2/17/15 – Lecture 10 – Learning, Memory, and Synaptic Plasticity- Goal: understand how changes in synaptic transmission are responsible for learning and memory- Learning and Memoryo Learning: the acquisition of new or modification of existing knowledge, behaviors, or skillso Memory: the storage of acquired knowledge or abilities for later recall Learning is not possible without memory – without storage of knowledge or abilities we cannot acquire or modify behavior or skills Stages of Memory- Sensation of Stimuli – taking in the sense of the world around you- Perception of Stimuli – making sense of particular sensations that are being taken in, what you are paying attention to- Encoding/working memory – receiving, processing and combining of sensory information and creation of a transient record of the encoded information- Consolidation – the stabilization of memory after its initial acquisition, keeping what webelieve is more important and moving it to short term memory and even to long term memory- Storage – the formation of a permanent record of the memory, goes into long term memory which is more permanent- Retrieval/recall – calling back the stored information in response to some cue for use in a process or activityo Memory is useless unless we are able to retrieve it Types of Memory- Memory can be categorized by o How long it lasts – very short term, short term, long term Very short term: lasts a few seconds to maybe a few minutes Short term: lasts minutes to days (weeks?) Long term: lasts days to decadeso Whether it requires conscious effort – implicit vs explicit, declarative vs procedural Explicit/declarative: requires conscious effort of recall- Personal memories of life (episodic memory)- Facts about the world (semantic memory) Implicit/procedural: memory of skills that requires no conscious effort of recall- Riding a bike, driving a car, playing an instrument, reading, writing, etc Neuroanatomy and Memory: brain structures associated with explicit memory are different from those of implicit memory- Brain Regions Involved in Explicit Memoryo Basal Forebrain: involved in attentiono Prefrontal Cortex: important in initial encoding of memorieso Medial Temporal Cortex and Hippocampus: consolidation and storage of spatial and episodic memory Birds and rodents that “cache”/hide food in their environment have a larger hippocampi than animals that do not store food Cab drivers in London have to pass a “the knowledge” exam of over 20,000 streets, addresses, etc. and they have much larger hippocampi than non-cab drivers The hippocampus has “place neurons” that fire in response to a particular view or orientation, and learning to navigate a maze increases hippocampal size in miceo Rest of the Cortex: long term storage of semantic memory- Brain Regions Involved in Implicit Memoryo Premotor Cortex: creates a movement pattern for a task and sends it to the motor cortexo Motor Cortex: receives movement pattern from premotor cortex and sends information about movements to the body and to the basal gangliao Basal Ganglia and Cerebellum: receive input from the frontal cortex about movements and sensory cortices about their consequences and sends it to the thalamuso Learning, Synaptic Transmission and Synaptic Plasticity Synaptic Transmission: process by which neurotransmitters are released by a presynaptic neuron and bind to and activate the receptors of the postsynaptic neuron and induce a postsynaptic potential Synaptic Plasticity: a change in the strength of synaptic transmission between two neurons- Can change intensity, where the synapses take place, the amount of synapses released, etc.- Our neurons can and do change the strength of synaptic transmissiono Mechanisms of Synaptic Plasticity 1) changes in the strength of synaptic transmission at existing synapses (one neuron being stronger or weaker) 2) changes in the number of synaptic connections between neurons (one neuron gaining or losing a synapse) 3) changes in the number of neurons and thus synaptic connections between neurons (multiple neurons affecting one neuron)- Synaptic Plasticity and Memoryo Very Short Term and Short Term Memory: changes in the activity of existing synaptic proteins that results in a very short term change in postsynaptic responsiveness of existing synapses Habituation: focusing on certain things without paying attention to other items (paying attention to lecture but not the sound of typing and coughing, how things feel on you, smelling something, etc)- Temporary decrease in responsiveness of a synapse to repeated stimuli, allows organisms to avoid stimuli that aren’t harmful or important- Aplysia Californica: a sea slug with a simple nervous system, if the siphon or gill is poked the aplysia withdraws quickly, if its repeatedly poked it responds much less and even stopso Sensory neuron in skin senses pokes and fires action potentials in response to themo Sensory neurons synapse with motor neurons and control contraction of siphon withdrawal muscles- Normal Synaptic Transmissiono 1) action potential moves down axon to the synapseo 2) action potential opens voltage gated Ca2+ channel so they move into the presynaptic cello 3) Ca2+ influx causes NT vesical fusiono 4) NTs bind to receptors on postsynaptic cells, inducing PSP- Habituation Synaptic Transmissiono In response to repeated action potentials, voltage gated Ca2+ channels close and inactivate temporatilyo Decreased Ca2+ influx means decreased NT vesical fusion and less NT releaseo Decreased NT release means less activation of NT receptors on postsynaptic cell (post synaptic potential is decreased)o Habituation typically involves reversible changes to existing synaptic proteins like calcium channels at existing synapses- By temporarily changing the synaptic transmission by inactivating the Ca2+ channels, we have temporarily modified the aplysia’s behavior- The aplysia has learned to not withdraw its siphon and the memory is stored in the inactivation of the Ca2+ channels in response to repeated pokeso If the pokes stop, eventually the Ca2+ channels will de-inactivate and will respond normally to a new stimuluso There might be a new stimuli that is dangerous so the aplysia needs to be able to respond like normally Sensitization: the same stimulus can cause a greater than normal response to the same stimuluso Long Term Memory: change in gene expression