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Biopsych - Memory (Y2) - Coggle Diagram
Biopsych - Memory (Y2)
Memory systems
Atkinson-Shiffrin Multi Store Model of memory -
- Sensory register - modality specific information held for milliseconds
- Short-term memory - information held for less than 20 seconds, limited capacity, chunking
- Long term memory - information limitless in duration and capacity
- Information is stored and transferred in a linear, sequenced fashion - maintenance and elaborated rehearsal, and recall for transfer between stores - decay if not maintained
Baddeley's working memory model -
- Central executive - coordinates the activity of the slave systems
- Phonological loop - phonological store and articulatory process
- Visuo-spatial sketchpad - visual cache and inner scribe
- Episodic buffer - coordinates the sensory input from the other two and records temporal information
- Central executive = manipulation, storage function, STM = working with memory
Long term memory - Tulving:
- Declarative memory - episodic and semantic - explicit
-> Medial temporal lobe and diencephalon
- Non-declarative memory - implicit
-> Procedural memory - skills and habits
-> Repetition priming
-> Classical conditioning - emotional responses in amygdala and skeletal musculature in cerebellum
Memory is supported by distinct systems of time, capacity and content
- Encoding - moving information via sensory system -> STM -> LTM
- Requires mental effort
- Information can be lost
Where are memories stored - five brain areas implicated in memory:
- Memories are stored diffusely in the brain and thus can survive destruction of any single structure
- Memories become more resistant to disruption over time
- Inferotemporal cortex - visual memory function (Misyashita, 2019)
- Amygdala - emotional significance of experiences and thus emotional attachment to memory; strengthens emotional significance of episodic memories - explicit
- Prefrontal cortex - different parts have different roles, and mainly relates to loss of episodic memory - temporal order of events and deficits in working memory are noted - explicit
-> Some areas seem to perform fundamental cognitive processes during working memory and other regions participate in other processes
- Cerebellum and striatum - implicit procedural / sensorimotor memory as part of sensorimotor circuits
-> Cerebellum - Participates in storage of memories of learned skills through neuroplastic memories; conditioning stored in the way cerebellar neurons respond to stimuli - skill formation
-> Striatum - stores memories for stimuli-response relationships - habit formation
-> Also have a role even if the task is not motor based - have issues with probability tasks and amnesic patients struggle with remembering explicit training for a task
Working memory
A cognitive process of reatining, refreshing and manipulating visual and verbal information
Role in daily living -
- Without WM: Stimuli -> simple behaviour
- With WM: Stimuli -> internal representation -> concepts and plans -> complex behaviour
- WM impairment -> behavioural disorders
Delayed saccade task -
- Target flashed, outside the fixation, delay, saccade; move to place of the stimuli
- Neurons in the lateral intraparietal cortex are active also during the delay period
- Neurons in the prefrontal cortex are active only during the delay period
- Electrophysiological recording of two regions - PFC and LIP
Match-to-sample task - Todd and Marois, 2004 - Visual WM:
- Intraparietal sulcus (IPS) active during delay period
- The number of encoded dots increases up 3-4
- Neural activity in the IPS correlates with number of encoded dots
- IPS is a limited capacity storage of visual information
- Electric brain activity reaches its maximum at about 3-4 items
- IPS is responsible is transient and limited storage of visuo-spatial information (STM)
- Inferior occipital areas involved in visual processing (sensory memory) - not storage
- Medial frontal brain areas is monitoring the task - not storage
Articulatory loop - PET study - verbal WM -
- Cognitive subtraction design
-> Articulatory loop - includes storage and rehearsal
-> Rhyming judgement - includes rehearsal
-> Common in AL and RJ - rehearsal
-> AL and RJ - storage
-> Broca's area involved in rehearsal
-> Supramarginal gyrus involved in storage
- Phonological loop operates in supramarginal gyrus and Broca's areas
- Visual-spatial sketchpad operates in lateral intraparietal cortex, prefrontal cortex and intraparietal sulcus
-> Monitored by medial frontal brain areas and uses information from inferior occipital areas
- Central executive -
-> Wisconsin sorting task - neural activity in the occipital (visual) cortex, superior parietal lobule and prefrontal cortex
-> Neural activity in the PFC correlates with task difficulty - explicit rule changes have less activity than implicit ones
-> PFC is important for central executive
-> Chunking - memorisation of structured patterns (cognitive subtraction design)
--> PFC is more active during memorising structured patterns
--> PFC involved in chunking
- Working memory involves retaining, refreshing and manipulating information
- Allows complex and adaptive behaviour
- WM functions are supported by a distributed frontoparietal network
-> Parietal regions - limited capacity storage for STM - visual memory
-> Broca's area and supramarginal gyrus for phonological loop
-> Frontal regions - manipulation in CE
- WM and attention are strongly linked - dual-task interference makes WM operations harder
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Damage to memory
Amnesic effects of bilateral medial temporal lobectomy:
- Case of HM - removal of hippocampus, amygdala and adjacent cortex
-> Retrograde amnesia - occurred with HM
-> Anterograde amnesia - cannot store new memories in short or long term
- Formal assessment of HM
-> Digit span + 1 test - long term memory test; asked to repeat 5 digits read in 1 second intervals
