Stripping Down Science (24 page)

To resolve this problem, three Australian researchers – Helen Christensen, Liana Leach and Andrew Mackinnon
⁸⁰
– have now carried out a longitudinal study in which participants are followed up over a long period of time to look for
‘before and after' changes in relation to various lifestyle factors, including having children. The Australian team contacted 1241 women who had been enrolled in a study called the Personality and Total Health (PATH) Through Life Project, a community survey concerned with health and wellbeing. These subjects had joined the study in 1999 when they were between 20 and 24 years of age. At this time, baseline measurements of cognitive speed, working memory and immediate and delayed recall abilities were collected. The women were then reassessed using the same parameters in 2004 and 2007, five and eight years later.

Over this timeframe, more than 250 of the enrolled women had become pregnant and had children, which meant that Christensen and her colleagues could directly compare an individual woman's cognitive performance before, in some cases during and also after pregnancy. Reassuringly, the study didn't find any significant pre- and post-pregnancy cognitive differences between the participants in any of the tests. One significant difference was detected – a small drop in cognitive speed amongst women who were pregnant at the time – but this only emerged
when the pregnant cases were split up into two subgroups – early and late pregnancy – which means that it could be statistically unreliable.

Instead, it's much more likely that women succumb to dodgy dogma and think themselves into a cognitive corner while they're pregnant, rather than suffering any real reduction in mental processing power. This was also the conclusion of another researcher from the University of Sunderland, Ros Crawley.
⁸¹
She asked a mixture of people, including men and women, both with and without children, how they thought women
were affected by pregnancy. Amongst all the groups who replied, the responses indicated the clear belief that cognitive abilities decline during pregnancy. She also asked pregnant women to rate whether they felt their cognitive prowess, including their driving abilities, had been dented during gestation. This elicited a significant ‘yes' response compared with non-pregnant women.

Predictably, however, when she tested the same subjects using memory tests and a driving simulator task during which they had to react quickly when a vehicle in front stopped, or pull out safely from a junction into a stream of traffic, the pregnant women performed as well as the non-pregnant participants. (Although, admittedly, driving along with the indicators on or the handbrake still applied were not assessed.)

The moral of the story is that it's probably not the pregnancy brain drain that we should be worried about so much as the wallet drain that inevitably ensues once the baby is born …

It's often said that fish have a microsecond memory, with every lap of the tank representing a fresh foray into uncharted waters. Nor does Disney do fish any favours with its box office smash
Finding Nemo
telling the story of Dory, a Regal Tang with a memory problem. However, a trawl through the published literature reveals that fish probably have much better memories than we first thought, and are also adept at social networking, educating each other, slipping through nets, categorising music and even learning online (on fishing line, that is, because after they've been hooked once, it turns out that they're much less likely to make the same mistake again, assuming they survive the experience).

One very elegant experiment to showcase these skills in action was carried out by Culum Brown, a marine researcher now based at Macquarie
University in Sydney.
⁸²
He engineered a net that contained an escape route. This was swept along the length of a tank housing groups of five spotted rainbowfish, which had been collected previously from Amamoor Creek in Queensland. Over a series of trials, he timed how long it took the fish, once they entered the net, to find the hole and to escape. After just five goes at the task, which took less than 15 minutes, the fish had almost halved the time it was taking them to escape, which is hard to reconcile with an allegedly cerebrally challenged animal.

Even more convincing was that when the same fish were re-tested 11 months later, having not seen the apparatus in the interim, they all escaped as quickly as they had when fully trained previously, indicating that they must have remembered the way out from before. For a species that only lives for a few years and apparently has a memory deficit, that's pretty impressive recall!

Fish also appear to have a musical side, as revealed by Ava Chase, from the Rowland Institute for Science in Massachusetts, US,
⁸³
who
successfully trained three carp to discriminate between blues and classical music played through a speaker submerged in their tank. Ironically, the blues tracks she chose were by John Lee Hooker, but this still proved highly catchy with the three koi study subjects – Beauty, Oro and Pepi – who could all accurately tell, by pressing a button with their mouths in return for a food reward, classical genres (including both baroque and non-baroque composers like Mozart, Beethoven and Schubert) from blues numbers. Incredibly, the fish could also correctly categorise music they'd not heard previously, although they did initially struggle with a series of Vivaldi guitar concertos. This was remedied by switching on a sound filter to screen out low frequencies around 200 Hz, which seemed to be distracting the fish, possibly by stimulating their ‘lateral lines', sense organs which pick up low-frequency vibrations from water.

