When you compare the brain's detectives, neuroscientists, to other detectives, the neuroscientists seem to fall short in solving mysteries. After all, Agatha Christie's Hercule Poirot and Miss Marple needed only about 250 pages each to get to the bottom of their cases. Ditto for Nancy Drew. On television, Jessica Fletcher and Kojak were all able to find their answers in an hour or less, while Veronica Mars needed only about the length of a television season. Even the pride of South Florida, Encyclopedia Brown, was able to solve his cases with little more than a casebook, his trusty sneakers and a wide variety of miscellaneous factoids. If Encyclopedia Brown only required 25 cents per day (plus expenses) to solve his cases, then what's taking neuroscientists so long to unravel the mysteries of the brain?

OK, so the brain is a bit more complex than Encyclopedia Brown's nemesis, Bugs Meany. But with the brain only weighing in at 3 pounds (1.4 kg), you could be forgiven for wondering if neuroscientists are just big slackers. As it is, mysteries galore abound in those 3 pounds, and until fairly recently, scientists lacked the equipment to accurately study the brain. With the advent of brain imaging technology, it's possible that they'll continue to learn more.

T­he workings of the brain, however, determine such fundamental questions about personhood that we may never know everything about what's going on. That doesn't mean we can't speculate, though. While we may not be able to solve these capers with clues that point to Colonel Mustard in the library with a revolver, we can dive into the current thinking on some of the brain's famous unsolved mysteries. Get your casebook ready and go to the next page for our first puzzler.

Top 5 Unsolved Brain Mysteries

1: The Conundrum of Consciousness
2: Whodunit and Other Questions of Memory
3: The Secrets of Sleep and Dreams
4: The Puzzle of Why the Brain Stops Functioning
5: The Case of Nature vs. Nurture


1: The Conundrum of Consciousness

This section might just "blow your mind," to use a common expression. But do you even have a mind? Scientists don't know where the brain ends and the mind begins. Are they the same thing? What about souls? Are these located in our brains? What is responsible for all of the unique thoughts and feelings that make us who we are? Everyone from philosophers to physicists has taken up this question of consciousness and come up empty.

For a long time, the study of consciousness was considered too far out to study. How do you scientifically study something so subjective? How can what one person feels become something that another person can quantify? But now, in their relentless pursuit to understand every single thing about the world, scientists are trying to figure out what exactly is going on with consciousness.

Though deep metaphysical questions about the nature of a soul, a mind and brain leave questions as to whether this issue is in the realm of scientists, the brain is likely involved in some way with our conscious thoughts. With the help of brain imaging, scientists can watch different parts of the brain light up, and they know they can alter the brain and our consciousness with surgeries or chemicals [sources: Eagleman, Pinker]. But what scientists don't know is at what stage of the process a firing neuron becomes a conscious thought. The things that make up consciousness may be scattered all over the brain, with different cranial parts responsible for different pieces of a person. But, as we've mentioned, there are tons of other brain mysteries about how these parts might work together.

Scientists are also trying to figure out the relationship between conscious and unconscious experiences. There are some things -- like breathing and maintaining a regular heart beat -- that we don't have to think about. How are these unconscious actions wired differently than the conscious ones? Is there any difference at all? We like to think we make our own decisions, but one recent study shows that we may not even do that. This study found that by using brain scanners, researchers could predict how a person was going to act a full seven seconds before the person knew that a decision had been made [source Keim]. Our consciousness might just be an illusion.

It's possible that something like free will could enter into the equation at the last possible moment, overriding the decision made by the brain. The researchers in the study also admitted that this test was best suited to a simple laboratory test that involved pushing a button, as opposed to a more important decision like taking a job [source: Keim]. TOP


2: Whodunit and Other Questions of Memory

In the 2004 film "Eternal Sunshine of the Spotless Mind," the characters played by Jim Carrey and Kate Winslet undergo a process to erase all memories of their relationship from their minds. The film uses a variety of methods to show how the memories disintegrate and disappear, and it becomes a race against time when Carrey's character decides he doesn't want to complete the process. He tries to protect his memories about Winslet's character by hiding them in unrelated memories.

