Consciousness and the Brain

Last month a commenter suggested that “I would be interested to see you research and post on ‘How science addresses the subjective, in relation to consciousness and freewill'”, to which I responded that I might write up a summary of the ways this is addressed in the book I was reading, Stanislas Dehaene’s “Consciousness and the Brain: Deciphering How the Brain Codes Our Thoughts”. Furthermore, the comment offered a particular direction to consider, namely that science can “collate and analyse subjective reports and hope something comes out of this – e.g. by correlating objective measurement with the subjective reports. … The problem with this is that these results are generally not accorded the same scientific status.” Dehaene actually spills a considerable amount of ink in the opening chapters addressing this concern. For example:

Consciousness and the Brain“This research strategy was simple enough, yet it relied on a controversial step, one that I personally view as the third key ingredient to the new science of consciousness: taking subjective reports seriously. … The participant’s introspection was crucial: it defined the very phenomenon that we aimed to study.” (pg 11)

“The correct perspective is to think of subjective reports as raw data. A person who claims to have had an out-of-body experience genuinely feels dragged to the ceiling, and we will have no science of consciousness unless we seriously address why such feelings occur. In fact, the new science of consciousness makes an enormous use of purely subjective phenomena, such as visual illusions, misperceived pictures, psychiatric delusions, and other figments of the imagination. Only these events allow us to distinguish objective physical stimulation from subjective perception, and therefore to search for brain correlates of the latter rather than the former.” (pg 12)

“All this evidence points to an important conclusion, the third key ingredient in our budding science of consciousness: subjective reports can and should be trusted. … introspection is a respectable source of information. Not only does it provide valuable data, which can often be confirmed objectively, by behavioral or brain-imaging measures, it also defines the very essence of what a science of consciousness is about.” (pg 42)

The Recipe

Those quotes refer to three key ingredients which go beyond the objective data about brain activity that we can gather through fMRI, EEG and the like. Dehaene identifies these ingredients as conscious access, manipulation of conscious perception and, as noted, careful recording of introspective reports. He then goes on to further define each of these.

Conscious access is defined as the awareness of specific information – it’s the foundational definition of consciousness that underpins more elaborate attributions, like self-awareness. As is elucidated in the book, our brains actually consume massive amounts of perceptual data. Much of what is received by our senses and processed in our brain eludes our conscious awareness. Conscious access is that sliver of data which enters our stream of thought from amongst the mountain of perceptions which bombard us from without and arise from within.

Our conscious access is reportable. As I type this, you are receiving a report of my conscious access. We cannot report on that which we are unaware of, so it is by definition that reports are only informative with regard to the content of our conscious access. Experiments can build upon this by asking participants to focus on a particular element of their perceptual space that has been carefully crafted by the experimenters. This manipulation of conscious perception is the experimental variable that allows the researchers to segregate the data into that which correlates with consciousness and that which does not. Dehaene outlines several primary manipulations – binocular rivalry, attentional blink, subliminal stimuli – and references several others throughout the course of the book. Each of these present an opportunity to separate conscious processing from unconscious processing and so look for the signatures of consciousness.

Dehaene then goes on to highlight the massive amount of work that our brains are doing subconsciously and how this surreptitiously influences our conscious access. Research in this domain paints a picture of the inverse side of consciousness and offered a baseline against which consciousness can be compared. After taking a side trip into discussions about the viability of the evolutionary origins of consciousness as a tool for organizing and prioritizing the competing interests in our subconscious processes, we are introduced to the findings that this recipe has thus far wrought.

Finding Consciousness

The toolkit described above has been extensively deployed in the lab and the cumulative results led Dehaene to identify four reliable signatures of consciousness. They are:


[1] “Although a subliminal stimulus can propagate deeply into the cortex, this brain activity is strongly amplified when the threshold for awareness is crossed. It then invades many additional regions, leading to a sudden ignition of parietal and prefrontal circuits” (Fig 16, pg 119)

(2) "In the EEG, conscious access appears as a late slow wave called the P3 wave. This event emerges as late as one-third of a second after the stimulus: our consciousness lags behind the external world."

