A second possibility is that our memories are distributed and stored in different regions of the brain. Third, how does memory work? What types of changes occur in the nervous system when a memory is formed and stored, are there particular genes and proteins that are involved in memory, and how can a memory last for a lifetime?
Fourth, is the issue of importance to many people, especially as we age: How can memory be maintained and improved, and how can it be fixed when it is broken? Psychologists and neuroscientists have divided memory systems into two broad categories, declarative and nondeclarative Figure 7. The declarative memory system is the system of memory that is perhaps the most familiar. It is the memory system that has a conscious component and it includes the memories of facts and events. A fact like 'Paris is the capital of France', or an event like a prior vacation to Paris.
Nondeclarative memory, also called implicit memory, includes the types of memory systems that do not have a conscious component but are nevertheless extremely important. They include the memories for skills and habits e. Sensitization will be discussed in detail later in the Chapter. Declarative memory is "knowing what" and nondeclarative memory is "knowing how".
Figure 7. Modified from Squire and Knowlton, 7. Everyone is interested in knowing how well they remember so let us take a simple memory test. The test Figure 7. Sorry, you have to put your pen down for this test and do not read further in the Chapter until you complete the test.
It was not meant to be a trick, but to illustrate a very interesting and important feature about memory. But memory is more like taking a picture and tearing it up into small pieces and putting the pieces in different drawers.
The memory is then recalled by reconstructing the memory from the individual fragments of the memory. They cannot make the normal associations involved in the recall of a memory. To avoid these problems, psychologists have developed other memory tests. One is the object recognition test Figure 7. This test is also good because, as we will see later, it can even be used on animals. The test involves presenting a subject with two different objects and they are asked to remember those objects.
There is a pause and then two objects are shown again, one of which is new and the other having been shown previously. Subjects are asked to identify the novel object, and to do so, they need to remember which one was shown previously. A somewhat related test is the object location test in which subjects are asked to remember the location of an object on a two-dimensional surface.
Examples of nondeclarative memory, such as associative learning, can be tested by pairing one stimulus with another and later testing whether a subject has learned to make the association between the two stimuli.
The classical example is the paradigm developed by the Russian physiologist Ivan Pavlov , which is now called classical or Pavlovian conditioning. In classical conditioning Figure 7. After sufficient training with contingent CS-US presentations which may be a single trial , the CS is capable of eliciting a response conditioned response, CR , which often resembles the UR or some aspect of it.
Now let us turn to this issue about where is memory located. There are three basic approaches. Owen, et al. The color code is such that the brighter, redder regions indicate increased brain activity. The most active region is the hippocampus.
In discussions of memory, the hippocampus is mentioned repeatedly because it is a major part of the brain involved in declarative memory function. This illustration clearly indicates that the hippocampus is involved in object location memory.
But as we will see soon, it is not where all memories are stored. Consequently, H. Before the operation, H. Specifically, after the operation H. So if H.
This study clearly indicated that the hippocampus was critical for memory formation. But whereas H. Specifically, he had all his childhood memories, and all of his memories prior to the operation.
This type of memory deficit is called anterograde amnesia. In contrast, retrograde amnesia refers to loss of old memories. The studies on H. It is now known that those old memories are stored in other parts of the brain, such as in the frontal cortex.
The process by which an initially labile memory is transformed into a more enduring form is called consolidation. This process involves the memory being stored in a different part of the brain than the initial site of its encoding. While he could form new memories for skills and habits, he did not know that he had the skills!
This finding clearly indicated that the memory for skills and habits are not formed in the hippocampus. Collectively, we learned from these studies on H.
The medial temporal lobe and structures like the hippocampus are involved with memories for facts and events; the striatum is involved with memories for skills and habits; the neocortex is involved with priming; the amygdala is involved with emotional memories; and the cerebellum with simple forms of associative learning.
Lower brain regions and the spinal cord contain even simpler forms of learning. In summary, memory is not stored in a single place in the brain. It is distributed in different parts of the brain. Modified from Squire and Knowlton, One of those model systems is illustrated in Figure 7.
Aplysia californica is found in the tidal pools along the coast of Southern California. Although these short-term memories are lost due to interference with new incoming information, they are essential for planning behaviours and deciding what actions to perform based on the current situation.
A short-term memory can be consolidated into an enduring long-term memory. This involves a system of brain structures within the medial temporal lobe that are essential for forming declarative memories. The hippocampus is a key region in the medial temporal lobe, and processing information through the hippocampus is necessary for the short-term memory to be encoded into a long-term memory. The long-term memory does not remain stored permanently in the hippocampus.
These long-term memories are important and having them stored in only one brain location is risky — damage to that area would result in the loss of all of our memories. Instead, it is proposed that long-term memories become integrated into the cerebral cortex responsible for the higher order functions that make us human. This process is referred to as cortical integration; it protects the information stored in the brain. However, damage to areas of the brain, particularly the hippocampus, results in loss of declarative memories, which is known as amnesia.
Removal of the temporal lobe, including the hippocampus, led to the inability to form new memories, known as anterograde amnesia. However H. These are called neurofibrillary tangles and amyloid-beta plaques. Amyloid plaques disrupt communication between neurons. Damage to neurons in the hippocampus prevents the formation of new memories and also disrupts neurons that have formed networks encoding existing memories.
This leads to the loss of these memories, called retrograde amnesia. As the die-off of neurons increases, affected brain regions begin to shrink and waste away.
Procedural memories motor skills are the last ability to be destroyed. Human memory is complex, and neuroscientists are still trying to uncover the mechanisms that lead to memories being formed. The amygdala doesn't just modify the strength and emotional content of memories; it also plays a key role in forming new memories specifically related to fear.
Fearful memories are able to be formed after only a few repetitions. Understanding how the amygdala processes fear is important because of its relevance to post-traumatic stress disorder PTSD , which affects many of our veterans as well as police, paramedics and others exposed to trauma. Anxiety in learning situations is also likely to involve the amygdala, and may lead to avoidance of particularly challenging or stressful tasks.
QBI researchers including Professor Pankaj Sah and Dr Timothy Bredy believe that understanding how fear memories are formed in the amygdala may help in treating conditions such as post-traumatic stress disorder.
There are two areas of the brain involved in implicit memory : the basal ganglia and the cerebellum. The basal ganglia are structures lying deep within the brain and are involved in a wide range of processes such as emotion, reward processing, habit formation, movement and learning.
They are particularly involved in co-ordinating sequences of motor activity, as would be needed when playing a musical instrument, dancing or playing basketball. The cerebellum, a separate structure located at the rear base of the brain, is most important in fine motor control, the type that allows us to use chopsticks or press that piano key a fraction more softly. A well-studied example of cerebellar motor learning is the vestibulo-ocular reflex, which lets us maintain our gaze on a location as we rotate our heads.
The prefrontal cortex PFC is the part of the neocortex that sits at the very front of the brain. It is the most recent addition to the mammalian brain, and is involved in many complex cognitive functions. Human neuroimaging studies using magnetic resonance imaging MRI machines show that when people perform tasks requiring them to hold information in their short-term memory , such as the location of a flash of light, the PFC becomes active.
There also seems to be a functional separation between left and right sides of the PFC: the left is more involved in verbal working memory while the right is more active in spatial working memory, such as remembering where the flash of light occurred.
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