Quiz #1 Topics PDF

Quiz #1 Topics Chapter 1: Behavioral Dynamics of Episodic Memory ​ Definition of Episodic Memory ○​ Definition: (Tulving, 1972) the recollection of specific sensory experiences tied to particular times and places. Requires a sense of personal experience (as if r...

Quiz #1 Topics Chapter 1: Behavioral Dynamics of Episodic Memory ​ Definition of Episodic Memory ○​ Definition: (Tulving, 1972) the recollection of specific sensory experiences tied to particular times and places. Requires a sense of personal experience (as if reliving the event), represented as “short time slices” related to specific goals or event, providing a continuous sense of time and place ○​ Contrast w/ other Memory Types ​ Semantic Memory - refers to memory or facts and general knowledge; does not involve specific experiences or context (time & place) like episodic memory ​ Procedural Memory (Implicit Memory) - involves knowing how to do things, often involves motor movements; does not rely on conscious recollection or time-specific experiences but rather on skills and habits ​ Working Memory - involves actively holding and manipulating information in the short term; does not focus on past experiences or events but on present information that may not be stored long term ​ Comparison to Mental Time Travel - episodic memory involves mental time travel where individuals can mentally relive past events ​ Episodic Memory as a Spatiotemporal Trajectory ○​ Definition: episodic memory as a spatiotemporal trajectory involves encoding and retrieving experiences as a continuous sequence of spatial and temporal information ​ Key Components ​ Absolute location - memory includes specific places visited ​ Movement and direction - the trajectory captures walking speed, path, and point of view ​ Timing - events are remembered in relation to time, including duration at each location  ​ Includes sensory experiences, thoughts, and internal cognitive states - encodes and retrieves non-physical features similarly to spatial and temporal information ​ Can retrieve full trajectory or recall isolated segments and jump between moments ​ A Model of Episodic Memory ○​ Computational models simulate brain dynamics to reconstruct full episodic trajectories ○​ Forms a multidimensional memory space beyond just physical navigation ○​ Position in time and space is coded by the relative timing of rhythmic activity in different populations of neurons ​ representation of trajectory through space and time is determined by the nature of inputs that change the relative timing of rhythmic peaks in activity ​ Brain Systems for Episodic Memory ○​ HM underwent bilateral medial temporal lobe resection - resulted in severe anterograde amnesia (prevent formation of new episodic memories) ​ Retrograde amnesia was temporally graded—older memories were relatively preserved, but recent ones were impaired. ​ Working memory and procedural memory remained intact, indicating distinct memory systems. ○​ Anatomical Structures Lesioned in HM ​ Hippocampus - bilateral removal ​ Entorhinal Cortex & Perirhinal Cortex ​ Parahippocampal Cortex ​ Amygdala (partially removed) ○​ Brain Systems involved in episodic memory ​ Medial temporal lobe system - hippocampus, entorhinal cortex, perirhinal cortex, parahippocampal cortex ​ Required for encoding, consolidation, and retrieval of episodic memories ​ Hippocampal-cortical interactions ​ Hippocampus encodes new experiences and interacts with cortical regions for consolidation  ​ Prefrontal Cortex ​ Involved in retrieval strategies, organization, and evaluation of episodic memory ​ supports goal-directed recall and working memory integration ​ Thalamus and mammillary bodies ​ Critical for memory circuit connections ​ Damage leads to episodic memory deficits ​ Posterior parietal cortex ​ Support attention, spatial processing, and retrieval of episodic memories ​ Basal forebrain ​ Provides cholinergic input to the hippocampus, crucial for memory function ​ Tests of Episodic Memory ○​ Neuropsychological Tests ​ Wechsler Memory Scale - Assesses different components of memory function in neuropsychological testing. ​ Composed of multiple memory tasks, each engaging different memory systems ​ California Verbal Learning Task- Assesses verbal learning and memory ​ MMSE - short screening tool for cognitive impairment ○​ Free recall ​ Requires encoding and retrieval of episodic memories. ​ H.M. showed profound deficits in recalling word lists. ○​ Cued Recall ​ Participants are given word pairs and asked to recall the second word when given the first. ​ H.M. could not recall any second words in difficult pairs. ○​ Richness of Episodic Detail ​ specific behavioral scoring methods have been developed to fully quantify the richness of detail in human episodic recollection by scoring the amount of contextual detail internal to specific remembered episodes ○​ Spatial Memory ​ Visual maze task with HM (Array of metal pegs on a board; Use a metal stylus to navigate from start to finish; Errors indicated by a click (trial-and-error learning)) ​ Patient HM: Failed to improve over 215 trials → Suggests impaired memory for spatiotemporal sequences. ​ Shortened maze version - HM showed a slow reduction in errors over several days; Suggests some learning possible via semantic or procedural memory. ​ HM was able to draw a floor plan of his house 8 years after surgery; Suggests slow neocortical semantic memory updating over time, contrasting with impaired rapid spatial learning. ○​ Recognition ​ Participants see a list of words during