Good luck, Jim. Not even scientists are completely sure how memories are formed, how we retrieve them or how they disappear. There are many types of memory; we humans are pack rats who file away information ranging from how to make our grandmother's favorite pie to how to solve algebra equations. But which things does the brain decide to save? Where does it put this information, and why can't we get to some of that information when we really want it?

Scientists have been able to pinpoint where certain types of memory are stored. They've also discovered how neurons fire and synapses are strengthened when storing these memories. But they don't know exactly what goes into that neuron to store the memory, or how to dissolve that synaptic connection if you want to forget something. In September 2008, new clues about memory emerged that may eventually help us crack this cold case. In one study, researchers found that the neurons activated in the recall of a memory are likely the ones that fired when the event originally occurred [source: Carey]. So when you talk about reliving old memories, you actually are, because the brain is doing the exact same thing it did the first time.

But what if there wasn't a first time? One of the problems of getting to the bottom of memory is that it seems to play tricks on the brain sometimes. For example, we often create false memories. On July 7, 2005, London experienced a series of bombings. A follow-up study found that four out of 10 people have false memories of the event because they claimed to have seen nonexistent television footage [source: Randerson]. If we're storing things that are unreliable, does memory serve any purpose at all? According to thinkers as ancient as Aristotle, we might only need memories as a way to predict and anticipate the future [source: Eagleman]. TOP

3: The Secrets of Sleep and Dreams

"Sweet dreams are made of this," sang Annie Lennox during her stint in the Eurythmics in the 1980s. But you might notice that Lennox is suitably vague about what exactly "this" is. And really, no one knows what sweet dreams are made of, why we have them or even what we're doing sleeping our life away anyway.

Can you believe that? Every night we carve out a few hours of shut-eye, and scientists don't even know why! They do know that it's extremely damaging if a person doesn't get enough sleep, and it's possible that sleep once served some sort of evolutionary benefit. Sleep would be an extremely beneficial distraction if early man had wanted to take a midnight stroll at the time when saber-tooth tigers were on the prowl [source: BBC]. On the other hand, it's not a particularly advantageous trait to carry forward in this age of electricity as the process takes up a lot of time (about a third of our life) and renders the dreamer defenseless against predators [source: Eagleman].

There are a few theories as to why we need so much sleep. One idea is that sleep is restorative to the body, giving it an opportunity to rest. But if rest is the goal, why does our brain remain hard at work? It's possible that while we sleep, the brain is practicing and running problem-solving drills before completing actions in the real world. There are several studies that show that learning can't take place without sleep to reinforce the knowledge [source: Schaffer].

Some of these studies may have real implications for students. One researcher claims that it would be better for students to review information until they were tired, then slept, as opposed to pulling an all-nighter [source: BBC]. Some schools have changed the time of that first bell so that middle and high school students can get a little more snooze time [source: Boyce, Brink].

So let's say these students actually go to sleep, as opposed to engaging in more nefarious behaviors. What happens then? When the dreaming state of REM sleep was discovered in 1951, it was described as a "new continent in the brain" [source: Schaffer]. Though scientists have tried to make inroads on this uncharted continent, mysteries remain about its topography. Like sleep, dreaming may represent some sort of personal gym time for the brain, with dreams allowing a person to work out emotional issues and solidify thoughts and memories.

Or, it's possible that life is but a dream, as the song "Row, Row, Row Your Boat" taught us. When you're asleep, you're experiencing a ton of visual stimuli that the brain is somehow processing. In an awake state, there may be additional stimuli for different senses, but the brain may be doing the same thing with them. If the brain works just as hard sleeping as it is when we're awake, then maybe life is a waking dream [source: Eagleman]. TOP


4: The Puzzle of Why the Brain Stops Functioning

When a killer is on the loose in novels or on the silver screen, there's a special urgency for the detective on the case. It's a race against time to capture the culprit before he or she strikes again. The mystery of how brain cells are killed off by degenerative neurological diseases is no different. As millions of individuals and their families can attest, a brain disorder or injury can be frightening, frustrating and ultimately fatal.

