杏吧原创

Green death

Animals have a point of clinical death. Do plants, and if they do, how is it determined?

鈥� The concept of clinical death in animals is not as straightforward as you might think. For people, it鈥檚 really just a hard-and-fast legal and medical justification for stopping treatment, because in practice there is a continuum of deterioration, marked by a number of events.

What鈥檚 more, indicators of clinical death in some animals do not necessarily mean the same in others. For instance, cessation of respiration or heartbeat or brain activity is a bad sign in mammals, but in some creatures it is a regular event during hibernation.

In plants the events are less well marked than in animals, but they amount to the same thing. Where wilting, poisoning, disease or starvation exceeds a given intensity, we can say the plant is dead. But you could argue that most of its cells are still alive and that you could culture them and get a new plant, or maybe even clone the same plant. This might be true, but the same applies to any person at the point of clinical death. Most of that person鈥檚 cells are alive and many of them would be good for cloning 鈥� for a while anyway.

Jon Richfield

Somerset West, South Africa

鈥� Some recent research in Switzerland looked at pine trees infected by honey fungus. The fungus invades via the roots and kills the cambium 鈥� the tissue that produces new wood. Once this happens the tree is effectively dead and no tree ever recovers. However, using the parts of the tree that live above the ground to pinpoint the time of death gives a very different answer. In one tree, canopy death was an astonishing 31 years after cambial death. New needles grow and old ones survive, sometimes for many years after the tree is effectively dead. So, when is the tree dead? It all depends on what you mean by dead.

Ken Thompson

Department of Animal and Plant Sciences University of Sheffield, UK

The wonder years

Why don鈥檛 we remember much about our early childhood? In particular, the period from 0 to 5 years seems to be totally forgotten.

鈥� There are two main reasons why you can鈥檛 remember things when you were young.

First, when children are born, they have very little in the way of developed cortex 鈥� the higher processing areas of the brain. These areas develop as you grow, with most of the major growth completed by the age of eight. Long-term memories all start in the hippocampus and ultimately end up in the temporal cortex (although there is still some debate on this process). Because these areas are not fully developed in young children, their early memories can鈥檛 be stored with great accuracy.

Secondly, if you have ever studied memory, you鈥檒l know the things you remember come from the fact they have context and meaning 鈥� I remember my first kiss, because it was my first kiss and I knew it was a kiss. Children have less understanding of the context in which they live, so events tend to carry less meaning and consequently their brains do not retain them.

Dalin Brinkman

Camarillo, California, US

鈥� Few people can remember events in their lives before three or four years of age. Developmental explanations for childhood amnesia focus on the young child鈥檚 cognitive limitations.

A particularly promising explanation for childhood amnesia is the social interaction hypothesis. Adults use language to model and teach the child what autobiographical memory is, how to use it and why it is important. Accordingly, autobiographical memory emerges after the appearance of language, as narrative memory is constructed through parent-child conversations about the past. Parental responsiveness to children鈥檚 needs, including engagement in supportive talk about past, present and future events, influences this autobiographical memory.

Narrative memory first appears at about age two when children begin to talk about the past, but early memory narratives are sparse and usually fail to preserve the causal and temporal structure of complex events. Later, as adults, our attempts to remember may fail because early memories are incompatible with our new purposeful recall efforts.

This ties in with Freud鈥檚 鈥渟elective-reconstruction鈥� model, where early memories remain outside our conscious awareness because of a failure of translation between lower and higher-order levels of cognitive processing. The more sophisticated and elaborate the child鈥檚 narrative memory, the more likely those memories can be accessed later in life through purposeful retrieval efforts.

Annabelle Wilde

Vermont, Victoria, Australia

鈥� The ability to remember much about one鈥檚 early childhood is closely linked to the age at which one has acquired complex language. The earlier a child can use language, the farther back their memory will extend. In other words, memory is closely linked with language, although memory seems to consist of non-verbal scenes or pictures.

This has been a special interest of mine in cognitive psychology since my memory goes back to my second birthday. I found it odd others could not remember equally far back. After researching the subject, I asked my older relatives if I was able to talk well at an early age. They found this question amusing because apparently I did not stop talking from my first birthday until I learned to read 鈥� at which point I was never heard from again.

Thomas J. Martin, Jr

Fair Haven, New Jersey, US

This week鈥檚 questions

Drinking games

My brother, an avid bodybuilder and a far more rigorous self-disciplinarian than I, tells me that a common practice on competition days is to drink alcohol, which causes the muscles to swell temporarily. His tipple of choice is brandy, but it allegedly works with any strong spirit. Is this a genuine phenomenon, and if so, how does it occur?

Brian Palmerstone

Birmingham, UK

Lighting up

When you go to the toilet on an airliner, bolting the door operates the light inside the cubicle. However, after you complete the circuit by sliding the bolt, the light takes a couple of seconds to come on. Why does it do this?

Mick Towne

Washington DC, US