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Do the pigeons recognise the hand that feeds them?
Memory in its simplest form is as ancient as life itself. But do other creatures remember like we do, asks Emma Young
E
VERY morning, you take a walk in the park, bringing some bread to feed the pigeons. As the days wear on, you begin to see the birds as individuals; you even start to name them. But what do the pigeons remember of you? Do they think kindly of you as they drop off to sleep at night, or is your face a blank, indistinguishable from the others strolling through the park? These questions may seem whimsical, but knowing what other creatures recall is crucial if we are to understand their inner lives. It turns out that the range of mnemonic feats in the wild is nearly as varied as life itself. If you take memory to mean any ability to store and respond to past events, even the simplest organisms meet the grade. Blobs of slime mould, for instance, which can slowly crawl across a surface, seem to note the timing of changes to their climate, slowing their movement in anticipation of an expected dry spell – even when it never actually arrives. With the emergence of the first neurons about half a billion years ago, memories became more intricate as information could be stored in the patterns of electrical connections within the nervous system (see “The making of a memory”, right). This type of learning may have been behind the Cambrian explosion – the sudden appearance and rapid evolution of more complex species about 530 million years ago – because it enabled animals to exploit new niches, say Eva Jablonka at Tel Aviv University and Simona Ginsburg at the Open University of Israel. Over the following few hundred million years, increasingly advanced skills could emerge with different forces driving the evolution of each creature’s mind. The result is a surprising range of mnemonic feats throughout the animal kingdom. Migratory cardinal fish, for instance, can remember where they laid their eggs during the breeding season and, after over-wintering in deep
34 | NewScientist | 6 October 2012
Hey, it’s that guy with the bread again
The making of a memory When we talk about memory, we can mean many things. In the short term, we use our working memory to juggle small lists of information, such as a round of drinks. These are held in fleeting changes in the brain’s electrical or chemical activity that quickly fade as the mind wanders. Long-term memories, in contrast, can last a lifetime. They can be classed as semantic memories of facts, or episodic memories of events. Psychologists also refer to autobiographical memories, which include the episodic and semantic memories that relate to our life story. All these different kinds of long-term memories are woven into the webs of connections between brain cells. By the creation of new receptors at the end of a neuron, by a surge in the production of a neurotransmitter, or by the forging of new ion channels that allows a brain cell to boost the voltage of its signals, the brain alters the communication between networks of cells.
As a result, the same pattern of neurons will fire when we recall the memory, bringing the thought back into our consciousness. Many brain regions are involved in this process, but the hippocampus, near the base of the brain, is considered to be especially important in consolidating our memories. Ultimately, these changes to the neural network are probably stored semi-permanently through epigenetic changes, which involve small alterations to the structure of a gene and determine its activity within the cell. Certain genes linked to the formation of memories have been shown to have fewer methyl groups attached to their DNA after learning, for instance – a clear example of an epigenetic change. But the brain is not like a video camera. Every time we recall a memory, new proteins are made and the epigenetic markers will alter – changing it in subtle ways.
SHORT-TERM MEMORY
7 pieces of
1
information
2
3
7
6 5
at any one time, be it shapes, names, colours or numbers
4
If the brain processed binary information like a computer, with each synapse holding a single bit of information, we could store roughly
LONG-TERM MEMORY
12,000 GB
You could hold a 700-page book like Moby Dick nearly 10 million times, or 2.5 million songs
or
10m
2.5m
Speed and motivation are probably our biggest limits. Memorising a substantial work of literature word for word can take
years decades SHORT-TERM MEMORY
or even
A mid-range computer may
6GB
hold in its random access memory (RAM), many million times more than human short-term memory A computer hard drive stores data by magnetising sections of a ferromagnetic disk. On a computer with a
500GB
hard drive, you could store Moby Dick 400,000 times
01100110 101 001101 001110100 101011100
k ic D
LONG-TERM MEMORY
matt jacob/tendance floue
We can remember about
by o M
Emma Young is a writer based in Sheffield, UK
Just how do our memories compare to today’s PCs?