[2] “In the EEG, conscious access appears as a late slow wave called the P3 wave. … For conscious words only, the wave of activity is amplified and flows into the prefrontal cortex and many other associative regions, then back to visual areas. This global ignition causes a large positive voltage on the top of the head – the P3 wave.” (Fig 18, pg 123)


[3] “A long burst of high-frequency activity accompanies the conscious perception of a flashed picture … When viewers failed to see the picture, only a brief burst of high-frequency activity traversed the ventral visual cortex. … Conscious perception was characterized by a lasting burst of high-frequency electrical activity, which indicates a strong activation of local neuronal circuits.” (Fig 20, pg 136)


[4] “The synchronization of many distant brain regions [form] a global web … during conscious word perception, causal relations show a massive bidirectional increase between distant cortical regions, particularly with the frontal lobe. Only a modest and local synchronization occurs when the participants fail to perceive the face or word.” (Fig 21, pg 138)

The common attribute which ties these signatures together is that they all represent prolific activity across large areas of the brain. In contrast to Descartes’ pineal soul-suite, the evidence points to consciousness as a phenomenon that is spread throughout the brain when a massive avalanche of distributed activity is launched. This excitation is what Dehaene calls “global ignition”. After having presented all of the correlative data Dehaene anticipates a common objection – correlation does not equal causation – and so he offers evidences to support the proposal that brain activity is more than just a side-effect of the ghost in the machine and that there are reasons to believe we are glimpsing consciousness itself.

“Let us play devil’s advocate again … Might [global ignition] bear no specific relation to the details of our conscious thoughts? Might it just be a surge of global excitation, unrelated to the actual contents of subjective experience? … Calling such a brain event the medium of consciousness would be like confusing the thump of the Sunday newspaper on our doorstep with the actual text that conveys the news.” (pg 142-143)

The first stop for the counter against this objection comes at the Centre for Systems Neuroscience at the University of Leicester in the UK, where Rodrigo Quian Quiroga enjoys probing individual neurons and finding ways to incorporate pop culture icons into his experiments. He has spent the last decade examining the relationship between conscious access and discrete patterns of neural firing at the level of individual neurons. The short story is that through a novel technique pioneered by Itzhak Fried, we have been able to take advantage of the surgeries performed on epilepsy patients to implant fine electrodes that record from individual neurons. When these are monitored during experiments there are very specific relationships found between perceptual and recollected concepts and individual neurons. Those experiments have not only identified a link between concepts and individual neurons, but the same tools used to investigate consciousness have been utilized to show that some neurons are only linked to conscious perception of stimulus – in effect, the neuron can be said to be a part of a conscious thought. These findings have been documented across many publications, but a few of the key overview papers are “Concept cells: The building blocks of declarative memory functions” and “Brain Cells for Grandmother“. Furthermore, similar findings led to the awarding of the 2014 Nobel Prize in Physiology or Medicine for the discovery of place cells; individual neurons which correlate with our location in space. These were first discovered in rats and then subsequently also identified in humans. The extrapolations we can draw from the discovery of an association between individual cells and conscious perception are potentially monumental. In particular, it does not seem inconceivable that perhaps some day we may be able to translate the philosopher’s qualia as a pattern in the brain.


Transcranial magnetic stimulation in 1911 (C.E. Magnusson and H.C. Stevens)

While fascinating, the added specificity of the single neuron experiments has not yet established causation. It could be that those individual neurons are simply assigned dedicated roles as the bridge between body and particular concepts of the mind. Perhaps in those experimental observations we are simply bystanders watching as the train of thought passes by. That is not impossible, but there’s more to examine. The next stop starts with a bit of time travel back to the early 20th century, when several parties began toying with transcranial magnetic stimulation (TMS) and reporting various sensory anomalies in conjunction with the activation of the coils. Vast improvements in the equipment have allowed these experiments to continue today with sharp precision that enables experimenters to focus the stimulus to specific regions of the brain. In doing so, they have been able to trigger domain specific sensory illusion – light when there is none to be found, motion while sitting still and color in a monochrome scene.

