Festival bites: BNA 2013 Day 2
Over the next four days BNA 2013: Festival of Neuroscience is filling the Barbican with an extravaganza of brain science. A lucky group of science writers from the Wellcome Trust are attending the Festival. Each day, we’ve asked them to give a short account of the seminars and lectures which they attend, to share the new research, stimulating discussions, and the unanswered questions, which they encounter. Today’s bite-sized pieces, from Penny Bailey, Theresa Taylor and Ryan O’Hare, offer glimpse of the great range of events taking place on Monday, the second day of the festival.
Plenary Lecture 3 – Imaging Pain, Relief and Altered States of Consciousness in the Human Brain
by Ryan O’Hare
“Pain is one of the oldest sensations we have and is shared across different species” – Professor Irene Tracey
The second day of the Festival of Neuroscience kicked off with an early morning plenary lecture by Professor Irene Tracey of the University of Oxford, on the imaging of pain, relief and altered states of consciousness in the human brain.
Pain is a complex experience influenced by numerous internal and external factors. It can start when a harmful stimulus, such as a burn or a sting, triggers nociceptors in the skin and sets off a rapid fire chain of neural processing throughout the brain and central nervous system.
From an evolutionary standpoint it’s crucial that we’re able to control pain. If we are distracted by it we may not be able to escape and fall victim to predators in life and death situations. Professor Tracey explained the neurological pathways which can dampen the effects of painful stimulus as a ‘top down’ control that’s been millennia in the making. In some circumstances the brainstem can intervene and act as the gatekeeper of pain perception, allowing us to modulate and even suppress signals coming from the nociceptors, ultimately limiting our perception of pain.
It’s all in the mind
The much maligned placebo effect elicits the same control in dampening down pain signals, and can have a substantial impact on our perception of pain. In trials, subjects were exposed to a pain stimulus but weren’t told when they would receive an analgaesic (which blocks the transmission of pain). Despite pharmaceutical intervention throughout, subjects would register only a slight decrease in pain if they didn’t know they were receiving the drug. Once told that they were receiving a drug, they perceived a pronounced drop in pain. The positive expectation of receiving a drug which would decrease the pain seems to intervene in the normal neural pathway.
But the opposite effect to the placebo, dubbed the nocebo effect, is also true. If subjects were told they were no longer receiving the pain killer their negative expectations largely cancelled out the effect of the drug, even when they were still receiving it. This could have profound impact on those with chronic pain conditions, where individuals have years of negative experience with drugs compounding their condition.
Impulsivity, compulsivity and habit formation
by Penny Bailey
Speakers at this morning’s session highlighted some intriguing differences between a group of disorders whose core is considered to be compulsion. While addiction, obsessive compulsive disorder (OCD), trichotillomania (pulling one’s own hair out), and pathological gambling all share a lack of top-down cortical control, they have very different drivers. The repetitive habits seen in OCD are driven by anxiety and the desire to avoid negative consequences (in a study, people with OCD continued to press a pedal to avoid a mild electric shock, even though they had been told the shock had been disconnected, and they were aware the action is senseless). Trichotillomania on the other hand, seems to be a purely ‘motor’ driven tick in which thought – or anxiety – plays little part.
People with OCD are spared in one cognitive domain: they might not be able to repress impulsive action but they have more control than gamblers or addicts when it comes to impulsive choice. Unlike gamblers, when offered the choice between a win that is more certain but of a lower value and one that is less certain but of a higher value, they opt for certainty. They also put up more resistance to the pull of addiction than addicts – but can become equally stuck in addiction if they do get drawn in.
Pathoglogical gambling will be separated from OCD in the forthcoming DSM-V (the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders) and listed instead as an addiction – the first behavioural addiction in the DSM. Recent brain scans have indicated some differences between gamblers and addicts, however. Reduction in dopamine (D2) binding in the striatum has previously been shown to predict addiction, but compulsive gamblers had the same amount of D2 binding as the control group. Surprisingly though, there were differences within the gambling group. Those who showed more ‘mood-related impulsivity’ (urgency) did have less D2 binding. This suggests the link between dopamine and addiction may be more complex than previously thought – the link is there but it may be mediated via impulsivity.