k ic D
”Santino the chimp collects and hides rocks to later throw at visitors”
Us vs the machines
by o M
water, return to within half a metre of the same spot. Animals as diverse as lizards, bees and octopuses can learn the way out of a maze, and pigeons have an excellent visual recognition, learning to recognise more than a thousand different images. They can even recognise individual humans and aren’t fooled by a change of clothes. Such skills, although impressive, don’t match our experiences of episodic memory, in which we immerse ourselves in specific events. A pigeon might learn to associate your face with food, but it probably can’t remember your last meeting in the way you might be able to recall details of your last trip to the park. It is an important distinction, because episodic memory is thought to allow us to
imagine and plan for the future. This skill, known as mental time travel, was long thought to be unique to humans, but there are now some signs that a handful of other species might also be able to escape the present. Some of the most convincing evidence comes from Nicola Clayton and Sergio Correia at the University of Cambridge, who have shown that western scrub jays can learn from their experiences to anticipate the actions of other birds. If one bird knows that another is watching it bury its food, for instance, it will later move the stash, presumably to prevent it from being stolen. But they will only do this if they have previously stolen food themselves – suggesting that they were drawing on their memories while forming the plan. Similar studies have suggested that bonobos and orang-utans are also capable of mental time travel. Initially, the work attracted a lot of scepticism from researchers like Michael Corballis at the University of Auckland, New Zealand, who believed that the results could be explained by a complex kind of classical conditioning, for instance. But some recent work has begun to change his mind. He points to a study of activity in the hippocampuses of rats, which suggests that they replay their movements through a maze, and may even imagine future paths that they could take. He is also impressed by Santino, a chimp at Furuvik Zoo in Sweden that collects and hides rocks to throw at visitors, using premeditation that would rely on episodic memory. Unfortunately, so few animals have been studied that it is difficult to pinpoint exactly when this skill emerged, though the researchers suspect that it evolved separately in the different lineages, rather than emerging in one of our common ancestors. Thomas Suddendorf at the University of Queensland in Australia is less willing to accept that animal memories rival our own. He proposes that episodic memory depends on a host of different components, and although some animals may be able to use limited foresight when it comes to food, for instance, only humans demonstrate the kind of capacity and flexibility that can allow us to imagine all kinds of futures. “These simulations allow us to plan, prepare for and deliberately shape the future, like no other animal appears to do,” Suddendorf says. Santino might be able to plan a rock attack – but he could not plan anything so conniving as a bid for freedom. n
400,000
A computer can lay down memories astonishingly quickly – absorbing Moby Dick in about
0.5 seconds
6 October 2012 | NewScientist | 35
E
VERY morning, you take a walk in the park, bringing some bread to feed the pigeons. As the days wear on, you begin to see the birds as individuals; you even start to name them. But what do the pigeons remember of you? Do they think kindly of you as they drop off to sleep at night, or is your face a blank, indistinguishable from the others strolling through the park? These questions may seem whimsical, but knowing what other creatures recall is crucial if we are to understand their inner lives. It turns out that the range of mnemonic feats in the wild is nearly as varied as life itself. If you take memory to mean any ability to store and respond to past events, even the simplest organisms meet the grade. Blobs of slime mould, for instance, which can slowly crawl across a surface, seem to note the timing of changes to their climate, slowing their movement in anticipation of an expected dry spell – even when it never actually arrives. With the emergence of the first neurons about half a billion years ago, memories became more intricate as information could be stored in the patterns of electrical connections within the nervous system (see “The making of a memory”, right). This type of learning may have been behind the Cambrian explosion – the sudden appearance and rapid evolution of more complex species about 530 million years ago – because it enabled animals to exploit new niches, say Eva Jablonka at Tel Aviv University and Simona Ginsburg at the Open University of Israel. Over the following few hundred million years, increasingly advanced skills could emerge with different forces driving the evolution of each creature’s mind. The result is a surprising range of mnemonic feats throughout the animal kingdom. Migratory cardinal fish, for instance, can remember where they laid their eggs during the breeding season and, after over-wintering in deep
34 | NewScientist | 6 October 2012
Hey, it’s that guy with the bread again
The making of a memory When we talk about memory, we can mean many things. In the short term, we use our working memory to juggle small lists of information, such as a round of drinks. These are held in fleeting changes in the brain’s electrical or chemical activity that quickly fade as the mind wanders. Long-term memories, in contrast, can last a lifetime. They can be classed as semantic memories of facts, or episodic memories of events. Psychologists also refer to autobiographical memories, which include the episodic and semantic memories that relate to our life story. All these different kinds of long-term memories are woven into the webs of connections between brain cells. By the creation of new receptors at the end of a neuron, by a surge in the production of a neurotransmitter, or by the forging of new ion channels that allows a brain cell to boost the voltage of its signals, the brain alters the communication between networks of cells.
