Learning and Memory: location, location, location!
In 1848, an explosion drives a steel tamping bar through the skull of a twenty-five-year-old railroad foreman named Phineas Gage, obliterating a portion of his frontal lobes. He recovers, and seems to possess all his earlier faculties, with one exception: The formerly mild-mannered Gage is now something of a hellion, an impulsive shit-starter. Ipso facto, the frontal lobes must play some function in regulating and restraining our more animalistic instincts.
In 1861, a French neurosurgeon named Pierre-Paul Broca announces that he has found the root of speech articulation in the brain. He bases his discovery on a patient of his, a man with damage to the left hemisphere of his inferior frontal lobe. The man comes to be known as “Monsieur Tan,” because, though he can understand what people say, “tan” is the only syllable he is capable of pronouncing.
Thirteen years later, Carl Wernicke, a German neurologist, describes a patient with damage to his posterior left temporal lobe, a man who speaks fluently but completely nonsensically, unable to form a logical sentence or understand the sentences of others. If “Broca’s area,” as the damaged part of Monsieur Tan’s brain came to be known, was responsible for speech articulation, then “Wernicke’s area” must be responsible for language comprehension.
And so it goes. The broken illuminate the unbroken.
Edit, 5-25-11: There’s been some interesting research on using brain stimulation to aid learning: essentially using tiny amounts of electricity to induce changes in rats’ brains that makethem better learners. After the current is shut off, the rats’ brains go back to normal but they keep their learned skills. We don’t know what the specific trade-offs may be, but between this approach and approaches which could mimic developmental neuroplasticity triggers, we may have the basis for a very desirable form of cognitive enhancement.
Here’s “Scienceblog” on the a theory on how the brain picks which of its neural networks to use for a new skill:
The study by Reed and colleagues supports a theory that large-scale brain changes are not directly responsible for learning, but accelerate learning by creating an expanded pool of neurons from which the brain can select the most efficient, small “network” to accomplish the new skill.
This new view of the brain can be compared to an economy or an ecosystem, rather than a computer, Reed said. Computer networks are designed by engineers and operate using a finite set of rules and solutions to solve problems. The brain, like other natural systems, works by trial and error.
The first step of learning is to create a large set of diverse neurons that are activated by doing the new skill. The second step is to identify a small subset of neurons that can accomplish the necessary computation and return the rest of the neurons to their previous state, so they can be used to learn the next new skill.
By the end of a long period of training, skilled performance is accomplished by small numbers of specialized neurons not by large-scale reorganization of the brain. This research helps explain how brains can learn new skills without interfering with earlier learning.
Edit, 7-28-11: Scientists have traced the recall of a specific memory and found it partially activates other memories from around the same time. Unsurprising, given it’s common to experience memories as strongly linked, but still good science, and perhaps it supports the viewpoint that all memory is ultimately episodic in some real sense.
Researchers have long known that the brain links all kinds of new facts, related or not, when they are learned about the same time. Just as the taste of a cookie and tea can start a cascade of childhood memories, as in Proust, so a recalled bit of history homework can bring to mind a math problem — or a new dessert — from that same night.
For the first time, scientists have recorded traces in the brain of that kind of contextual memory, the ever-shifting kaleidoscope of thoughts and emotions that surrounds every piece of newly learned information. The recordings, taken from the brains of people awaiting surgery for epilepsy, suggest that new memories of even abstract facts — an Italian verb, for example — are encoded in a brain-cell firing sequence that also contains information about what else was happening during and just before the memory was formed, whether a tropical daydream or frustration with the Mets.
The new study suggests that memory is like a streaming video that is bookmarked, both consciously and subconsciously, by facts, scenes, characters and thoughts.
“When you activate one memory, you are reactivating a little bit of what was happening around the time the memory was formed,” Dr. Kahana said[.]
[Nader] began with the simplest question he could think of. While it was clear that new proteins were needed for the making of memories—proteins are cellular bricks and mortar, the basis of any new biological construction—were additional proteins made when those memories were recalled? Nader hypothesized that they were, and he realized that he could test his notion by temporarily blocking protein synthesis in a brain and looking to see if that altered recall. “This is the kind of question you ask when you don’t know how else to approach the subject,” Nader says. “But I had to do something, so why not this?”
