Among brain researchers, there is a truism that the reason people underestimate the amount of unconscious processing going on in your brain is because you are not aware of it. And while there is a lot of unconscious processing, the truism also points to a duality: your brain performs both processing that leads to consciousness and processing that does not. As you will see below, this duality opened up a scientific approach to the study of consciousness.
Are the subjective results scientific?
In science, we are used to empirical test results, to verifiably performed measurements, to a reading from a calibrated meter where that reading can be taken over and over again by different people. But what if all you have to do is what a person says they experience, subjective observation? It doesn’t sound very scientific.
This lack of non-subjective evidence is much of what has blocked scientific research on consciousness for many years. But consciousness is unique. Although we have measurement tools to observe brain activity, how do we know if this activity contributes to a conscious or unconscious experience? The only way is to ask the person whose brain you are measuring. Are they aware of an image presented to them? If not, it is being treated subconsciously. You have to ask them, and their response is, of course, subjective.
Skepticism of subjective results and a lack of tools held back scientific research on consciousness for many years. It was even taboo to use the C word until the 1980s, when researchers decided the subjective results were correct. Since then, there has been a lot of scientific research on consciousness and here is a sample of that research. And as you’ll see, it even saved a life or two.
The number of methods and tools for examining the human brain has increased over the years. The first was to learn from neuropsychological patients who suffered brain damage, correlating the physically damaged areas with the resulting effects. Then there is the type of experiments often associated with psychologists where subjects perform tasks and their behavior is monitored to test certain hypotheses.
Another early method was the insertion of electrodes into the brain, usually while patients were undergoing surgery. The advantage of electrodes is that they can be used both to monitor neuronal activity and to stimulate it.
Electroencephalography (EEG) involves placing electrodes on the scalp to measure voltage fluctuations resulting from ionic current in neurons in the brain. It is an old method that has evolved a lot, sometimes with the placement of up to 256 electrodes. Magnetoencephalography (MEG) is similar to EEG, except that it measures magnetic fields using firecrackers placed on the scalp. Both EEG and MEG are particularly useful for tracking the timing of events, as they measure neural activity as it occurs. You’ve probably heard of EEG in the context of observing brain waves.
Positron emission tomography (PET) and magnetic resonance imaging (MRI) have also been widely used for some time. Functional MRI (fMRI), invented in 1990, provides a 3D image of brain activity by detecting small changes in blood flow that follow the onset of this brain activity. But while the fMRI gives a good full view of the brain of or activity has occurred, it delays neural activity by about 1 or 2 seconds and therefore does not offer the precise timing you get with EEG or MEG.
Besides electrodes in the field of brain stimulation, there is transcranial magnetic stimulation (TMS) and optogenetics. TMS uses electromagnetic induction to cause current through the cell membranes of neurons, which can trigger them. Optogenetics triggers neurons by stimulating them with light, usually from a laser.
Subliminal masking and priming
Return to consciousness. Imagine being able to design an experiment where you can control what is being processed unconsciously and what is being processed consciously so that you can then use instruments to determine which neural pathways are being used in either case. Masking is a tool that allows this level of control. An example of masking is displaying an image for 33 milliseconds, but before and after displaying it, display another image called a mask. You will be aware of the mask image but not the middle one which was only displayed for 33 milliseconds. This duration is ideal, and the longer it is displayed, the more likely you are to be aware of it.
An example of such an experiment shows a 71ms mask, then a numeric digit or the word for a number for 43ms, then another 71ms mask, then a second digit, this time for 200ms. You will not have processed the first number consciously, but you will be asked to indicate whether the second number was less than or greater than 5 by raising your left or right hand respectively. If the value of the first digit was close to the value of the second digit, then you can move your hand earlier.
Why? Because even if you weren’t aware of the first digit, unconscious pathways in your brain involving the motor cortex will have been activated due to the first digit. And even if you don’t know, the current treatment has been observed using EEG and fMRI. This experience is also called priming or subliminal priming, where the first digit initiates the activity of the second.
