And so Neuroscience 2009 comes to an end, and it’s time to put away my badge, rest my weary feet and note-taking hand and think about biology below the neck again. Here’s the final installment of our live coverage, but come back tomorrow for a roundup of the conference with highlights, loose observations and links to other people’s thoughts on the conference. Thanks for reading!
2:30 PM – The Final Talk
The schedule may say that Neuroscience 2009 runs through the end of the day today, but judging by how many suitcase-toting scientists were jumping in airport cabs this afternoon, a small portion of the 30,000+ attendance makes it to the very end. Indeed, even the main stage ends its conference early, shutting down after a talk by Mt. Sinai School of Medicine’s Eric Nestler, an expert in the field of molecular psychiatry.
Nestler’s research focuses on the gritty details of how drugs of abuse change the expression of a person’s genes – yes, it was another addiction talk, and the former addiction researcher that I am, it was great to see the topic getting so much attention this year. In the addiction press conference I attended yesterday, Nestler hinted at a bombshell idea – frequent users of addictive drugs such as cocaine, heroin or alcohol may change the mechanics of their genes so permanently, the modifications could be passed on to their children. This “inheritable addiction” has already been observed in lab rats, Nestler said, mirroring similar results seen with the offspring of obese rats (which I talked about on Monday).
But that data must be too fresh for mass consumption, despite Nestler telling a roomful of reporters about it the day before. His talk today focused on the steps leading up to that discovery, carefully examining how repeated cocaine increases or decreases the activity of hundreds of genes in the reward pathway of the brain. Those long-lasting changes, which can cause cells of the reward pathway to actually grow and change shape, help explain why addiction is such a difficult condition to treat – it may require a complete re-re-structuring of the brain.
Much of the addiction research I’ve talked about this week has taken place in animals, but before Nestler’s talk, I came across a rare experiment that looks at the behavioral effects of a commonly-used drug in humans. It might seem strange that we know a ton about the specific genes that are up or down-regulated by cocaine, but not so much about its effects upon humans, but that’s due to procedural reasons – it’s quite hard to get approval for a study that gives illegal drugs to humans.
Michael Ballard, from the University of Chicago laboratory of Harriet DeWit, was trying to fill in at least one of those gaps in the research by testing the effects of THC (the active ingredient in marijuana) to presumably eager volunteers. Ballard then tested the subjects’ ability to judge facial expressions and determine the emotional content of pictures and personality trait words while they were under the influence of the drug. Interestingly, higher doses of THC caused the subjects to misjudge the facial expressions they were shown, suggesting an effect of the drug on social perception. The other tests were normal during the drug effect, but when brought back to the laboratory a week later, the subjects showed a decreased ability to remember neutral and negative personality traits, possibly indicating that their memories of the drug effect were biased toward happier stimuli. Ballard hopes to continue that research into other drug types – he’s currently testing amphetamine – to give the field of addiction research much-needed, laboratory-controlled human data to make sense of the flood of animal experiments.
In the movie Eternal Sunshine of the Spotless Mind, Jim Carrey hires a service to selectively erase his memories of an ex-girlfriend. Surely, such a thing is impossible in reality, right? According to Elizabeth Phelps from NYU, such a process is actually possible, and has been demonstrated in rats. But the method used to eliminate memory in those animals – the targeted injection of protein synthesis inhibitors into the amygdala – was far too invasive and dangerous for human use.
But Phelps lab, in work that is as of yet unpublished, has developed a method that appears to selectively eliminate specific fears in people. The researchers put human subjects through a fear learning task, where they are taught to associate certain color squares with an electric shock. For instance, when they are shown a blue or yellow square, they are shocked, but a red square is accompanied by no shock. When this type of training is performed, people will show an unconscious reaction to the sight of a blue or yellow square days or even years after the initial training.
In Phelps’ experiments, the researchers brought their subjects back to the lab the day after training, and reminded them of the blue square’s association with shock, but didn’t mention the yellow square. The subjects were then shown the blue, yellow and red squares without shocks, a process called extinction that is already used by psychiatrists to eliminate fears. Fascinatingly, the “shock square” that the subjects were reminded of was more sensitive to extinction – on Day 3, the subjects showed no fear response to blue squares, but still showed fear when yellow squares were shown. This effect persisted for one year, with re-testing a year later finding no fear to blue squares and intact fear to yellow.
Phelps warned that the studies were still very preliminary, and it was unknown how this selective memory deletion could work outside of laboratory settings, or on memories that weren’t based on fear conditioning. But even she had to admit, “it seems a little like a science fiction.”
10:00 AM – The Origin Story of the Brain
I called an audible at the start of the final day of the Neuroscience 2009 meeting, deciding I had paid enough attention to obesity research yesterday to skip Sadaf Farooqi’s early-morning talk. Instead, I sat in on the symposium designed so Neuroscience can get in on the 2009 wave of Darwin birthday salutes – a collection of lectures on the evolution of brain and behavior. A favorite talking point of creationists is to argue that complex organs like the brain could not have evolved through the non-directed mechanisms of natural selection and genetic mutation. But as with other areas of evolutionary biology, this argument grows more and more ridiculous as scientists use genetic information as a roadmap back through the billion-year process of creating the incredible human brain.
The thread through the three talks I observed was one frequently made in evolutionary biology: humans are not unique. This is a good thing, because it allows us to study other animals as both a proxy for human biology (as we’ve seen repeatedly in my dispatches from the conference) as well as to unravel our evolutionary history by looking at ancestral animals. Seth Grant, the moderator of the symposium, spoke first about the origins of the synapse, the billions of connections between neurons in the brain. The synapse is incredibly complex, with about a 1000 unique proteins just in the very surface of the neuron facing the synapse. But those proteins can be traced back to very simple animals – 25% of them are present in single-cell organisms like fungi, which don’t have anything that resembles a neuron, much less an entire brain. These early proteins, which arose about 1 billion years ago, can be called a “protosynapse,” Grant said, and shows how far back in the history of life on earth the building blocks of the brain can be found.
German scientist Detlev Arendt found a model for the origins of the brain and the eyes in a somewhat gross place – the plankton worm Platynereis, which looks a little bit like the house centipedes that creep me out every winter. But the larva of Playtnereis is demonstrates the type of early nervous system development that likely occurred in the evolution of the first invertebrate brains, hundreds of millions of years ago, making this plankton a sort of living fossil.
Still, perhaps the best argument of humans’ lack of unique status in the animal world has come lately from bird laboratories, and Erich Jarvis of Duke presented video and data on the surprisingly robust language systems of birds like parrots, hummingbirds and songbirds. Birds have also been recently shown capable of using tools, counting, telling lies and planning ahead, providing a convincing argument that evolution can generate complex behaviors – it’s so easy, it’s happened multiple times in nature.