This sensitivity of fish to sound has led some scientists to investigate the possibility of using sonic techniques to make them easier to catch. Plymouth University psychologist Phil Gee
⁸⁴
has recently been working with the UK's National
Marine Aquarium to train Bentley, a metre-long, six-year-old giant humphead wrasse, to swim into a special holding area connected to his main swimming tank at meal times. The dinner bell consists of simply banging on the door of the tank, and the fish responds because it has learned, rather like the piscine equivalent of Pavlov's dogs, that it gets a reward whenever it cooperates. As further evidence that fish don't forget, when the training schedule was interrupted by maintenance work being carried out on his tank, Bentley still performed faultlessly after a gap of four months.

Phil Gee has also reported previously, using goldfish from a garden centre, that the animals can be trained to press a lever to release food rewards. Even more cunningly, when the lever was rigged to feed the fish only at a certain time of day, the fish all learned to press the lever solely when it would reward them, indicating that they can also keep track of time.

This tallies with what fish owners report themselves, which is that fish in home aquaria and ponds seem to know when it's feeding time and swim to the side of the tank in anticipation of a meal. As a result, researchers are now testing whether it's possible to use these observations
to set up free-range pisciculture (fish farming) systems which can rely on sounds to ‘call in' the fish at feeding (and harvesting) time. This could save Third World fishermen a fortune in expensive equipment if it can be made to work. So far, tests have taken place in Norway and a pilot study has been set up in Ghana. There's been no word yet, however, regarding whether this scientific splash will actually work or just turn out to be a belly-flop …

So, far from being forgetful, fish appear to have a ‘carp-acious' appetite for learning and memory and even a taste for music. Whether it goes as far as ‘back to my plaice' for some ‘drum' and ‘bass' remains to be seen!

‘TACKLE' BOX

Ecological significance of fish memory

Apart from being able to spot when it's dinner time or remember the best places to hide in their home ranges, researchers have also shown that fish do most of their learning by watching each other. This was demonstrated recently by Durham University scientist Jeremy Kendal
⁸⁵
using 270 sticklebacks (known non-scientifically as ‘tiddlers') he had caught in a local river in Leicester.

In the laboratory, small groups of the fish were placed in a tank equipped with feeders at either end, one of which dished out generous portions of bloodworms, which the fish love to eat, while the other was much stingier in its offerings. The fish quite quickly learned the drill, showing a strong preference for the more generous feeder. At this point, they were then confined within a ‘viewing gallery' section
of the tank while a new group of fish were introduced.

As an added twist, this time the scientists reversed the feeders so that the previously generous one was now stingy and vice versa. While this was going on, the confined ‘educated' sticklebacks were left to watch how the newly introduced fish fared. Afterwards, the viewing fish were released again so the team could observe which of the two feeders they now favoured.

Incredibly, just by watching how the other fish had got on, over 75% of the observing fish had learned that the feeder situation had reversed, which they demonstrated by making a beeline straight to the opposite end of the tank. More impressive still was that in a subsequent experiment when the team adjusted the relative generosity of the feeders, the observing fish changed their behaviour only if they saw the other fish doing better in the new situation than they had in the old one.

This kind of learning approach, known as a ‘hill climbing strategy', is probably key
to helping these animals to escape from predators. ‘These fish are too vulnerable to forage alone,' explains Kendal, ‘so they have to move around in groups. They are therefore social, and by watching the outcomes of others, and responding appropriately, this is a sound strategy to avoid predation and maximise returns.'

This social learning strategy also suggests that, in the same way that human culture passes down knowledge and learning – such as how to read, write and count – from one generation to the next, fish and other animals may have a similar set-up. Knowledge of the best feeding grounds, the best breeding grounds and the best migration routes is perhaps actually being passed non-genetically amongst members of a population.

This could partly explain, Culum Brown points out, why Atlantic stocks of cod have collapsed so severely – because the big fish with all the know-how have ended up on people's dinner plates, taking their life experiences with them.

One of Aesop's famous fables tells of a thirsty crow that, unable to push over a pitcher of water or reach down to the liquid inside, drops in stones until the level rises to within a beak's-length of the top, enabling the bird to take a refreshing drink. The story seeks to emphasise the importance of brains over brute force and was thought to be just that – a story. But now scientists have shown that at least one member of the crow family really can do this, proving that it's a myth that this Aesop's fable is a fable.