Memory Systems

Memory Systems

1. Retention of Learned information

   • 1. Declarative Memory
     • 2. Non-declarative memory
       • Working memory
         • Temporal information storage
       • procedural memory - skills, habits
     • Facts and events

2. Karl Lashley

   • Trained rats to run through the maze to the food (Engram). He lesioned the rats brain and tested them before or after the learning of the task.
     • The rats who hadn't learnt the task yet really struggled to learn after the damage/lesion
       • The ones who had learnt the task made frequent mistakes indicating damage to their memory
   • 3 different types of lesions --> no one was different (in terms of effects) from the other
     • Found, instead that it was the overall size of the lesion that determined the deficit of impairment to rat
       • He didnt really have a very sensitive test though so it was hard to conclude definitive answers: what it did determine was that memory was sensitive to the whole brain (not one select region - memory storage is distributed around the brain)

3. Donald Hebb

   • Cell Assembly Theory
     • 1. Networks of neurons are activated at the same time by a stimulus
       • 2. When stimulus is gone, there is some residual activity between connections - the connected neurons
         • 3. Exposure to just part of the stimulus can activate the whole network again
           • "Fire together, wire together"
             • i.e. if cells fire at the same time, when the stimulus is presented again (the next time), the cells link together strongly
             • Example: The sight & smell of coffee, triggering neurons (activated next time by the sight and smell) in the hippocampus (connections are formed because they are activated at the same time = a cell assembly of coffee)
               • If you see it more than once, the connection is strengthened i.e. connections remain strong if cells are periodically activated
                 • If not activated again, assembly loses connections

4. Information flow through medial temporal lobe

   • Cortical Association areas
     • Parahippocampal and Rhinal cortical areas
       • Hippocampus
         • Thalamus, hypothalamus
         • Feedback mechanism to the cortical again

5. Radial Arm Maze Test

   • (a) Rats go down each arm for food only once
     • (b) Learn which arms are baited and avoid the rest
   • Rat model of hippocampal damage
     • Testing: 1. Memory for food location / 2. Memory for which area rat has been down before (hippocampus involved)
       • If you damage specifically the hippocampus in the rats, they remember food location but forget, which arm they've already been down before
         • Findings:
           • (a) normal rats go down each arm for food only once but not with Hipp lesions
             • (b) lesioned rats recall which arms were baited & which were not BUT they forget that they have already been down the baited arm!!!
               • Damaged Hippocampus: Impaired performance on the standard task (but not the modified task)

6. Striatum & Procedural Memory

   • Caudate nucleus + Putamen = Striatum
     • Lesions to the striatum disrupt procedural memory (habit learning)
       • NB: Raidal Arm Maze test relies on hippocampus.
         • BUT The modified radial arm maze, with lighted arms (lights guid rat to food, so only has to learn food-light :habit" or association), relies on striatum
         • Damaged Striatum: Impaired performance on the modified task (procedural memory) (but not the standard task)
           • NB: Parkinson's patients (Striatal impairments) show that human striatum plays a role in procedural memory
     • Modified Radial Arm Maze Test
       • = Double dissociaton