1. Copyright © 2009 Allyn & Bacon How Your Brain Stores Information Chapter 11 Learning, Memory, and Amnesia

2. Studying Memory Neuroscientists Psychophysiologists Behavioral Paradigms Morris Water Maze Copyright © 2009 Allyn & Bacon

3. Brain Mechanisms in Memory Engram: physical representation of memory in brain Karl Lashley (1929)- earliest psychologists to study Believed memory stored in association cortex Performed series of lesion Deficit related to size of lesion, not location His conclusion: equipotentiality

4. Generally accepted Copyright © 2009 Allyn & Bacon

5. Localization of Memory Penfield (1958)-stimulation in parts of temporal lobe produced specific memories in human patients; flawed because could’ve been related to seizures Sparked interest in Temporal lobes in role of formation and retention of long- term memories

6. Copyright © 2009 Allyn & Bacon Temporal lobe and Memory Patients w/ anterograde amnesia (deficit in ability to form NEW memories) Case Study: HM Accident led to seizures  bilaterial removal of temp lobes (hippo, amygdala, & some assoc cortex) Seizures improved; IQ, personality, skills unchanged, earlier memories intact Suffered anterograde amnesia

7. Copyright © 2009 Allyn & Bacon Amnesic Effects of Bilateral Medial Temporal Lobectomy H.M. – an epileptic who had his temporal lobes removed in 1953 His seizures were dramatically reduced – but so was his long-term memory Mild retrograde amnesia and severe anterograde amnesia

8. Copyright © 2009 Allyn & Bacon Tissues typically excised in medial temporal lobectomy

9. Copyright © 2009 Allyn & Bacon

10. Conclusions from HM studies Aspects of memory managed by diff parts of brain Damage to medial temp lobes  affects explicit NOT implicit memories Not affect LTM, but does affect transfer of STM to LTM

11. Copyright © 2009 Allyn & Bacon Amnesia Retrograde (backward-acting) – unable to remember the past Anterograde (forward-acting) – unable to form new memories While H.M. is unable to form most types of new long-term memories (LTM), his short-term memory (STM) is intact

12. Copyright © 2009 Allyn & Bacon Where Are Memories Stored? Each memory is stored diffusely throughout the brain structures that were involved in its formation Hippocampus – spatial location Perirhinal cortex – object recognition Mediodorsal nucleus – Korsakoff’s Basal forebrain – Alzheimer’s disease

13. Copyright © 2009 Allyn & Bacon Where Are Memories Stored? (continued) Damage to a variety of structures results in memory deficits Inferotemporal cortex – visual perception of objects – changes in activity seen with visual recall Amygdala – processes emotional memories

14. Copyright © 2009 Allyn & Bacon Where Are Memories Stored? (continued) Damage to a variety of structures results in memory deficits (continued ) Prefrontal cortex Temporal order of events and working memory Different part of prefrontal cortex may mediate different types of working memory – some evidence from functional brain imaging studies

15. Copyright © 2009 Allyn & Bacon Let us assume that the persistence or repetition of a reverberatory activity (or "trace") tends to induce lasting cellular changes that add to its stability.... When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased.

16. Copyright © 2009 Allyn & Bacon Synaptic Mechanisms of Learning and Memory What is happening within the brain structures involved in memory? Hebb – changes in synaptic efficiency are the basis of LTM Repeated stimulation of neural circuits Long-term potentiation (LTP) – synapses are effectively made stronger by repeated stimulation

17. Copyright © 2009 Allyn & Bacon Long-term Potentiation (LTP) Rapid series of electrical shocks to hippo pathway increases PSPs in target cells. Experience makes these synapses more efficient Change in responsiveness in target cells called LTP Memories are thought to be encoded by modification of synaptic strength

18. Enhancement in signal transmission between two neurons that results from stimulating them synchroniously Enhanced communication between pre- and post synaptic neurons  improvement in postsyn. To receive signals from pre Increasing activity of receptors and number of receptors Copyright © 2009 Allyn & Bacon

19. Long-Term Potentiation (LTP) LTP is consistent with the synaptic changes hypothesized by Hebb LTP can last for many weeks LTP only occurs if presynaptic firing is followed by postsynaptic firing Hebb’s postulate for learning Co-occurrence of firings in pre- and postsynaptic neurons necessary for learning and memory

20. Copyright © 2009 Allyn & Bacon LTP as a Neural Mechanism of Learning and Memory Elicited by high frequency electrical stimulation of presynaptic neuron; mimics normal neural activity LTP effects are greatest in brain areas involved in learning and memory

21. Copyright © 2009 Allyn & Bacon Structural Changes from LTP Increase in number and size of synapses Increase in number and size of postsynaptic spines Changes in the pre-and post-synaptic membranes

22. Durbach (2000) Two changes in brain 1) Internal structure of neurons around area of synapse 2)Increase in number of synapses between neurons Copyright © 2009 Allyn & Bacon

23. Next Class Copyright © 2009 Allyn & Bacon Stress and the Brain