory are unknown to us — whatever cognitive mechanisms our brains use, we are not conscious of them.
And memory is just one example. Non-conscious processes pervade each and every one of our cognitive processes, from visual imagery to language, from motor control to decision-making. We do not have conscious access to the full list of operations required for such cognitive processes but, instead, just to their outcome**.
But if most of our brain activity is not associated with consciousness, what about that small part that actually produces consciousness? What are the special properties of the neural correlates of consciousness, of that “minimum set of neural activity necessary and sufficient to give rise to consciousness”? Several attempts have been made to answer to this question** but, in my opinion, there is still no satisfactory answer. This remains one of the biggest mysteries of science.
We might get closer to a solution once we will finally recognize how to properly address this problem. What is the explanation about consciousness that we (neuroscientists) are pursuing? What is the problem that a theory of consciousness should address and how can science help to solve it?
This is one of my main current scientific interest.
* Note that when we say “I woke up” we make it sound like a conscious action, even if we do not have any control over it — we identify ourselves as subjects, while we are actually objects of consciousness. Instead of saying “having consciousness” a more precise formulation of the act of consciousness would actually be “consciousness has us”.
**Many neural markers have been proposed as possible neural correlates of consciousness. One of those candidates has been the P3 component in EEG recordings — Joaquin Navajas and I wrote a short opinion article on the relationship between the electroencephalogram P3 component and conscious access that you can read here.