Monday, 28 November 2011

Cognitive neuropsychology - Week 9 - Memory

According to Martin, 2006 memory is one of the most difficult functions to master because it is an ongoing process and not merely a simple thing. Teng & Squire, (1999) suggest that the 'hippocampus is a part of a system of structures in the medial temporal lobe that are essential for memory'. The processes of memory include; encoding, retrieval, recall and recognition. Two main types of memory have been outlined by broadbent (1958) these are; Long term memory (LTM) which is prominent in the hippocampus. The excitatory neurotransmitter glutamate seems to be important for long-term memory. The second is short term memory (STM) he postulated that items from the STM would make their way via specific mechanisms to the LTM. Other dichotomies of memory have been proposed such as; procedural and declarative memory. Procedural memory is involved in automatic operations such as riding a bike. Declarative memory has been linked as similar to explicit memory and involves recall and recognition of items that are consciously available. Another dichotomy is episodic memory (memories that are personally meaningful) and semantic memory (memories based on knowledge of events, people or places). In addition to this, working memory allows a person to participate in one activity whilst contemplating another. It is clear that there are many factors involved in memory and that each involve specific systems and regions of the brain, consequently if these are damaged it can result in many different memory disorders; such as retrograde and anterograde amnesia.

Important information from the article - "Memory for places learned long ago is intact after hippocampal damage (Teng & Squire, 1999).

Teng & Squire (1999) state that the "hippocampus is a part of a system of structures in the medial temporal lobe that are essential for memory". It is suggested that the hippocampus plays a role in the acquisition & retrieval of spatial knowledge. The hippocampus is outlined as constructing and storing spatial maps and is important for learning and remembering places including places that were learned many years ago.
A patient E.P was tested who suffered from virtually complete bilateral damage to the hippocampus and also severe damage to surrounding structures situated in the medial temporal lobe. E. P was capable of describing the layout of roads and houses from where he grew up, but when asked to describe his current neighbourhood he had no knowledge, suggesting that he had antereograde amnesia. Results "support the view that the hippocampus and other structures in the medial temporal lobe are essential for the formation of long term declarative memories, both spatial & non spatial, but not for the retrieval of very remote memories, either spatial or non spatial.

Important notes from the lecture:

- Memory has evolutionary significance as it allows us to predict future outcomes on the basis of experience and be able to adapt to new situations.

Processes in Memory:
- Encoding - process used to store information in memory.
Storage - process used to maintain information in memory.
Retrieval - process used to get information back out of memory.

Types of memory:
-Sensory memory (iconic) - high capacity, very short lived-decays within seconds.
- Short term memory (STM) - Information currently held 'in mind'. Limited capacity. Miller (1956) 7+or-2. Chunks rather than words or syllables are stored.
- Working memory - Extension of STM, temporary storage & manipulation of info: central executive.
- Long-term memory (LTM) - Stored information, doesn’t need to be consciously accessed. Has unlimited capacity. Stored memories from hours, weeks and years ago.

- Amnesic patients who have normal digit span cannot acquire new information such as word lists.
- Impairments in short term phonological and long-term memory is associated with left parietal and media-temporal respectively.
-STM may represent the temporary activation of the LTM.

- To recall lists of items from STM, phonological similarity is needed.
- To recall lists of items from LTM requires semantic similarity.

- The central executive coordinates the slave systems by retrieving things from memory, specifying task goals, initiating and terminating cognitive routines.

Procedural memory
- This is a memory that is required for activities such as riding a bike. Basal ganglia are linked to this.

Perceptual representation systems
- This is needed for perceiving sounds, words and objects. Stores knowledge of the perceptual world and is capable of learning. Evidence for this comes from priming studies which suggest that information is easier to access if it has recently been encountered.

In an object recognition task only known objects showed priming effects suggesting that priming only tap a perceptual store of known objects.
- Priming involves brain regions that are involved in perception.

Semantic memory (autobiographical memory) - Knowledge about the world, places, & meaning of objects and words. Knowledge that is culturally shared.

Episodic memory - Autobiographical memory & specific events in one’s own life.

Retrograde amnesia = loss of memory for events that occurred before the trauma.
Antereograde amnesia - No memory for events that occur after the trauma and have difficulty in learning new information.

- Amnesia generally consists of severe impairments to anterograde memory with less impairment to retrograde memory.

Preserved & Impaired memory in amnesia:
- STM is spared.
- Episodic memory is impaired.
- Semantic memory is impaired (partially)
- Procedural and perceptual memory is spared

- Results from studies with amnesic patients support 'multiple memory systems' view of the brain in which episodic memory is partially affected.
-Episodic memory may be spared because they contain rich contextual detail. These contextual details may be linked by structures in the medial temporal lobe, including the hippocampus, and may gradually be consolidated over time.

Hippocampus and memory
- Contents of memory are stored in the neocortex but are unclear whether the hippocampus is needed for consolidation or even retrieval.
- Hippocampus - Is critical for integration and consolidation. Without the hippocampus only learning of skills and habits, simple conditioning and phenomenon of priming can occur.

Forgetting and encoding

- Information that is encoded semantically is more likely to be remembered than information that is processed perceptually.

Storage and retrieval
- Encoding specificity hypothesis = Contextual similarity between the retrieval attempt and the initial encoding phase predicts the likelihood of remembering versus forgetting.

Frontal lobes and LTM
- Damage to the lateral frontal lobes does not produce memory dysfunction, but disrupts cognitive control, which can produce false and incoherent memories.
- Ventro-lateral is activated during memory encoding and incidental learning not specific to LTM. It is also involved in maintaining and retrieving semantic memories.
- Dorso-lateral prefrontal region is associated with selecting from a range of alternatives that are not specific to memory tasks. Recognized for playing a role in memory retrieval.

Explicit memory tasks - Involves conscious recollection e.g. participants know that they are trying to retrieve information from their memory.
Implicit Memory - Requires participants to complete a task - the completion of a task indirectly indicates memory.

- Amnesia results support a multiple memory system view of the brain in which explicit memory is particularly affected.
-  Episodic memories may be special because they contain rich contextual detail
- Contextual details may be linked together by structures in the medial temporal lobe including; hippocampus, may be gradually consolidated over time.
- Newly learned semantic facts may initially be context dependent but become less so over time.

No comments:

Post a Comment