Neuroplasticity:. Happens in at least 3 ways: - - -

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1 BRAIN PLASTICITY Neuroplasticity:. Happens in at least 3 ways: Recently, it was found that new neurons and glial cells are born in specific brain regions - reorganization. Brain plasticity occurs during: DEVELOPMENT OF NERVOUS SYSTEM: 1. Neural proliferation (neurogenesis - neuronal birth ) 2. Migration and differentiation (neural cell precursors travel home and grow up ) 3. Axon growth and synapse formation (growth cones and filopodia) 4. Neuron death and synaptic pruning: too many neurons and synapses produced - competition for neurotrophic factors (ex., NGF - ) 1

2 Examples of the effects of EXPERIENCE on NEURAL DEVELOPMENT and PLASTICITY Early visual experience - studies of early found deprived eye to ability to activate visual cortex - only occurs if other eye is open, not if it is also deprived - - these are structural effects - - concept of Two eyes open One eye shut Environment and the cortex - studies of rat litters separated at birth into - enriched environments produces: more glial cells; - larger postsynaptic zones; - larger protein content. - some of these effects can be produced in adult animals by giving them extensive maze training 2

3 LEARNING AND MEMORY Learning: Memory: ability to recall or recognize previous experience in the form of behavioral change. If behavior at a later time B is different than at earlier time A, say that learning has taken place between time A and B TYPES OF LEARNING: NON-ASSOCIATIVE LEARNING: A. Habituation: B. Sensitization: Marine snail Aplysia Californica Til Tail Head Gill-withdrawal reflex used to study habituation and sensitization (Eric Kandel s laboratory) Habituation - touch siphon repeatedly every 30 sec leads to short-term habituation of gill-withdrawal reflex - can lead to long-term habituation if touch is repeated over days Sensitization - one electric shock to the tail can lead to shortterm sensitization of gill-withdrawal reflex - several electric shocks can lead to sensitization that will be observed for weeks (long-term) 3

4 ASSOCIATIVE LEARNING: A. Classical conditioning (also called Pavlovian conditioning ): the process by which a neutral stimulus acquires meaning through associations with another stimulus (often a biologically relevant stimulus) Terminology UCS = (food, water, etc.) UCR = (salivation, etc.) Examples: UCS > UCR pinprick withdrawal food salivation sudden loud noise startle airpuff eyeblink CS = (bell, light, etc.) CR = (salivation to bell) so CR is the response Development of Classical Conditioning Example: conditioning of emotional responses - Pavlov s dog) UCS > UCR (food) (salivation) Initially CS > no response (bell - neutral stimulus) Repeated pairings of CS + UCS > UCR (bell) + (food) (salivation) Bell eventually comes to elicit salivation without the presentation of food CS > CR (bell) (salivation) Note that salivation here is called conditioned response (CR) because it is not elicited directly by food; classical conditioning has taken place Also conditioning of motor responses - example of eye blink conditioning 4

5 CLASSICAL CONDITIONING: NEURAL BASIS Classical conditioning of emotional responses (freezing in rats - changes in heart rate/blood pressure or skin conductance in humans) is learned after only a few pairings Electric shocks produce freezing in rats and changes in heart rate/skin conductance in humans Repeatedly pair auditory stimulus (CS) with shocks (UCS). - the auditory CS come to elicit freezing and changes in heart rate/skin conductances - the to produce classical conditioning of emotional responses Classical conditioning of motor responses, such as eyeblink in response to puffs of air is learned only after 100s of pairings of an auditory stimulus with puffs of air - the is necessary to produce classical conditioning of motor responses B. Instrumental Conditioning (also called ): Terminology: Discriminative stimulus (S D ): cue that triggers the motor response (ex. sight of a lever bar). Favorable outcome: positive reinforcers (ex. food, water, etc) or termination of negative reinforcers (termination of pain, isolation, etc). 5

6 Example of instrumental conditioning: Cats have to learn to press a lever in order to obtain palatable food (Thorndike s experiment) Neural Basis of Instrumental Conditioning: - necessary for instrumental motor response learning - necessary for detection of reinforcer. HUMAN MEMORY The various stages of memory: I. Sensory registers (high capacity, low duration) With Attention - II. Short-term memory (low capacity & duration) With Consolidation - III. Long-term memory (high capacity & duration) Retrieval - recall and recognition Implicit memory (similar to ): Examples: - mirror drawing tasks - playing video games - riding a bicycle - word associates (define fall after different stories) Explicit memory (similar to ): Two types - (time and places) - (facts and knowledge) 6

7 NEUROBIOLOGICAL BASES OF MEMORY Karl Lashley (1920 s s) and the search for the engram or memory trace: He derived two principles from his studies: - = memories stored diffusely all over neocortex - = neocortex all over the brain plays an equal role in memory storage What was wrong with these interpretations? - task difficulty; - different learning systems/strategy used to solve problems. Donald Hebb (early 1950 s) and of short-term memories into long-term memories via - cell assemblies: - reverberation: LESSONS FROM HUMAN AMNESIAS Amnesia: Retrograde amnesia: forget events brain trauma Anterograde amnesia: forget events brain trauma The beginnings of Explicit Memory mechanisms Case of H.M.: because of severe epilepsy (removal of enthorinal and perirhinal cortex, part of amygdala and most of hippocampus) H.M. experienced: 1. No loss of intelligence (IQ) 2. Mild retrograde amnesia 3D 3. Devastating anterograde amnesia What we learned from H.M.: 1. Supports short- & long-term memory processes 2. Existence of explicit vs. implicit memory 3. Existence of consolidation process 4. Challenges view of diffuse memory process 5. Implicates discrete brain regions in memory 7

8 Implicit memories: various forms of implicit knowledge. Amygdala: Cerebellum: Basal ganglia: 8