-> Block-tapping test - global amnesia - had amnesia for all information presented in all sensory modalities; repeating sequence of block tapping
-> Mirror-drawing test - star drawing - anterograde amnesia
-> Incomplete-pictures test - able to form long term memories as he could identify objects
-> Pavlovian conditioning
- Scientific contributions
-> Medial temporal lobes are important, challenged the idea that memory functions are distributed - specific mnemonic processes in individual structures
-> Supported different modes of storage for short term, long term and remote memory and the importance of the medial temporal lobes in memory consolidation
-> Led to discovery of explicit and implicit memories
Effects of global cerebral ischemia on the hippocampus and memory:
- Patients who experienced an interruption of blood supply to their entire brain - often suffer from medial temporal lobe amnesia
- Selective hippocampal damage can cause medial temporal lobe amnesia comes from cases of transient global amnesia, which is the sudden onset of amnesia without any cause
- Leads to cell loss in the pyramidal cell layer of the CA1 hippocampal subfield
- Medial temporal lobe amnesia - severe anterograde amnesia and moderate retrograde amnesia for explicit episodic memories
Amnesia of Alzheimer’s disease -
- Progressive deterioration of memory, and the dementia becomes so severe the individual becomes incapable of simple activities
- Both retrograde and anterograde amnesia, and loss of explicit memory in short term and some areas of implicit memory
- Acetylcholine levels are greatly reduced - basal forebrain also linked to amnesia and so this depletion could be a cause - damage to basal forebrain
- Also involves prefrontal cortex and medial temporal lobes
Posttraumatic amnesia:
- Victims of closed head traumatic brain injuries and comas often feel confusion - permanent anterograde and retrograde amnesia for many of the events leading up to it and directly following it
- More severe blows to the head produce longer comas, longer confusion and longer periods - islands of memory; surviving memories for isolated events that occurred during periods for which other memories have been wiped out
Gradients of retrograde amnesia and memory consolidation:
- Hebb's theory of memory consolidation -
-> Memories of experiences are stored in the short term by neural activity reverberating in closed circuits
-> These patterns of neural activity are susceptible to disruption but eventually they induce structural changes in the involved synapses, which provide stable long term storage
-> Electroconvulsive shock seemed to provide a controlled method of studying memory consolidation
Brief, intense, diffuse, seizure-inducing current that is administered to the brain through large electrodes attached to the scalp
- By disrupting neural activity, ECS would erase from storage only those memories that had not yet been converted to structural synaptic changes; the length of retrograde amnesia would therefore provide an estimate of the length of memory consolidation
- Theory implies it is a relatively brief process, but some studies have found evidence of longer gradients
-> Squire, Slater and Chace (1975) - long gradient of ECS-produced retrograde amnesia; they measured the memory of a group of ECS treated patients for TV shows that had played for one season only - tested patient twice on different forms
-> Once perform they receive a series of five shocks and once after - difference between scores served as an estimate of memory loss - disrupted retention in the shows that had played 3 years prior but not those that had played earlier
Memory consolidation is that it continues for a very long time if not indefinitely - lasting memories become more and more resistant to disruption throughout a person’s life
- Each time a memory is activated it is updated and linked to additional memories - increases memory resistance to disruption by cerebral trauma, concussions or ECS
- Hippocampus - memories are temporarily stored here until they can be transferred to a more stable cortical storage system
-> Standard consolidation theory or dual trace theory
-> When a conscious experience occurs, it is rapidly and sparsely encoded in a distributed fashion throughout the hippocampus and involved structures
-> Retained memories become more resistant to disruption by hippocampal dysfunction because each time a similar experience occurs or the original memory is recalled, a new engram (chane in the brain that stores a memory) is established and linked to the original one
-> Aspects of original memory are transformed into semantic memory which has storage less dependent on the hippocampus and more on cortical structures, making it easier to recall and the engram more difficult to disrupt
Reconsolidation -
- Each time a memory is retrieved from long term storage, it is temporarily held in labile (changeable or unstable) short-term memory, where it is once again susceptible to posttraumatic amnesia until it is reconsolidated
- Interest in the process of reconsolidation - Nader, Schafe and LeDoux (2000)
-> Infused protein-synthesis inhibitor anisomycin into the amygdalae of rats shortly after the rats had been required to recall a fear-conditioning trial
-> The infusion produced retrograde amnesia for the fear conditioning, even though the original conditioning had occurred days before
-> Most research on reconsolidation had involved fear conditioning but some evidence suggests it may be a general phenomenon in the nervous system
Role of the hippocampus
- Started with animal models and HM case - lesions are not ethical to recreate and animal models not fully generalisable, and as a result leads to some issues of knowing how far the damage extends
- Mostly tested implicit memory
- Incorrectly assumed amnesic effects of media temporal lobe lesions were largely, if not entirely, attributable to hippocampal damage - and thus, most models focused on hippocampal lesions