One thing that makes these disorders especially fearsome is just how little is known about why they happen or what you can do about them. Take, for example, the case of Alzheimer's. This disorder leaves behind two very important clues: amyloid plaques and neurofibrillary tangles. But what do these clues mean? Does their presence begin the process of Alzheimer's, or do they develop as a result? And if these two features are the perps, what can be done about keeping them off the scene of the brain? As of yet, there's no magic bullet that can restore brain function or re-grow brain cells after they're lost.

In 1990, President George H.W. Bush declared that the last decade of the 20th century would be known as the "Decade of the Brain." Bush's proclamation regarding the brainy decade acknowledged the advances that had been made in understanding how the brain works while pointing out just how much more needed to be learned about what happens up there [source: Bush]. The president cited a number of neurological disorders he hoped to understand further, including Alzheimer's disease, stroke, schizophrenia, autism, Parkinson's disease, Huntington's disease and muscular dystrophy.

As you might guess, just one decade of the brain was not enough to solve all of the problems that plague the lump atop our spinal cord. To understand how the brain stops working, researchers need to do more work on how the brain actually functions. While scientists know the general function of various parts of the brain, there's only a very basic sense of how the brain's systems work together, especially with all of the functions a person requires of it in a single day. How does it work so fast? What other systems in the body does it use or rely upon? TOP


5: The Case of Nature vs. Nurture

Twins -- when Brad Pitt and Angelina Jolie have them, it's fascinating. When they appear to Jack Nicholson in the corridors of the Overlook Hotel in the film "The Shining," it's freaky. When Arnold Schwarzenegger and Danny DeVito claim to be them, it's comedy gold. And while multiple births represent one of the great wonders of life in their own right, they provide important clues in the mysterious case of nature versus nurture.

This case is concerned with how much of our personhood is due to what we came into the world with -- our genes. Do our genes determine how smart we'll be? Who we'll love? What we'll prefer to eat for dinner? Or does what happens once you're in the world make a bigger difference? Will parents or peers or pop stars ultimately shape the person you become? One way for researchers to figure out where genes end and where environment begins is in the study of identical twins, who share the same genes. Scientists have been studying twins to figure out the impact of genes on everything from math ability to predisposition for breast cancer. Twins represent such a rich research minefield for neuroscientists that an annual festival in Twinsburg, Ohio serves as a recruitment party of sorts [source: Revill, Asthana].

The separation of twins is when scientists may be able to really examine nature versus nurture. So far, however, only one study has ever looked at separated twins from infancy through adulthood, and we won't know the results of that study until 2066. In the 1960s, 1970s and 1980s, child psychiatrist Peter Neubauer and child psychologist Viola Bernard led a study in which twins and triplets that were given up for adoption at a certain New York adoption agency were separated and studied throughout the duration of their lives [source: Wright].

When the siblings were placed with their respective families, the parents were told that the child was part of an ongoing research study that would require regular interviews and evaluations. No one, however, was told that the child was a twin or triplet, or that the study involved the influence of nature versus nurture. In 1981, the state of New York began requiring that siblings be kept together in the adoption process, and Neubauer realized that the public might not be receptive to a study that used this separation method [source: Richman]. The results were sealed and placed at Yale University until 2066.

The memoir "Identical Strangers" is the story of Paula Bernstein and Elyse Schein, who were a part of the study. The sisters were reunited when they were both 35 years old; all but four subjects of the 13-child study have found their missing sibling [source: Richman]. In promoting the book, Bernstein and Schein may provide a sneak peek at Neubauer and Bernard's results. Bernstein and Schein say it's undeniable that genetics play a major role; Bernstein puts the number at more than 50 percent [source: Sunday Herald Sun]. The women discovered they had things in common that included a habit of sucking on the same fingers and the same major in college [source: Sunday Herald Sun]. As for other matters, the women report that they are, as Bernstein put it in an interview with National Public Radio, "different people with different life histories" [source: Richman]. TOP