The mind-body problem was first raised, rather circuitously, as a non-problem by Aristotle more than 2,000 years ago. He postulated that, "It is not necessary to ask whether soul and body are one, just as it is not necessary to ask whether the wax and its shape are one." Plato disagreed, as he thought that souls could transmigrate during reincarnation. But a more radical opponent to Aristotle's theory arose about two millenniums later in the person of René Descartes. He tried to rip Aristotle's theory apart. His philosophy introduced the notion of dualism, opposing "the surrounding spirits" that directed thoughts to the mechanism of the human body. Can today's advances in neurobiology help us make a decision on the matter?
A quick scroll through the names of biology laboratories worldwide -- from Connecticut to London, to Sataima, Japan -- might throw up names like "Molecular Psychiatry" or "Receptors and Cognition" suggesting they have begun to bridge the mind-body gap, long the preserve of philosophers. "What language does the brain use to generate consciousness?" Francis Crick, the scientist who discovered DNA, once asked. But have scientists really understood the real nature of consciousness? And if it's a language, why are its grammar and syntax not better understood? Scientists are looking to be the first to propose an unified theory of consciousness.
Research in the 1950s led scientists to call the brain, like the heart, a "battery" and a "hive." The examination of the brain has generally taken place along these lines. Electrophysiology (the discipline that examines the brain as a "battery") studies the electrical waves that flow between neurons, or ensembles of neurons, and Biochemistry (the "hive") approaches the brain's function through measurements of the interactions between brain molecules as they catalyze, regulate, replicate and destroy. Unfortunately no biochemical substrate have been proposed to correlate with consciousness yet. Only electrophysiological studies have proposed such correlates.
Current advances in Electrophysiology and Consciousness trace their way back to research done by Crick himself in the 1990s, his late research period. He and his colleague, Christof Koch, were the first to propose that visual awareness correlates with certain brain regions electrical waves. Using electroencephalography, a way of recording electrical activity along the scalp, they worked out that these waves were being fired at 40 Hertz (1). In other words, from all the electrical activity generated by the brain, they isolated a frequency -- 40 Hertz -- of the electrical waves involved in attention. These ways were called gamma waves.
Since then, myriads of interesting studies on gamma synchrony have been published, in particular the earlier work of Wolf Singer and today's work of Pascal Fries. We had the chance to chat over the phone with Pr. Earl Miller at M.I.T. to hear about his latest discoveries on gamma waves and neural correlates of consciousness.
"Some parts of consciousness are very subjective, but the most objective thing about conscious thoughts is that it is a limited capacity: you can hold a store of lifetime experiences in your head but somehow you can only express thoughts in consciousness three or four at the time," he told me . This goes someway towards a theory of consciousness, but not all the way. One of the core tenets in neuroscience is that neurons -- cells that transmit electrical energy in the brain -- are grouped together to form thoughts. Scientists call this "an ensemble."
"Neurons associated with cognition and consciousness are like utility players in baseball: they do many things and have many different functions," Miller continued. He told me that research has shown that you don't just need groups of neurons, but neurons that have many functions. "You can't build a complex thought without these multifunctional neurons. But then how do you separate one ensemble from another if they often share the same connections?"
The gamma wave theory fits thoughts into a cycle, Miller said. "That's an inherent limitation--that of the bandwidth of consciousness." But it's also helpful to scientists who want to discover more about the brain.
Miller's research suggests that fluctuations in this bandwidth could hold the key to understanding the language of consciousness. In a 2009 experiment he was involved in, the team trained monkeys to hold two images in mind at the same time. The protocol used is simple: a monkey is given a set of geometric objects on a tray, for instance: three triangles and two squares. Each object is red or yellow. The primate is trained to memorize them. The researcher then removes secretly one object and gives the set back minus one object to the monkey. The primate is then asked which object is missing. With this question, the images formed in his mind are 1. The shape of the object (triangle or square) and 2. The color of the object (yellow or red). When recording brain activity in an area of the monkeys' brains that are known to regulate choice and function, the team discovered oscillations in the bandwidth, "as if the brain was doing a gamma wave juggling act," he said. "Gamma band oscillations allow to pull out individual thoughts from an overlapping circuitry by this oscillatory process, holding thoughts simultaneously in mind but somehow preventing them from interfering with one another. My guess is that the way thoughts become conscious is through these gamma waves types of oscillations." Consciousness would then be a form of oscillation between electrical waves that are involved in the representation of choices.
The second field in which research on Consciousness is taking place is through the measure of blood flow in the brain, called fMRI (2). The primary principle of fMRI is very simple: it measures the exchange of Oxygen between the blood cells and the consuming neurons. The more a neuron is active, the more oxygen it consumes, and so the stronger the signal gets (from blue to red on the scale) on the brain image scan.
About 20 years ago, neuroscientist Antonio Damasio from U.S.C. published Descartes' Error: Emotion, Reason and the Human Brain. With today's techniques, he argued, we are able to observe what is happening in someone's brain while he or she experiences emotions or feelings. Damasio's belief was that these techniques would one day make it possible to map the architecture of the mind.
More recent research by Damasio involved patients' brains reacting to a story they are told whilst inside a scanner. These stories are designed to induce their admiration or compassion. While the story is being told, the scanner measures the flow of blood through the brain, which correlates with neural activity (functional MRI images). Damasio interprets the regions associated with the highest changes of blood flows, while stories reach moments of admiration or compassion, as "neural correlates of admiration and compassion." On a screen, one can appreciate the ensembles of neurons lighting up correlating with a supposed state of admiration or compassion. But if neuroanatomical maps are being drawn in order to identify centers for specific feelings or emotions, other neural correlates of consciousness have been proposed (3).
So, does the nature of consciousness lie in precise areas of neurons, or in specific types of oscillation generated by a type of neurons? Studies haven't decided on the matter yet. Some scientists even propose that consciousness could arise from quantum biology. Quantum theory posits that tiny quantum activities -- not electrical pulses or biological interactions, but quantum interactions between ions and the proteins that surround them --determine consciousness. Infinitely small waves of energy are maybe the most mysterious explanation proposed for the nature of consciousness yet. But there is a long way to go before this idea gains traction. Even though many scientists find it easy to accept that quantum waves are controlled by nature in photosynthesis, or smell for example, their contribution to consciousness is highly criticized by a rapidly growing number of scientists -- and philosophers -- for the simple lack of evidence. For Earl Miller at M.I.T., the quantum theory of mind sounds like an updated version of mind-body dualism. According to him, and thanks to gamma wave oscillations, consciousness might not be looking for itself very long now.
(1) Robert Pollack reported that "these waves originate in the thalamus, sweeps the brain from front to back, 40 times per second (40 Hz), drawing different neuronal circuits into synch with the precept, and thereby bringing the precept into the attentional foreground. If the thalamus is damaged even a little bit, this wave stops, conscious awareness's do not form, and the patient slips into profound coma." Robert Pollack, the Missing Moment, 1999. It became the so-called "Forty Hertz theory of consciousness."
(2) fMRI : Functional Magnetic Resonance Imaging, discovered by Seiji Ogawa in the 1990s.
(3) There are also some fascinating results from deep brain stimulation (DBS). DBS can produce the will to move an arm (w/o actually moving it), can induce the recall of forgotten memories, can reverse depressive states, or even promote lucid dreams during REM (Rapid Eye Movement) sleep.