Jeroen Raes is a man with a lot of poo on his hands. He can't get enough of the stuff and has Petri dishes full of it, from people over the world, piling up in his laboratory's fridges. Let me cut off any rash assumptions you might be making right now - Raes is a leader in the study of the human microbiome, the trillions of microbes that live on (and in) our bodies that, as scientists have discovered over the past decade, we cannot do without.
Around 90% of the cells in a typical body are not human, they're micro-organisms. Scientists have found more that 8 million genes in total in the tiny life-forms that live on the human body, which compares with just 21,000 in our own cells. Most of these microbes are harmless, but we would become quickly unhealthy or ill without many others, which help us digest food and fight off infections from pathogens.
Raes is among a band of scientists intent on building a reference database of the microbes found in different people, in different parts of the body and in different places in the world. He collects samples from volunteers who swab their mouths, noses and genitals. To get at the most interesting and largest number of microbes, those found in the gut, he needs faeces. As he took me around his lab at VIB University in Brussels, Raes explained that samples of poo would one day become a routine diagnostic tool for doctors, in the way blood or urine samples are today. Understanding these microbes would be critical to maintaining our health in the future.
I met Raes while making a film about the human microbiome for the new series of the BBC2 programme, Dara O Briain's Science Club. Among the many pleasures of talking to scientists for a living is that it's easy to volunteer to take part in some of their most cutting-edge experiments. In that spirit of scientific investigation, I had collected a sample of my own gut microbes some weeks before and sent them off to scientists to sequence the countless millions of bacteria within.
Scientists think that the microbiome will be crucial in working out why some people seem more susceptible than others to conditions such as diabetes, Crohn's disease or obesity. At University College Cork, I met neuroscientist John Cryan, who has been testing whether gut microbes could be linked to mood, behaviour or even autism.
"Knowing myself" seemed to become a theme for the films I made for this series of Science Club. On last week's episode, Carnegie Mellon University psychologist Marcel Just tried to read my mind using an fMRI scanner, showing me pictures of everyday objects - from melons to tools to tents - while I lay in his scanner and racks of computers in another room recorded and processed the activity in my brain. His theory is that when we think of particular categories of object - fruit or newspapers, say - different people will generally have the same recognisable patterns of activity.
While impressive, you'd be forgiven for thinking it doesn't get into many of the most special things about human thought. We introspect, for example, play narratives out in our heads and can imagine things that aren't even there. At Plymouth University, psychologist Giorgio Ganis showed me how he was able to examine some of these more complex, dynamic processes in action. He scanned my brain while I watched a series of dates go by on a screen in front of me; I had to pretend not to recognise my birthday when it appeared. By analysing my brain activity during the experiment, Ganis tried to spot my deception.
Why does any of this matter? The technology is in its earliest stages but, already, lawyers and neuroscientists have begun talking about when it might be used in courtrooms as a souped-up lie detector. There are a number of ethical conundrums here, not least the inevitable false positives or situations when a witness genuinely mis-remembers something, but there is a potential future where brain scans might be as common as genetic fingerprints in legal cases.
Studying the brain in ever-greater depth is the big challenge for the 21st century, thanks largely to the incredible technology now available. Harvard University neuroscientist Dr Van Wedeen is leading the charge here, in particular getting high-definition images of how clumps of neurons in the brain are wired together.
Neuroscientists believe that this map of connections, the "connectome", will be at the root of a proper understanding of everything from how memories are made to what goes wrong in mental disorders. Perhaps it will also give us our first window into why we have different personalities and, whisper it, what consciousness actually is.
At the Massachusetts General Hospital, Wedeen is working on a remarkable machine - the Connectom, which can generate far stronger magnetic fields than any other brain scanner and, therefore, resolve 10 times more detail. Fewer than 100 people have had their brains mapped by this machine, which took an hour to map my brain's thread-like connection pathways. The results - the multicoloured tangle of lines that make me me - were humbling. As beautiful as its results were, the connectome is no art project for neuroscientists. To make these scans useful, they will need to embark on a programme to carry out thousands more scans on people of all ages, in many states of mental health, and at different times in their lives, in order to build up a reference of how the human brain is wired up and how this wiring is affected during disease. This, Wedeen believes, is how we will get to the root of understanding the human mind.
As a scientific volunteer, I have seen which bits of my brain switch on when I look at a piece of fruit or a newspaper or a tent, and which are active when I am lying. I've had a glimpse at the colonies of bacteria living in my guts, the silent organisms that keep me healthy. And the key to my personality and consciousness was hidden somewhere in the coloured tangle of lines that emerged from the Connectom scanner.
It all sounds so trivial, doesn't it? But these incremental bits of knowledge are hard-won tour-de-forces of scientific effort. Each of my personal insights took scientists weeks of computing time to reveal, coupled with a decade or more of basic research beforehand to put it all into context and give it meaning. These technologies, and many more like them, are starting to crack open the black box that we all carry around with us, in which body and brain processes hum along subconsciously to make us function. This is just the start; there is a long, long road ahead.
The new series of Dara O Briain's Science Club continues on BBC2 at 8pm on 1 August
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