He flipped the radio on while getting ready to go to work and heard the banter of the morning disc jockeys turn panicky as they related the events unfolding in Lower Manhattan. Nader ran to the roof of his apartment building, where he had a view of the towers less than two miles away. This is the wrong movie. In the following days, Nader recalls, he passed through subway stations where walls were covered with notes and photographs left by people searching desperately for missing loved ones.
Like millions of people, Nader has vivid and emotional memories of the September 11, , attacks and their aftermath. But as an expert on memory, and, in particular, on the malleability of memory, he knows better than to fully trust his recollections. Most people have so-called flashbulb memories of where they were and what they were doing when something momentous happened: the assassination of President John F.
Kennedy, say, or the explosion of the space shuttle Challenger.
Unfortunately, staggeringly terrible news seems to come out of the blue more often than staggeringly good news. But as clear and detailed as these memories feel, psychologists find they are surprisingly inaccurate. Nader, now a neuroscientist at McGill University in Montreal, says his memory of the World Trade Center attack has played a few tricks on him.
He recalled seeing television footage on September 11 of the first plane hitting the north tower of the World Trade Center. But he was surprised to learn that such footage aired for the first time the following day. Nader believes he may have an explanation for such quirks of memory. His ideas are unconventional within neuroscience, and they have caused researchers to reconsider some of their most basic assumptions about how memory works.
In short, Nader believes that the very act of remembering can change our memories. Much of his research is on rats, but he says the same basic principles apply to human memory as well. In fact, he says, it may be impossible for humans or any other animal to bring a memory to mind without altering it in some way.
Memories surrounding a major event like September 11 might be especially susceptible, he says, because we tend to replay them over and over in our minds and in conversation with others—with each repetition having the potential to alter them. For those of us who cherish our memories and like to think they are an accurate record of our history, the idea that memory is fundamentally malleable is more than a little disturbing. Not all researchers believe Nader has proved that the process of remembering itself can alter memories.
But if he is right, it may not be an entirely bad thing. It might even be possible to put the phenomenon to good use to reduce the suffering of people with post-traumatic stress disorder, who are plagued by recurring memories of events they wish they could put behind them.
Nader was born in Cairo, Egypt. His Coptic Christian family faced persecution at the hands of Arab nationalists and fled to Canada in , when he was 4 years old. He attended college and graduate school at the University of Toronto, and in joined the New York University lab of Joseph LeDoux, a distinguished neuroscientist who studies how emotions influence memory.
Even the most cherished ideas in a given field are open to question. Scientists have long known that recording a memory requires adjusting the connections between neurons. Each memory tweaks some tiny subset of the neurons in the brain the human brain has billion neurons in all , changing the way they communicate.
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Neurons send messages to one another across narrow gaps called synapses. A synapse is like a bustling port, complete with machinery for sending and receiving cargo—neurotransmitters, specialized chemicals that convey signals between neurons. All of the shipping machinery is built from proteins, the basic building blocks of cells.
One of the scientists who has done the most to illuminate the way memory works on the microscopic scale is Eric Kandel, a neuroscientist at Columbia University in New York City. In five decades of research, Kandel has shown how short-term memories—those lasting a few minutes—involve relatively quick and simple chemical changes to the synapse that make it work more efficiently. But after the memory is consolidated, it changes very little. Nader would challenge this idea. Nader got to wondering about what happens when a memory is recalled.
Researchers had found that a memory could be weakened if they gave an animal an electric shock or a drug that interferes with a particular neurotransmitter just after they prompted the animal to recall the memory.
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This suggested that memories were vulnerable to disruption even after they had been consolidated. To think of it another way, the work suggested that filing an old memory away for long-term storage after it had been recalled was surprisingly similar to creating it the first time.
Both building a new memory and tucking away an old one presumably involved building proteins at the synapse. Nader decided to revisit the concept with an experiment. That was easy—rodents learn such pairings after being exposed to them just once. Afterward, the rat freezes in place when it hears the tone.
But if memories have to be at least partially rebuilt every time they are recalled—down to the synthesizing of fresh neuronal proteins—rats given the drug might later respond as if they had never learned to fear the tone and would ignore it. If so, the study would contradict the standard conception of memory. It was, he admits, a long shot. Nader, who looks slightly devilish in his earring and pointed sideburns, still gets giddy talking about the experiment. But the data struck a more harmonious chord with some psychologists. How does the brain create a representation of an object, like an apple, from multisensory information?
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This question is crucial since these representations are the basis for higher cognitive processes such as category formation, reasoning and language. One of our goals is to develop a "deep learning" neuronal network that learns to recognize objects and functions in a way similar to real neurobiological systems. One of the deepest unsolved problems in science is the nature of consciousness - how is consciousness generated by the brain?
There are several clinical and ethical problems that limit how we can address this question, such as assessing the level of consciousness in patients following brain injury. Novel ways to measure consciousness levels will make clinicians less dependent on purely behavioural measurements; this will benefit, for example, coma patients.
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Similarly, how can disparate phenomena such as sleep and wakefulness emerge from the same cortico-thalamic systems in the brain? To answer this question, we will investigate slow-wave activity and simulations of large populations of firing neurons in mice and humans. Episodic memories are our personal, conscious experiences set within space and time. All the information gathered from these rigs can help researchers identify neurons that might play a special role in making the human mind.
Such scrutiny, for instance, revealed what researchers think is a rare cell called a von Economo neuron, named for the Austrian neurologist who first described the cell type in the s. The extra-long, extra-spindly neuron was found in live brain tissue donated by a year-old woman who had surgery to remove a tumor. The neuron displayed an unusual electrical response to the current applied to it , Allen Institute scientists and colleagues reported online May 7 at bioRxiv. Studies on live human cells also turned up an important difference between humans and mice: A certain kind of human neuron is covered with a protein called an h-channel; in mice, those channels are rare.
H-channels help cells respond to electrical signals and can be affected by drugs, including one for epilepsy. This basic difference, described in in Neuron , might explain why certain kinds of drugs work differently in the brains of mice and people. More broadly, these newly discovered properties of human neurons might be the things that enable some of the most sophisticated features of our brains.
Allen Institute scientists fly into action when a brain sample arrives from a nearby hospital, wringing as much information as they can out of the precious tissue. Every fifth slice is fixed in preservative. The rest are kept alive for more same-day experiments. The cells glow for better visibility.
The overall number of cell types in the human cortex and in the mouse cortex is roughly the same, says a study led by Allen Institute researchers that is in press at Nature. But the fact that the overall resident population of the human brain and mouse brain is remarkably similar — based on brain tissue from surgeries as well as postmortem tissue — adds to the list of blows to the human ego.
First, Darwin downgraded humans to just another animal on the tree of life.
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