TABLE OF CONTENTS
KEY CONCEPTS IN THIS LECTURE 1. Learning is the acquisition of new knowledge and memory is the retention of learned information. Memory is laid down in stages. Short term memory last seconds to hours and has limited capacity. Long term memory last days to years, has much greater capacity, and is derived from short term memory through the process of consolidation (involving practice). Remembering is retrieving information from memory stores. Forgetting is the inability to retrieve information. There are a number of different types of memory. Declarative memory is for remembering facts and events (e.g., places you have visited or learning a chemistry formula). Procedural memory is for habitual motor behaviors (e.g., writing your name). Working memory temporarily holds and interrelates information for a particular mental task (e.g., the delayed task response). Associative learning is a type of learning which forms a relationship between different events. There are two types of associative learning: Classical Conditioning, which is an association between two stimuli (e.g. the air puff and sound in the eye blink reflex), and Instrumental Conditioning, which is an association between a response and a stimulus (e.g., pushing a level for a food pellet) 2. Long term potentiation (LTP) is a neuronal model for learning. LTP is a permanent change in a neural circuit following strong or repeated stimulation resulting in an increased strength of synaptic connections (e.g., increased dendritic spine number). LTP has been studied in the CA1 field of the hippocampus where strong stimulation of the pyramidal cells results in LTP. The cellular basis for LTP is complex but involves release of glutamate, an excititory neurotransmitter, from the presynaptic cell. Glutamate acts on both the NMDA (Ca++ gated) and AMPA (Na+ gated) receptors. Ca++ entering the post-synaptic cell eventually causes phosphorylation of the AMPA receptor, increased protein synthesis, and release of nitric oxide (NO), a gas. NO diffuses back to the presynaptic cell where it encourages release of additional glutamate (=positive feedback). This feedback loop is critical for development of LTP. The increased protein synthesis in the post-synaptic cell ultimately results in the insertion of additional AMPA receptors and selective strengthening of the synapse. Drugs which selectively block these cellular pathways inhibit learning. 3. Long term depression (LTD) is the inhibition of an event following strong stimulation. LTD has been studied in the Purkinje cells of the cerebellum, and has some functional characteristics which parallel LTP. 5. Acquisition of bird song also has been studied extensively as a model for learning. Birds have individual dialects that are learned as juveniles. Development of bird song involves 1) listening to the father's song following hatching (Sensory Phase), 2) repeating and filtering (dropping syllables and adding modifications) those songs as a juvenile (Sensorymotor Phase), and 3) acquiring the permanent, unchanging song of adults (Crystallization). Singing in male birds relies on the presence of Testosterone. The brain of the male bird consists of unique song learning (LMAN, Area X, DLM) and song producing (HVc, RA, nXIIts) pathways. Some birds, like the canary, relearn their song each season (the Sensorymotor Phase and Crystallization are repeated annually). In this species, most neurons in the HVc die during late summer followed by an increased neurogenesis in the fall. LECTURE OBJECTIVES 1. Provide some basic ideas about
learning and where in the brain learning occurs
2. Present basic neuronal models for learning in mammals 3. Establish the role of learning in bird song LECTURE OUTLINE
I. INTRODUCTION
A. Learning is the process by which we acquire new information.
Memory is a cognitive process that resulting in the storage of
learned information.
1. Memories can last a short time (Short term memory) or a long
time (Long term memory)
2. Working memory temporarily holds and interrelates information for a
particular mental task
3. The general process of how we learn
a. Consolidation of information occurs through practice
4. Consolidation occurs in the hippocampus
a. Case Study: H.M.
b. There are two forms of amnesia **
II. LONG TERM POTENTIATION AND LONG TERM DEPRESSION
A. Long Term Potentiation (LTP)
1. Neuronal architecture in the hippocampus
a. Tetany of CA1 neuron results in LTP
b. Tetany and summation can occur in graded responses
c. LTP is a long term change in EPSP
2. How behavior and LTP are related: Fear-potentiated startle
a. Learning associations: If it looks like a rose and smells like a
rose, it must be a rose.
