1Overview of Unit 3Forms of Memory, Cognitive Theories-short- and long-term memory, etc.Neuroplasticity and Models of Plasticity-LTP and LTD (review)Memory and the Human Brain-Amnesia and its causes-Temporal lobe,hippocampus-Imaging studies of human memoryPlasticity of Cortical RepresentationsNeural and Cognitive Development (overview)2MemoryLearning and memory defined:“Learning is the process of acquiring newinformation, while memory refers to thepersistence of learning in a state that can berevealed at a later time.” - Larry Squire, 1987Learning = acquisition of new information orknowledge.Memory = retention of learned information orknowledge.3MemoryMemory at different time scales – encoding(acquisition, consolidation), storage and retrieval4Sensory Memory: LimitationsOnly 7 items are present in short-term memory, butmore are present immediately after, e.g., a visual sceneis shown (iconic memory, sensory memory trace).Sensory memory is not directly (consciously) accessible,has large capacity (image-based), decays quickly (< 1sec), not semantic.Experiments by George Sperling, 1960 (originally aimed atdetermining memory span)“partial report”5Serial Position EffectItems at the beginning and end of a serial list are more easilyremembered (primacy and recency effects).6Immediate Memory: 7+/-2Irrespective of the nature of the information(words, objects, numbers), human subject canretain in immediate memory around 7(plus/minus 2) items. “Span of immediatememory” (George Miller)7The Modal Model of MemoryAfter Atkinson and Shiffrin (1968)8Working Memory-Contains information that can be acted on andprocessed.-Limited capacity-Distinct from immediate short-term memory-Role of attention-In CNS: elevated firing rate in temporal andfrontal areas9Working MemoryBaddeley, 1995coordinates working memory,controls actionsacoustical encodingvisual encoding10Long-Term MemoryBasic distinctions:Declarative – explicit: facts, events, conscious access,“remembering with awareness”.Nondeclarative (procedural) – implicit: (motor) skills,behaviors, priming, conditioning, no conscious access,“remembering without awareness”.Episodic memory – “personal knowledge”,autobiography, memory for specific events, “autonoeticconsciousness”, conscious access (grouped withexplicit).Semantic memory – “world knowledge”,dictionary/encyclopedia, memory for facts, rules,relationships, “noetic consciousness”, explicit (implicit?– Tulving).11Multiple Memory Systems12Multiple Memory Systems13Memory: The Search for the EngramEngram = localized memory trace.Lesion studies: Lashley, equipotentiality of thecortex, distributed memory traces.Lashley found a correlation betweenseverity of behavioral deficit and size(but not location) of cortical lesions(“equipotentiality”).14Localization of MemoryDonald Hebb: Conceptual link between memory storage andrepresentation of stimuli within the cortex.Stimulus activates a cell assembly (reciprocally connected anddistributed set of cells).Reverberation of activity within the assembly corresponds to short-term memory.Persistence of activation leads to strengthening of the assembly’sconnections (“growth process”).Subsequently, the assembly can be triggered by a weaker stimulus,or by only a portion of the stimulus. The reciprocal connection willautomatically “complete” the cortical representation of the stimulus.Consequences of the model: the engram could be widely distributedand the same neurons that are involved in perception alsoparticipate in memory. Partial destruction of the assembly may notcause loss of all memory.15Localization of Memory16Memory: The Search for the EngramMolecular memory: synthesis of specific RNA orprotein molecules – a blind alley.17Neuronal MemoryMemory is the result of biochemical changes in neurons andconnections occurring at multiple time scales.Most important are changes that alter synaptic strengths orefficacies.Other important components involve cellular changes ingene transcription and translation, intracellular signaling, orsecond messengers.In most cases, memory-related changes are activity-dependent.Developmental process extend into adult life – mechanisticcontinuity between development and “mature” function.Lasting changes can occur almost anywhere in the nervoussystem.18Neuronal Memory: Model SystemsInvertebrate Systems:-Aplysia (20,000 neurons), DrosophilaAdvantages of invertebrate nervous systems:Small nervous systemsLarge neuronsIdentifiable neuronsIdentifiable circuits“Simple” genetics, rapid life cycleEvolutionary conservation of basic molecular mechanisms Easily accommodated in laboratory environment“Cheap” (relatively)19Neuronal Memory: Model SystemsVertebrate Systems:-conditioning (eyeblink conditioning, fearconditioning)-cerebellar cortex-hippocampus and neocortexWhat makes a good model system? – smallNS, large neurons, few connections,identifiable neurons and circuits, simplegenetics, low cost.20Animal Models of Learning(Invertebrates)The “star” of invertebrate learning models: Aplysia californicaNobel Prize 2001 (Eric Kandel)21Model Systems: Aplysia22Animal Models of Learning (Invertebrates)Hermissenda in its natural environment23Model Systems: AplysiaExample of nonassociativelearning:-Habituation of the gill-withdrawal reflex (habituation =learned suppression of responseto a repeated stimulus)-Neuronal basis: changes inpresynaptic terminal of sensoryneuron making contact withmotor neuron (reduced Ca2+flux due to channel inactivation,reduced neurotransmitterrelease)24Model Systems: AplysiaExample of associative learning:-Classical conditioning (US-shock to the tail,CS-siphon stimulation)-Neuronal basis:US - release of 5-HT, activation ofadenylyl cyclase in sensory presynapticterminalCS – presynaptic AP and influx of Ca2+coincidence of Ca2+ pulse and adenylylcyclase activation – production of cAMP(second messenger) → lasting changes inpotassium channels and transmitter releaseefficacy.2526272829Vertebrate Models: The Hippocampus30Vertebrate Models: The