As a result, the same pattern of neurons will fire when we recall the memory, bringing the thought back into our consciousness. Many brain regions are involved in this process, but the hippocampus, near the base of the brain, is considered to be especially important in consolidating our memories. Ultimately, these changes to the neural network are probably stored semi-permanently through epigenetic changes, which involve small alterations to the structure of a gene and determine its activity within the cell. Certain genes linked to the formation of memories have been shown to have fewer methyl groups attached to their DNA after learning, for instance – a clear example of an epigenetic change. But the brain is not like a video camera. Every time we recall a memory, new proteins are made and the epigenetic markers will alter – changing it in subtle ways.
SHORT-TERM MEMORY
7 pieces of
1
information
2
3
7
6 5
at any one time, be it shapes, names, colours or numbers
4
If the brain processed binary information like a computer, with each synapse holding a single bit of information, we could store roughly
LONG-TERM MEMORY
12,000 GB
You could hold a 700-page book like Moby Dick nearly 10 million times, or 2.5 million songs
or
10m
2.5m
Speed and motivation are probably our biggest limits. Memorising a substantial work of literature word for word can take
years decades SHORT-TERM MEMORY
or even
A mid-range computer may
6GB
hold in its random access memory (RAM), many million times more than human short-term memory A computer hard drive stores data by magnetising sections of a ferromagnetic disk. On a computer with a
500GB
hard drive, you could store Moby Dick 400,000 times
01100110 101 001101 001110100 101011100
k ic D
LONG-TERM MEMORY
matt jacob/tendance floue
We can remember about
by o M
Emma Young is a writer based in Sheffield, UK
Just how do our memories compare to today’s PCs?
k ic D
”Santino the chimp collects and hides rocks to later throw at visitors”
Us vs the machines
by o M
water, return to within half a metre of the same spot. Animals as diverse as lizards, bees and octopuses can learn the way out of a maze, and pigeons have an excellent visual recognition, learning to recognise more than a thousand different images. They can even recognise individual humans and aren’t fooled by a change of clothes. Such skills, although impressive, don’t match our experiences of episodic memory, in which we immerse ourselves in specific events. A pigeon might learn to associate your face with food, but it probably can’t remember your last meeting in the way you might be able to recall details of your last trip to the park. It is an important distinction, because episodic memory is thought to allow us to
imagine and plan for the future. This skill, known as mental time travel, was long thought to be unique to humans, but there are now some signs that a handful of other species might also be able to escape the present. Some of the most convincing evidence comes from Nicola Clayton and Sergio Correia at the University of Cambridge, who have shown that western scrub jays can learn from their experiences to anticipate the actions of other birds. If one bird knows that another is watching it bury its food, for instance, it will later move the stash, presumably to prevent it from being stolen. But they will only do this if they have previously stolen food themselves – suggesting that they were drawing on their memories while forming the plan. Similar studies have suggested that bonobos and orang-utans are also capable of mental time travel. Initially, the work attracted a lot of scepticism from researchers like Michael Corballis at the University of Auckland, New Zealand, who believed that the results could be explained by a complex kind of classical conditioning, for instance. But some recent work has begun to change his mind. He points to a study of activity in the hippocampuses of rats, which suggests that they replay their movements through a maze, and may even imagine future paths that they could take. He is also impressed by Santino, a chimp at Furuvik Zoo in Sweden that collects and hides rocks to throw at visitors, using premeditation that would rely on episodic memory. Unfortunately, so few animals have been studied that it is difficult to pinpoint exactly when this skill emerged, though the researchers suspect that it evolved separately in the different lineages, rather than emerging in one of our common ancestors. Thomas Suddendorf at the University of Queensland in Australia is less willing to accept that animal memories rival our own. He proposes that episodic memory depends on a host of different components, and although some animals may be able to use limited foresight when it comes to food, for instance, only humans demonstrate the kind of capacity and flexibility that can allow us to imagine all kinds of futures. “These simulations allow us to plan, prepare for and deliberately shape the future, like no other animal appears to do,” Suddendorf says. Santino might be able to plan a rock attack – but he could not plan anything so conniving as a bid for freedom. n
400,000
A computer can lay down memories astonishingly quickly – absorbing Moby Dick in about
0.5 seconds
6 October 2012 | NewScientist | 35