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.

Monday, 21 November 2011

Cognitive Neuropsychology - Blog 8 - Frontal Lobes

As outlined by (Martin, 2006) the frontal lobes are the most recently developed out of the four lobes (Occipital lobe, temporal cortex, parietal cortex & the frontal lobes) and hold approximately 1/3 of the cerebral cortex. The frontal lobes are split into the 'orbito-frontal cortex' which is responsible for decision making and behavioural self regulation and the 'dorso-lateral region' which is responsible for cognitive & executive functioning, working memory and attention. The frontal lobes have been described as being the leader and are massively connected to other brain regions suggesting that the frontal lobes play a big part in the communication to the rest of the brain and support the notion that it is the master brain region. The frontal lobe is responsible for most types of our behaviour such as social behaviour, personality and motor movement and its roles include; engaging in abstract thought, planning and organisation, inhibiting inappropriate social and emotional responses. But more specifically the frontal lobes are involved in; working memory, encoding and retrieval of information, motor movement, attention and executive functions. Damage to the frontal lobes can destruct executive functioning which Banich (2009) said is vital to be able to live an independent life. A great example of this is the story of Phineas Gage who suffered major personality changes after a lateralization to his left frontal area (Damasio etal, 1994). Evidence shows that the frontal lobes play a crucial and perhaps master role in the brain, therefore damage to this area of the brain could consequently cause the inhibitoriest disorders. Many tests can be performed to test whether a patient has frontal lobe damage; the most frequently used test is the Wisconsin card sorting task where an examiner will change the rules without informing the patient and the patient will not adapt to this but will continue using the old and now inappropriate rule to sort out the cards.

Notes from article - Executive function: The search for an integrated account.

- Brian damage can damage the frontal lobes which in turn can damage executive functioning which is said to be required to live an independent life.

Banich (2009) suggests that executive functioning is necessary to 'effortfully guide behaviour toward a goal' and is especially needed for nonroutine situations. Executive function is sad to be required for; prioritising, sequencing behaviour, inhibiting familiar or stereotyped behaviours, creating and maintaining an idea, switching between task goals, decision making and categorizing.

- Executive functioning covers a wide amount of skills so there is not one general test but many different ways to test executive functioning.

- The Wisconsin card sorting test is most frequently used. This involves the participant learning a rule and then the examiner will change the rule without telling the participant. Patients with frontal lobe damage will still try and sort the cards out using the old and inappropriate rule.

- Stroop task (Decisions made on task relevant information when faced with distracting information.) the task involves identifying a word's colour and ignoring the word. Executive functioning is needed here because word reading is automatic so it's needed to over-ride this automatic response and instead name the colour.

- Many psychiatric illnesses involve executive functioning these are; schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder.

-There seems to be little knowledge about how the frontal lobes support executive functioning although it is clear that damage to the frontal lobes is associated with executive functioning. Therefore making this a hard problem to prevent or treat.

Notes from lecture

- Wisconsin card sorting task - needs a shift in strategy after an unexpected rule change. Patients with lateral prefrontal cortex damage show 'perseveration'

Frontal lobes function (tests)

- Error correction & trouble shooting (entails sorting cards by shape, colour or numbers and then changing the rules.

Executive functions of the frontal lobes

Divided attention, sustained attention, processing speed, initiation, sequencing, self-shifting, cognitive flexibility & planning.

-Important for planning & controlling behaviour.

-Frontal lobes are needed to enhance performance in situations that involve coordination between a series of cognitive processes.

- It is not domain specific but is more of a supervisory role to memory, perception and language.

- The frontal lobes are linked to prefrontal cortex.

- Five general situations that require the frontal lobes executive functions as stated by Norman & Shallice (1986) are;

- Planning or decision making
-Error correction or trouble shooting
-When responses are not well learned or contain novel sequences of actions
-Situations that are judged to be dangerous or technically difficult
- Also needed when overcoming a strong habitual response or resisting temptation.

What areas do what?

- Lateral prefrontal cortex = working memory.
- Ventromedial zone = emotions & decision making
- Anterior cingulate (ACC) = monitoring behaviour (conflict & error detection).

(ACC) Anterior cingulate cortex

- Is vital for reward, anticipation, decision-making, empathy and emotion.
- Dorsal ACC is related to rational cognition & ventral is related to emotional cognition.

- OCD sufferers have high ACC activation.

- Depression can be as a result from low ACC activity.

Friday, 18 November 2011

Cognitive Neuropsycholgy - Blog 7 - Hemispheric Lateralisation

The human brain is split into two parts, which appear to work individually and have separate roles; these are the 'right' and 'left' hemispheres. These two hemispheres are connected by a thick layer of nerves called the corpus callosum. Research has consistently shown that the left hemisphere is predominantly involved in language and logic and the right hemisphere is predominantly involved in aspects of visuospatial ability and creativity (Martin, 2006). Although research indicates that the right and left hemisphere have exclusive roles it has been shown that this is not entirely true e.g. the right hemisphere has some language capabilities and the left hemisphere has some visuospatial abilities. Vogel, Bowers & Vogel, 2003 suggest that a person can have a dominant hemisphere meaning that if a person holds a creative personality they will have a dominant right hemisphere. Lateralisation’s to either hemisphere consequently carries great consequences and can alter a person’s social and mental skills. In order for doctors to help patients affected by these deficits, research needs to address whether hemispheres are exclusively used for specific abilities, however only brains that are brain damaged are testable as obviously it is unethical to carry out such invasive research on healthy humans therefore it is causes ambiguity to which particular parts of the brain control what activities in a normal healthy working brain.
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Extra notes;

  • Lesions in the left hemisphere affects language (aphasia).
  • It is suggested that the brain does not duplicate functions on both sides of the hemispheres, meaning that the two hemispheric sides are specalised for different functions.
  • The left hemisphere is more effective in language processing whereas the right hemisphere is more effective for visuospatial abilities.
  • The right hemisphere holds some linguistic ability but cannot perform phonological decoding.
  • In general the perceptual system first sees an object globally, it is reported that patients with a left-sided lesion are slow to identify local targets and that patients with right-sided lesions are slow to detect global targets.

Friday, 11 November 2011

Cognitive neuropsychology - Week 6 - Emotions

Emotions are fundamental in every aspect of a person’s life and can regulate behaviour either consciously or unconsciously. It has been reported that the orbito-frontal cortex and sub cortical structures such as the amygdala and hippocamal system are heavily involved in the expressing and recognition of emotions. There is much debate about the meaning of emotion and also the role of emotion but it seems clear that it is anything that in the short-term alters a person’s psychological state. Ekman (cited in Martin, 2006) suggest that there are six 'basic' emotions that are recognised the most across different cultures, these are; Happiness, sadness, anger, fear, disgust and surprise. Emotions are a key way to engage in social interaction and express feelings and can prepare for the fight or flight response. Ekman (1992) suggest that emotions have evolved to help deal with certain life events however some emotional responses can be inhibitory, e.g. if a person often experiences sadness then this would decrease arousal and motivational levels, so if faced with an aversive stimulus the body would have a slower emotive reaction. According to the oxford dictionary of psychology the amygdala's role is "controlling the experience and expression of emotion." (p31). It seems that different subcotical structures play a role and are activated more frequently in some emotions than others, for example the emotion fear has been linked with a high activation of the amgydala however overall these sub cortical structures all interlink and  implement the expressing and recognition of emotion.