Brain Waves as Neural Correlates of Consciousness

When we are thinking, thoughts flicker in and out of our minds. What does that mean on the level of the brain? Recent research, conducted by researchers at at MIT and Boston University, suggests that when thoughts are in our minds, corresponding groups of neurons are oscillating in synchrony in a high frequency range, around 30 or higher, whereas thoughts that are no longer in our minds oscillate at lower frequencies. When several, distinct thoughts are held in mind simultaneously, several oscillating bundles are out of sync with each other.

The normal waken brain has brain activity that fluctuates between 8 and 100 Hz. An alert and active brain will tend to have neural oscillations, roughly, in the 40 Hz range in at least some parts of the brain. These brain waves are also known as gamma waves. Alpha waves—oscillations in the 8 to 12 Hz frequency range—and beta waves—oscillations in the 12 to 30 Hz range—become more prominent when you are inactive, for example, when you are passively watching television. Brain dead people and coma patients can have oscillations that approach zero. And in seizure patients the brain oscillates even faster and more regions of the brain vacillate in the same frequency range. In a grand mal seizure large areas of the brain flicker in synchrony at extremely high frequencies.

To find out how neurons oscillate when we think or perform tasks, the research team, led by Earl Miller, the Picower Professor of Neuroscience at MIT, first identified two groups of neurons in monkeys that encode specific behavioral rules by oscillating in synchrony with each other. The research animals were trained to respond to objects based on either their color or orientation. When the animals switched between the tasks encoded by the rues, the researcher measured brain activity in the prefrontal cortex, where working memory is located. The researchers found that the neurons associated with orientation oscillated in synchrony at higher frequencies when the monkeys were completing the orientation task, whereas the neurons associated with the color took over when the animals switched from thinking about orientation to thinking about color.

The team also found that the brain uses lower-frequency brain waves to inhibit neurons when they are not needed. For example, when the monkeys engaged in the color task, the neuron group corresponding to the orientation task would oscillate at a lower frequency, in the lower alpha range. This would inhibit these neurons sufficiently to enable the moneys to engage consciously in the color task.

It appears, then, that consciouness associated with working memory, the ability to keep a few pieces of information in mind at a time, correlates with groups of neurons oscillating at at a high frequency but out of sync with each other. Its the brain's ability to keep bundles of neurons simultaneously oscillating at 40 Hz that determines how much information you can hold in mind at any given time.

The findings, published in the November 2012 issue of Neuron, are consistent with the so-called 40 Hz theory of consciousness. British molecular biologist and neuroscientist Francis Crick, better known for his co-discovery of the structure of DNA, argued that consciousness arises when certain brain regions fire in synchrony in the 40 Hz frequency range. The researchers didn't locate gamma-range activity in the moneys during task completion, but this could be because different frequencies are required for consciousness in humans and monkeys.

This 40 Hz theory of consciousness explains some of our findings in the St. Louis Syn Lab. In our lab we have worked with several people who developed special abilities as well as obsession as a result of traumatic brain injury (TBI). TBI occurs when the brain is injured by an external force. TBI can occur either as a result of blunt force trauma or shock waves from a blast. In both situations, the inside of the accelerated skull comes into contact with one side of the brain, generating a secondary shock wave throughout the soft tissue. If the force is strong enough, it can cause the brain to “bounce” off the other side of the skull, resulting in another shock wave. The waves emanating through the brain twist and pull on the connections between neurons, tearing them apart, causing damage to different areas. Depending on the severity of the shock wave, TBI can be very extensive, and multiple TBI incidents can have compounding effects. It is a particularly devastating problem for soldiers who repeatedly sustain mortar shell attacks at close to mid range. Many of them report memory coordination problems years later.

Physical force to the head triggers a centralization of brain activity in local areas, causing a concussion. During a concussion the nerve function of several distinct brain regions become paralyzed as a result of the brain bumping into the skull as it shakes inside the head. When this happens, positively charged potassium ions inside the nerve cells rush outside the nerve cells and calcium ions replace them inside the cells. This shuts down the neuron’s internal engine preventing the nerve cells from burning energy sources (primarily glucose) and giving rise to huge uncontrolled release of neurotransmitters, which bombard or “frag” neighboring neurons. This neuronal fragging causes the affected neurons to die off, leading to scar tissue, whereas other affected neurons gradually regain normal function.

Though we don’t yet fully know the long-term effects of traumatic brain injury, it is possible that the uncontrolled release of neurotransmitters from dying neurons massively enhances brain activity in neighboring brain regions, giving rise to syncronized brain oscillations in the gamma frequency range, and that the brain activity in these regions remains abnormally high on a more permanent basis.

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Visual imagery is far the most common way for the brain to represent the world. So it is unsurprising if brain waves in the high frequency range were to yield visual images corresponding to the hyperactivity. After being beaten up Jason Padgett experienced visual images are complex mathematical patterns, and Derek Amato experienced visual images of black and white musical notes after the impact with the pool floor. The visual images appear to make it possible for the two unschooled geniuses to act on excessive brain activity in ways that would not otherwise be possible.