Perhaps more significant, however, is not the creation of sensory perception through TMS, but rather the disruption of consciousness itself through the same mechanism. Magnetic pulses targeted toward the long-distance networks that facilitate global ignition have been shown to eradicate a conscious perception that would have otherwise obtained. Even more relevant to the question of the interplay between the subjective and the objective is a study in which the prefrontal lobes were overwhelmed with pulses, leaving an effect which lasted up to 20 minutes. During this time, the subjects were asked to perform simple tasks of judging shapes that were presented to them. Objectively, their accuracy was effectively equivalent to their performance prior to the stimulation. Subjectively, however, they reported significant doubt in their answers. Objectively they were just as capable but their conscious awareness of their judgement had been impaired.

Before closing this section I must acknowledge that for the resolute dualist, we still haven’t fully addressed the objection. Maybe the TMS is acting in the place of our sensory input, stimulating or disrupting those neural mind-bridges in such a way that the mind thinks it is receiving or missing sensory data. OK, then let’s go beyond the content of the book and take a look at some additional research. If we say that the mind is distinct from matter then theoretically our memories are also made of mind stuff. However, starting about 70 years ago with Wilder Penfield experiments have been shown to trigger memory recall through direct electrode stimulation of specific brain regions. Whereas the dualist could argue that this stimulation is no different than the recall we experience when a familiar sight or sound is encountered through sensory input, the distinction becomes apparent when stimulation is used to disrupt conscious memory recall. For example, by acting directly on brain regions associated with verbal memory, electrical stimulation can directly impair recall of names for familiar objects and this phenomenon is often used to locate brain function through the process of cortical stimulation mapping. It is not that the person’s sensory perception of the object is disrupted but rather that their recall of the memory content which associates words with the object has been impaired. I find it difficult to understand how this result fits into a dualist framework.

In total, there is a large body of evidence that the content of our thought-life is causally connected to our neurology. We have opened an objective window onto the world of the subjective and on to consciousness itself. Massive projects are underway and, though we are still far from grasping the means of translation between the subjective and the objective, the future appears to be one in which mind and matter are proven to be one and the same.

The Diving Bell and the Butterfly

Dehaene outlines his theory of consciousness in the fifth chapter but it’s really just a review of the ideas that he has already outlined in the previous chapters. His theory, in short, is that consciousness is roughly equivalent to the concept of “global ignition” introduced above, with the added dimension of feedback loops containing the information which persists to define our subjective experience. This is what he calls the “global neuronal workspace” theory. Information is shared throughout the brain as an evolutionary adaptation which allows us to utilize it in various ways and prioritize our attention. Within this discussion several neural computer simulations are presented which demonstrate a similar type of threshold ignition and feedback, which is central to the theory, even though that particular behavior was not deliberately designed into the model. Then, having built his theory of consciousness upon the key signatures identified above, Dehaene sets out to find a way to test it. It is one thing to find correlates of consciousness, it is quite another to use that information to build a reliable “consciousness-o-meter”.