His boss, the famed neuroscientist Joseph LeDoux, couldn’t have been more discouraging. “I told Karim he was wasting his time,” LeDoux says. “I didn’t think the experiment would work.” To LeDoux, the reason was obvious: Even if Nader blocked protein synthesis during recall, the original circuitry would still be intact, so the memory should be too. If Nader could induce amnesia, it would be temporary. Once the block was removed, the recall would return as strong as ever. And so LeDoux and Nader made a bet: If Nader failed to permanently erase a set of fear memories in four lab animals, he had to buy LeDoux a bottle of tequila. If it worked, drinks were on LeDoux. “I honestly assumed I’d be spending a bunch of money on alcohol,” Nader says. “Everyone else knew a lot more about the neuroscience of memory. And they all told me it would never work.”
He taught several dozen rats to associate a loud noise with a mild but painful electric shock. It terrified them—whenever the sound played, the rats froze in fear, anticipating the shock. After reinforcing this memory for several weeks, Nader hit the rats with the noise once again, but this time he then injected their brains with a chemical that inhibited protein synthesis. Then he played the sound again. “I couldn’t believe what happened,” Nader says. “The fear memory was gone. The rats had forgotten everything.” The absence of fear persisted even after the injection wore off.
The secret was the timing: If new proteins couldn’t be created during the act of remembering, then the original memory ceased to exist. The erasure was also exceedingly specific. The rats could still learn new associations, and they remained scared of other sounds associated with a shock but that hadn’t been played during the protein block. They forgot only what they’d been forced to remember while under the influence of the protein inhibitor.
The disappearance of the fear memory suggested that every time we think about the past we are delicately transforming its cellular representation in the brain, changing its underlying neural circuitry. It was a stunning discovery: Memories are not formed and then pristinely maintained, as neuroscientists thought; they are formed and then rebuilt every time they’re accessed. “The brain isn’t interested in having a perfect set of memories about the past,” LeDoux says. “Instead, memory comes with a natural updating mechanism, which is how we make sure that the information taking up valuable space inside our head is still useful. That might make our memories less accurate, but it probably also makes them more relevant to the future.”
Likewise, the fact that recalling a memory alters explains not only the efficacy of talk therapy, but suggests the combination of talk therapy and drugs which ‘take the edge off’ or ‘put a little glow on things’ may be significantly better than either alone.
Other scientists have achieved impressive results with less extreme drugs. In 2008, Alain Brunet, a clinical psychologist at McGill University, identified 19 patients who had been suffering for several years from serious stress and anxiety disorders such as PTSD. (Their traumas included sexual assaults, car crashes, and violent muggings.) People in the treatment group were given the drug propranolol, a beta-blocker that has long been used for conditions like high blood pressure and performance anxiety; it inhibits norepinephrine, a neurotransmitter involved in the production of strong emotions. Brunet asked subjects to write a detailed description of their traumatic experiences and then gave them a dose of propranolol. While the subjects were remembering the awful event, the drug suppressed the visceral aspects of their fear response, ensuring that the negative feeling was somewhat contained.
One week later, all the patients returned to the lab and were exposed once again to a description of the traumatic event. Here’s where things got interesting: Subjects who got the placebo demonstrated levels of arousal consistent with PTSD (for example, their heart rate spiked suddenly), but those given propranolol showed significantly lower stress responses. Although they could still remember the event in vivid detail, the emotional memory located in the amygdala had been modified. The fear wasn’t gone, but it no longer seemed crippling. “The results we get sometimes leave me in awe,” Brunet says. “These are people who are unable to lead normal lives, and yet after just a few sessions they become healthy again.”
The potential to use chemical manipulation of memory for ill also seems significant and troubling. E.g., we could consider the scenario where a precision memory-destroying drug like a PKMzeta synthesis inhibitor was slipped into someone’s food then they were asked to “think about how much you love your husband/wife/kids”, or “think about the happiest moment in your life”, or “think about why you want to marry your fiance”, or “think about what gives you meaning and purpose in your life.” There are few drugs which in a single dose could do as much psychological harm as this, administered poorly or maliciously. A sobering thought.