AP Biology class blog for discussing current research in Biology

Tag: Hippocampus

The Discovery of Time Cells and Their Time Stamps

Have you ever wondered how we remember things, how we know one event followed another, how we are able to chronologically compartmentalize our memories? A recent article on a study published this summer in the Journal of Neuroscience reveals that time cells found in the hippocampus may be the answer. 

Neuroscientist Leila Reddy of the French National Center for Scientific Research and her team conducted a study to confirm the existence, and reveal the function of time cells in the brain through understanding how neurons in the hippocampus relay temporal information. 

HippocampusThey found that these time cells consecutively fire during tasks in order to organize the specific moments of an experience in accordance to time. The study also confirmed that these time cells exist in the hippocampus (pictured on the right), which is an important location for memory processing. As an event plays out and a memory is created, these time cells turn on and start firing, recording each moment with a chronological time stamp. The work done in this study is crucial as it reveals a key component in memory formation and function.

The co-author of the study, Matthew Self of the Netherlands Institute for Neuroscience, further relayed the importance of their findings, saying they believe “that time cells may be the underlying basis for encoding when something happened.” 

Time cells have been known to exist in rodents for a while now, but this study, conducted just late last year, was the first to identify these time cells in the human brain as well. But the study did not stop there. Reddy and her team continued to investigate these time cells. They looked at the hippocampal activity of willing epilepsy patients with electrodes implanted in their brain.

A schematic of the neuroprosthesis showing the external control unitPatients with epilepsy were most likely chosen for this study because their nerve cells communicate with one another in abnormal ways and send each other messages that get mixed up. Electrode implants would not only benefit the patient by producing impulses to regulate abnormal impulses, helping with an preventing seizures, but would work well for the study because the implant also allows neuron activity to be monitored (shown to the left).

About one week after their electrode implant surgery, the patients would participate in two experiments, during which their hippocampus activity would be monitored. The first experiment presented the patients with a sequence of five to seven images containing different settings or people – each image shown for 1.5 seconds with a .5 second break in between. This sequence was presented to the patient several times in the same order. Randomly, for one fourth of the intervals, the sequence would pause and the patient would be asked to identify which of two images should be the next one to occur. The research in this study found that, for all sixty repetitions of the sequence, all of the time sensitive neurons in the hippocampus of the patients fired at specific moments between each random pause in the sequence.

The second experiment was the same, except it included another component: a distraction. A black screen would show for 10 seconds after five sequences were repeated to half the patients, and after two sequences were repeated for the other half. The sequence was repeated to both groups a total of 30 times. In this experiment the patients were again tested about the order of the images. The results showed that neurons would fire corresponding to specific images, and that the time cells still turned on during the 10 second black screen distraction. The black screen was found to actually kelp the patients remember the correct order of images.

To find if there was time information in the activity of neurons in the hippocampus, the researchers stimulated time cell neurons already activated by an image in the experiment to test the firing activity of each neuron as a specific moment in time connected to a specific image. As a result they found that, “the activity pattern across the hippocampus [appeared] to simultaneously provide [them] with both the time stamp and the contents of the experience,” said Matthew Self. The researchers ability to decode moments in time from the neuron activity proved that the hippocampus in the human brain contains neurons capable of time-tracking.

These findings could explain why damage to the hippocampus can result in individuals having the ability to recall events, but not place them in chronological order. This problem is also seen in Alzheimer’s patients and those with other neurodegenerative conditions. A better understanding of cellular contributions to memory function can help us understand how and why people suffer from memory loss diseases, and give us a little bit of hope for the possibility of finding new and improved treatments and preventions.


Can Repression Help Create Memories?

       Have you ever wondered how long term memories form? Well there have been recent studies that show certain repressor genes are being distinguished at certain times after memory formation, which helps form memories. Sometimes remembering certain memories are hard to recall. It would be great if we could remember memories for long periods of time. Remembering memories all beings with memory formation, which consists of encoding, storing, and recalling information. Specifically the storing of the memory formation uses gene regulation, which will determine the productivity of gene products.  The use of gene regulation and Therefore, in order to gain a better understanding of how long term memories are created through the help of genes the scientist, Jun Cho Et Al, has created an experiment based on the hippocampuses of mice.

       Jun Cho Et Al specified the ribosome profiling and RNA sequencing of the mice’s hippocampi and he was able to do so by electrically shocking the mice. The small electrical shock made sure the mice associated the electrical shock with the setting. The mice were influenced by the fear of the electrical shock. When the scientists looked into the genes of the mice that were acting differently due to the electrical shock they found that half of the genes were being repressed. The repression was specifically caused by the protein,ESR1. However, once the ESR1 played a role there was a problem of the mice losing the ability to learn from the original fear of the electrical shock. After the ESR1 played a role immediately the gene, Nrsn1, acted as a memory suppressor. If the gene Nrsn1 is initiated too much then the ability to form memories will become very hard.

       Overall, the use of repressive genes could help us form long term memories. However, the problem of everything becoming long term knowledge is that we do not know how our brain will react. There is the possibility that the brain will eventually not be able to withhold all of the long term information. Do you think our brains would be able to withhold all of the information? Scientists have hypothesized that it is impossible for our brains to hold that much information and eventually our brains would turn into slop. 



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Caffeine- helpful or harmful?

CC licensed photo by Manny Hernandez

As we all know, the highly addictive drug, caffeine, found in our coffee, tea, soda, etc… simulates us. Many people use caffeine to stay a wake which works really well. But it also causes a build up of fatty acid in the blood, raises blood pressure,  stimulates the heart, respiratory system, and central nervous system, causes stomach to produce more acid, harder to digest food because muscles surrounding the intestinal system relax, increased urination, and many other symptoms.

Is caffeine more helpful or more harmful? And where does caffeine really affect our body?

Recently, scientist have been testing caffeine on lab rats to figure out which part of the brain caffeine stimulates the most. In the first trial, they gave the rats more caffeine than what a human would normally ingest. They then decided to use  smaller amounts of caffeine which affected the hippocampus. The hippocampus is part of the brain which allows for long term memory and spacial navigation. In humans, the hippocampus is located inside the medial temporal lobe. Damage to the hippocampus may cause oxygen starvation and/or amnesia. The rats received caffeine equivalent to two human cups of coffee which is two milligrams per kilogram of body weight. The scientists measured the nerve cell’s electrical messages but examining different parts of brain tissue.

The region that had the most response to the caffeine was called CA2. CA2 showed a burst of electrical energy, while other brain regions in the hippocampus showed no sign of stimulation. The then tested the rats giving a greater dosage which caused an even greater stimulation to CA2. After that the scientists directly injected caffeine into nerve cells in a dish and the results were the same as before. About 5 minutes of caffeine intake allowed for the synapses to stay amped for three hours.

The scientists believe that when humans use caffeine the same area, CA2, will be stimulated and may strengthen a persons ability to learn and memorize, but this is just a hypothesis since they only tested on rats. So you decide… is it helpful or harmful?

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