Rat version of the delayed non-matching-to-sample test - specific role of hippocampal damage noted
- Lesion achieved through aspiration of the hippocampus and medial temporal cortex - in rats, the extraneous damage associated with aspiration lesions of the hippocampus is typically limited to a small area of parietal neocortex
- Mumby Box task closely matches monkey task
- Rats were assumed to not be able to perform a task as complex as that required for the delayed nonmatching to sample test, but rats perform similarly to monkeys
- Bilateral lesions of the rats’ hippocampus, amygdala, and medial temporal cortex combined produce major deficits at all but the shortest retention intervals
Animal models of recognition amnesia -
- Monkey version of the delayed non-matching to sample test - monkeys with a bilateral medial temporal lobectomy have major problems forming long-term memories for objects encountered in the delayed nonmatching to sample test
-> Presented with distinctive object under which it finds food, and after a delay they are presented with another object and the same, and they must remember the sample object to find food - well trained monkeys performed correctly, but those with the damage had major deficits
-> Mirrored HM as performance was normal at delays of a few seconds but increased to delays of a few minutes, and their performance was vulnerable to distraction - humans with same damage mirror this
-> Amnesia resulting from medial temporal lobe damage is due to three structures - the amygdala, the hippocampus and adjacent medial temporal cortex
Infantile amnesia -
- Remember little of the events of our infancy
- However, we do have implicit memories stored for things we experience even if we do not explicitly remember them - explicit memory develops with experience
Neuroanatomical basis of the object-recognition deficits resulting from bilateral medial temporal lobectomy:
- Removal of this area leads to severe or permanent deficits in performance on these tests, whereas bilateral removal of the hippocampus produces modest deficits, and amygdala interference produces none
- Damage to pyramidal layer of the CA1 hippocampal subfield leads to severe performance deficits
- Hippocampus appears to have a role in object recognition deficit
-> Damage to other brain structures contributes to observed amnesia following a global cerebral ischemia (Mumby et al, 1996) - damage can be diffuse after this
-> Those with reduced hippocampal volume were much more likely to suffer from anterograde amnesia, but they also have extensive neocortical damage (Allen et al, 2006)
- Medial temporal lobe has a specific role in forming explicit episodic memories, and hippocampus has a minor role in object recognition compared to adjacent medial temporal cortex
Neurons of the medial temporal lobes and memory -
- Tests - Morris water maze test (rats struggle with hippocampus damage), radial arm maze test (measure of reference and working memory)
-> Reference memory - memory for general skills and tasks that are required to perform a task
-> Rats with lesions display major deficits on both reference memory and the working memory measures of this test
- Hippocampal place cells and entorhinal grid cells -
-> Hippocampus role in spatial processing - place cells which are neurons which respond only when a subject is in a specific location
-> When in a novel environment, none of the hippocampal neurons have a place field - then, as you familiarise, many neurons acquire a place field and so each will fire only when the rat is in a particular part of the environment
-> Each place cell has a place field in the environment which it operates in
The hippocampus as a cognitive map: not only involved in spatial processing
- Some cells code for the temporal aspects of an experience, and the hippocampus has been shown to play a role in learning about social organisation in humans and in mice
- Also has a role in coding of concepts
- Generates a cognitive map, not just a spatial one
Engram cells -
- Optogenetics - insertion of an opsin gene into neurons, and then use of light to hyperpolarize or depolarized the neurons - used in learning
- Neurons that undergo persistent change as the result of experience so that when they are inhibited or activated, the retrieval of the original experience is triggered or suppressed
- Engram cells are identified through tagging (locate the learning task that activates it) and manipulated
- Able to reverse behaviour or cause memory retrieval through manipulating these cells - Alzheimer's may be due to retrieval deficit rather than encoding deficits
Spatial processing in entorhinal cells -
- Entorhinal cortex - area of medial temporal cortex which is a major source of neural signals to the hippocampus
- Grid cells are neurons with repeating patterns of evenly spaced hexagonal shaped place fields that tile an environment, and they fire when an animal transverse a point of intersection or when its gaze reaches an intersection
- Inform place cells of their field and spatial information
- Flexible - when spatial cues are rotated or sheared, the grid pattern is also rotated or sheared
- Even spacing of place fields in grid cells could enable spatial computations in hippocampal place cells
- Head-direction cells tuned into head orientation also inform spatial awareness, as does border cells which fire when a subject is near the border of its immediate environment
Two lines of explanation for the relationship
- Major pathway from entorhinal cortex and hippocampus
- Entorhinal grid cells respond in an ongoing fashion to an animal’s location, whereas hippocampal place cells are only active in particular spatial locations
However, relationship is complex - properties of hippocampal place cells emerge before the emergence of stable entorhinal grid cell firings
- Place cells can still function after entorhinal grid cells have been eliminated
- Intact inputs from place cells are necessary for the reliable firing of grid cells
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