Posts Tagged ‘entorhinal cortex’

Amnestic Mild Cognitive Impairment

September 21, 2019

This post is based on an important book by Scott D. Slotnick titled “Cognitive Neuroscience of Memory.” Remember to consult the website http://www.brainfacts.org/
to see the anatomical information referred to in this post.

Amnestic mild cognitive impairment (aMCI) occurs in a small but significant percentage of adults who are older than 60 years of age, with incidence increasing as a function of age. Approximately 50% of these cases will become Alzheimer’s sufferers. Individuals with aMCI have a selective impairment in long-term memory as compared to healthy age-matched control participants, and are unimpaired in other cognitive domains. There is an increasing body of evidence indicating that the long-term memory impairment in aMCI patients is due to atrophy of medial temporal lobe sub regions that is increased by a paradoxical increase in fMRI activity within the medial temporal lobe.

Structural MRI was used to compare the size of the hippocampus and the entorhinal cortex in aMCI patients and control participants. aMCI patients had a smaller hippocampal value and a smaller entorhinal cortex volume in both hemispheres as compared to age-matched control participants, indicating atrophy of these regions. In addition, the white matter pathway between the entorhinal cortex and the hippocampus had a smaller volume in aMCI patients than control participants, and this was the only white matter region in the entire brain that differed in volume. These results indicate that the long-term memory impairments in aMCI patients are due to isolated atrophy in the entorhinal cortex and the hippocampus.

A relatively higher magnitude of fMRI activity within the CA3/DG sub-region during a pattern separation task reflects a non-compensatory change in processing related to neural disruption in aMCI patients.

Navigation

January 6, 2019

A large part of this post is based on Helen Thomson’s book, “Unthinkable: An Extraordinary Journey Through the World’s Strangest Brains.” We have two basic means of navigation. One is to have specific landmarks that tell us what to do at that landmark. And the other is to have a map of the area of interest in our mind, a mental map. Although GPS’s might have an analogue of a mental map in the database they are interrogating, the instructions they provide to the user is a series of instructions as what to do when you arrive at what point. Point to point instructions are fine until you get lost or redirected and need to find an alternative route.

At one time cab drivers in London were tested on whether they had stored a mental map of London in the brains. It took years of study to pass this test, but to get the desired license they needed to memorize twenty-five thousand roads within a six-mile radius of Charing Cross station. An interesting and important question was if this knowledge affected their brains, and if so, which part of their brain. To answer this question, Eleanor Maguire scanned the brains of 79 trainee taxi drivers several times over four years as they began to learn what is called the Knowledge. Those who passed the test had a bigger posterior hippocampus than when they started, whereas there were no changes in trainee taxi drivers who had failed their exams or in 31 people whose age, education and intelligence were similar to the taxi drivers’, but who had never attempted to learn the Knowledge. Clearly, the hipppocampi were growing alongside navigational abilities.

How the hippocampus learns to navigate was done buy using rats as subjects. O’Keene placed a set of thin electrodes into their hippocampi, which could record the little spike of electricity that occurs when an individual neuron is communicating with its neighbors. O’keene discovered a type of cell that fired only when the animal was in a specific location. Each time the rat passed through this location—pop!—that cell would fire. A nearby cell seemed to care only about a different location. Pop! It would fire whenever the rat walked through that location. The next cell would respond only to another location, and so on. The combination of activity of many of these cells could tell you exactly where that rat was to within five square cm. O’keene named them place cells and showed how together they told the rest of the brain.

Place cells don’t do this job alone. They receive input from three other kinds of cells in a nearby region called the entorhinal cortex. One type of cell is called a grid cell, and was discovered by May-Britt Moser and Edvard Moser. The Mosers realized that our ability to navigate relies on us being able to think about how we are moving and where we have come from. Consider the way you head to the ticket machine in a parking lot and then reverse the movements of your body to return to your car. The Mosers discovered that grid cells were the neurons responsible for integrating this information into our cognitive map.

Our ability to recognize familiar landmarks is so important that there’s a part of the brain that is dedicated to the task.. This is the retrosplenial cortex and when it’s damaged it leads to severe problems in navigating.

