Question

We know that the hippocampus is important for memory, but that it isn't the storage site for either short- or long-term memories. (a) How do we know that the hippocampus doesn't store short- and long-term memories? (b) How, then, is the hippocampus involved in memory?

Answer 1

• Long-term memory is, obviously enough, intended for storage of information over a long period of time. Despite our everyday impressions of forgetting, it seems likely that long-term memory actually decays very little over time, and can store a seemingly unlimited amount of information almost indefinitely.Short-term memories can become long-term memory through the process of consolidation, involving rehearsal and meaningful association.
• The hippocampus area of the brain essentially acts as a kind of temporary transit point for long-term memories, and is not itself used to store information. However, it is essential to the consolidation of information from short-term to long-term memory, and is thought to be involved in changing neural connections for a period of three months or more after the initial learning.
• Consolidation is the processes of stabilizing a memory trace after the initial acquisition. It may perhaps be thought of part of the process of encoding or of storage, or it may be considered as a memory process in its own right.
• It is usually considered to consist of two specific processes, synaptic consolidation (which occurs within the first few hours after learning or encoding) and system consolidation (where hippocampus-dependent memories become independent of the hippocampus over a period of weeks to years).
• 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.
• Case study- In 1953, a patient named Henry Molaison had his hippocampus surgically removed during an operation in the United States to treat his epilepsy. His epilepsy was cured, and Molaison lived a further 55 healthy years. However, after the surgery he was only able to form episodic memories that lasted a matter of minutes; he was completely unable to permanently store new information.
• As a result, Molaison’s memory became mostly limited to events that occurred years before his surgery, in the distant past. He was, however, still able to improve his performance on various motor tasks, even though he had no memory of ever encountering or practising them. This indicated that although the hippocampus is crucial for laying down memories, it is not the site of permanent memory storage and isn’t needed for motor memories.