This week we read three journal articles that all focused on the role of medial temporal lobe structures in memory. The role of the medial temporal lobe structures in memory has been extensively debated and researched. One article presented research by Chun and Phelps conducted the first study. They wanted to see the role of the hippocampus and adjacent medial temporal lobe structures in the encoding of implicit contextual information. Amnesiac patients were the subjects of this study and their performance in a visual search task was analyzed. To examine contextual learning in this task, the experimenters repeated old displays throughout the session. Their performance on old displays (context dependent) was then compared to their performance on new displays (context independent). The results of this study showed that the amnesiac patients with MTL damage showed normal implicit perceptual learning but were impaired in implicit contextual learning. These findings are consistent with the fact that the hippocampus and adjacent medial temporal structures are necessary for encoding and learning conceptual information.
The second article we read presented the results of a study conducted by Professor Davachi, Jason P. Mitchell and Anthony D. Wagner. This study looked at the role of various medial temporal lobe structures on source and item memory or recognition by using event related functional MRI. They wanted to look at the differences in activation in different areas of the MTL during the formation of the memory, the recognition of an item that was previously seen, and the recollection of the context or source of the previous encounter. The subjects of this study were healthy adults with no medial temporal damage. The participants’ scans showed that encoding activation in the parahippocampal and hippocampal areas were correlated with later source recollection. This activation was absent in item recognition. Increased activation was also seen in the perirhinal cortex but it was correlated with later item recognition and not source recognition. These results indicates the role of different parts of the MTL in different types of memory.
The third article presented the research findings of a study performed by Eldridge and her colleagues. This study discussed the hippocampus’s role in episodic memory retrieval by using event related functional MRI. The subjects in this study were healthy individuals and they were required to memorize a list of words. They then underwent fMRI scans while they were presented with previously studied and new items. During this test, they were asked to determine if the item was old or new and they were given a remember-know task. The results of this were consistent with present theories that state that the hippocampus is necessary for the retrieval of episodes. This activation of the hippocampus required conscious awareness or recollection of the event. Researchers propose that the hippocampus might help put together the features and context of the event.
All of these journal articles show how complex the role of the medial temporal lobe’s in memory really is. Even though these structures all have their distinct purposes, they all complement each other and contribute to our memory of events and items. One problem I had with these studies was that none had an equal amount of men and women and the amount of subjects used was small. The amount of subjects used could be explained by the price tag of conducting these studies and the amount of amnesiac patients that are available to researchers. I do not understand why researchers did not use a close to equal amount of male and female subjects because some research has shown sex differences in activation of brain regions. My guess is that this difference was not taken into account because it is probably not significant.
While I was reading the article on the hippocampus and the retrieval of episodic memories all I kept thinking about are the times that I forgot where the car was parked after a long day of shopping and forgetting where I put my keys after I put them in a “safe place” the day before. How was the encoding of the object location flawed?
I found an article that tries to explain how we remember locations whether it be where we put our keys or the directions to our favorite restaurant.The hippocampus is important in the formation of these types of memories because it contains place cells. These cells become active in response to a specific location. In a study done on rats, they put them in maze and the activity of the place cells was measured while the rats worked their way around the maze. The results of this study were that the activity of the place cells while they were looking for food in the maze, signaled location. However, other cells were sensitive to recent or impending events, which showed that the rats planned their movements prior to making them.
The implications of this study are that the hippocampus’ neurons fire in a way that helps express location and is very goal oriented. This firing can be in response to external cues (i.e. street name, stores, restaurants, etc…) that guide us to our desired location. So the reason why I did not remember where I parked my car was that the place cells did not fire properly, which could be caused by failure to encode the spatial information successfully. Failure to encode the information properly then leads to flawed storage of the location.
So why is it that when we intentionally place something in a safe place that we sometimes forget what this place is? Is it that the association of the object with this “safe place” is weak?
The second article we read presented the results of a study conducted by Professor Davachi, Jason P. Mitchell and Anthony D. Wagner. This study looked at the role of various medial temporal lobe structures on source and item memory or recognition by using event related functional MRI. They wanted to look at the differences in activation in different areas of the MTL during the formation of the memory, the recognition of an item that was previously seen, and the recollection of the context or source of the previous encounter. The subjects of this study were healthy adults with no medial temporal damage. The participants’ scans showed that encoding activation in the parahippocampal and hippocampal areas were correlated with later source recollection. This activation was absent in item recognition. Increased activation was also seen in the perirhinal cortex but it was correlated with later item recognition and not source recognition. These results indicates the role of different parts of the MTL in different types of memory.
The third article presented the research findings of a study performed by Eldridge and her colleagues. This study discussed the hippocampus’s role in episodic memory retrieval by using event related functional MRI. The subjects in this study were healthy individuals and they were required to memorize a list of words. They then underwent fMRI scans while they were presented with previously studied and new items. During this test, they were asked to determine if the item was old or new and they were given a remember-know task. The results of this were consistent with present theories that state that the hippocampus is necessary for the retrieval of episodes. This activation of the hippocampus required conscious awareness or recollection of the event. Researchers propose that the hippocampus might help put together the features and context of the event.
All of these journal articles show how complex the role of the medial temporal lobe’s in memory really is. Even though these structures all have their distinct purposes, they all complement each other and contribute to our memory of events and items. One problem I had with these studies was that none had an equal amount of men and women and the amount of subjects used was small. The amount of subjects used could be explained by the price tag of conducting these studies and the amount of amnesiac patients that are available to researchers. I do not understand why researchers did not use a close to equal amount of male and female subjects because some research has shown sex differences in activation of brain regions. My guess is that this difference was not taken into account because it is probably not significant.
While I was reading the article on the hippocampus and the retrieval of episodic memories all I kept thinking about are the times that I forgot where the car was parked after a long day of shopping and forgetting where I put my keys after I put them in a “safe place” the day before. How was the encoding of the object location flawed?
I found an article that tries to explain how we remember locations whether it be where we put our keys or the directions to our favorite restaurant.The hippocampus is important in the formation of these types of memories because it contains place cells. These cells become active in response to a specific location. In a study done on rats, they put them in maze and the activity of the place cells was measured while the rats worked their way around the maze. The results of this study were that the activity of the place cells while they were looking for food in the maze, signaled location. However, other cells were sensitive to recent or impending events, which showed that the rats planned their movements prior to making them.
The implications of this study are that the hippocampus’ neurons fire in a way that helps express location and is very goal oriented. This firing can be in response to external cues (i.e. street name, stores, restaurants, etc…) that guide us to our desired location. So the reason why I did not remember where I parked my car was that the place cells did not fire properly, which could be caused by failure to encode the spatial information successfully. Failure to encode the information properly then leads to flawed storage of the location.
So why is it that when we intentionally place something in a safe place that we sometimes forget what this place is? Is it that the association of the object with this “safe place” is weak?
1 comment:
Could very well be! This is one of the mysteries of memory, of course, is that we cannot 'make' it happen. We can only increase the probability of it occurring..
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