Thursday, 24 June 2010

Double blind & placebo controlled, but where are the statistics?

For those of you who missed this morning's The Today Programme on BBC Radio 4, listen here to a fragment where homoeopathy-sceptic Simon Singh and conservative MP David Tredinnick take opposing views on the healing powers of homoeopathic remedies. Based on a couple of studies published recently, Tredinnick feels it is worth re-opening the debate on whether or not the NHS should fund homoeopathic remedies; Simon Singh explains why this would be a mistake. The latter's description of a French homoeopathic flu medicine that contains one crushed and highly diluted duck that serves millions of people - and therefore earns the company who created the remedy millions of Euros - as the ultimate quack remedy is a wonderful and almost perfect put-down for the values of homoeopathy.

Wednesday, 9 June 2010

Reading between the lines

Whenever we compare human and animal behaviour, one major difference that always comes up is our ability to use words to communicate with our fellow human beings. We can use words to order food in a restaurant and chat about everything and nothing over coffee with our friends, and the act of talking has become so normal to us that we don't even give much thought as to how extraordinary speech really is. And now researchers have discovered that our use of language gives away more than just the literal meaning of the words: there are hidden clues about ourselves in our words, in the frequency with which we use certain words, in the number of different words there are in our personal vocabulary and in the richness of our sentences.

In 'Vanishing Words', a recent episode of my ever favourite science-based radio programme Radiolab, Jad and Robert talk about those hidden messages. Drs Ian Lancashire, Kelvin Lim and Serguei Pakhomov are all interested in how characteristics of our personal vocabulary may be an indication of our likelihood of developing memory related diseases such as Alzheimer's. Moving from analysis of the crime novels of Agatha Christie to a comparison of how the linguistic content of teenage essays by a group of nuns relates sixty years on to their cognitive function, these researchers have found surprising associations between the richness of our language and our later susceptibility to cognitive decline.

And more messages can be found in this blog post on the British Psychological Society's Research Digest blog. Dr Paul Rozin of the University of Pennsylvania showed in a study published in Cognition and Emotion that our existential feelings about positive and negative events are reflected in our language. Analysing the frequency of positive and negative words in our language, the researchers found a large prevalence of the former type of utterance, mirroring, they claim, the preponderance of positive events that occur.  Nonetheless, while negative words are comparably scarcer, they exist in greater variety, which the authors argue again is typical of how such events occur in our everyday environment.

Perhaps this latter is not so surprising.  Even at its most gossipy or mundane, language is partly a translation of our needs and desires, and partly a reflection of our environment.  Slips-of-the-tongue have endlessly been interpreted, not just as mistakes, but as windows onto our souls (see, for instance, the furore when Gordon Brown once accidentally said that he had "saved the world" rather than just the monetary crisis). Similarly, the past fifty years have seen fierce battles over Whorfian linguistic relativism, questioning how language affects thought, perception and behaviour.

All this does give the phrase 'reading between the lines' quite a different meaning!

Wednesday, 2 June 2010

Illuminating the brain's bright future

In the 1920s Felix the Cat had a brilliant idea and a light bulb appeared over his head; thus was created the signature of an epiphany. But recent advances in neuroscience leave you wondering whether in the future we will be more familiar with light bulbs actually driving our thoughts and inspiration rather than just being a visual metaphor. Gero Miesenböck, currently Waynflete Professor of Physiology at Oxford University, has been pioneering work that uses light to control brain cells, a field known as optogenetics.

Our brain consists of approximately 100 billion neurons that, as Miesenböck lyrically describes, form “an intricate tapestry”. To understand how neuronal signalling drives our behaviour, he says, we need to tease apart the disparate contributions that each of the different populations of neurons make to our behaviour. Nobel laureate Francis Crick remarked in a famous article in 1979 that one thing scientists have dreamed about is a tool that would allow them to selectively activate or turn off certain groups of cells while leaving others unaffected. Twenty years later, he suggested how this might be achieved: with light and molecular engineering. And this is precisely what optogenetics does.

To understand this technique we have to go back to the 1990s when German biologist Peter Hegemann discovered that green algae, commonly found in ponds, respond to light by wagging their tail. This behaviour was intriguing because algae are unicellular creatures without eyes. Hegemann discovered that when light photons hit the protein coils packed in the algae’s cell membrane, a chemical reaction creates a tiny gap in the membrane, causing an ionic current to be produced and the algae’s tail to wag. The protein that allows this reaction with light is called channelrhodopsin and is comparable to rhodopsins found in our own eyes.

