Long term memory and the brain- Lecture 5 Flashcards
HM case study
Suffered severe epilepsy
Abnormal electricity in temporal lobes
Surgery to remove parts of left n right medial temporal lobes
Developed issues retaining new information more than seconds or minutes.
Evaluation of HM case as evidence for locating memory in the brain
- Revolutionary at the time- well documented
- Locates specific memory functions in the brain
- Lead to Milner’s work on patients with unilateral MTL lobectomies- revealed content specific memory deficits
Causes of Amnesia
- Anoxic or ischaemic episodes
- Progressive disorders
- Chronic Alcoholism
- Viral or bacterial infections
- Brain Tumours
- Head injury
Areas of damage typical in amnesia
Medial temporal lobes Thalamus Fornix & Mammillary bodies Basal Forebrain Interconnected structures
Anterograde Amnesia
Impaired memory for events and facts learned experienced after onset of amnesia
Retrograde Amnesia
Impaired memory for events and facts before onset of amnesia
Things that are unaffected by organic amnesia
Intelligence perception attention language short term memory (to extent) Working memory
Organisation of Long-term memory
- Memory is related but distinct from info processing
- LTM exists in multiple forms, anatomically dissociable
- New classification of LTMs
Explicit memories
Conscious retrieval of information
-Involves structures damaged in amnesia
Implicit memories
Do not require consciousness
Like learned procedures
-Involves structures non damaged by amnesia
Skill Learning- Knowlton, Mangels & Squire (1996)
Implicit/procedural memories
Probabilistic learning (learning to associate specific combinations of cards with a specific outcome)
- Damage to basal ganglia (like in Parkinson’s) are impaired in this
- When task made implicit> basal ganglia is engaged
- When explicit> medial temporal lobe is inactive
Eye- blink conditioning & the cerebellum
Bracha et al (2000)
NOT IN AMNESIA -Cerebellum is linked with creating the eye-blink reflex- when damaged, they do not respond to the neutral stimulus (tone) that is associated with the puff of air.
AMNESIC’S HAVE IMPLICIT MEMORY INTACT
Priming
Implicit memory
Change in the ability to identify or produce an item as a result of a specific prior encounter with the item
Priming in Amnesics
Warrington & Weiskrantz, 1968;1970
-Used fragmented versions of words- start with most fragmented and asked if the ppt can identify
-When this task is repeated over and over, will see that amnesics and controls show learning and become better
Priming is preserved in amnesics
Neuroimaging studies of Priming
Perceptual and conceptual priming
Perceptual priming activates areas in extrastriate cortex
Conceptual priming activates an area in the inferior frontal gyrus (dorsal & inferior prefrontal cortex)
Wig et al. (2005)
Investigated areas of haemodynamic response of conceptual priming using TMS
- When TMS applied in the front left area of brain (the inferior frontal gyrus) didn’t interfere with task itself
- but did effect haemodynamic response- was as if novel items
Functional deficit of Anterograde amnesia
Explicit memories
> Impairment in creating associations between separate items of information (Eichenbaum & Cohen, 1991)
impairment of episodic memory (Aggleton & Brown, 1999)
Affects both episodic and semantic memory (Squire, 2009)
Episodic Memory deficits
Declarative Memories
Memory for events containing contextual information (TULVING, 1983)
-semantic memories start as components of episodes but surrounding episode is forgotten
Aggleton & Brown (1999)
Episodic memory deficit
There is 2 systems that are implicated in Episodic memory deficits, both the MTL and diencephalic structures
-Two systems are independent but interacting
Episodic Memory Deficit
Recollection System
Involves the hippocampus, anterior thalamus , fornix and mammillary bodies
Ability to remember episodes
Episodic memory deficit
Familiarity system
Sense of familiarity, the feeling that something has been experienced before in the absence of additional information.
Involves the rhinal cortex (entorhinal and perirhinal), parahippocampal cortex and dorsomedial thalamus (MTL)
Tsivilis et al (2008)
Damage to the fornix creates wasting of Mammillary bodies Patients with large mammillary body volumes tended to do better at recall (recollection network) than patients with small mammillary body volumes
-no effect on familiarity network
The role of the Perirhinal cortex
Bowles (2008)
When damage to the Perirhinal cortex- the familiarity memory is impaired but not recollection
Remote memories
Memory of events from the distant past
Ribot’s Law
Remote Memory
The older the memory, the less likely it is to be effected in the event of memory damage
Remote memories
ECT therapy
ECT used for depression
BUT causes both anterograde and retrograde amnesia for events around the treatment
However, older memories appeared intact
ECT Therapy studies
Criticisms
Not all studies have replicated this finding
- Depression could be linked with encoding deficits
- We are not aware of why the memory disruption occurs- thus dont know why the older memories are not affected
Reed & Squire (1998)
Retrograde amnesia can be quite limited or very extensive, depending on whether the damage is restricted to the hippocampal formation or also involves additional temporal cortex
The Consolidation theory
Squire and Alvarez (1995)
Consolidation of memory occurs when the cortico-connections to the hippocampus are strengthened
Memories become remote when the hippocampus is no longer engaged in consolidation
Damage to hippocampus
Should only affect recent memories in consolidation, not remote memories as they are already consolidated.
Issues with Consolidation Theory
- Unspecified period for consolidation to complete
- Unclear mechanism by which long-term consolidation occurs
Cipolotti et al (2001)
Remote memory for facts impaired
Remote autobiographical memories were also severely affected
Impairment affected all periods of life
Issues with Neuroimaging studies in Autobiographical memories
- Memories asked to recall are self selected
- Activity may become contaminated by this procedure which makes people rethink of their memories.
Gilboa (2004)
Avoided self selected memories by asking friends and relatives to provide pictures relating to autobiographical events
Restrospective Neuroimaging studies
- Both remote and recent memories triggered by personal photographs- at the hippocampus
- Remote memory activation tended to have a more widespread distribution relative to recent memories
Multiple Trace Theory (MTT)
Nadel & Moscovitsch (1997
Dismissed that hippocampus has time limited role in memory
Re-encoding of older memories creates new hippocampal traces. As a result, incomplete hippocampal lesions will affect recent memories (few traces) more than remote memories (more traces) in a probabilistic manner.
