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

Copyright © 2009 Allyn & Bacon

How Your Brain Stores Information

Chapter 11Learning, Memory, and Amnesia

Studying Memory Neuroscientists

Psychophysiologists Behavioral Paradigms

Morris Water Maze


http://www.youtube.com/watch?v=24kDZncAC9M&feature=fvsr


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

Generally accepted



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


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


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


Tissues typically

excised in medial

temporal lobectomy



Conclusions from HM studies Aspects of memory managed by diff

parts of brain Damage to medial temp lobesaffects

explicit NOT implicit memories Not affect LTM, but does affect transfer

of STM to LTM


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


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


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


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


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.

http://en.wikipedia.org/wiki/File:Cajal-Restored.jpg


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


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

Enhancement in signal transmission between two neurons that results from stimulating them synchroniously

Enhanced communication between pre- and post synaptic neuronsimprovement in postsyn. To receive signals from pre Increasing activity of receptors and number of

receptors



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


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


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

Durbach (2000) Two changes in brain 1) Internal structure of neurons around

area of synapse 2)Increase in number of synapses

between neurons


Next Class


Stress and the Brain

http://www.youtube.com/watch?v=OHl7BewJ0yU&feature=related

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