Meanwhile, Miesenböck and his colleagues, working in New York and later at Yale, wondered whether they could exploit a similar mechanism to control brain cells. They took light sensitive proteins like the photoreceptors of our eyes, transplanted them into neurons and, by simply shining a light on them, the team was able to activate the modified neurons, a first step towards neuronal control.

To exploit the full power of this method, however, the researchers needed to discover a way just to excite or inhibit selected populations of cells, and with genetic engineering they were able to achieve this. By harnessing the cunning of viruses or by creating genetically-modified mice and flies, it was possible to make expression of the rhodopsin-encoding gene specific to particular neurons, meaning that only those neurons would become active when illuminated.

The road to success for optogenetics was not easy. The first difficult step was to find out whether they were able to transplant the rhodopsin-containing photoreceptors of flies to other cells in a culture and activate them with a flash of light. Once they succeeded in doing this, the second, even more complicated challenge was to move from changing neuronal activity in a cell culture to changing the behaviour of a living being, in Miesenböck’s case the fruit fly. The promise became initially clear when Susana Lima, Miesenböck’s PhD student at the time, showed him the first baby steps taken by a fruit fly on command of light. Within 5 years, they had learned how to remote control a fly.

The technique is now so advanced there is a large volume of work looking at how brain cells control behaviour. Last year in Cell, Miesenböck and his team exposed the learning mechanisms of a fly by creating false memories (1). They placed a fly in a narrow chamber, half of which smelled of an old tennis shoe, the other half of sweet fruit. By observing how much time the fly spent on either side, the researchers were able to work out which was the fly’s preferred smell. When this location was later paired with a memorable, aversive signal – a painful electrical shock – the fly learned to avoid this location and spend more time on the opposite side of the chamber. From previous research, Miesenböck knew which neurons were involved in learning to associate the shock with an odour and could therefore directly target this system with optogenetics. By activating these cells with light when the fly was in the location of its preferred smell, Miesenböck’s team was able to provoke identical avoidance behaviour even though no electric shock was given. Thus, the fly learned from an experience it never had.

Might we be able to use this technique to control our minds in the future? Miesenböck thinks that it will be a while before optogenetics can be used in humans: “You would have to express a foreign gene in a targeted fashion and this is where the show-stopper currently lies”. While using this technique in humans may be a long way off, he does believe that optogenetic research in flies might nonetheless directly aid our understanding of the human brain because biology is generally conserved. “Nature rarely invents the wheel twice”.

For now, Miesenböck thinks the field should focus on blurring the boundaries between work in whole organisms and fine-scale research in cell cultures. They could make use of the fact that tissue in a cell culture can be treated as if it was still part of a functioning brain by activating the cells with flashes of light – a use of optogenetics that is currently underappreciated. “There will be room for brain-free neurobiology, where optogenetics provides the interface to allow researchers to really talk to and feed artificial information into neuronal systems”.

Miesenböck also advocates using light “to enable scientists to drive nervous systems outside their normal operating limits, because this is often where mechanisms reveal themselves”. Miesenböck’s team used this approach to investigate the origin of sex differences in flies. While male and female fly brains are very similar, they nonetheless display sex-specific courting behaviours. The gene that controls male courting behaviour is expressed in a very small number of neurons in the abdominal ganglia of the fly. By specifically targeting these cells with optogenetics and shining light onto this circuitry, Miesenböck’s team was able to produce male courting behaviour in all the flies, even the females (2). Thus, they were able to show that females possess a bisexual brain containing a motor programme necessary for male courtship behaviour, but do not activate it because the neuronal commands required for the behaviour are absent.

With the ability to dissect neuronal functioning in the healthy brain, optogenetics might also hold potential to help understand the exact mechanisms that cause neurological and psychiatric diseases such as depression and schizophrenia and even help treat them. For example, Karl Deisseroth and his team at Stanford University in California published a study in Science last year that used optogenetics in rats to investigate directly how deep brain stimulation might alleviate symptoms of Parkinson’s Disease, something that had previously been poorly understood (3).

Thus, despite the difficulties in applying the method to humans, Miesenböck is hopeful: “With optogenetics we can really identify the players that are responsible for particular behaviour and that may give us knowledge for targets of more conventional treatment. Then conventional treatment can become more effective and cleaner.

1. Claridge-Chang et al., 2009. Writing memories with light-addressable reinforcement circuitry. Cell 139:405- 415.
2. Dylan Clyne & Miesenböck, 2008. Sex-Specific Control and Tuning of the Pattern Generator for Courtship Song in Drosophila. Cell 133:354-363.
3. Gradinaru et al., 2009. Optical deconstruction of parkinsonian neural circuitry. Science 324:354-359.

This article appeared in 'Phenotype'. Here you can read the magazine its entirety.

A shorter, related post can be found on my blog here.