Jean Dominique Bauby and his secretary

The proving ground for this theory is found in one of the most difficult medical scenarios; that of the vegetative patient. We are introduced to the spectrum of states which manifest in response to a severe insult to the brain: from brain death, to a vegetative state, to minimal consciousness and locked-in syndrome. That last of these occurs when a fully conscious brain is “locked in” to an unresponsive body, as was the case for Jean-Dominique Bauby when he authored The Diving Bell and the Butterfly with just one blinking eye. The difficulty in these cases is that with only the subject’s external, objective behavior available to the clinician, the ability to determine whether there still any internal conscious life and hope for recovery is radically impaired. What’s worse, the manipulative tools which were used to detect the signatures of consciousness in the lab are also taken out of contention due to the inability to rely upon the subject’s ability to focus their sensory perception and report on their conscious access. An alternative technique relies on the observation that we are wired to detect novelty, such that changes in our surroundings trigger a response in the brain. This trigger, however, fires even if the novelty never enters our conscious awareness. That, in turn, means that the novelty itself is not sufficient for establishing the baseline that discriminates between the unconscious response and conscious detection of the change. To get around this the research team devised a clever tool called “global auditory novelty”. Relying upon the fact that the sense of hearing is rarely lost in these brain injuries, the subjects were presented with a pattern of four “beeps” following by a “boop”. The “boop” represents the local novelty which triggers the subconscious alert that something has changed, which may or may not enter our consciousness. Our long-term, or “global” conscious perception, however, is a bit more sophisticated. Once this pattern is repeated enough times the “boop” becomes part of the expected sequence even though it triggers the alert in the brain. This causes the “boop” to eventually slip out of our conscious awareness. So, by repeating the pattern several times and then replacing the local deviant “boop” with a global deviant “beep”, the team was able to induce a situation in which the subconscious alert was silent while the conscious detection of a global novelty was ignited.

What was the result? In the initial trial with eight patients, all three of the minimally conscious patients whose EEG’s lit up with the P3 wave in response to the global novelty later regained consciousness. In a subsequent study with 22 vegetative subjects only two yielded a P3 wave and they both became minimally conscious in the following days. While these initial tests were perfect in that they never yielded a false positive, there were still several false negatives. To address this the group compiled their data and ran a statistical analysis to refine the prediction from the EEG waveforms. This refined calculation, which incorporated the full suite of EEG data and the other signatures beyond just the P3 wave, led to an exciting result. Using a data set of over 200 patient they found that in 33% of the cases where the clinical diagnosis was “vegetative state”, the refined analysis yielded an alternative diagnosis of “minimally conscious”. Of these, a full 50% recovered to a clinically obvious conscious state in the next few months, whereas this false negative rate was otherwise only at 20%. Adding these up, we see that the clinical diagnosis was overly pessimistic for 30% of the patients while the EEG signature diagnosis was overly pessimistic for only 13% of the patients. For families struggling with questions about how to manage the care of their loved one as they cling to life, this objective detection of consciousness through physical measurement of brain activity may be the key to maximizing the realization of their hopes.

The Future

Dehaene spends the last chapter of the book examining the ways in which the science of consciousness will continue its assault on the mystery of the subjective experience. Here we are presented with data to show that the global workspace theory of consciousness tells us that infants are conscious at birth and that several other animals exhibit the signatures of consciousness. He then turns his attention to the philosophical problems of qualia:

“My opinion is that Chalmers swapped the labels: it is the ‘easy’ problem that is hard, while the hard problem just seems hard because it engages ill-defined intuitions. Once our intuition is educated by cognitive neuroscience and computer simulations, Chalmers’s hard problem will evaporate. The hypothetical concept of qualia, pure mental experience detached from any information-processing role, will be viewed as a peculiar idea of the prescientific era, much like vitalism” (pg 262)

and free will:

“Our brain states are clearly not uncaused and do not escape the laws of physics – nothing does. But our decisions are genuinely free whenever they are based on a conscious deliberation that proceeds autonomously … When this occurs we are correctly speaking of a voluntary decision – even if it is, of course, ultimately caused by our genes, our life history, and the value functions they have inscribed in our neuronal circuits.” (pg 264-265)

While I am not yet willing to express a level of confidence on par with Dehaene regarding his conclusions, I am obliged to say that I agree (and I posted similar thoughts on free will in the post which inspired those introductory comments last month). Even so, neuroscience may never be able to deal an incontrovertible death blow to the dualist paradigm. Like Sagan’s infamous garage dwelling dragon, the mind can always be excused from questioning and made into an extra immaterial layer that mirrors the brain even at the level of individual neurons and synapses. At some point, however, it becomes clear that we are just playing games. When that time comes, if it hasn’t already, we need to acknowledge the data for what it is and the implicit conclusion that we are nothing more than our physical body; that our identity – our conscious self – is found in our brain.