|
Exercises
Pay Attention，
Rover
by
Amy Davis Mozdy
8:15
a.m. A flight lands at Melbourne's Tulamarine 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's 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 .
The cleverly concealed drugs don't 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 percent chance of making it in drug detection. The new
breeding programme, run by the Australian Customs Service,
is so successful that more than 50 percent 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's not
Florence's 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 "attentional processing", the brain mechanisms
that determine what a person pays attention to and for how
long, and its , 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 traits that make a detector
dog. "First, every good detector dog must love praise," she
says, because this is the only tool the trainers have at their
disposal. Then the dog needs a strong hunting instinct, and
the strength 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 "selective attention". 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 "sustained attention".
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 percent of the difference between dogs in their ability
to pay attention. That's 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,
"the success
of the breeding programme jumped way beyond our expectations,"
says Champness. "We hoped that 30 percent of the pups from
the programme would become detector dogs, but the actual
success rate consistently exceeds 50 percent."
Vandeloo and Champness assess the dog's 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 pad dock.
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's ability to pay attention, like
a dog's, depends on a number of overlapping cognitive behaviours,
including memory and learning—the neurobiologists' 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
"vigilance test". 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 detector dogs 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's prefrontal
are especially important for attentional processing. Trevor
Robins, an experiment psychologist at the University of Cambridge,
explains that in humans "when a task gets difficult, the anterior
[in the frontal lobe of the brain] seems
to work overtime". 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 "executive"
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's arousal centres and are located below the cortex.
The prefrontal cortex provides the lion's share of the brain's
neuronal input to these areas, and the whole cortex receives
a lot of stimulation from the brainstem and the basal forebrain
via neurons that feed its 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—"it may turn the volume up and down".
Although the prefrontal cortex is obviously
vital to an animal's ability to focus its attention, researchers
are divided over the exact nature of its role. Neuroscientists
like Raja Parasuraman 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.
"Memory [also] plays an absolutely critical
and essential role in guiding attention," says Robert Desimone,
who studies the link between memory and attention, 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 of keys, he says. The search begins in the prefrontal
cortex, where neurons process the goal "find keys". These
neurons make connection 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.Desmone's
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 distracting images.
"The end result is conscious perceptual awareness
of the thing that is important right then, and unawareness
of the things that aren't important," 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 lost keys, for example, is driven
by the goal of finding the keys, or "top-down" 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 "bottom-up" effects are based
solely on the properties of the stimulus itself and the brain's
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't 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 "consistently and surprisingly
show very substantial genetic influences—in the order of
60 per cent heritability". 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 range of different defects
that come under one .
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.
"At the behavioural level," says Plomin,
"humans
are much closer to dogs than to [rodents]." Rats are one of
the favourite animals in which to study attentional processing.
"Dogs are [also] more trainable than [rodents]," 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's
super-detector dogs aren't still very useful. During their
first year of operation, the dogs made 1 500 drug seizures,
including one 5-tonne load of cannabis in a shipping container
and a smaller load concealed in condoms inside a smuggler's
stomach.
(2 050 words)
(From New Scientist, 10 May 1997 )
Text
|
