Pb on the Brain


I’ve got lead on my mind. Lead the element, not the verb; the toxic metal that used to grace every gas tank and paint can in this grand country of ours. For the most part we’ve stopped spewing lead into our environment, but the lead of prior generations doesn’t go away. It lingers on the walls and windows of older buildings, on floors as dust, and in the soil. These days it lingers in my thoughts as well.

I started worrying about lead when my daughter became a toddler and began putting everything in her mouth. I fretted more when I learned that lead is far more damaging to young children than was previously thought. Even a tiny amount of it can irreversibly harm a child’s developing brain, leading to lower IQs, attention problems and behavioral disorders. You may never even see the culprit; lead can sit around as microscopic dust, waiting to be inhaled or sucked off of an infant’s fingers.

Public health programs use blood lead levels (BLLs) to evaluate the amount of lead in a child’s system and decide whether to take preventative or medical action. In the 1960s, only BLLs above 60 μg/dL were considered toxic in children. That number has been creeping downward ever since. In 1985 the CDC’s stated blood lead level of concern became 25 μg/dL and in 1991 it went down to 10. But last year the CDC moved the cutoff down to 5 μg/dL and got rid of the term “level of concern.” That’s because scientists now believe that any amount of lead is toxic. In fact, it seems as if lead’s neurotoxic effects are most potent at BLLs below 5 μg/dL. In other words, a disproportionately large amount of the brain damage occurs at the lowest doses. Recent studies have shown subtle intellectual impairments in kids with BLLs as low as 2 μg/dL (which is roughly the mean BLL of American preschoolers today). All great reasons for parents to worry about even tiny exposures to lead, no?

Yes. Absolutely. Parents never want to handicap their children, even if only by an IQ point or two. But here’s what’s crazy: nearly every American in their fifties, forties, or late-thirties today would have clocked in well over the current CDC’s cutoff when they were little. The average BLL of American preschoolers in the late ‘70s was 15 μg/dL – and 88% had BLLs greater than 10 μg/dL.

These stats made me wonder if whole generations of Americans are cognitively and behaviorally impaired from lead poisoning as children. Have we been blaming our intellectually underwhelming workforce on a mismanaged education system, cultural complacency, or the rise of television and video games when we should have been blaming a toxic metal element?

I was sure I wasn’t the first person to wonder about the upshot of poisoning generations of Americans. And lo and behold, a quick Google search led me to this brilliant article on Mother Jones from January. The piece chronicles a rise in urban crime that began in the ‘60s and fell off precipitously in the early-to-mid ‘90s nationwide. The author, Kevin Drum, walks readers through very real evidence that lead fumes from leaded gasoline were a major cause of the rise in crime (and that increased regulation restricting lead in gasoline could be credited for the sudden drop off.)

The idea certainly sounds far-fetched: generations of city-dwellers were more prone to violence as adults because they breathed high levels of lead fumes when they were kids. It doesn’t seem possible. But when you put the pieces together it’s hard to imagine any other outcome. We know that children of the ‘50s, ‘60s, and ‘70s had BLLs high enough to cause irreversible IQ deficits and behavioral problems (of which aggression and impulse control are particularly common). Why is it so hard to imagine that more of these children behaved violently when they became adults?

In the end, this terrible human experiment in mass poisoning has left me pondering two particular questions. First, what does it mean for generations of children to be, in a sense, retroactively damaged by lead? At the time, our levels were considered harmless, but now we know better. Does knowing now, at this point, explain anything about recent history and current events? Does it explain the remarkable intransigence of certain politicians or the bellicosity of certain talk show hosts, athletes, or drivers with a road rage problem? Aside from the crime wave, what other sweeping societal trends might be credited to the poisoning of children past? How might history have played out differently if we had all been in our right minds?

Finally, I’ve been thinking a lot about the leads and asbestoses and thalidomides of today. Pesticides? Bisphenol A? Flame retardants? What is my daughter licking off of those toys of hers and how is it going to harm her twenty years down the line? This is not just a question for parents. Think crime waves. Think lost productivity and innovation. Today’s children grow up to be tomorrow’s adults. Someday when we are old and convalescing they’ll take the reigns of our society and drive it heaven-knows-where. That makes child health and safety an issue for us all. We may never even know how much we stand to lose.


