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  • 1. Neural Basis of Cognition Neural Basis of Cognition Lecture 5 Learning and Memory Learning and Memory
  • 2. The Famous Patient, H.M. The Famous Patient, H.M. • Severe epilepsy can be debilitating and even lead  p py g to death. In extreme cases, surgery is used to  treat epilepsy • In 1953 a patient called H M (to preserve In 1953, a patient called H.M. (to preserve  anonymity) with severe epilepsy was treated  surgically via removal of portions of his left and  right medial temporal lobes – Removed: two thirds of his hippocampus,  parahippocampal gyrus, and amygdala gyrus, and amygdala – Damaged/Atrophied: the remainder of his  hippocampus, entorhinal cortex, some of his  anterolateral temporal cortex temporal cortex
  • 3. H.M. • What happened? at appe ed? – His epilepsy was successful brought under control. – He developed severe memory deficits ‐ amnesia. • Why is his case so famous? – His memory abilities were extensively studied prior to  the operation, allowing extensive postoperative  h ll analysis. – Today’s imaging techniques did not exist; the fact that Today s imaging techniques did not exist; the fact that  damage was done during surgery meant that it was  known exactly what parts of his brain were damaged.
  • 4. H.M. • What abilities have been destroyed? What abilities have been destroyed? – Creation of new short term memories – he cannot  recall recent weather, the current date, where he  currently lives, or even a conversation with  someone if there is an interruption that lasts a few  minutes – Learning of new information – He would misidentify current pictures of himself He would misidentify current pictures of himself  as pictures of his father – He had no idea of his fame
  • 5. H.M. • What abilities were not destroyed? What abilities were not destroyed? – Linguistic ability, recall of memories formed before  the operation, ability to reason  almost all  the operation ability to reason ‐ almost all abilities he had before the operation aside from  those listed on the previous slide – Learning of new skills – Working memory (until distracted) g y( )
  • 6. H.M. • The extensive study of H M taught us much The extensive study of H.M. taught us much  about what we now know about learning and  memory in humans. memory in humans • He passed away in 2008, still unaware of his  fame. fame
  • 7. Memory • What is memory? What is memory? – Memory is the storing of information related to  day to day experiences for later retrieval. day‐to‐day experiences for later retrieval • Are there different types of memory? – Yes Yes. • Is memory stored in a single part of the brain? – No.
  • 8. How can amnesia occur? How can amnesia occur? • Damage to the medial temporal lobe Damage to the medial temporal lobe – Herpes simplex encephalitis, blockage of blood  supply, hypoxic ischemia, trauma, Alzheimer s  supply hypoxic ischemia trauma Alzheimer’s disease • Damage to the midline diencephalic region Damage to the midline diencephalic – Korsakoff’s diease (due to chronic alcohol abuse),  blockage of blood supply, third ventricle tumors blockage of blood supply, third ventricle tumors
  • 9. Is amnesia always permanent? Is amnesia always permanent? • No No. – Closed head injury (such as in a motorcycle  accident) can cause amnesia that almost  accident) can cause amnesia that almost completely disappears – Electroconvulsive therapy (memory recovers over Electroconvulsive therapy (memory recovers over  weeks to months) – Seizures can temporarily induce amnesia that  p y heals completely.
  • 10. Memory impairment Memory impairment • Anterograde amnesia: Impairment in forming new memories. – Almost always associated with some retrograde amnesia. • Retrograde amnesia: Impairment in memory for information  acquired prior to amnesia‐inducing event – I l dh di j In closed head injury, retrograde amnesia extends back less than a  t d i t d b kl th week before the injury in 80% of patients, but can extend to years. – H.M.’s retrograde amnesia extended 11 years; unclear how much of  this was due to the seizure disorder, which began 11 years before  surgery, and how much was due to the surgery – Retrograde amnesia that extends back decades is often seen in  progressive disorders such as Korsakoff’s, Alzheimer’s, Parkinson’s, or  u t gto s Huntington’s – Temporal gradient (Ribot’s Law): generally, more recent memories are  more severely affected, e.g. identifying Ronal Reagan – “Flat” Gradients have been observed
  • 11. Amnesia • Modality general, including in H.M.’s case Modality general, including in H.M. s case • Therefore, amnesia is a deficit in memory  functions rather than perceptual, linguistic, or  functions rather than perceptual, linguistic, or other cognitive processes • Unilateral hippocampal damage CAN be Unilateral hippocampal damage CAN be  modality‐specific – Left hemisphere damage can lead to selective  p g impairment for verbal material, right hemisphere  damage for nonverbal material
  • 12. Working Memory Working Memory • Digit span task: repeating back, in order, a Digit span task: repeating back, in order, a  string of digits – H.M.: Normal performance (7 +/‐ 2 digits) p ( / g ) • Extended digit span task: once a patient’s digit  p , g y span is known, the same string is iteratively  lengthened by one digit until a limit is reached – Normal performance: 20+ digits – H.M.’s performance: no longer than the digit span  task
  • 13. Retained abilities Retained abilities • Skill learning Skill learning – H.M. did exhibit some forms of learning, though  he was unaware of having done so he was unaware of having done so – Mirror tracing task: tracing the outline of a figure  by looking at it in a mirror by looking at it in a mirror • Across sessions, H.M. began to perform this task more  accurately and more quickly – Rotary pursuit: tracking a circularly moving target • With practice, amnesiacs become more adept
