At some point today you will disengage from the rest of the world and just think. It could happen any number of ways: if your mind wanders from work, while you’re sitting in traffic, or if you just take a quiet moment to reflect. But as frequently as we drift into our own thoughts, a new study suggests that many of us don’t like it. In fact, some people even prefer an electric shock to being left alone with their minds.

“I’m really excited to see this paper,” says Matthew Killingsworth, a psychologist at the University of California (UC), San Francisco, who says his own work has turned up a similar result. “When people are spending time inside their heads, they’re markedly less happy.”

To conduct the study, Timothy Wilson, a social psychologist at the University of Virginia in Charlottesville and colleagues recruited hundreds of undergraduate student volunteers and community members to take part in “thinking periods.” Individuals were placed in sparsely furnished rooms and asked to put away their belongings, such as cellphones and pens. They then were given one of two tests that lasted between 6 and 15 minutes. While some were told to think about whatever they wanted, others chose from several prompts, such as going out to eat or playing a sport, and planned out how they would think about it during the period.

Afterward, the team asked the volunteers to rate their experience on a nine-point scale, where the higher the number, the more enjoyable their time was. In both the free-thinking and planned-prompt scenarios, about 50% of people did not like the experience, reporting an enjoyment level at or below the midpoint of the scale. Participants generally gave high ratings of boredom, too, according to Wilson.

To see if a change of scenery would help, the team let participants do the studies in their own homes, but still found similar results. Overall, the subjects said they enjoyed activities like reading and listening to music about twice as much as just thinking.

The researchers then decided to take the experiment a step further. For 15 minutes, the team left participants alone in a lab room in which they could push a button and shock themselves if they wanted to. The results were startling: Even though all participants had previously stated that they would pay money to avoid being shocked with electricity, 67% of men and 25% of women chose to inflict it on themselves rather than just sit there quietly and think, the team reports online today in Science.

“We went into this thinking it wouldn’t be that hard for people to entertain themselves,” Wilson says. “We have this huge brain and it’s stuffed full of pleasant memories, and we have the ability to construct fantasies and stories. We really thought this [thinking time] was something people would like.”

He suggests that the results may be mixed signs of boredom and the trouble that we have controlling our thoughts. “I think [our] mind is built to engage in the world,” he says. “So when we don’t give it anything to focus on, it’s kind of hard to know what to do.”

Although daydreaming is spontaneous and can be enjoyable, Wilson says the pressure to think on command—whether it’s being demanded by researchers, or while you’re waiting in line with nothing else to do—may be what’s difficult and unpleasant for so many.

“I found it quite surprising and a bit disheartening that people seem to be so uncomfortable when left to their own devices; that they can be so bored that even being shocked seemed more entertaining,” says Jonathan Schooler, a psychology professor at UC Santa Barbara who studies consciousness. “But I can’t help but feel that there has to be more to the story. I’m confident that there are conditions in which at least a subsample of the population enjoys this quiet opportunity for self-reflection.”

Some people seem to enjoy thinking more than others. For instance, the study found that people who are more agreeable or cooperative were more likely to enjoy themselves when they were told to think about anything. Individuals who admitted that their daydreams normally leave them happy fared better, too.

Because people so often find themselves intentionally or unintentionally wrapped up in their thoughts, the research team suggests that meditation or other techniques to relax and learn how to gain control of the mind could be helpful. If we knew how to steer our thoughts in a pleasant direction and enjoy the experience, maybe we wouldn’t hate to be alone with ourselves.

Drugs designed to ease the symptoms of mental health problems such as depression, obsessive compulsive disorder and post-traumatic stress can have major disruptive effects on aquatic animals’ brains, say scientists.

Anti-depressants are some of the most commonly prescribed drugs in the world. In 2012, there were more than 50 million prescriptions of the drugs in the UK, and in some towns and cities as many as one in six of us are taking them.

In recent years, researchers have found increasing concentrations of the drugs in rivers around the world. Most of them find their way into waterways via sewage and waste water systems, from human waste or from people flushing unwanted prescriptions down the toilet.

A suite of new research, published in a special issue of the journal Aquatic Toxicology, points to mounting evidence that they could be damaging aquatic species.

Researchers have found that fish exposed to tiny concentrations of the drugs in the laboratory can become more aggressive, less cautious, and even lose their ability to camouflage.

In other aquatic species, their ability to find food and reproduce was affected, their behaviour patterns were altered, and some became more attracted to light. There is also evidence that the drugs may disturb genes controlling the brain function of shrimp.

‘In the 90s there was lots of concern about the so-called gender-bending properties of contraceptive drugs that were finding their way into our rivers,’ says Dr Alex Ford from Portsmouth University, who edited the special issue.

‘There is now substantial evidence from laboratory tests that anti-depressnats can affect animals’ behaviour and basic functions even at the very low concentrations that they would be likely to encounter in the wild.’

Most anti-depressants work on the part of the brain which controls the amount of mood-influencing hormones released into the blood stream – usually serotonin. Many aquatic creatures also produce serotonin and appear to be sensitive to the effects of the drugs.

In one experiment, a shrimp was placed in a test-tube which was then lowered into a tank with cuttlefish. Whereas fish not exposed to the drugs would soon give up on the unobtainable snack, those exposed to the anti-depressant continued to slam into the tube, wasting vital energy in the process.

In another, a group of male crayfish became more aggressive – fights lasted longer and rates of female mortality rose sharply. There was even evidence that the ability of cuttlefish to camouflage against their backdrop was hampered by the drugs.

If this were repeated in the wild, it could make the creatures more vulnerable to predators. But for now, difficulties in accurately monitoring exposure levels and animal behaviour in the wild are proving a significant barrier to understanding the threat of anti-depressants in the real-world environment.

And some scientists caution that the effects of the drugs need to be tested at a variety of doses before more robust conclusions can be drawn.

‘As a proportion of the whole US population, there are probably as many people taking these drugs now as there are on the contraceptive pill,’ says Ford.

‘At the moment, it’s almost impossible for regulators to work out what is a safe level for these drugs in the environment.’

He warns that these problems are not unique to anti-depressants. Humans consume hundreds of different drugs every day, and many are likely to find their way into sewage and, eventually, the environment.

There has been talk of increasing the requirements on sewage treatment plants to remove the chemicals, but the costs of doing so make it unlikely to happen anytime soon.

Many countries are instead focusing on those drugs which go unused, encouraging people to take unwanted prescriptions back to their pharmacist instead of flushing them away.

‘Like many people, my kitchen drawer at home is full of drugs that are long out of date and no good to anybody,’ says Ford. ‘We don’t want to stop people taking drugs, they obviously save countless lives and bring all sorts of benefits to people, but we need to manage the way that we get rid of them.’