Credit: Tim Green
Credit: Tim Green

Electric Brain Stimulation Triggers Eye-of-the-Tiger Effect

“I started getting this feeling like I was riding into a storm… like you’re headed into a storm that’s on the other side, maybe a couple of miles away, and you’ve got to get across the hill. And all of a sudden you’re sitting there going how am I going to get over that through that?”

Those are the words of the man in the video above. He suffered from severe epilepsy and the only treatment left to him was to cut out the part of his brain that triggered his debilitating seizures. But first, his doctors had to pinpoint the offending region. They implanted a web of electrodes in his brain and started stimulating different areas with small electric pulses, one at a time.

In the video, he had just been stimulated in the anterior mid-cingulate cortex (AMCC)—a hook-shaped area towards the front of the brain. It didn’t set off any seizures, but it did produce a weird sensation. His chest tightened, his heart rate went up, and he felt the need to push through an impending challenge—like being in a cart with a flat tyre, and having to drive on regardless.

“Was it negative or positive?” asks his surgeon, Josef Parvizi from Stanford University.

“It was more of a positive thing like: push harder, push harder, push harder to try and get through this,” replies the patient.

Shortly after, Parvizi was working with another epilepsy patient, and stimulated the man’s AMCC. The patient felt a shaky sensation in his neck, a stronger heartbeat, a worry that something bad was going to happen, and sense that he had to fight through whatever was ahead.

“It was so similar to what I had seen in the earlier patient!” says Parvizi. “It reminded me of the other patient. Both of them had a similar set of changes—the foreboding sense of anxiety and the motivation or determination to meet the challenge face-to-face.”

“So basically, it’s the feeling most people get when Katy Perry’s song “Roar” comes on the radio, but even more so,” says Ben Hayden from the University of Rochester, who studies the neuroscience of decision-making. Parvizi calls the feeling “the will to persevere”. Hayden suggests calling it “the eye of the tiger” instead.

The two patients felt the same combo of foreboding and determination every time their AMCCs were stimulated, and never on ‘sham trials’ when Parvizi’s team went through the same motions without actually delivering any electric pulses. And they only felt this way when the team stimulated a very specific part of their brain. “If we went 5mm away, we didn’t see the same thing,” says Parvizi.

There’s only so much you can conclude from two patients, but neuroscientists have a long tradition of making important discoveries by studying just one or two people.

For example, Henry Molaison, the man known as HM, lost the ability to make new memories after surgeons cut out a part of his brain in an attempt to cure his epilepsy. His loss taught us a great deal about how memories work. Another woman called SM reportedly feels no fear after a genetic disorder destroyed the amygdalae—a pair of almond-shaped structures in her brain involved in emotions.

In the past, these amazing case studies have come to light after operations or brain damage. But now, neuroscientists can discover more of these strange effects using implanted electrodes. Studies like these are never going to be very big, since the number of people undergoing surgery for epilepsy is very small. But Hayden says, “It’s very important to have these types of qualitative results in the scientific record. In many cases these kinds of things lead people to rethink the brain area of interest and come up with new discoveries.”

Parvizi’s two patients provide more questions than answers. Do differences in the aMCC account for individual differences in our likelihood to persevere with problems? How early can these differences be identified, to what extent are they influenced by our genes, and can we change them through training, drugs, or electrical stimulation?

Could understanding this part of the brain may teach us more about conditions that involve apathy or lack of motivation, from chronic depression to akinetic mutism—a disorder where people barely move or speak? On the flipside, could they help us to understand obsessions and compulsions, where people do something relentlessly without giving up?

Certainly, the case studies seem to fit with a lot of past research. Based on brain-scanning studies, some scientists have suggested that the aMCC uses information about future stress and pain to help us plan our decisions. And when Matthew Rushworth from the University of Oxford removed the ACC from rodents, they gave up more easily when they had to climb over a barrier to reach a food pellet.

The AMCC is also part of a larger area called the anterior cingulate cortex (ACC), which has been studied intensely. It helps to control unconscious, lower-level responses like blood pressure, heart rate and sweating.  But it’s also involved in conscious, higher-level stuff like decision-making, planning, and processing emotions.

Jon Cohen from Princeton University thinks that the ACC plays an important role in cognitive control—the ability to focus on a goal in the face of distractions. You use it when you refrain from snacking while on a diet; I’m using it right now by writing this post when I really want to be checking Twitter again. Based on past studies, Cohen believes that the ACC monitors the costs of any actions that involve control—is it really worth not eating that cupcake, and what happens if we fail? It also decides is those actions are worth pursuing, and how much effort to invest in them.

He thinks this theory “aligns eerily” with how Parvizi’s patients reacted to the electrical bursts. Their sense of foreboding corresponds to the costs of cognitive control, and their sense of determination echoes the commitment of effort.

“These similarities should, of course, be treated with as much caution as the findings themselves,” he says. “But at the very least, the findings make it clear that this is an extremely interesting area of the brain and, as has long been suspected, it appears to be associated with some of the faculties we cherish most as humans.”

Reference: Parvizi, Rangarajan, Shirer, Desai & Greicius. 2013. The Will to Persevere Induced by Electrical Stimulation of the Human Cingulate Gyrus. Neuron