Eyeblink Conditioning: From Reflex to Consciousness

1. Eyeblink Conditioning: From Reflex to Consciousness PSY391S April 3, 2006 John Yeomans

2. Pavlov and Search for Engram • Visceral reflexes: Salivation and gastric acid. • Laws of conditioning: pairing, extinction, recovery, generalization, etc. • Conditioning in Cortex? • Search for Engram: Lesions of cortex don’t block learning of mazes or conditioning (Lashley). • Correlates of learning: whole cortex active initially.

4. Eyeblink Conditioning • Easier to measure in rodents and humans. • Slow acquisition and extinction. • Disynaptic reflex circuit for unconditioned reflex (US-shock and UR) in brain stem. • Activity in hippocampus and cerebellum correlates with acquisition of delay conditioning. • Hippocampus not critical; ipsilateral cerebellum is!

6. Recording from Cerebellum • Activity in Interpositus or Red N. precedes and predicts conditioned response (CR). • Microlesions or inhibition of Interpositus or Red N. blocks learning (Thompson). • Circuits for CS (tone), US (shock) found in CBel. • Purkinje cells inhibited by pairing climbing fiber and parallel fiber stimulation: Long-term depression. • Similar for leg flexion and vestibular-ocular reflex (Ito)

7. Interpositus activity Greater Eyeblink CS and US Pathways To Cerebellum

9. Trace Conditioning • Gap between CS and US. Harder to learn. • Hippocampus needed for trace conditioning, but not delay conditioning. • Blocked by MAM, a poison that prevents neurogenesis in dentate gyrus. • MAM does not block fear conditioning, but that is easier task.

11. Awareness • Eye-blink conditioning in humans. • Hippocampus damage blocks trace conditioning, but not delay conditioning. • When asked later, normal subjects can say whether CS and US were paired for trace task, but not for delay task (Clarke and Squire). • Awareness related to success of trace conditioning, but not delay conditioning. • Hippocampus stimulation. • Search for Consciousness—Imaging correlates and testing awareness?

12. Plasticity and Learning PSY391 April 5, 2006 John Yeomans

13. Neurons and Learning • Simple circuit approach—Aplysia • Monosynaptic reflex. • 7 giant Motoneurons identifiable. • 30 sensory neurons identified. • Habituation, sensitization, conditioning. • Short term and long-term changes. • Synaptic changes, proteins and genes. • Kandel.

15. Sensitization: 3 facilitating interneurons 5HT increases release in presynatic terminals Larger EPSP in Motoneuron L7

16. Mechanisms of Plasticity • Habituation leads to smaller EPSP; Sensitization leads to larger EPSP. • Changes in presynaptic terminal lead to more or less transmitter release (Ca++). • Sensitization involves more cAMP, protein Kinase A, and K+ channel changes. • Long term changes require gene transcription protein synthesis and CREB. • Is this the same as mammals?

18. Hippocampus • Slices allow intracellular study of neurons and synapses. • Hippocampus is needed for new long-term declarative memories in humans. • LTP plasticity has many properties of memory. • Problem: Circuits into and out of hippocampus aren’t known, so the functions of neurons aren’t known.

20. Long-Term Potentiation • Three glutamate synapses in series, dentate gyrus, CA3, CA1. • All show LTP with high-frequency stimulation (100 Hz “tetanus”). • LTP lasts for hours (early phase), days or weeks (late phase). • Input specific, and associative. • Like learning and memory?

22. LTP Mechanisms in CA1 • AMPA depolarizes postsynaptic neuron to remove Mg++. • Glutamate can open NMDA receptors. • Hi Ca++ entry activates CaMKII and PKC. • More AMPA receptors are added to postsynaptic membrane  early LTP (hours). • In addition, NO can increase presynaptic release in some synapses (“retrograde transmission”). cGMPCa++ channels

23. NO made in Synapse not nucleus Nucleus

24. LTD Mechanisms in CA1 • Low frequency stimulation (1-5 Hz). • Low Ca++ activates phosphatases. • Internalization of AMPA receptors Long-Term Depression.

25. Early and Late-phase LTP • Early phase LTP (hours) does not require new protein synthesis (gene transcription). • Gene transcription is needed for long-term LTP (days). • Several kinases activate CREB, which activates gene transcription. Many signals (e.g. Ach, DA, NE, opiates) influence many kinases. • Many proteins are needed for growth of dendritic spines and synapses for long-term changes.

