Neuroanatomy of Memory Zara A. Melikyan (some slides are courtesy of Dr. G.P.Sutton) February 17, 2015

Lecture Goals: Brain structures involved in: - Declarative memory - Non-Declarative memory How are memories formed: - STM vs. LTM

Gross Brain Anatomy

Brain Structures Involved in Memory

The Limbic System Cortical areas: Limbic lobe Orbitofrontal cortex - decision making Piriform cortex - part of olfactory system Enthorhinal cortex - memory and associative processes Subcortical areas: Hippocampus - consolidation of new memories Fornix - connects hippocampus to other areas Septal nuclei - a pleasure zone Amygdala - emotional processes, episodic autobiographical memory, social processing Nucleus accumbens - reward, pleasure, addiction Diencephalon: Hypothalamus - regulates autonomic processes. Mammilary bodies transfer signals from hyppocampus to thalamus

Subtypes of LTM LTM Declarative Episodic Semantic Nondeclarative (Procedural) Skill learning Priming Conditioning

Declarative: Formation of Memories Medial temporal lobes: - Hippocampus - ability to retain and recall episodic memories, different neurons are activated depending on stimulus modality. Morris water navigation tasks, Patient H.M. Eichenbaum et al. (2001), hippocampal functions: 1. recording of episodic memories, 2. identification common features between episodes, 3. Linking these episodes in memory space - Hippocampus + Parahippocampus - formation of new declarative memories - Parahippocampus - recognition - Damage: More severe impairments when both temporal lobes are damaged Connections between limbic system and hippocampus - Damage: Korsakoff syndrome - Retro- and anterograde amnesia, confabulation, lack of insight, apathy - B1 defficiency, viral encephalitis, alcohol abuse

Declarative: Storage of Memories Episodic memories - Prefrontal (remembering context, more episodic than semantic memory) and parietal cortex Encoding memories: Left DLPC, Retrieving memories: RDLPC Amygdala - encoding and retrieval of emotionally charged memories, flashbulb memories. Remembering emotionally charged pictures. - Damage: impairs episodic formation/retrieval (not semantic formation/retrieval) Episodic and semantic memories - Multiple different parts of cortex

Non-Declarative: Skill Learning Basal ganglia, striatum, motor cortex, cerebellum, limbic system Evidence: - Impaired with damage to these areas - Activation demonstrated in neuroimaging studies

Non-Declarative: Priming Exposure to a stimulus influences response to another stimulus Positive priming - increases the speed of response, experiencing the stimulus Negative priming - decreases the response speed, experiencing the stimulus and then ignoring it Perceptual priming (perceptive aspect of stimulus: table - table top) - Reduced bilateral occipito-temporal cortical activation Conceptual priming (semantic aspect of stimulus: table - desk) - Reduced activation of left frontal cortex

Non-Declarative: Associative Learning Classical conditioning - Cerebellum involved in eye-blink conditioning - Humans and non-humans Operant conditioning - A group of brain regions are involved because many aspects of behavior involved. Frontal lobes are important.

How are Memories Formed? Sensory Memory - limited capacity 12 elements (G. Sperling), limited duration (hundreds of milliseconds). Registers all the sensory information. - Iconic - Echoic - Haptic Short-Term Memory - limited capacity (7+/-2, or 4-5 elements), limited duration (18-30 sec). Registers information to which attention is paid. Transient patterns of neuronal connection in prefrontal & temporal lobes, hippocampus essential for information consolidation from STM to LTM. Information is rehearsed and chunked. Subtype: Working memory. Manipulate information for immediate use. E.g., reverse a phone number in your head. Long-Term Memory - close to unlimited capacity, unlimited duration. More stable and permanent changes in neuronal connections throughout the brain.

How are Memories Formed? 1. Encoding - Raw info (sensory channels) transformed to STM 2. Consolidation - STM transformed to LTM 3. Retrieval - Stored info brought out from LTM for use Emotionally arousing experiences are remembered best

STM vs. LTM Hippocampal involvement - Consolidation of declarative STMs to LTMs Effect of head trauma - Often causes retrograde amnesia - Does not affect other memories - May interrupt consolidation of STM to LTM

LTM: Remembering and Forgetting No “upper limit” Forgetting is natural - Beneficial to forget some things - Filter out unimportant information, free up cognitive resources Memory interference - Proactive interference - Previously learned info interferes with learning of new info - Retroactive interference - Newly learned info interferes with previously learned info

Reconsolidation and False Memories Synaptic consolidation occurs within first few hours of learning Systems consolidation - hippocampus-dependent memories become independent of hippocampus Memory consolidation during sleep: reactivation of hippocampal memories, transfer information to neocortex to reintegrate with existing memories. Slow-wave sleep, sleep spindle - consolidation of declarative memory REM - consolidates emotional declarative memories Reconsolidation - previously consolidated memories are recalled and actively consolidated to maintain, strengthen and modify memories in LTM. ECT for phobias. Bringing up a memory can make it susceptible to distortion. https://www.youtube.com/watch?v=9BrCBq2FY_U

Thank you for your attention! Questions? Thank you for your attention!