杏吧原创

Melbourne

8:15am : A flight lands at Melbourne鈥檚 Tullamarine International Airport. Several hundred pieces of baggage are rushed from the plane onto a conveyor belt in the baggage reclaim annex. Over the sound of roaring engines, rushing air vents, and grinding generators, a dog barks. Florence, a sleek black Labrador, wags her tail.

Among the cavalcade of luggage passing beneath Florence鈥檚 all-smelling nose is a nondescript hardback suitcase. Inside the case, within Styrofoam casing, packed in loose pepper and coffee, wrapped in freezer paper, and heat-sealed in plastic, are 18 kilograms of hashish.

The cleverly concealed drugs don鈥檛 fool supersniffer Florence, and her persistent scratching at the case alerts her handler. Florence is one of a truly new breed: the product of what is perhaps the only project in the world dedicated to breeding dogs solely to detect drugs. Ordinary dogs have a 0.1 per cent chance of making it in drug detection. The new breeding programme, run by the Australian Customs Service, is so successful that more than 50 per cent of its dogs make the grade.

And what began as a wholly practical exercise in keeping illegal drugs out of Australia may end up playing a role in an entirely different sphere-the comparatively esoteric world of neurobiology. It turns out that it鈥檚 not Florence鈥檚 nose that makes her a top drug dog, but her unswerving concentration, plus a few other essential traits. Florence and her relatives could help neurobiologists to understand both what they call 鈥渁ttentional processing鈥�, the brain mechanisms that determine what a person pays attention to and for how long, and its flip side, problems such as attention deficit/hyperactivity disorder.

The Australian Customs Service has used dogs to find drugs since 1969. Traditionally, the animals came from pounds and private breeders. But in 1993, fed up with the poor success rate of finding good dogs this way, John Vandeloo, senior instructor with the detector dog unit, joined forces with Kath Champness, then a doctoral student at the University of Melbourne, and set up a breeding programme.

Champness, now with the Royal Guide Dogs Association of Australia, began by defining six essential traits that make a detector dog. 鈥淔irst, every good detector dog must love praise,鈥� she says, because this is the only tool the trainers have at their disposal. Then the dog needs a strong hunting instinct, and the stamina to keep sniffing at the taxing rate of around 300 times per minute. The ideal detector is also fearless enough to deal with jam-packed airport crowds, and the roaring engine rooms of cargo ships.

Ivan the terrible

The remaining two traits are closely related and cognitive in nature. A good detector must be capable of focusing on the task of searching for drugs, despite the circus of distractions in any airport or dockside. This is what neurobiologists call 鈥渟elective attention鈥�. And finally, with potentially tens of thousands of hiding places for drugs, the dog must persevere and maintain focus for hours at a time. Neurobiologists call this 鈥渟ustained attention.鈥�

To create the supersniffer, Champness selected for these traits over three generations of dogs. She also discovered that of the six traits, selective attention was the most heritable. This finding, which Champness intends to publish later this year, shows that genes account for about 25 per cent of the differences between dogs in their ability to pay attention. That鈥檚 about as heritable as it gets for a complex behaviour in animals, according to Robert Plomin, deputy director of the social, genetic and developmental psychiatry research centre at the Institute of Psychiatry in London.

After only three generations 鈥渢he success of the breeding programme jumped way beyond our expectations,鈥� says Champness. 鈥淲e hoped that 30 per cent of the pups from the programme would become detector dogs, but the actual success rate consistently exceeds 50 per cent.鈥�

Vandeloo and Champness assess the dogs鈥� abilities to concentrate by marking them on a scale between one and five according to how well they remain focused on a toy tossed into a patch of tall grass. Ivan scores a feeble one. He follows the toy, gets halfway there, then becomes distracted by places where other dogs have peed or by flowers in the paddock. Rowena, on the other hand, has phenomenal concentration: some might even consider her obsessive. When Vandeloo tosses the toy, nothing can distract her from the searching, not other dogs, not food. And even if no one is around to encourage her, she keeps looking just the same. Rowena gets a five.

A person鈥檚 ability to pay attention, like a dog鈥檚, depends on a number of overlapping cognitive behaviours, including memory and learning-the neurobiologists鈥� attentional processing.

Attention in humans can be tested by asking subjects to spot colours on a screen while ignoring shapes, or to spot sounds while ignoring visual cues, or to take a 鈥渧igilance test鈥�. Sitting a vigilance test is like being a military radar operator. Blips appear on a cluttered monitor infrequently, and at irregular intervals. Rapid detection of all blips earns a high score. Within about five minutes, one in ten subjects will start to miss the majority of the blips, one in ten will still be able to spot nearly all of them, and the rest will come somewhere in-between.

Vigilance tasks push the limits of attention by providing signals that are infrequent and unpredictable-which is exactly what is expected of the sleuths of the canine world when they are asked to notice just a few odour molecules in the air, and then to home in on the source. During a routine mail screen that can take hours, the dogs stay so focused that not even a postcard lined with 0.5 grams of heroin and hidden in a bulging sack of letters escapes detection.

Dogged focus

By combining attention tests with brain scanning techniques in normal people, and in people with brain damage due to strokes and bullets, neurobiologists have identified which bits of the brain are activated when a person pays attention. Others have investigated what happens to the ability of a rodent or a monkey to focus when parts of their brains are lesioned, or when they are given drugs that block or enhance the effect of different neurotransmitters.