Photo credit: Zara Evens

Good Morning, Sleepyhead

A few weeks ago, I passed out. One moment I was standing by the door to our apartment, wishing my departing husband a good day at work. The next, my eyes had rolled back in my head and I fell face-first into the wall. My forehead struck the lower hinges of the door; I bruised my cheek and arm and knee, nothing badly. My husband, who was halfway out the door when I fell, rushed to gather me up. He held me and said, “Are you all right? Are you okay?” And that was how I awoke, as if from a long dreamless sleep, on the floor beside our front door.

I was only out a few seconds, but it felt like it could have been hours. I remembered the minutes leading up to my dramatic tumble, but they felt like long ago. A bit ethereal, and separated from the present by a gap that didn’t feel odd to me in the slightest.

I’ve always tended toward low blood pressure and often felt dizzy when standing up. After the fall, doctors checked me out and said I was fine. (My prescriptions are to drink more water and maybe eat more salt.) Still, the experience got me thinking about memory and how it’s a strange and elusive creature. How we always think we’ve caught it but we never have.

Back in my grad school days, we studied the case of H.M., the famous amnesic patient who was unable to form new memories. We learned that his journal was filled with descriptions of waking up as if for the first time and having no recollection of writing any of the prior journal entries, nor of how he came to be where he was. I wonder if the feeling was something like my contradictory experience on the floor, when I lacked memory of the preceding moments and yet felt as if nothing were missing. Time felt continuous, despite the fact that my memory was not.

The experience also reminded me of a dramatic story I read in the nonfiction book Soul Made Flesh. In 1650, a young British servant named Anne Green was seduced by her master’s grandson and gave birth to a stillborn baby. Thanks to the social mores of the time, she was tried and convicted of infanticide and sentenced to death. She proclaimed her innocence to the crowd that gathered in the courtyard of Oxford Castle to watch her hanging. After her speech, the executioner kicked the ladder out from under her and she hanged for almost half an hour before they cut her down and sent her body down the street to be dissected for science. Her designated dissectors were Drs. William Petty and Thomas Willis (of the Circle of Willis). But when they opened the coffin, they heard a rattle in her throat and managed to revive her with water, heat, and herbs.

When Anne Green came to, she began reciting the speech she’d delivered at the gallows. She didn’t remember leaving the prison, climbing the ladder, or giving the speech, much less (thankfully) hanging. A pamphlet later circulated about the event described her memory as “a clock whose weights had been taken off a while and afterward hung on again.” The incident illustrated the machine-like quality of memory. Today we describe it as flipping a switch. Anne Green’s memory had been turned off and then turned on again.

As strange as the stories of H.M. and Anne Green sound, their wild memory lapses aren’t so different from what happens to us everyday. We all experience time as continuous and ongoing, even though our memory is often shot through with holes. We spend a full third of our lives in unconscious slumber and remember little of our dreams. Even our waking lives are terribly preserved in the vault of our memory. How many of your breakfasts can you recall? How many birthday parties and drives to work? How many classroom lectures and airplane rides and showers can you individually call to mind?

Our recollections are mere fragments. They pepper the timeline of our past just enough to form a narrative – one’s life story. This story may feel solid and unbroken, but don’t kid yourself. Your memory is not. We are all amnesic, all a little untethered from the passing moments of our lives. We are continually rediscovering and resurrecting our past to move forward in the present. In one way or another, we have all roused from our coffin reciting a speech from the gallows or come to on the floor with a sore face and an astonished husband. We are all perpetually in the process of waking up for the very first time.

Why Bigger Isn’t Always Better

One of my entertainments this holiday season was following the online buzz over a recent article in Nature Neuroscience. The authors’ findings were covered by Wired, Time, Slate, U.S. News & World Report, and the BBC, to name a few. One headline read: Scientists Discover Facebook Center of the Brain. Another: How to Win Friends: Have a Big Amygdala?

The authors of the Nature Neuroscience article report a correlation between the size of a subcortical brain structure called the amygdala and the extent of a person’s social network. In effect, people with larger amygdalas tended to have more friends and close acquaintances than those with lesser-sized amygdalas. The popular press and the public leapt on this idea. We are predestined by our anatomy to be popular or not. If we were alone on New Years Eve, if our Facebook friend count is low, it’s not our fault. Chalk that one off to our brains, our genes, our parents.

All of this struck me as both amusing and sad because of a book I was reading at the time. The book, Postcards from the Brain Museum by Brian Burrell, chronicles the history of neuroscience in the context of our search for greatness (as well as criminality, idiocy, and inferiority.) It tells how scientists spent most of the 19th century collecting human brains from geniuses, criminals, and the poor to try to understand why some people demonstrate remarkable abilities while others flounder and fail.

