I just poured my third cup of coffee today. It's mid-afternoon, so I do this knowing that it means I will lie in bed tonight staring at the ceiling entirely unable to sleep after I have fully annoyed my spouse with my inability to cease talking or stop moving. But, my energy is flagging, and I have words to write right now.
Even though coffee and (more specifically) caffeine are known to produce unpleasant side-effects, the majority of the US citizenry is just like me. At least 80% of us consume caffeine daily. According to a study released in March of this year by the National Coffee Association of the USA, 61% of Americans drink coffee daily, and according to a review prepared for the FDA in 2012 based on data for the years 2003-2008, we consume about 300mg of caffeine per day on average.
What does caffeine do for us? Why am I reaching for another cuppa?
Number one on the list of benefits is that it improves energy. Through the mechanisms of metabolism, a compound called adenosine builds up in our brains while we are awake. The longer we are awake, the more adenosine builds up, and the more fatigued we feel. Caffeine blocks special adenosine receptors on our cells, so that adenosine can't play its energy reducing role. Voila! You feel more awake.
Secondly, caffeine increases our ability to pay attention and improves our mood. This is primarily achieved by blocking adenosine, but also through increasing levels of dopamine, acetylcholine, and serotonin, which act in areas of the brain related to the control of attention and mood.
This all sounds great, but there is also the well-known downside of too much caffeine: headaches, irritability, anxiety, twitchiness, insomnia, and the risk of dependency. These stem from the dose-dependent effects of caffeine, which also influence norepinephrine release when you head over the 400mg level of consumption.
But, what if we could get the energy boost without the coffee? What if we could improve our mood, ability to pay attention, feel more energetic, and reduce fatigue without all the negative effects that come from hammering our body systems with the drug we call caffeine? Am I asking trick questions??? Kind of.
Andy McKinley, a Biomedical Engineer for the Air Force Research Lab is working on a solution to this problem for the military. Soldiers are regularly asked to maintain their energy levels and vigilance for extended time periods, and their rations commonly contain caffeinated gum that can be chewed as needed. However, it would be ideal if soldiers could be energetic and attentive without a twitchy trigger finger.
What's the solution developed by a researcher who got his start in cognition by spinning people around in a human centrifuge at high G's? It's shocking.
Seriously, his lab uses a technique called transcranial direct current stimulation (tDCS for short) to pass a mild direct electrical current between electrodes that are placed on the scalp in order to modify neuron behavior in the brain.
Currently, there are two forms of non-invasive (i.e. no holes are poked in your head) brain stimulation available for the brain. tDCS, which relies on electricity that passes through the skull to modulate the current potential in neuron membranes, can influence the excitability of neurons, and is considered only neuro-modulatory. Transcranial magnetic stimulation, or tMS, which you might have heard of previously in relation to stimulating spiritual experiences or improving your math ability, uses magnetic induction to induce electrical currents in very focused areas of the brain. tMS can actually trigger action potentials in the brain's neurons, so is considered neuro-stimulatory and neuro-modulatory.
tDCS is also easier in application than tMS. While tMS might have better resolution for accessing a very specific region of the brain, it's procedurally more difficult to execute. tMS requires the experimenter to hold a magnetic wand very still over the head of the subject who also can't move. If anyone moves, the magnets stimulate the wrong focal point. It's hard to imagine this being easy to implement on a battlefield, whereas tDCS relies on electrodes placed in approximate locations on the surface of the head, and has the potential to be incorporated into an easily positioned headband or helmet.
So, using tDCS, McKinley's lab kept 30 people up for 30 hours to see how they fared with and without fatigue interventions. Essentially, they compared the effects of 200 mg of caffeine (about equal to 2 cups of coffee) to 30 minutes of tDCS at two milliamps (mA) applied to an area of the brain called the dorsolateral pre-frontal cortex, which is very important for the cognitive processes of attention and vigilance. The results suggest that applying electricity to a brain for half an hour is more effective than consuming something caffeinated.
Specifically, the people who were electrically stimulated were more vigilant for longer than those given caffeine — up to six hours versus two. Previous studies found that a shorter duration of tDCS could modulate vigilance for 30 to 90 minutes, which is within the range of the two hours of caffeine action. This time, said McKinley with excitement, "we recorded 6 hours after we gave the stimulation. This time it was 30 minutes of stimulation, and we did not see the performance taper off… there's got to be a point where it drops off again, we just haven't reached that… We were very surprised that 6 hours later it was still working… exciting, but also a little baffling."
Additionally, based on subjective questionnaires, they were able to deduce that people actually felt better on tDCS than caffeine. McKinley expressed that, "their overall mood rating was just better. They felt less fatigued, less drowsy, and more energetic… The reason that we included the subjective questionnaires is that we've been getting a lot of anecdotal evidence with people leaving saying 'I feel more focused' or 'I feel more energized', so we wanted to get some data that we could analyze that would help answer the question. Do people feel differently when they get the stimulation? And, at least when they are sleep-deprived, the answer is yes."
It is unknown exactly how tDCS has the lasting effects on performance and mood that it does. An experiment on rabbits using tDCS showed that it blocked adenosine receptors, similar to caffeine, but that would only modulate more immediate changes. It's suggested by other researchers that tDCS might influence receptor-based mechanisms responsible for synaptic plasticity and long-term memory formation, or that it could be stimulating the glial cells that surround neurons.
Dr. McKinley thinks tDCS has advantages in performance and in terms of side-effects. And, yes, he has used the tDCS system on himself, saying with a small laugh, "When I do it to myself sometimes… I do feel jazzed up. I feel like I've had a bunch of coffee or something." The question that he can't answer at present is whether people adapt to tDCS over time. He acknowledges, "that's one of the downsides of caffeine. Chronic use diminishes its effect. And, we don't know if the same is true of tDCS yet."
He also stresses that this research is in its early stages. "I think at this point there's enough questions, and you need to have proper safety incorporated into it. We still need to do a bit more research before people should start to doing this on their own, but I do think eventually it will be at that state, and I do think it will make it into the consumer shelves… People should not run out and buy a battery and a couple of electrodes, and try it. Someone's going to get hurt doing that."
He predicts having a working unit of some kind ready to present to the military in about five years. After that it's inevitable that this technology will become widespread within the civilian population. The only question that will remain at that point is whether you will be the one to go for the jolt over the cup of joe at the start of your work day. I think I would.