Lecture 17 - Types of Learning and Memory - PSYC 211 Notes PDF

Introduction to Behavioral Neuroscience PSYC 211 Lecture 17 of 24 – Types of learning and memory Chapter 12 in the textbook (END OF MIDTERM 2 MATERIAL) Professor Jonathan Britt Questions? Concerns? Please write to [email protected] MIDTERM 2 –...

Introduction to Behavioral Neuroscience PSYC 211 Lecture 17 of 24 – Types of learning and memory Chapter 12 in the textbook (END OF MIDTERM 2 MATERIAL) Professor Jonathan Britt Questions? Concerns? Please write to [email protected] MIDTERM 2 – Monday, Nov. 11th Midterm 2 covers lectures 9-17. First letter of Room It has 56 multiple-choice questions. your last name A The exam will start at 4:05 pm (no admittance after 4:30 pm) B LEA 232 It should take about an hour, but you have until 5:45 pm. C ARTS W-120 D E MCMED F 1034 Please take the test G H I in your assigned room  J K L M N Sit every other seat O P Q LEA 132 R S Bring a pencil and an eraser T U V W X Y Z  LEARNING & MEMORY Most synapses in the brain are highly plastic. They grow stronger or weaker (primarily by adding or removing postsynaptic receptors) in response to changes in activity throughout the brain. We know there are proteins (enzymes) on the postsynaptic side of most synapses that monitor how often neurotransmitter is released into the synapse and whether the postsynaptic cell tends to spike at these times. Weak excitatory synapses tend to grow stronger if they are consistently active when the postsynaptic cell spikes (when strong synapses are also active). Excitatory synapses tend to grow weaker when their activity does not positively correlate with postsynaptic spiking. We suspect there is much more going on, but we have not had much success identifying the rules that govern synaptic plasticity in any brain region. 3 3  TYPES OF MEMORY: IMPLICIT VS EXPLICIT Unconscious memory (implicit memory, nondeclarative memory) You may not know whether you can still ride a bike or play the piano until you try. These memories influence behavior in an automatic, involuntary manner. These memories reflect unconscious adjustments to perceptual, cognitive, and motor systems during previous experiences To probe these memories, we say “show me”. Examples include…  procedural memories (how to ride a bike)  perceptual memories (how to tell identical twins apart, unconsciously)  stimulus-response memories (salivating in response to a tone) Consciously accessible memory (explicit memory, declarative memory) Memories of events and facts that we can think and talk about. To probe these memories, we say “tell me”. This category includes… – Episodic memory: Personal experiences associated with a time and place. Autobiographical memories and associated contextual information that is learned all at once. – Sematic memory: Encyclopedic memory of facts and general information, often acquired gradually over time. This information remains constant (remains true) across multiple episodic memories, and thus it need not be associated with a specific time or place (like when we first learned the information). 4  TYPES OF LEARNING Motor learning (procedural learning)  implicit memory – Learning to make skilled, choreographed movements – The basis of motor skills (bike riding, ball throwing, etc.…) – Involves different brain areas involved in movement Perceptual learning  implicit memory – Learning to recognize stimuli as distinct entities – The basis of recognition & categorization – Largely dependent on the neocortex – sensory association areas Relational learning (stimulus-stimulus learning)  explicit memory – Learning relationships among individual stimuli. –The basis of declarative memory (episodic and semantic) – Largely dependent on the hippocampus and sensory association areas Stimulus–response learning  implicit and explicit memory – Learning to perform an action in response to a stimulus. –The basis of classical (Pavlovian) and instrumental (operant) conditioning – Involves different brain areas depending on the stimulus and response 5  STABILITY OF MEMORY Sensory memory (perceptual memory; lasts only a couple seconds or less) Allows an individual to retain the experience of the sensation slightly longer than the original stimulus. Occurs in each of the senses. For example, people often reflexively say “what?” when they hear something while distracted, but then they quickly realize they did hear what was said. Short-term memory (lasts for seconds to minutes). Only a small fraction of sensory information enters short-term memory. The memory capacity of short-term memory is limited to a few items, such as the digits in a phone number or the letters in a name. The length of short-term memory can be extended through rehearsal. For example, you might be able to keep a phone number in short-term memory by repeating it to yourself. Long-term memory (persists after getting distracted and after a nap). Select information from short-term memory is consolidated into long-term memory. Long-term memories can be retrieved throughout a lifetime and are strengthened with every retrieval event. 6  MOTOR LEARNING Motor learning (procedural learning) involves learning how to make a sequence of coordinated movements. When we move, we get feedback from our joints, vestibular system, eyes, ears, etc. We use this information to improve and optimize our movements, making them more effective and efficient. As with all forms of learning, there is a rapid component to motor learning as well as a slower process called between-session learning, where improvements in motor behavior are seen following a period of memory consolidation (in part during sleep). Many areas of the brain contribute to motor learning, including the frontal lobe (motor cortex), thalamus, basal ganglia, cerebellum, brainstem, and spinal cord. But we do not yet know how any of these areas process information, let alone how they interact with each other. 