Another technique for creating conscious and unconscious processing in an experience is to take advantage of the fact that there is a limit to how many things can be taken care of at the same time you are saturating the consciousness. One way to demonstrate this is to show a sequence of numbers and in the middle, to show two letters. You are told to watch the letters. The first letter is easy to remember. However, if the second letter comes too soon after the first, you won’t notice it at all. This is called the attentional blink. With a few tweaks, this allows you to study what happens in the brain when the letter is consciously perceived versus when it is not.
These priming, masking, and attentional blinking techniques have been so finely tuned that all kinds of experiments can be pre-planned where researchers can produce unconscious and conscious activity at will and then observe brain activity that result.
Observe conscious activity
An experience that involved observing conscious activity involving attentional blinking and ultimately contributed to the ability to sense consciousness in coma patients. The experiment used the EEG so that events could be observed as they occurred. Subjects were shown a sequence of images of letters and words. They were asked to spot words in the sequence, but were also shown pictures containing letters for them to report on. The letters acted as a distraction, causing them to miss the word. It was the wink of attention. The experimenters adjusted the parameters so that they could control when the subjects would consciously see the word and when they were unaware of it, it would be invisible.
The diagram shows the EEG results comparing brain activity when the word was seen versus when it was not seen. Activity at around 96ms and 180ms was roughly the same for both. This is an unconscious activity where the first image processing took place. But then, around 276 msec, there started a big difference in activity between when the word was seen and when the word was not seen. This continued until about 576 ms. This difference is conscious processing.
This time and activity are common for conscious activities involving vision. Almost identical processing occurs for about the first 300 ms in experiments where subjects report being unaware or aware of what is being tested. However, for experiments where subjects report being aware of what is being tested, starting at around 300 msec there is an avalanche of activity.
In Stanislas Dehaene’s book, Consciousness and the Brain: Deciphering how the brain codes our thoughts, he describes four signatures of conscious thought, that is to say the activity that is observed during this avalanche:
- a sudden onset of activity in the upper back part of the brain where sensory processing occurs (the parietal region) and the front part of the frontal lobe of the brain (the prefrontal cortex) which is involved in decision making, short-term memory, planning and other high-level activity,
- a P3 wave observed on the EEG which sweeps the parietal region and the prefrontal cortex,
- a late and sudden explosion of high frequency oscillations, and
- massive synchronization of electromagnetic signals throughout the cortex – the wrinkled outer layer of the brain.
So these are signatures of consciousness, and examining what is going on in the brain during this time may one day shed light on exactly how consciousness works. In the meantime, this research has resulted in a consciousness detector.
Detect consciousness in coma patients
In his book, Dahaene describes how he and his colleagues used this research to detect consciousness or lack of consciousness in coma patients. To make it cheap, they used EEG, which is available in many intensive care units. They tested the P3 wave, the 2nd signature of consciousness.
They play four identical sounds followed by a deviant fifth: beep, beep, beep, beep, boop. The deviant triggers a P3 wave. Unfortunately, the auditory cortex also produces an unconscious mismatch response, called MMN, which also results in a P3 wave. To compensate for this, they play the four repeated beeps and the deviating boop for a while, then suddenly play five beeps without the deviating. Without the deviant, the unconscious mismatch response does not activate, but conscious processing notices that there was no deviance and that the P3 wave is still occurring. A patient who was not conscious would not produce the P3 wave.
Their test identified different patients as unconscious or conscious and those who showed consciousness regained partial or full consciousness within a few days. The subsequent use of the test even saved a life. Doctors had a patient they were ready to give up when this detection technique convinced them to wait a little longer. They did, and the patient eventually made a full recovery.
So the next time someone tells you that we don’t know what consciousness is and that it is something mystical, unknowable, tell them that there is some real scientific research on consciousness that has already produced beneficial results, although the field is still in its infancy.