Dan Stein on Trichotillomania
by Theresa Taylor
Pulling your hair out can be more then a cute turn of phrase to express a bad day or stressful time. In the symposium ‘Impulsivity, compulsivity and habit formation’ Dr Dan Stein from the University of Cape Town explained that Trichotillomania is a relatively common disorder in which sufferers feel compelled to pull out, and sometimes eat, their hair.
In his book, Trichotillomania, Stein quoted a patient as saying that pulling out her hair was a force stronger then herself, and a constant need. ‘The movement happens by itself, there is something in my arms that pulls me along irresistibly. If I resist I have these irritable and stifling feelings which are totally unbearable, I just have to give into this need,’ she said.
Today Stein said the causes of this impulse condition were still unknown. In a study, researchers found that in identical twins there was a 40% chance that if one twin was a sufferer, the other would be. He said this meant there may be a partial genetic element, but that this was not the entire picture. Environmental factors such as childhood abuse may also play a role in the disorder, but evidence is inconsistent.
The condition can lead to other more well recognised problems such as depression or anxiety, and patients can also experience other physical symptoms such as repetitive strain injuries and or bowel obstructions caused by the hair they have ingested. The current treatment for trichotillomania involves habit reversal therapy, in which patients are taught to use a different and less destructive habit such as snapping a rubber band on their wrist when they feel the compulsion to hair pull. But studies on mice, which can also have this pathological grooming behaviour, have raised the possibility of new treatments.
Mice that exhibit such behaviour are known as barbering mice. A group of these mice have a disruption in a gene known as the HoxB8. Researchers found that the only cells expressing the gene were cells involved in immune responses. When they gave these HoxB8 mice a bone marrow transplant, it reversed their obsessive grooming. Stein explains this is a potentially exciting avenue for human treatment.
by Ryan O’Hare
Animals are specialists at processing the sounds of their own species. Dr Berthold Hedwig from Cambridge University explored the topic, guiding us through the neurological processing of call sounds in crickets.
Female crickets are mute, but they are able to pick out the chirp of a potential mate in a field full of noisy males of other species. In a process called phonotaxis they are able to zero in on a male and move towards him. When the males rub their front legs they create short bursts of sound which are interspersed with gaps. The resulting set of call and silence is called the pulse period pattern.
As these patterns are species specific, females tune in to the pattern of their species, showing little interest in calls which fall outside of this range. Dr Hedwig explained how different sets of neurons in the cricket’s brain have a role in processing the sound and can ‘tune’ their hearing accordingly.
How do mosquitoes hear their mate?
From chirping crickets to multi-tonal mozzies. Female mosquitoes fly headlong into the whining, buzzing clouds of males, and then pair off. The whine we associate with the insects is generated by their wings as they fly, with females producing a tone at around 400Hz whereas the males are at a slightly higher pitch of 700Hz. This can make it hard for females to listen out for males over the sound of their own buzz. Dr Ben Warren of the University of Cologne discussed how female mosquitoes have tuned their hearing to find a partner.
Mosquitoes hear using long antennae which vibrate as they come into contact with sound waves, passing the signal through a collection of specialised cells called the Johnston’s organ, which is effectively the mosquito’s ear. Playing a tone at the male frequency alone doesn’t get much of a response. Dr Warren showed that it is in fact a combination of the female and male tones simultaneously which form a so called ‘distortion product’, which the females are sensitive to, and which allows them to find their mate.
At the Festival today? Tell us what your highlights are and keep up to date with the latest Festival news on Twitter using the hashtag #BNAneurofest.
The scientific programme for BNA 2013: Festival of Neuroscience is not open to the public, but there are also public events happening throughout the week at the Barbican as part of the Wonder season. Including the Wonder Street Fair – a free public event bringing together science and art on the brain. There’ll be interactive exhibits, activities to help you explore the brain and much more. Visit the website for more information.