7  PERCEPTUAL LEARNING Perceptual learning enables us to identify and categorize objects and situations. It is a pattern recognition system. Perceptual learning is a skill like any other. Consider this assessment of perceptual skills: Examine these 50 photographs of cars. Now look through this other pile of photographs and identify which ones are identical to the photos in the original stack. Can you also identify which of the photos contain the same type of car (make/model/color) even if the context or angle of the photograph is different? This skill is learned unconsciously, implicitly. It not only requires that you have seen lots of cars before, but that you have formed associations with different types of cars (conscious or unconscious associations). These associations reflect changes in the strength of synaptic connections between primary and association areas of sensory cortices. 8  VISUAL AGNOSIA AND MEMORY Damage to sensory association cortex not only impairs the ability to recognize (identify) certain stimuli, but it also disrupts memory of these types of stimuli. Below are drawings copied from photographs from someone with a visual agnosia. This person cannot easily identify what is in the image that they are copying. Copied Drawn from Copied Drawn from memory moments memory moments later later 9  STIMULUS RESPONSE LEARNING (TYPE 1) CLASSICAL CONDITIONING (PAVLOVIAN LEARNING) Baseline state: US  UR Unconditioned Stimulus: Unconditioned Response: a stimulus that has inherent value, a behavioural response that like food or a painful shock. is largely innate, hard-wired (unlearned, unconditioned). Learning episode: US + CS  UR After learning: CS  CR Conditioned Stimulus: Conditioned Response: a stimulus initially perceived as neutral a behavioural response that occurs in (e.g., a tone) becomes associated with an response to a CS. The behaviour is often US through learning. similar to the UR that was elicited by the US during training. A key aspect of classical conditioning is that the animal has no control over its environment. The animal can react to things (and we measure these reactions to infer learning), but the animal’s actions do not influence the course of events. 10  STIMULUS RESPONSE LEARNING (TYPE 2) Instrumental Learning from the consequences of your actions, from conditioning the receipt of reinforcement or punishment. The likelihood of you repeating an action depends on aka whether it was previously reinforced or punished. Operant conditioning Animals are always exploring their environment and aka sometimes their actions have consequences. Instrumental behaviours start off as flexible, volitional Reinforcement exploratory behaviours. learning In contrast to Classical (Pavlovian) learning, operant conditioning requires that the animal can move and make decisions that influence their environment (i.e., decisions that have consequences). 11  REINFORCEMENT LEARNING Reinforcing Appetitive stimulus. When it follows a particular stimulus behavior, it increases the likelihood the animal will repeat the behaviour. Reinforcement makes the behavior more likely to occur. Punishing Aversive stimulus. When it follows a particular stimulus behavior, it decreases the likelihood the animal will repeat the behaviour. Punishment makes the behavior less likely to occur. 12  INSTRUMENTAL CONDITIONING Reinforcement learning alters the connection strength between neural circuits involved in perception (e.g., the sight of a lever) and neural circuits involved in decision making (e.g., the decision to press a lever). 13  INSTRUMENTAL CONDITIONING There are two main pathways between sensory and motor cortices: Direct transcortical connections (connections from one area of the cerebral cortex to another) are involved in conscious thought processes and the creation of new complex motor sequences that involve deliberation or instruction. The basal ganglia are a collection of nuclei in the forebrain that automate stimulus-response behaviours according to reinforcement learning. This structure integrates sensory and motor information from throughout the brain, and it can trigger habitual responses (outside of conscious awareness). It can also inhibit behaviours that the animal consciously intends to do. The basal ganglia initially act as a passive “observer”. But when successful behaviors are repeated over and over, this structure automates the decision-making process. It creates habitual ways of responding, leaving transcortical circuits free to do something else. Habitual behaviours can be performed without conscious consideration of the details. Dopamine signaling drives habit learning by providing a “thumbs up / thumbs down” signal that determines the likelihood an animal will repeat a decision or a behaviour. Neurons in every area of the cerebral cortex (motor and sensory areas) project to the basal ganglia and synapse in an area called the striatum (the input nucleus of the basal ganglia). Dopamine signaling regulates the strength of these synaptic connections. 14  DOPAMINE INPUT TO THE STRIATUM Dopamine neurons in the midbrain (substantia nigra and ventral tegmental area) release more or less dopamine in the striatum (caudate, putamen, nucleus accumbens) to broadcast perceptions of reinforcement and punishment, respectively. Caudate + putamen The overall amount of dopamine in the striatum seems to reflect the animal’s motivational state and the value of moving in and engaging with the environment. Transient fluctuations in dopamine signaling seem to drive reinforcement learning by signaling how unexpectedly good or bad the current moment is. 15  THE STRIATUM Different areas of the striatum process information from different cortical areas. For example, the limbic striatum (the nucleus accumbens) receives input from the hippocampus, amygdala, and parts of PFC. It is involved in regulating people’s priorities and cravings. The sensorimotor striatum contributes to motor learning (motor habits). The associative striatum contributes to habits of thought (habits of mind). Lesions of the basal ganglia disrupt reinforcement learning, habit learning, and motor learning, but they do not strongly affect perceptual learning or stimulus-stimulus learning. 