Transcript Chapter 14
Chapter 14 The Biology of Learning and Memory Learning and Memory Definition Learning • A long term change in behavior as a function of experiences. Memory • The capacity to retain and retrieve past experiences. Types of Learning Habituation • A decrease in response following repeated exposure to a non-threatening stimulus. Sensitization • An increase in reactivity to a stimulus following exposure to an intense event. Classical (Pavlovian)Conditioning • Occurs through associations between an environmental stimulus and a naturally occurring stimulus. Operant Conditioning • Learning that occurs through rewards and punishments for behavior. Types of Learning: Pavlovian Conditioning Learning in which a neutral stimulus is paired with a stimulus that elicits a reflex response until the neutral stimulus elicits the reflex response by itself. • Unconditioned stimulus (US) - A stimulus that involuntarily elicits a reflexive response. • Unconditioned response (UR) - A reflexive reaction to an unconditioned stimulus. • Conditioned stimulus (CS) - An initially neutral stimulus that eventually elicits a conditioned response after pairing with a US. • Conditioned response (CR) - A learned reaction to a CS. Classical Conditioning Types of Learning: Operant Conditioning Learning how to behave to obtain reinforcement Reinforcers - events or activities that increase the frequency of the behavior that precedes that event or activity. Punishers - events or activities that decrease the frequency of the behavior that precedes them. Contingency -The specified relationship between a behavior and its reinforcement or punishment. Operant Conditioning Models of Memory Storage and Retrieval: Atkinson-Shiffrin model An experience is sequentially stored in the sensory register, and the short-term store, and the longterm store. Models of Memory Storage and Retrieval: Baddeley’s Rehearsal Systems approach An alternative to Atkinson-Shiffrin in which Baddeley argued that memories go directly from the sensory register to long-term storage. Models of Memory Storage and Retrieval: Craik and Lockhart Craik and Lockhart - have a theory that memories differ in the extent to which they have been processed. Types of Memories Types of Memories Declarative Memory Memory whose formation does depend on the hippocampal formation Memory that can be verbally expressed • Episodic memory • Semantic memory • Spatial memory Slow-wave sleep facilitates consolidation of declarative memories Role of the Hippocampus Input from motor and sensory association cortexes and from subcortical regions such as basal ganglia and amygdala Through efferent connections with these regions modifies the memories being consolidated there, linking them together A gradual process controlled by the hippocampus transforms memories into long term storage in the frontal cortex Before process completes, hippocampus is necessary for retrieval Procedural Memory Memory whose formation does not depend on the hippocampal formation Collective term for stimulus-response, perceptual, and motor memory Non-declarative memories control behaviors Learning to drive, type REM sleep facilitates retention of non-declarative memories Ian Waterman Perceptual Learning Learning to recognize stimuli occurs when synaptic changes take place in the appropriate regions of the sensory cortex that establish new neural circuits Learning to recognize sensory stimuli • Primary visual cortex Ventral stream – object recognition Dorsal stream – object location Other sensory information activate similar areas of the association cortices Perceptual Short-term memory Activates the circuits and continues after the stimuli disappears Successfully remembering short-term is a two step process • Filter out irrelevant information • Maintain relevant information Also in prefrontal cortex • Manipulate and organize • Strategies for retrieval Delayed matching-to-sample task • Faces – fusiform face area – face blindness • Places – parahippocampal place area The Anatomy of Learning and Memory: Procedural Memory Procedural or nondeclarative memory involves the neocortex and neostriatum. Basal ganglia structures needed for procedural learning Classical conditioning of reflexes depends on the cerebellum. (Budson & Price, 2009) The Memory Consolidation Process: Hebb’s Cell Assemblies Cell assembly - A circuit of neurons that become active at the same time; serves as the site of permanent memory. Reverberatory activity - Continued reactivation of a neural circuit following an experience. • Reverberatory activity is followed by physiological changes that produce a relatively permanent record of the event. Phase sequence - interconnected cell