In later years, researchers discovered that the hippocampus, which had been removed in HM's surgery, is primarily responsible for the consolidation of short-term into long-term memories. This process can take up to three years, hence HM's retrograde amnesia for events close to the surgery. The hippocampus is not the only structure involved in memory, however.
There are many different types of memory, and the hippocampus is involved in declarative, spatial, contextual, episodic, and working memories, as well as in the detection of novel stimuli. Non-declarative memories, such as motor skills, are dealt with in the neostriatum.
Although testing declarative memory in animals is problematic, evidence for spatial memory in them has been found.
One example of the type of task used to test spatial memory is the Morris Water Maze. In this task, a tank is filled with milky water with a platform concealed somewhere beneath the surface. When a rat is placed in the tank, he will swim around until he finds the platform. When this task is repeated many times, he learns to use cues from outside the tank and can find the platform almost immediately from any spot in the tank.
He can do this because he has created a spatial map of the tank and its surroundings. If the rat's hippocampus is lesioned after he learns the task, there will be no effect; if it is lesioned before when he is naive , however, he is unable to learn it.
Clearly, the hippocampus is involved in creating the spatial map, but not in storing it for long periods of time. This is also evident in the fact that migratory birds have large hippocampi and as adults still experience neurogenesis in the hippocampal region. The hippocampus is not fully developed at birth; that takes about two and one half years. An interesting effect of this is infantile amnesia--most people do not have declarative memories from their first couple years of life.
The hippocampus is a looped structure; information is funneled into it, then is sent back. It is a cylindrical structure around the thalamus. It is found in the inner folds of the bottom middle section of the brain, known as the temporal lobe.
Humans have known about the hippocampus for more than 4 centuries. It is one of the most studied parts of the brain.
The name comes from the Greek words hippo, meaning horse, and kampo, meaning monster, as its shape resembles that of a sseahorse. Its main functions involve human learning and memory. Knowing about the hippocampus has helped researchers understand how memory works. The hippocampus is part of the limbic system, which is associated with the functions of feeling and reacting. The limbic system is situated on the edge of the cortex, and it includes the hypothalamus and the amygdala.
The hippocampus helps humans process and retrieve two kinds of memory, declarative memories and spatial relationships. Declarative memories are those related to facts and events. Examples include learning how to memorize speeches or lines in a play.
Spatial relationship memories involve pathways or routes. For example, when a cab driver learns a route through a city, they use spatial memory.
Spatial relationship memories appear to be stored in the right hippocampus. The hippocampus is also where short-term memories are turned into long-term memories. These are then stored elsewhere in the brain.
Research has shown that nerve cells continue to develop throughout adulthood. The hippocampus is one of the few places in the brain new nerve cells are generated. They may be unable to remember some things that happened shortly before the hippocampal damage, but they may still remember things that happened longer ago. This is because the long-term memories are stored in another part of the brain, once they become long term.
Transient global amnesia is a specific form of memory loss that develops suddenly, seemingly on its own, and then goes away fairly quickly. Most people with transient global amnesia eventually regain their memories, but the reasons why the problem occurs and why it resolves are unclear. It may be that damage to the hippocampus is involved.
Damage to the hippocampus can make it hard to remember how to get from one place to another. And, as these areas of our brain continue to change and develop, so does our memory. In other words, we are most likely to favour memories that reinforce our ideas of who we are.
Often used as a kind of shorthand for the cells of the brain, grey matter is largely composed of densely packed neurons. This is white matter. The cables are coated in a fatty substance called myelin, which give them the white colour that shows up on an MRI GLOSSARY MRI magnetic resonance imaging, a technique that uses a magnetic field and radio waves to create detailed images of the organs and tissues in your body.
Myelin acts like insulation around the axons, allowing messages in the form of electrical signals to be carried more quickly between areas of the brain. The more myelin, the quicker the messages will travel. Thanks to MRI technology, scientists have been able to observe what happens to myelin in our brains during childhood and adolescence.
Over the following few years, these connections are gradually pruned. Depending on our experiences, some connections are strengthened while others disappear until, eventually, the density of our synapses reaches adult levels. But, in our prefrontal cortex, it seems that this happens a second time. As we hit puberty, corresponding with a turbulent time of growth and learning in the rest of the body, there is another wave of synaptic proliferation in the brain. Then, as we move through adolescence, these connections are again pruned back and reorganised.
Because our frontal and prefrontal cortex continue to develop in these ways during puberty and adolescence, we might expect to see a corresponding improvement in executive functions to do with memory which are associated with these frontal regions of our brain.
And indeed, this has been found to be the case: experiments have shown that our performance on complex working memory tasks continues to improve in adolescence, as does our prospective memory our ability to remember to do things in the future. Memory milestones from birth to adulthood Birth — 1 ability to remember events for short periods of time length of time gradually increases 1 — 2 ability to remember events for longer and longer amounts of time 2 — 3 years declarative memory memory for facts and events improves 4 — 7 years prospective memory remembering to do things in the future starts to emerge 8 — 10 years improved recall of facts improved recall of spatial relationships 10 — 12 years long-term memory improves increasing ability to consciously supress memories 13 — 21 years prospective memory improves working memory improves.
We all know that our childhood and adolescence is a time when our bodies go through huge changes. What might not be so obvious are the hidden changes in that dynamic, and sometimes mysterious, place that is our brain.
How our memory develops Expert reviewers. First, a quick recap of the basics. Memories are made when neurons fire Neurons are nerve cells which send electrochemical signals to each other. There are different kinds of memory There are a number of different kinds of memory. Rather, different interconnected parts of the brain specialise in different kinds of memories. For example, an area of the brain called the hippocampus is important for storing memories of particular things that happened in your life, known as episodic memories.
Memories are formed by neurons pictured that fire in our brains, creating or changing networks of connections. From birth to adolescence Infancy and childhood Can you remember your first birthday? What do babies remember? Watching an emotional movie after studying could help you get better marks.
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