  • 14. Retained abilities Retained abilities • These are motor skills that are repeated over These are motor skills that are repeated over  and over; are amnesiacs learning the specific  instance of those tasks (such as drawing a  instance of those tasks (such as drawing a particular figure) or the skill in general? • Mirror reading task: mirror images of word Mirror‐reading task: mirror images of word  triplets shown –A Amnesiacs show the same improvement in this  i h th i t i thi task – even with new words – that non‐amnesiacs  do, even if the patients cannot recall practicing do even if the patients cannot recall practicing
  • 15. Retained abilities Retained abilities • Repetition priming: performance is enhanced Repetition priming: performance is enhanced  as a result of previous exposure to an item – Gollin incomplete pictures task: patients are incomplete pictures task: patients are  shown very degraded and incomplete line  drawings of objects and are asked to name them g j • The procedure is repeated with increasingly incomplete  drawings • Amnesiacs showed improvement on this task
  • 16. Retained abilities Retained abilities • Word‐stem completion task Word stem completion task – Patient is given a list of words to study – After a delay memory is tested in two ways using After a delay, memory is tested in two ways using  three‐word stems of these words: • Patient is asked to recall the word from the study list Patient is asked to recall the word from the study list  that began with the given three‐letter stem – Amnesiacs perform poorly • Patient is asked to give “the first word that comes to  mind” when given a three‐letter stem – Amnesiacs performed at normal levels p
  • 17. Memory loss patterns Memory loss patterns • Explicit memory: Explicit memory: – Conscious recollection of some prior event • Implicit memory: Implicit memory: – Subconscious recollection of information about some  p prior event – Does not depend on consciously remembering that  event – “memory without awareness” • Explicit but not implicit memory can be impaired  or destroyed due to hippocampal damage
  • 18. Eye movement monitoring Eye‐movement monitoring • Amnesiac is shown an image with three points of  interest – Eye movements indicate he looks at each of the three  p points of interest • After a delay, the amnesiac is shown the same image  with one point of interest removed – There are about as many eye movements to the now‐ There are about as many eye movements to the now‐ absent third point of interest as there are to the other two  points of interest, but if the patient is asked, he will not  remember that there was a third point of interest p • This is a demonstration of implicit versus explicit  memory impairment due to hippocampal damage
  • 19. Neuroimaging evidence • PET and fMRI provide converging evidence PET and fMRI provide converging evidence  that the hippocampal system is associated  with relational memory with relational memory • Higher activation when given a task that  requires memory of relations among items requires memory of relations among items
  • 20. The role of the hippocampal The role of the hippocampal area • After damage to the hippocampal area After damage to the hippocampal area,  amnesia can develop • Therefore the hippocampal area is vital for Therefore, the hippocampal area is vital for  the formation of new memory • Af d After damage, previously formed memories  i l f d i can still be recalled • Therefore, the hippocampus neither stores  memories nor is mandatory for memory recall
  • 21. Where is memory stored? Where is memory stored? • Imaging studies and cell recording studies show  g g g that declarative memory is distributed by  modality, in the regions which initially process  sensory input sensory input – Visual information is stored in the visual system,  auditory information is stored in the auditory system,  and so on and so on • Similar studies show that procedural memory is  stored in the parts of the brain involved in  p carrying out the related action – For example, motor skills are learned and “stored” in  the motor cortex the motor cortex
  • 22. Integration of memory systems Integration of memory systems • Unclear Unclear.
  • 23. The memory system The memory system • Encoding: – Memories must be created and stored • Consolidation Consolidation: – Memories may be “strengthened” • Retrieval: – Memories must be retrieved for later use
  • 24. Hippocampus • Encoding: cod g: – Activation during encoding of faces, words, scenes,  objects; degree of activity is proportional to degree of  memorization i ti – fMRI studies show that the amount of activity at the  time an item is first seen and encoded predicts how  p well that item is remembered later on – Subsequent memory effect: subsequently  remembered items are associated with greater  b d it i t d ith t activation at encoding time than items not  subsequently remembered
  • 25. Hippocampus • Consolidation: – Unclear mechanism – Theory: reactivation of already stored memories Theory: reactivation of already stored memories  during the time after learning plays a crucial role  in consolidation in consolidation – There is some evidence tying such reactivation to  activity in the hippocampus during sleep  y pp p g p subsequent to a learning event
  • 26. Hippocampus • Retrieval: – Hippocampal system activation occurs during  retrieval of memory retrieval of memory – The purpose of this activation has not been  determined
  • 27. Next Lecture Next Lecture • Other areas involved in encoding Other areas involved in encoding,  consolidation, retrieval • Mechanism of the forming of memories Mechanism of the forming of memories  (learning) • C Computational and theoretical modeling of  i l d h i l d li f learning