Lecture 6 - Learning & Memory Mammals

Lecture 6 - Learning & Memory Mammals

1. Working memory 'on task memory'

   • Task specific - ordered in time and space as required
   • Limited capacity system that temp. holds info available for processing
   • Important for reasoning and guiding decision making
   • Different from STM as allows stored info to be updated/manipulated
   • Has a limited capacity - few bits of info at a time
     • Deleted after use
   • Dynamic memory that can be disturbed easily, prone to interference
   • If the info. is lost (due to interference/distraction) there is no retrieval
   • Classic rodent task: 8-arm radial maze test
     • Every arm is baited with a piece of food
       • Animals can explore arms but to be efficient they have to remember during the task which are has already been visited
         • Information is of no value after the task has been completed and memory is reset for the next task

2. Time course of memory

   • STM - milliseconds to minutes
     • Storage of info but this info is not manipulated
     • Limited capacity ~7 items
     • Often data rich, not suitable to store all info in the LTM
     • Selectively transferred over to LTM
   • LTM - unlimited capacity?

3. Classifications of LTM

   • Explicit/declarative memory
     • Conscoius memory
     • Episodic (events) and semantic (facts)
     • Flexible - multiple pieces of info associated under different circumstances
     • 4(+) distinct operations of explicit learning
       • Stage 1: Encoding
         • Attending to the relevant info & linking it with an established memory
         • Influenced by motivation
       • Stage 2: Storage
         • Neural mechanisms by which memory is retained over time
       • Stage 3: Consolidation
         • Temporary and labile info becomes more stable
         • Involves gene expression, protein synthesis and structural synaptic changes
         • Newer concept of consolidation of LTM into neural systems (systems consolidation)
       • Stage 4: Retrieval
         • Retrieve stored info
       • Stage 5(?): Re-consolidation
         • Once recalled info is actually labile and can be altered slightly (false-memories)
   • Implicit/nondeclarative memory
     • Unconscious memory/automatic
     • Inflexible - tightly connected to conditions under which the learning occurred
     • Covered in last lecture
     • Associative implicit memory
       • Classical conditioning
         • CS = food, US = bell, CR = salivation to bell *CHECK*
       • Operant conditioning
         • 'Trial and error learning'
         • Random activity becomes paired with a reinforce (+ or -)
         • Complex behaviour (e.g. pressing a lever) becomes paired with a positive reinforcer (e.g. food) or a negative stimuli (e.g. loud noise)
         • 5-choice serial reaction time task in rates
           • Uses a nose-poke box with 9 holes
             • One of the holes will light up and the rat has to poke it with his nose to get food
     • Non-associative implicit memory

4. Patient H.M. - the most important man in L&M?

   • Pateint H.M. had uncontrollable temporal lobe epilepsy
     • Underwent a bilateral lesion (removal) of the temporal lobes (including the hippocampus, amygdala and associated cortex)
     • Henry Gustav Molaison, 1926-2008
       • Same IQ
       • Working memory intact
       • Semantic memory intact
       • No evidence of retrograde amnesia (has an intact memory of events that occurred prior to surgery)
       • Intact motor skills but would forget he'd done the task the day before
       • However had devastating and specific anterograde amnesia
         • Memory only lasts a couple of minutes
         • New STMs are not converted into LTM
   • Showed us about...
     • Memory is a distinct cerebral function, separate from other cognitive and perceptual functions and is not just an integral part of these functions
     • The 'Medial Temporal Lobe'
       • Hippocampus, amygdala, adjacent parahippocampal cortex
       • Plays an important role in memory formation

5. Brain areas are involved in different types of learning

   • Neocortex is the storage place for LTM
   • Tends to be specialised
     • Visual tasks -cortical areas involved in visual processing, such as object or spatial information processing
   • Prefrontal cortex
     • Executive function, working memory and influences memory retrieval
   • Parietal lobe
     • Navigation
   • Cerebellum
     • Motor memory
   • Occipital lobe
     • Visual processing
   • Temporal lobe
     • Hippocampus
       • Memory encoding, consolidation and retireval
       • Has an important role for rodents in spatial learning and memory
         • Can be tested using the Morris Water Maze
           • Animals are trained to find a submerged platform to escape from a tub of water
             • External cues were used for navigation
             • Acquisition phase
               • Time to find the platform is recorded and the length of the swim path is measured
                 • Shows over the days the rodent takes less time and the movements are less random as it begins to learn where the platform is
             • Memory recall test (probe trial)
               • Platform is taken out of the maze to see where the animal is searching
               • If a memory has been formed the animals should spend more time in the quadrant where the platform used to be
                 • This is impaired in rats with hippocampal lesion and in mice with beta-amyloid
           • Developed as a simple spatial task that avoids olfactory cues in the maze
       • Memory functions
         • Rodents - lesion of the hippocampus impairs complex association learning, spatial learning, memory and memory consolidation
         • Humans - hippocampal lesions are known to impair the transfer of STM to LTM
         • Plays a crucial role in converting STMs to LTMs by processing new memories and temp. storing them priro to permanent storage in the cortex
     • Amygdala
       • Emotional memory