16  RELATIONAL (STIMULUS-STIMULUS) LEARNING Our understanding of explicit relational memories largely comes from studies of Henry Gustav Molaison (HM), led by Brenda Milner in 1957. Doctors cut out his hippocampus bilaterally to cure his epilepsy. The surgery worked, but H.M. lost the ability to form new explicit memories (episodic and semantic). It was a severe case of anterograde amnesia: the inability to form new consciously accessible memories. H.M. also suffered from a graded retrograde amnesia: an inability to consciously recall memories that he had before the brain damage. He mainly lost memories from the year or two prior to the surgery, but some earlier episodic memories were also lost. Older semantic memories (general knowledge and things learned in school) were maintained. He still had a brief working memory and a high IQ, but he could not learn new words or names or learn to navigate new spaces. 17  AMNESIA Amnesia is a deficit in memory caused by brain damage or brain diseases (it can also be temporarily caused by different drugs). Anterograde amnesia refers to the inability to form new explicit memories after a brain injury. Memories of events that occurred before the injury largely remain intact. Retrograde amnesia refers to the inability to remember events that occurred before the brain injury. It is commonly seen in neurodegenerative diseases where there is brain-wide neurodegeneration. Complete amnesia in either direction is rare. A strong blow to the head typically causes a small amount of retrograde and anterograde amnesia. Strong hit to the head Seconds, hours, or days 18  AMNESIA IN H.M. H.M. had severe anterograde amnesia, but he could still learn some things unconsciously. He also experienced graded retrograde amnesia. Declarative memories learned the year or two prior to the surgery were gone. Declarative memories that were greater than 10 years old were maintained. Bilateral hippocampal damage 10 2 years years 19 OTHER CASES OF ANTEROGRADE AMNESIA Korsakoff's Permanent anterograde amnesia caused by brain syndrome damage, usually resulting from chronic alcoholism. Korsakoff’s patients are unable to form new memories but can still remember old ones before the brain damage occurred. Confabulation Reporting of memories of events that did not take place without intention to deceive Seen in people with Korsakoff's syndrome 20  RELATIONAL (STIMULUS-STIMULUS) LEARNING Without a functional hippocampus, animals cannot form new consciously accessible memories (episodic or semantic). Semantic information learned well prior to hippocampal damage is generally intact and consciously accessible. Episodic memories formed prior to hippocampal damage are less accurate and less vivid. Remembered episodic memories may be largely semantic in nature. After hippocampal damage, people stop reminiscing about previous episodes of their life, and they stop imagining future possibilities. They live in the here and now. Their short-term, working memory is generally fine. To some extent, they can develop new motor skills and perceptual skills. They also show evidence of Pavlovian conditioning and reinforcement learning. But they have no conscious memory of practicing anything or learning anything after the hippocampal damage. Altogether, these observations suggest that the hippocampus is critical for the formation (and persistence) of episodic memories. We think the formation of episodic memories is necessary for the formation of semantic memories. But well-learned semantic memories are clearly not stored in the hippocampus. 21 HIPPOCAMPAL-INDEPENDENT LEARNING Perceptual learning Motor learning 22 23  EXPLICIT MEMORY CONSOLIDATION Where in the brain are explicit memories stored? After training a rat to solve a maze… Rodents need a functional hippocampus to remember newly learned spatial information but not information learned 30 days ago. Memories are consolidated and stored in the cerebral cortex during this time. This kind of memory consolidation occurs over several years in humans. 24 Memory Encoding During any given moment, a unique pattern of neural activity (spread across the cerebral cortex) reflects the constellation of sensory input, thought processes, and emotion you are currently experiencing. The cortical activity associated with a given moment seems to be indexed in some manner in the hippocampus. Memories are technically not stored in the hippocampus, but the hippocampus forms a hub, node, or index that can reactivate the sensory systems that initially encoded an experience. Memory Encoding (pattern storage) Memory Retrieval (pattern completion) Cortical Cortical sensory Hippocampus Partial cue Hippocampus sensory systems systems 25 Memory Encoding Over time (years in humans), memory gradually becomes less and less dependent on the hippocampus, which simply means the memory will still be there if you lose your hippocampus. What is happening in the years when memories are dependent on the hippocampus? A prominent theory is that hippocampal activity (during recall events and during sleep) is “training” the cortex, causing a reorganization of the synaptic weights in the cortex so that intra- cortical connections can support memory recall on their own. Some people argue that the cortex only contains semantic information (facts). In this model, all memory starts off as episodic memory, which is always dependent on hippocampal nodes interacting with the cortex. Over time, as facts emerge from repeated episodic experiences, this semantic information is permanently stored in the cortex in a hippocampal-independent manner. Theory 26