Memory and the Brain
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The most important evidence of the role of the hippocampus in transferring long-term memories has been provided by subjects who had sustained damage to both hippocampi and could not keep things in their memories for more than a few moments. Information is transferred from short-term memory also known as working memory to long-term memory through the hippocampus, so named because its shape resembles the curved tail of a seahorse hippokampos in Greek. The hippocampus is a very old part of the cortex, evolutionarily, and is located in the inner fold of the temporal lobe.
All of the pieces of information decoded in the various sensory areas of the cortex converge in the hippocampus, which then sends them back where they came from. The hippocampus is a bit like a sorting centre where these new sensations are compared with previously recorded ones. When we remember new facts by repeating them or by employing various mnemonic devices , we are actually passing them through the hippocampus several times. The hippocampus keeps strengthening the associations among these new elements until, after a while, it no longer needs to do so.
The cortex will have learned to associate these various properties itself to reconstruct what we call a memory. But the hippocampus and the cortex are not the only structures involved in long-term memory and its various manifestations in the brain.
Neuroanatomy of memory - Wikipedia
Funding for this site is provided by readers like you. Collection of Carol Donner. 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.
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.
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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. 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.
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But the data struck a more harmonious chord with some psychologists. After all, their experiments had long suggested that memory can easily be distorted without people realizing it.
In a classic study led by Elizabeth Loftus, a psychologist then at the University of Washington, researchers showed college students a series of color photographs depicting an accident in which a red Datsun car knocks down a pedestrian in a crosswalk. The students answered various questions, some of which were intentionally misleading.
Later the researchers asked all the students what they had seen—a stop sign or yield sign? To Nader and his colleagues, the experiment supports the idea that a memory is re-formed in the process of calling it up. Hardt and Nader say something similar might happen with flashbulb memories. People tend to have accurate memories for the basic facts of a momentous event—for example, that a total of four planes were hijacked in the September 11 attacks—but often misremember personal details such as where they were and what they were doing at the time.
Hardt says this could be because these are two different types of memories that get reactivated in different situations. Television and other media coverage reinforce the central facts.
Neuroanatomy of memory
But recalling the experience to other people may allow distortions to creep in. Some experts think he is getting ahead of himself, especially when he makes connections between human memory and these findings in rats and other animals. Daniel Schacter, a psychologist at Harvard University who studies memory, agrees with Nader that distortions can occur when people reactivate memories. The question is whether reconsolidation—which he thinks Nader has demonstrated compellingly in rat experiments—is the reason for the distortions.
Alain Brunet, a psychologist, is running a clinical trial involving people with post-traumatic stress disorder PTSD. The hope is that caregivers might be able to weaken the hold of traumatic memories that haunt patients during the day and invade their dreams at night. Brunet knows how powerful traumatic memories can be. He decided to study traumatic stress and how to treat it.
Even now, Brunet says, the drugs and psychotherapy conventionally used to treat PTSD do not provide lasting relief for many patients. The drug, propranolol, has long been used to treat high blood pressure, and some performers take it to combat stage fright.
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The drug inhibits a neurotransmitter called norepinephrine. One possible side effect of the drug is memory loss. They began a therapy session sitting alone in a nondescript room with a well-worn armchair and a television.
But where do these memories come from and how do they get made? 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. The basal ganglia are a group of nuclei which are located in the medial temporal lobe, above the thalamus and connected to the cerebral cortex. If so, the study would contradict the standard conception of memory. When we want to access a memory from the dark recesses of our brain, signals from our frontal cortex link to that memory via uncertain means, and the memory is reconstructed from the information available.
Nine patients took a propranolol pill and read or watched TV for an hour as the drug took effect. Ten were given a placebo pill. Brunet came into the room and made small talk before telling the patient he had a request: The patients, all volunteers, knew that the reading would be part of the experiment. A week later, the PTSD patients listened to the script, this time without taking the drug or a placebo.
Compared with the patients who had taken a placebo, those who had taken the propranolol a week earlier were now calmer; they had a smaller uptick in their heart rate and they perspired less. Brunet has just completed a larger study with nearly 70 PTSD patients.