Question

Briefly differentiate anterograde and retograde amnesia and their relationship to the brain's hippocrampus. Explain the importance on the hippocrampus in the process of long term memory consolidation, includind the role of sleep, using one or more appropriate example.

Answer 1

Anterograde amnesia is a defect in the brain caused by brain injury. It is an inability to store new information and create memories. The individual is able to remember the memories and events that occurred prior to the brain injury. The information does not pass from the short term memory to the long term memory, thus the information is lost. Anterograde amnesia is caused by damage in the hippocampus and parts of the limbic system and the temporal lobe. Evidence about the role of hippocampus in formation of memory comes the famous case of HM. HM was an individual who experienced uncontrollable seizures and thus underwent surgery to control his life threatening condition. Large parts of the right and left temporal lobe including the hippocampus was removed during surgery. The surgery proved to be successful in terms of stopping the seizure, however, HM suffered from severe anterograde amnesia. Hippocampus is involved in transforming memories from the short-term memory to the long-term memory. Hippocampus is not storage for long term memories.

In retrograde amnesia, the individual is not able to recall memories that occurred prior to the brain injury. They are able to recall meanings and factual information but are unable to recall memories of specific events. Recent memories are more likely to be lost than memories that are relatively old. The severity of the amnesia is judged by the amount of information lost.

The hippocampus is a part of the limbic system and is involved in the process of learning and emotions. The hippocampus is located above the ear and is in both hemispheres of the brain due to lateralization. Hippocampus has an important role in memory formation and the emotions and sensations attached to those memories. The rear region of the hippocampus is involved in processing spatial memories. In a study conducted on cab drivers, it was found that activation of the rear region in navigation was linked to growth in the rear region. The hippocampus also plays an important role in consolidating information and memories during sleep. Studies have claimed that activation in the hippocampus during sleep before a learning activity will lead to better retention of that information.

There is evidence to support the role of hippocampus in memory. In a postmortem done in patients with amnesia, it was observed that there was damage to the hippocampus. Studies have also found that damage to the left hippocampus has effects on the recall of verbal information whereas damage to the right hippocampus has effects in processing verbal information. MRI scans of the brain have found that there is a 13% shrinkage in the brain for individuals between the age group of 30-80 years. Hence age is also related to poor memory performance.