27. Long-term Memories PSY391S April 10, 2006 John Yeomans

28. Short and Long-term Memory • Retrograde amnesia after concussion. Memories return in order toward time of injury. • Electroconvulsive shock induces RA similarly in humans and animals. • Consolidation Hypothesis. • Protein synthesis inhibitors block long-term storage of memories, but not STM, in animals.

30. Hippocampal Damage • H.M. can’t form new, stable verbal (declarative) memories. • He can form immediate memories (for seconds), but they are lost when distracted. • He can learn new motor tasks (procedural learning). (Cerebellum and striatum, e.g.) • He has high IQ and remembers events before surgery well.

31. Long-term Storage of Memories • Hippocampus needed for laying down new LTMs, but not for long-term storage after weeks. • Permanent memories and abilities are believed to be stored in cortical areas for each function, e.g. speech, personal history, complex skills, feelings.

32. Hippocampus in Rodents • Needed for spatial memories: 8-arm-maze, water maze, Barnes maze. • Needed for contextual fear conditioning, but not simple fear conditioning. • Needed for trace conditioning but not delay conditioning. • Needed for social communication between rats. • Long and short term memories different: Protein synthesis needed for LTM and LTP.

33. Spatial Memory in Rats

34. How are memories converted to long-term, then to short-term forms? • Theory: Synaptic changes are the basis of all memories. • Number of synapses depends on dendrites and spines. • Many proteins are needed to make synapses grow and retract. • Dendrites and spines grow and retract.

35. Dendrite Growth

36. Spine Growth

37. Neurogenesis • New neurons are formed in dentate gyrus and olfactory bulb (BRDU, 3H-thymidine markers). • Needed for new olfactory memories, and for trace conditioning. • Can be stimulated by serotonin, estrogen, seizures or genes. • Can be inhibited by stress/depression and hormones, or by toxins (MAM, radiation).

39. Reconsolidation • If memories are recalled again (new tests in rodents), they become more vulnerable to ECS or to protein synthesis inhibition. • Are memories then reconsolidated in hippocampus? • Suggests transfer back and forth between more permanent (cortex) and less permanent (hippocampus) forms. • Limbic frontal cortex connected and active in these exchanges. • How are memories recalled and brought back into temporary storage?

40. Long-term Storage • How does hippocampus receive new information for memories? (via entorhinal cortex)? • How does hippocampus convert memories into long-term stores? (frontal cortex, e.g. anterior cingulate)? • How are long-term memories stored in cortex synapses? • Are long-term stores lost in reconsolidation, and if so, how? • How are memories exchanged between HPC, frontal cortex?

41. Genes and Memory PSY391S April 12, 2006 John Yeomans

42. Gene Control • Knockdown of RNA: Antisense oligos (DNA) to inhibit mRNA in vivo. • Knockout of Gene: Remove gene permanently from genome. • Transgenic: Add extra copies of gene permenently. • Inducible: Add promoter so that you canturn the gene on or off at will (tetracycline—Tet). • Gene transfection by virus, electroporation, or inhibition by repressors.

43. Long-term Memories and CREB • Long term memories improved by spaced trials vs. massed trials. • Aplysia: CREB knockdown blocks long-term, but not short-term, sensitization. • Block of Long-Term Memory (several tasks) and long-phase LTP in CREB knockout mice. STM and short-phase LTP unaffected.

44. Genes and Fruit Flies • Olfactory memory can be tested in test tubes full of flies. • Flies go toward smell, but shocked at one end of tube. • Smart flies avoid, but dumb flies return, to end where shock given. • Rutabaga, dunce, turnip all mutants that indicate that cAMP important for learning.

45. CREB • CREB repressor before training blocks olfactory memory in flies, on second day, but not first day. • Increasing CREB (by activator) leads to much improved long-term memory. One trial only needed for olfactory memory on next day. • “Genius fruit flies”?

46. Improved Memories with NMDA and CREB • Viral CREB in basolateral amygdala improves long-term, but not short-term fear-memories • Viral CREB in VTA or N. Acc improves drug sensitivity. • Memory improvement with stimulants, or added AMPA or NMDA receptors. • Doogie: NR2B improves LTP and LTM

47. Viral-CREB in Amygdala 3 days 14 days

49. Alzheimer’s Disease • Poor memory (senile dementia) + neural changes post mortem (plaques and tangles). • B-amyloid and tau proteins. • Early onset due to APP and presenilins. • Down’s, APP and Ch21. • Late onset due to environment and to ApoE eta4 copies. • Prediction of susceptibility by age and genes.

50. Amyloid Plaques and Neurofibrillary Tangles Dying of cholinergic axon terminalstauamyloid?