💪Physiology of Motivated Behaviors Unit 12 – Learning & Memory in Motivated Behaviors

Key Concepts and Definitions

• Learning involves acquiring new knowledge, behaviors, skills, values, or preferences through experience, study, or instruction
• Memory consists of the processes used to acquire, store, retain, and later retrieve information
• Synaptic plasticity refers to the ability of synapses to strengthen or weaken over time in response to increases or decreases in their activity
  • Long-term potentiation (LTP) strengthens synaptic connections
  • Long-term depression (LTD) weakens synaptic connections
• Neurogenesis, the birth of new neurons, continues throughout life in specific brain regions (hippocampus) and plays a role in learning and memory
• Consolidation converts short-term memories into long-term memories through the strengthening of neural connections
• Retrieval involves accessing stored memories and bringing them into conscious awareness
• Forgetting occurs when stored memories cannot be accessed or retrieved due to decay, interference, or lack of retrieval cues

Neural Mechanisms of Learning

• Hebbian theory proposes that repeated and persistent stimulation of the postsynaptic cell by the presynaptic cell leads to increased synaptic strength
• NMDA receptors play a crucial role in synaptic plasticity and memory formation by allowing calcium influx when activated
• AMPA receptors mediate fast synaptic transmission and are inserted into the postsynaptic membrane during LTP
• Calcium/calmodulin-dependent protein kinase II (CaMKII) is activated by calcium influx and triggers a cascade of events leading to synaptic strengthening
• Brain-derived neurotrophic factor (BDNF) promotes the growth, differentiation, and survival of neurons and enhances synaptic plasticity
• Structural changes in dendritic spines, such as increased size and density, occur during learning and memory formation
• Epigenetic modifications, including DNA methylation and histone modifications, regulate gene expression related to learning and memory

Types of Memory

• Sensory memory briefly holds sensory information (iconic memory for visual, echoic memory for auditory) before it is processed or forgotten
• Short-term memory temporarily stores a limited amount of information (7 ± 2 items) for a brief period (15-30 seconds)
  • Working memory manipulates and processes the information held in short-term memory
• Long-term memory stores information for an extended period, ranging from hours to years or even a lifetime
  • Declarative (explicit) memory involves conscious recollection of facts and events
    • Semantic memory stores general knowledge and facts about the world
    • Episodic memory stores personal experiences and specific events
  • Nondeclarative (implicit) memory involves unconscious retention of skills, habits, and conditioned responses
    • Procedural memory stores learned skills and habits (riding a bike, tying shoelaces)
    • Classical conditioning involves learning to associate a neutral stimulus with a biologically significant stimulus (Pavlov's dogs)
    • Operant conditioning involves learning to associate a behavior with its consequences (Skinner box)

Motivation and Its Impact on Learning

• Motivation directs behavior towards a goal and can be intrinsic (driven by internal factors like curiosity) or extrinsic (driven by external factors like rewards)
• Dopamine, a neurotransmitter associated with reward and pleasure, plays a crucial role in motivation and reinforcement learning
• Expectancy-value theory suggests that motivation depends on the expectation of success and the perceived value of the outcome
• Mastery goals focus on developing competence and mastering a skill, while performance goals focus on demonstrating competence relative to others
• Self-determination theory proposes that intrinsic motivation is fostered by satisfying basic psychological needs for autonomy, competence, and relatedness
• Motivation enhances attention, engagement, and effort during learning, leading to better retention and performance
• Positive emotions associated with learning (interest, curiosity) increase motivation and facilitate memory formation

Reward Systems and Reinforcement

• The mesolimbic dopamine pathway, connecting the ventral tegmental area (VTA) to the nucleus accumbens (NAc), is a key component of the brain's reward system
• Rewards activate dopamine neurons in the VTA, leading to dopamine release in the NAc and other brain regions involved in motivation and learning
• Positive reinforcement strengthens a behavior by providing a rewarding stimulus following the desired response (praise, treats)
• Negative reinforcement strengthens a behavior by removing an aversive stimulus following the desired response (taking painkillers to relieve a headache)
• Schedules of reinforcement influence the acquisition and maintenance of learned behaviors
  • Continuous reinforcement provides reinforcement after every desired response
  • Partial (intermittent) reinforcement provides reinforcement after some, but not all, desired responses
    • Fixed ratio schedules provide reinforcement after a fixed number of responses
    • Variable ratio schedules provide reinforcement after a variable number of responses
    • Fixed interval schedules provide reinforcement after a fixed time interval
    • Variable interval schedules provide reinforcement after a variable time interval
• Partial reinforcement schedules lead to more resistant and persistent behaviors compared to continuous reinforcement

Stress and Memory Formation

• Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, leading to the release of glucocorticoids (cortisol in humans) from the adrenal glands
• Acute stress can enhance memory formation by increasing arousal and attention, mediated by the release of norepinephrine and activation of the amygdala
• Chronic stress impairs memory formation and retrieval by causing structural changes in the hippocampus, such as dendritic atrophy and reduced neurogenesis
• The hippocampus has a high density of glucocorticoid receptors, making it particularly vulnerable to the effects of chronic stress
• Stress-induced impairments in memory can be mitigated by interventions that reduce stress (exercise, mindfulness) or block the effects of glucocorticoids (antidepressants)
• The timing of stress relative to learning is crucial: stress before or during learning can enhance memory, while stress after learning can impair memory consolidation
• Individual differences in stress reactivity, such as genetic variations in the serotonin transporter gene (5-HTTLPR), influence the impact of stress on memory

Practical Applications and Real-World Examples

• Spaced repetition, distributing learning over time with increasing intervals between review sessions, enhances long-term retention (Anki flashcards)
• Retrieval practice, actively recalling information from memory, is more effective for long-term retention than passive review (self-testing, quizzes)
• Elaborative rehearsal, connecting new information to existing knowledge and experiences, leads to deeper processing and better memory (concept mapping, storytelling)
• Mnemonics, using acronyms, rhymes, or visual imagery to associate new information with familiar concepts, can aid in memory retrieval (ROY G. BIV for colors of the rainbow)
• Sleep, particularly slow-wave sleep and REM sleep, plays a crucial role in memory consolidation and the transfer of information from the hippocampus to the neocortex
• Exercise enhances cognitive function and memory by increasing BDNF levels, promoting neurogenesis, and reducing stress (regular aerobic exercise)
• Mindfulness meditation improves attention, working memory, and emotional regulation by altering brain structure and function (increased gray matter density in the hippocampus)

Advanced Topics and Current Research

• Engram cells, specific populations of neurons that are activated during learning and reactivated during memory recall, represent the physical substrate of memory
• Optogenetics, using light to control the activity of genetically modified neurons, has enabled researchers to manipulate specific memory engrams and study their role in behavior
• Reconsolidation, the process by which reactivated memories become labile and susceptible to modification, has implications for treating disorders such as PTSD and addiction
• Epigenetic inheritance, the transmission of epigenetic modifications across generations, suggests that learned behaviors and experiences can influence offspring
• Neuronal replay, the reactivation of neural activity patterns during sleep or quiet wakefulness, is thought to play a role in memory consolidation and retrieval
• Brain-computer interfaces (BCIs) that decode neural activity patterns associated with specific memories have the potential to restore lost memories or enhance existing ones
• Research on the gut-brain axis suggests that the microbiome influences learning and memory through the production of neurotransmitters and modulation of the immune system
• Advances in artificial intelligence and machine learning, such as deep neural networks and reinforcement learning algorithms, are inspired by and inform our understanding of biological learning and memory