Here is something we can do to improve our navigational skills. If you’re in a new area you should return to one point—your home base—often this will help you build a better mental map. You should also pay much more attention to your surroundings, take note of specific landmarks and think about their orientation to one another. And don’t forget to turn around or look backwards from time to time: it’s a trick that animals do to make it easier to recognize their way home.

It is also good to have a fold out map of the area of interest. This is a literal map than can inform your mental map.

What is the Key to LeBron James Phenomenal Performance?

May 24, 2018

And the answer is his superior memory. Sally Jenkins captured this in her article, “How is LeBron James always one move ahead? Let’s ask the scientists” in the 18 May 2018 issue of the Washington Post. She begins, “Much as his brute-strength shoulders and legs define LeBron James, it’s the stuff in his head that elevates him.”

Ms. Jenkins continues, “Much has been made of James show-offy display of memory in his postgame analysis of Game 1. Replay it and notice not just the accuracy but the detail: in narrating six sequences in proper order, he noted the time on the shot clock, who took each shot and missed what, where the ball was inbounded from, and Jayson Tatum’s use of a Euro-step and right hand on a layup. When he was done, listeners broke into applause.

Zach Hambrick, a cognition-performance expert at Michigan State said, “It’s remarkable, but not surprising.” It is not surprising because there is a strong connection between cognitive science and human performance. Hambrick said, “This is one of the bedrock findings in research on human expertise: that experts have superior memory for information within their domain.”

Research has shown what seems to be “photographic memory” is really extrapolation based on habit-worn paths of knowledge, the vestiges and traces left in the brain by experience.

Adriaan de Groot conducted a famous study of chess players in the 1960s. Pieces were shown on a board for five seconds and then removed. The players were asked to recall what they had seen. Novices remembered poorly. The more expert the players, the more pieces they could recall, and the locations of the pieces. An important point in this study, which is frequently not mentioned, is that the superior recall of the experts only occurred when they pieces on the board were placed in a meaningful manner as would be found in a game between experts. If pieces were arranged in a random, nonsensical manner, the masters’ performance differed little from the novices. If so arranged in a meaningful manner, grandmasters could recall virtually everything.

Masters of games don’t just build static memories, but have a remarkable ability to intuit. Ms. Jenkins writes, “James’s anticipation is inseparable from his memory. Ericsson cited a study of elite soccer players where they were shown a game and the screen was halted at an unpredictable point. The best players remembered not only who was where but also predicted where they would go next.

Ms. Jenkins writes, “Think about the processes involved as James scans the court while moving down the floor. The optic nerves absorb and transmit small peripheral details, then shift to a sudden zoom focus as he throws a glancing no-look bounce pass that hits Kevin Love in the hands mid-stride. Then his attention broadens again stereoscopically to capture the whole floor. The cognitive flexibility to go in and out of those states fluidly is highly learned. And yet little short of magic.”

In 2014 researchers John O’Keefe, Maybritt Moser, and Edvard Moser won the Nobel Prize for explaining how the brain navigates. They answered the questions: How do we perceive position, know where we are, find the way home? O’Keefe found a specific cell in the hippocampus that throws off a signal to mark a specific place. The Mosers found that neurons in the entorhinal cortex fire in fields with regularity. When they drew lines corresponding to the neuronal activity they saw a grid. So LeBron James has a geometric projection in his brain that acts as a computation coordinate system. And so do we, but LeBron makes a much more effective use of this system.

There still is the question as to how James’s brain discriminates among multiple similar memories. Andre Fenton has published a possible answer to this question in the journal “Neuron.” The answer is that the “place” signaling is not so much a constant remapping. Actually it is highly synchronized. Think of the neurons in James’s head as birds. Starlings, “Like a flock of starling that takes on different formations while still maintaining cohesion as a flock,” Fenton said. “He’s not recording like a videotape. He’s not rebuilding. He doesn’t rebuild a picture of what is going on. He watches it evolve continuously and fluidly. There is a flock, and it’s moving down the court, and everybody has a place. All these birds form a structure, and the structure is important. We call it a flock. He calls it a play.”

Fenton says that this is actually what all human beings do. HM would add that this is also what many infra human species do. Our brains learn a series of models over our lives and is constantly making predictions.

Phenoms like James are masters of assessing the likelihoods of things. With an amazingly good set of models and expectations—of opponents, of teammates and of how the ball will move, it can look like total omniscience.