Gradually a coherent picture is emerging. Several areas in the brain鈥檚 prefrontal cortex are especially important for attentional processing. Trevor Robbins, an experimental psychologist at the University of Cambridge, explains that in humans 鈥渨hen a task gets difficult, the anterior cingulate gyrus [in the frontal lobe of the brain] seems to work overtime鈥�. The prefrontal cortex receives and sends inputs to most of the rest of the cortex which, among other tasks, processes visual and auditory information and language. But the prefrontal cortex alone is responsible for 鈥渆xecutive鈥� functions such as strategic planning and the allocation of cognitive resources.

The prefrontal cortex may even be able to boost the supply of stimulatory chemicals that reach the cortex during prolonged periods of concentration, by calling on parts of the brainstem and the basal forebrain, two areas that house the body鈥檚 arousal centres and are located below the cortex. The prefrontal cortex provides the lion鈥檚 share of the brain鈥檚 neuronal input to these areas, and the whole cortex receives a lot of stimulation from the the brainstem and the basal forebrain via neurons that feed it neurotransmitters like noradrenaline and acetylcholine. As Robbins says, through such mechanisms the prefrontal cortex is in a position to regulate the activity of the cortex-鈥渋t may turn the volume up and down鈥�.

Although the prefrontal cortex is obviously vital to an animal鈥檚 ability to focus its attention, researchers are divided over the exact nature of its role. Neuroscientists like Raja Parasuraman of the Catholic University of America in Washington DC, argue that there are discrete control centres for attentional processing that reside in the prefrontal cortex. Parasuraman says that the prefrontal cortex decides what needs to be attended to next and what must be ignored.

Others, like Robbins, envisage a more democratic mechanism. They argue that attentional processing is the sum of a multitude of different mental processes including, say, moving to focus the eyes or ears on a target, and feeling enthusiastic or indifferent about a topic. Rather than a central control, they envisage an integrated network of processing carried out by different brain regions that, in addition to the cortex, include the amygdala, which plays a role in emotional responses, and the basal ganglia, which govern voluntary movement.

鈥淢emory [also] plays an absolutely critical and essential role in guiding attention,鈥� says Robert Desimone, who studies the link between memory and attention at the National Institute of Mental Health near Washington DC, and has helped champion the idea that the attentional processing control centre lies in the prefrontal cortex.

Take the example of someone looking for a lost set of keys, he says. The search begins in the prefrontal cortex, where neurons process the goal 鈥渇ind keys鈥�. These neurons liaise with the visual cortex at the back of the brain, activating a mental image of keys. In order to stay focused on the task at hand, the key image must have priority over all other images already stored in the memory. Desimone鈥檚 work on monkeys suggests that the activity in the prefrontal and visual cortex which creates the image of keys also inhibits other neuronal connections that would conjure up distracting images.

鈥淭he end result is conscious perceptual awareness of the thing that is important right then, and unawareness of the things that aren鈥檛 important,鈥� says Desimone.

Although most people have a degree of conscious control over how much attention they will pay to a given object or task, it constantly risks being hijacked by environmental stimuli. The search for the lost keys, for example, is driven by the goal of finding the keys, or 鈥渢op-down鈥� voluntary control. But a cue from the environment, a knock at the door or the phone ringing, is likely to steer attention toward the door and away from the search. Such 鈥渂ottom-up鈥� effects are based solely on the properties of the stimulus itself and the brain鈥檚 involuntary, instinctive response, and has nothing to do with attaining a goal.

Good detector dogs excel at top-down control. Training takes advantage of that and creates the goal by getting the dogs to associate finding a toy that smells like cocaine, hash or heroin, with praise from their trainers. Dogs like Ivan, on the other hand, are all bottom up.

Ivan is a bit like a person with attention deficit/hyperactivity disorder. Children with ADHD are so distractable and their attention spans are so short that they can鈥檛 function normally or learn properly. As many as 3 to 5 per cent of children are thought to suffer from the disease in the US, where the incidence is highest, although the diagnosis is often controversial.

Wandering minds

In the past three years, ADHD researchers have begun to look for genetic components to the disorder. Plomin says that the studies 鈥渃onsistently and surprisingly show very substantial genetic influences-in the order of 60 per cent heritability鈥�. Behavioural traits in humans typically show higher heritabilities than they do in animals, perhaps because they can be characterised more easily in humans. Nonetheless, a 60 per cent heritability for ADHD is considered high because the disorder is likely to be a spectrum of different defects that come under one umbrella diagnosis.

With the current interest in attentional processing, as well as human diseases that have an attention defect component, such as ADHD and schizophrenia (sufferers appear to lose voluntary control over where they focus their attention), Plomin predicts that it is only a matter of time before the super-sniffer dogs attract the attention of neurobiologists.

鈥淎t the behavioural level,鈥� says Plomin, 鈥渉umans are much closer to dogs than to [rodents].鈥� Rats are one of the favourite animals in which to study attentional processing. 鈥淒ogs are [also] more trainable than [rodents],鈥� he points out. With their highly-heritable dynamo concentration, the Australian drug detection dogs could even help to identify some of the many genes that underlie attentional processing.

But so far, says Champness, nobody has beaten down her door with requests for dogs to study. Not that Melbourne鈥檚 super-detector dogs aren鈥檛 still very useful. During their first year of operation, the dogs made 1500 drug seizures, including one 5-tonne load of cannabis in a shipping container and a smaller load concealed in condoms inside a smuggler鈥檚 stomach.