It is a sad and sordid history. At first, some believed that the sheer size or weight of one’s brain predicted greatness, so that large brains were capable of better thinking. Since women’s brains (like the rest of their bodies) were on average smaller than those of their male counterparts, this provided a perfect explanation for their intellectual inferiority. Later, when the link between brain volume and intelligence was debunked, scientists suggested that the amount of folding on the brain’s surface was the marker of a brilliant brain. The more convolutions on the surface, the smarter the individual. Other scientists identified specific fissures that they deemed inferior, as they were supposedly found more often in apes and women. These lines of research would be used to justify racial and gender stereotypes and give rise to the practice of eugenics in the first half of the 20th century.

The peer review process and established statistical methods ensure that today’s science is more legitimate than it was in centuries past. But neuroimaging has allowed us to probe the living brain to a degree heretofore unimagined. With it, scientists amass enormous amounts of data that strain our standard statistical techniques and challenge our ability to distinguish between profound, universal discoveries and those idiosyncratic to our subject sample or functionally irrelevant. We still don’t know whether ‘bigger is better’ nor understand the source or functional consequences of individual differences in the size and shape of brain regions. Certainly we don’t know enough to look at a person’s brain and guess with accuracy how smart they are, how good they are, or, yes, even how many friends they have.

Just look at this graph from the Nature Neuroscience paper plotting amygdala volume on the horizontal axis and social network size on the vertical axis:

The figure above shows each subject as a black dot (for younger participants) or a gray triangle (for older ones). The diagonal line shows a mathematical correlation between amygdala volume and social network size, but look at how many dots and triangles lie away from the line. For the same amygdala volume (say, 3 cubic mm), there are dots that lie far above the line and others that lie far below it. No one looking at this figure can say that amygdala size determines one’s sociability. Perhaps it plays some small role, sure. But we are not slaves to our amygdala volumes, just like we’re not slaves to our overall brain size, our fissural patterns or cerebral convolutions. Our abilities and thoughts do come from our brains, but we have to keep in mind that those brains are far more complex than we can fathom. Who you are can never be reduced to a list of measured volumes. It’s important that we remember that, and that we never return to those days of ‘mine’s bigger than yours.’

Modern Relics

For millennia, Christians have saved the corpses of saints. Worshipers would make pilgrimages to view the bodies or body parts on display and share in their holiness.

I recently listened to an NPR book tour podcast featuring Peter Manseau, author of a recent book about holy relics. He described how worshipers would be so overcome with awe that a few bit off pieces of the saints’ bodies (in one case, a toe). I was both horrified and impressed. I’ve never believed in anything strongly enough to make me want to go Mike Tyson on the dead.

The relic discussion got me thinking about the modern era, and I realized that science is teeming with relics as well. This is true both on a general and an individual level. On a general level, we can point to archaeologists unearthing ancient remains of lost civilizations and species. A recent Nova special on Neanderthals documented the genomic analysis of Neanderthal remains to answer questions about our common ancestry. More commonly, bones are carbon-dated and skeletons are modeled for their aerodynamics or for bipedal versus quadrupedal motion.

But the most fascinating kinds of modern relics come from specific individuals. They are prized for the unusual features of that individual rather than their representativeness of a species as a whole. For example, Einstein’s brain was preserved and studied. Scientists found that the size and surface morphology of his parietal lobes were different from those in non-genius controls. Fragments of Beethoven’s skull and hair have revealed that the composer died of lead poisoning, which might account for his medical problems later in life, although probably not his deafness. And scientists have been trying to get a DNA sample from Lincoln’s tomb to conduct genetic testing for a specific type of genetic illness, spinocerebellar ataxia type 5.

To understand why relics have persisted over time, it’s useful to ask what purpose they serve. Why collect the dead? As I mentioned, the ancient relics were valuable for their holiness. At the time, religion was the only path to understanding the world. Why are we here? What came before us? How can we gain control of our lives, both on Earth and after death? God was the source of those answers and the relics were a portal to god.

Despite all that has changed about our society and our ways of thinking, modern relics serve the same purpose. They may not be thought of as a phone line to god, yet we still value them for what they can explain. They tell us about our evolution and about the lives of the historical figures who shaped society and have become our modern legends. They provide a window into the nature of human genius, creativity, good and evil; a portal to ourselves. And that is something I can truly believe in.

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