3. How does LTP work at the level of the synapse
a. Learning increases the number of dendritic spines
b. Glutamate release, NMDA & AMPA receptors, increased
Ca++ release and protein kinase are involved
c. Positive feedback occurs (NO and AMPA phosphorylation)
to enhance the response
d. Protein synthesis is involved
e. Increased AMPA receptors and enhanced dendritic spines strengthen
the synapse
f. Other possibilities for strengthening a synapse
B. Long Term Depression (LTD) in cerebellum
1. Role of cerebellum in conditioning and behavior **
III. MEMORY: THE DETAILS
A. Many brain areas are involved in memory.
1. What is dementia?
B. Declarative Memory stores information on form, position of an object,
sound, etc.
1. Declarative memories are stored in the association cortices as well as
other sites.
a. Evidence comes from lesion studies, local stimulation, and fMRI
2. Declarative memory has a large capacity
a. Demonstration of how quickly we learn visual content (Episodic learning)
C. Working Memory
1. Working memory is temporary information storage about immediate
perceptions and instant retrival of archived information.
a. Examples of working memory (planning a chess move)
2. Delayed Matching-to-Sample Response: An example of working memory
a. The cerebral cortices are essential inputs to working memory
b. Working memory occurs in the prefrontal cortex (PFC)
1) Lesions in this area affect working memory
2) Neurons in the PFC store memories
3) Working memory in young primates is absent until PFC
circuitry forms
3. The principle sulcus of the PFC has segregated functions
D. Procedural Memory ** **
1. Learning a behavior that is difficult at first, but becomes easy
with practice
a. Basal ganglia are involved in procedural memory (e.g., driving
a "stick shift" car)
b. Basal ganglia receive abundant sensory and motor inputs
for this task
E. Emotional Memory
1. Processing of this information involves multiple paths
(Example: Alarm Response)
F. Associative Memory forms relationships between different events.
1. Classical Conditioning is an association between two stimuli that is learned
a. Example: Eye Blink
1) One stimulus is the unconditional stimulus (US)--air puff
2) The other stimulus is the conditional stimulus (CS)--sound
3) A conditioning response (CR), the eye blink, occurs with time
4) Eye blink neuronal model
b. Conditioning takes time
1) With the US, an association is gradually learned (=Conditioning)--
Without the US the association is lost (=Extinction)
c. Classical conditioning involves a number of brain areas, such
as the amydgala
1) Specific role of the central nucleus and lateral nucleus in the amydgala
2) Fear-induced startle also activates the sympathetic nervous system
2. Instrumental (=Operant) Conditioning is a flexible type of learning where a
motor response is associated with a stimulus
a. This form of of conditioning can be reinforcing (+) or punishing (-)
b. Motivational state (e.g., hunger) is also important in instrumental
conditioning
c. Example: Pushing a lever for food
d. Instrumental conditioning involves a number of ventral tegmental
projections to the cerebrum
1) The Dopamine projection to the Nucleus accumbens (N acc) is
particularly important
a) N Acc ablation blocks reinforcement
b) DA increases in the N Acc during reinforcement
c) Numbing the dopamine projection to the N Acc eliminates
reinforcement
2) The N Acc is an important element in drug abuse **
G. Memory enhancement.
1. Nicotine, Aricept, etc.
IV. LEARNING IN BIRDS: THE SONG
A. Learning is present in other vertebrates
1. Birds--Homing pigeons and bird song
2. Bird song is unique to an individual
a. Sonograms are used to study song differences
B. Development of bird song
1. Sensory phase (babbling) --> Sensorimotor Phase (plastic song) -->
Crystallized song
C. Evidence that bird song is learned to some extent
1. Thorpe's critical contributions
a. Playback recordings
2. Basic sequence of events
a. Hatchling learns the father's song even though he can not sing--
Sensory phase
b. During the Sensorimotor Phase these songs are practiced with
some syllables modified and others dropped
1) The resulting song has individual characteristics
c. Hearing the practiced song is critical for normal song development
1) Deafened birds do not develop a normal song
D. Why do only male birds sing?
1. Role of testosterone in singing
a. Castration and T replacment studies
E. The "Singing brain"
1. Song learning pathways (LMAN, Area X, and DLM)
2. Song producing pathways (HVc, RA, and nXIIts)
F. Canary song is relearned each season (Sensorimotor phase -->
Crystallization)
1. HVc decreases in summer and enlarges in winter
a. New neurons form in winter
An Introduction to Learning,
Memory, and Long-Term Potentiation
Slide Show on Long Term Potentiation from MIT Go to: |
