A recent study coming out of Penn’s psychology department is challenging two beliefs: one about a trendy technology, and one long-held assumption about control in the brain. Best of all, it’s done so by testing a grown-up equivalent of playtime.

To probe types of of goal-oriented thinking in the brain, the study used transcranial direct-current stimulation, or tDCS — the trendy technology in the picture. tDCS works by placing electrodes over the scalp to either inhibit or promote activity in a targeted part of the brain. Led by Sharon Thompson-Schill, who directs the Center for Cognitive Neuroscience, the research team used this tool to inhibit activity in subjects’ prefrontal cortex (PFC) while measuring their performance on tests with different goals.

The results? Inhibiting left PFC — an area known to act as a filter for irrelevant information in goal-directed tasks — improved subjects’ abilities to come up with uncommon uses for common objects. Much as children would think to use, say, a broken antennae as a magic wand for play, adult subjects had to suggest uses for an object like Kleenex besides the obvious one, blowing your nose. It turned out they were better at doing this when the cognitive filter in their left PFC was temporarily turned off by tDCS.

The importance of left PFC in this study brings us to the idea of cognitive control. Cognitive control refers to brain processes that allow us to focus on immediate goals — in other words, processes like the PFC filter. Such mechanisms help us ignore any information that may bombard us when we’re completing a task, but which has nothing to do with our goal and so only serves as a distraction. Cognitive control is thus helpful in the opposite version of the playtime task, where subjects had to ignore any information about Kleenex that didn’t reflect its typical purpose of collecting snot.

So the role of the left PFC here was two-faced: As it promoted focus, it sapped away imagination. And that’s where the key insights from this study arise.

For one thing, it highlights that the effects of tDCS cannot be categorized along the binary of “good” or “bad.” This comes as a surprise to those who have wanted to see tDCS as a sort of holy grail treatment, a view recently questioned in Slate and Wired.

It’s reasonably tempting to venerate this treatment. tDCS has mild physical side effects, usually just some scalp tingling or generally manageable discomforts like headaches. It also can be applied all over the scalp. This last feature makes it a possible treatment for a range of psychiatric disorders and a viable form of cognitive enhancement. But as this study shows, if stimulating some part of the brain helps with one type of task, it is likely to impede others. It looks like with the brain, as with most things, we can’t expect to get something for nothing.

That same conclusion applies to the study’s findings with respect to cognitive control, a topic Thompson-Schill has been studying for twenty years. She said the focus has always been on how cognitive control enhances performance rather than how it might hurt. “I feel like there’s just kind of an assumption that having cognitive control would make anything better — or at least, neutral or better,” she said.

She began to question this assumption after reviewing the developmental psychology literature, which has plenty to say about things young children do better than adults. One of those things is thinking outside the box, at least when it comes to simple objects. The literature also shows that kids don’t start developing cognitive control until age 3 or 4. Combine these observations together, and you’ve got a hypothesis in the tradition of evolutionary psychology: Maybe those childhood years without cognitive control aren’t just a hindrance. “I started asking, what if late cognitive control development is an adaptation?” Thompson-Schill said.

It’s hard to show that any cognitive feature is an adaptation per se. Even so, this study at least supports the idea that cognitive control — like tDCS — should be framed as a trade-off, rather than something with only positive effects.

As Thompson-Schill explained, this finding could further influence the way the concept of cognitive control gets applied, especially in education. Some researchers have advocated lesson plans to improve cognitive control, so as to heighten kids’ focus and other traits important for learning. But when such plans are implemented, it’s important to remember that we might not want cognitive control all the time — that imaginative thinking also contributes to learning.

After all, isn’t the real lesson from this study obvious?  We all need playtime. And sometimes, even the most alluring tools and assumptions can get in the way of our play.