assemblies all activated at the same time in order to control complex processes. Structural Changes and Storing Experiences Experience enhances Ca2+ ion entry into the hippocampus (Lynch, 1986). • Exposing more glutamate receptors to stimulation from other neurons, making the postsynaptic neuron more sensitive. • This may eventually cause changes in the terminal button and Lynch believes this may be the biological basis of learning and memory. Importance of the Hippocampus • Damage results in memory deficits • Case of R.B. • hippocampal damage produced profound anterograde amnesia • Case of H.M. • memories acquired before surgery were retained suggesting that the hippocampus is involved in the storage of declarative memory but is not the site of storage. • Some researchers have found episodic encoding in the left frontal areas and episodic retrieval in the right frontal regions. PBS Nova – Aug 2009 Clive Wearing Long Term Potentiation A long term increase in the excitability of a neuron to a particular stimulus due to the repeated highfrequency activity of that stimulus A long-lasting strengthening of synapses between nerve cells. Long-term memories are thought to be based on LTP Without LTP, learning some skills might be difficult or impossible. Characteristics of LTP A brief, sensitizing stimulus is sufficient to produce LTP; demonstrates that hippocampal neurons can change synaptic responsivity following a single event. LTP-changed synaptic responsivity is confined to a specific neural pathway. LTP can be produced by either a single stimulus or by the convergence of stimuli that individually would not produce LTP. LTP can last for days or weeks, which suggests that it is not just a temporary change in synaptic responsivity. Long-Term Potentiation in the Hippocampus Long-term potentiation is an increase in the amplitude and duration of EPSPs in response to the test stimulus. Three pathways involved in LTP • Perforant fiber pathway • Mossy fiber pathway • Schaffer collateral fiber pathway LTP and the NMDA Receptor In the mossy fiber pathway, glutamate binds to both the NMDA and non-NMDA receptors. LTP apparently depends not on Ca2+ influx into the postsynaptic receptor, but on Ca2+ influx into the presynaptic cell after the LTP-inducing stimulus. Kandel refers to this as nonassociative - the organism learns about the properties of a single stimulus. Habituation and sensitization are examples of this type of learning. Neuroplasticity in the Hippocampus Neurogenesis - helps the brain to be modified in adaptation to changing environmental conditions. • Learning that involves the hippocampus results in new cells surviving at a higher rate. • The cells become part of neural circuits established by a temporal-based learning experience. • Enriched environments have been shown to increase the size of an animal’s brain, their level of cortical ACh, and their learning ability. • Studies have shown enriched environments increase hippocampal neurogenesis, even in adult animals. The Role of the Mediodorsal Thalamus Mediodorsal thalamus - A brain structure associated with profound memory impairment. People with Korsakoff’s syndrome often have atrophy of cells in the mediodorsal thalamus caused by a deficiency of Vitamin B1. Loss of declarative rather than procedural memory. Patients are unaware that they don’t remember; make up stories (confabulation) to fill in the gaps. Emotion is generally intact with medial temporal lobe damage but patients with mediodorsal thalamic damage tend to be emotionally flat and apathetic Caudate Nucleus-Putamen Memory System Caudate nucleus and putamen control the ability to develop procedural memory. The Amygdala and Memory Stimulation of the amygdala results in enhancing the memory of a task Inhibition of the amygdala results in decreasing the emotional arousal effects on memory. Alzheimer’s Disease A type of dementia characterized by progressive neurological degeneration and a profound deterioration of mental functioning. • Early onset - before age 65 • Risk factors include familial clustering of cases, increasing age, and Down syndrome. Alzheimer’s Disease The Cellular Basis of Alzheimer’s Disease Cellular basis of AD • Neurofibrillary tangles • Senile plaques • Amyloid beta protein Alzheimer’s Disease: Genetics There is a link with chromosome 21 Another gene identified is ApoE on chromosome 19 Some people have one or two ApoE4 alleles and have a greater risk of having late-onset AD. The product of ApoE4 is not an effective antioxidant for amyloid beta protein as are the products of other alleles. This may indicate a need to develop more effective methods to increase antioxidants in the brains of AD patients.