encoding; During testing, they identify previously seen words from word pairs (one old, one novel) or classify single words as "old" or "new" ​ Two Recognition Mechanisms: ​ Recollection: Explicit retrieval of episodic details (e.g., recalling where/when a word was seen). ​ Familiarity: A vague sense that a word has been seen before without specific details. ​ Debate exists on whether recognition is supported by one or two distinct mechanisms. ○​ Comparison with Short-Term Memory Tests ​ Short-Term Memory is Spared in Hippocampal Damage - articulatory loop (working memory) remains intact despite long-term memory impairment ​ patients with hippocampal damage struggle with longer lists, indicating that the hippocampus is required when working memory capacity is exceeded ​ The Brown-Peterson Task and Short-Term Memory - tests short-term memory decay ​ amnesics show reduced performance, suggesting that hippocampal circuits may play a role in short-term retention when active maintenance is disrupted ​ Functional Imaging Studies ○​ HM helped establish the hippocampus as critical for memory ○​ PET studies initially aimed to detect hippocampal activation during memory tasks but had mixed results. ○​ fMRI studies later showed robust hippocampal activation during encoding of complex visual scenes and event-related memory tasks ​ Episodic-like Memory in Animals ○​ Birds ​ Scrub jays exhibit episodic-like memory, recalling what, where, and when they hid food and even planning for future needs ○​ Nonhuman Primates ​ Studies on monkeys bridge human findings (e.g., patient HM) with broader mammalian research, demonstrating that analogous neural structures underlie episodic memory impairments ​ Initial hippocampal lesion studies showed minimal deficits, but later research improved sensitivity by using trial-unique objects in delayed nonmatch-to-sample tasks, shifting the focus to episodic memory. ​ Lesions in different medial temporal structures produce distinct effects—permanent impairments with hippocampal and perirhinal/parahippocampal damage, but transient deficits with entorhinal lesions, highlighting the fornix’s role in memory processing. ○​ Rodents ​ Delayed Spatial Alternation ​ T-shaped maze that is elevated or enclosed with high walls to keep the rat on the maze ​ Spontaneous alternation task: a rat is allowed to follow its natural inclination to visit the arm that it did not visit on the previous trial ​ Rewarded alternation task: rats are explicitly rewarded for making a choice on each trial that differs from the choice on the previous trial  ​ Delayed spatial alternation task: a delay is interposed between each of the trials, requiring the rat to remember its choice on the previous trial across the delay interval ​ Forced choice delayed alternation: the first choice in the maze is forced by the insertion of a barrier on one arm. After a delay (usually 10 seconds), the rat must then make the correct choice of the arm that was previously blocked ​ Hippocampal, septum, and fornix lesions impair performance in delayed spatial alternation tasks ​ Spatial Reversal ​ Study fornix lesions ​ rats are initially trained to find food on one side of a T-maze, after extensive training on one side, the food reward is moved to the opposite side ​ impairment of extinction ​ Eight-Arm Radial Maze ​ eight different segments (arms) radiating from a central area to hidden food reward sites at the end of each arm ​ navigate and remember which arms contain rewards while avoiding revisits to already explored arms ​ hippocampal lesions impair performance on the task, indicating the hippocampus's critical role in spatial learning and memory ​ Morris Water Maze ​ assesses rodents' ability to learn and remember the location of a hidden platform using spatial cues ​ Lesions to the hippocampus impair performance, demonstrating its role in spatial memory and navigation ​ probe trials, the platform is removed to measure how well the rodent remembers its previous location, reflecting long-term spatial memory retention ​ Object investigation Time ​ potential episodic memory function by testing the specific requirement for memory of what, where, and when  ​ tendency of rats to focus their investigatory behavior on novel stimuli with less investigation of more familiar stimuli ​ rats learn trajectories from a central choice point to two different hidden objects in the side arms of an E-shaped maze Chapter 2: Neural Dynamics of Episodic Memory ​ Anatomical Circuits for Episodic Memory ○​ Hippocampus: Central hub for encoding and retrieving episodic memories, crucial for spatial and contextual memory formation. ○​ Medial Temporal Lobe (MTL): Includes the entorhinal, perirhinal, and parahippocampal cortices, which process and relay episodic information to the hippocampus. ○​ Fornix: Major white matter pathway connecting the hippocampus to the mammillary bodies and anterior thalamus, supporting memory consolidation. ○​ Mammillary Bodies & Anterior Thalamus: Involved in relaying hippocampal outputs and integrating memory with executive and attentional processes. ○​ Prefrontal Cortex: Regulates memory retrieval, organization, and decision-making related to episodic recall. ​ Principles of Connectivity ○​ Consistent Scales of Space and Time ​ Hierarchical Spatial Coding: The entorhinal cortex and hippocampus maintain a structured topography that encodes memory across different spatial scales, from broad locations (e.g., room) to fine details (e.g., object placement). ​ Consistent Spatiotemporal Mapping: The hippocampal formation preserves the relationship between spatial and temporal scales, ensuring accurate retrieval of episodic sequences without mismatched details. ​ Topographic Organization: The dorsal entorhinal cortex projects to the dorsal hippocampus (septal end), while the ventral entorhinal cortex projects to the ventral hippocampus (temporal end), creating a structured flow of spatial and temporal information.  ​ Orchestra Analogy: Just as different musical sections play in harmony, hippocampal circuits maintain synchronized encoding and retrieval through systematic entorhinal-CA1 projections. ○​ Parallel Streams for What and Where ​ Separate ‘what” and “where” streams ​ What - lateral entorhinal cortex; processes items/events; receives input from perirhinal cortex ○​ Projects from the lateral entorhinal cortex to distal CA1 ​ Where - medial entorhinal cortex; processes spatial location; receives input from the parahippocampal cortex ○​ Projects from the medial entorhinal cortex to proximal CA1 ○​ Medial entorhinal cortex relies input from the postsubiculum ​ CA1 plays key role in linking spatial context (where) with specific events (what) to form cohesive episodic memories ○​ Reciprocal Richness ​ Episodic memories integrate sensory details through widespread neuronal activation across different sensory cortices ​ Entorhinal cortex maintains bidirectional connections with sensory cortices ​ Hippocampus strengthens associations between spatiotemporal trajectories and sensory details ​ Activation of entorhinal neurons during retrieval can reactivate hippocampal circus - triggering detailed sensory memories stored in neocortical areas ○​ Convergence for Context ​ Episodic memories can be triggered by different contextual cues (convergence mechanism) ​ CA1 and subiculum maintain separate “what” and “where” streams ​ dentate gyrus and CA3 receive convergent input from both lateral (object-related) and medial (spatial-related) entorhinal cortex  ​ Convergence in CA3 and dentate gyrus enables distinct episodic differentiation - allowing memories to be categorized by broader themes ​ Cellular Mechanisms and Episodic Memory ○​ Neuronal Properties ​ Spiking activity, synaptic potentials, and oscillatory dynamics support episodic memory in hippocampus and entorhinal cortex ​ Neurons maintain a resting potential (~-70mV) due to ion concentration differences ​ sodium (Na⁺) and chloride (Cl⁻) outside ​ potassium (K⁺) inside ​ changes in ion conductance drive depolarization (excitation) or hyperpolarization (inhibition). ​ Action potential mechanism - when neurons membrane crosses ~-50mV, voltage-gated sodium channels open -> triggers rapid spike followed by potassium efflux to restore resting potential = spike pattern ​ Glutamate excites neurons via sodium and potassium channels ​ GABA inhibits through chloride and potassium channels ​ Acetylcholine modulates spiking and synaptic plasticity ○​ Persistent Spiking ​ Definition: a phenomenon in which entorhinal neurons continue firing after a stimulus ends, even when synaptic transmission is blocked ​ Driven by a calcium-activated nonspecific cation (CAN) current: which maintains depolarization through interactions between calcium influx and acetylcholine receptor activation. ​ Some entorhinal cortex neurons exhibit bistable persistent spiking (on/off states), while others show graded spiking, where firing frequency adjusts based on input strength. ​ Holds information active beyond the stimulus duration ​ Critical for active memory maintenance ○​ Membrane Potential Oscillations and Resonance ​ Neurons in the entorhinal cortex resonate at specific frequencies - contributes to coding of space and time  ​ Stellate cells in layer II of the medial entorhinal cortex: exhibit strong oscillatory activity and resonance, influencing spike timing and theta-frequency oscillations (4-10 Hz) in entorhinal and hippocampal circuits ​ Neurons along the dorsal-ventral axis of the medial entorhinal cortex show systematic changes in resonance frequency ​ A hyperpolarization-activated cation current (h-current) underlies oscillations, allowing neurons to rebound from inhibition and generate theta-frequency oscillations. ○​ Spike Frequency Accommodation ​ Definition: A gradual slowing and stopping of neuronal firing during sustained input, acting as a form of short-term memory by adapting to prior activity levels ​ Mechanism: Caused by potassium currents, including: ​ Delayed rectifier channels (fast-acting, regulate afterhyperpolarization after each spike). ​ M-current (slowly activated by depolarization, reduces firing rate). ​ AHP current (calcium-sensitive, activated by calcium influx during spiking, causing slow hyperpolarization). ​ Supports short-term recognition memory by reducing responses to familiar stimuli. ​ Contributes to theta frequency oscillations ○​ Synaptic Modification ​ Hebbian Theory: neurons that fire together, wire together = synaptic strength increases when presynaptic and postsynaptic neurons fire together, forming the basis of memory encoding ​ Long-Term Potentiation (LTP): occurs when repetitive stimulation strengthens synaptic connections, potentially supporting long-term memory formation. ​ relies on NMDA receptors, which require both glutamate release and postsynaptic depolarization to remove a magnesium block, allowing calcium influx and synaptic strengthening.  ​ Spike-Timing-Dependent Plasticity (STDP): A form of Hebbian plasticity where synaptic strengthening occurs only if the presynaptic spike precedes the postsynaptic spike within a brief