Lecture 14: How Do Our Brains Store Information?

HOW DO OUR BRAINS STORE INFORMATION? Psychology 301 Lecture 14 Memory  Essential for adaptive behavior  Seen in just about all organisms  Simple attraction/avoidance conditioning in sea slug  World Memory Championships in London (3:46) Memory  E...

HOW DO OUR BRAINS STORE INFORMATION? Psychology 301 Lecture 14 Memory  Essential for adaptive behavior  Seen in just about all organisms  Simple attraction/avoidance conditioning in sea slug  World Memory Championships in London (3:46) Memory  Essential for adaptive behavior  Seen in just about all organisms  Simple attraction/avoidance conditioning in sea slug  World Memory Championships in London  More papers on topic than any other in CogNeuro literature. Organization Hippocampus in spatial navigation Hippocampus in Long term memory formation Evidence at encoding and recall Neural mechanisms Relational memory Taxonomy of Memory Knowledge Performance  Hippocampus in Spatial Navigation Morris Water Maze (MWM) Procedure: https://www.youtube.com/watch?v=leHLL4vcbCc After learning: https://www.youtube.com/watch?v=YJXLZlxi46M Control rats were faster at finding a hidden platform after a few trials than hippocampus-lesioned rats. Hippocampus-lesioned rats had no difficulty reaching a visible placeholder, but they could not learn the location of a hidden placeholder. Hippocampus is involved in forming a memory of space. Question 1 Morris, 1982  Hippocampus in Spatial Navigation Taxi drivers with more experience had larger posterior hippocampal volumes Experience was correlated with hippocampal volume hippocampal volume London Taxi Drivers London Controls Posterior Question 2 Maguire et al., 2000 Hippocampus in Spatial Navigation fMRI study of virtual navigation More active when navigating without cues than following arrows on the road Hippocampus creates an representation of space, parietal lobe uses “the map” to compute direction (Maguire et al., 1998) What do episodic memory and “map-making” have in common? Long history of spatial navigation research in animals After HM develops anterograde amnesia after hippocampal lesions, hippocampus becomes known for forming long term memories  Episodic memory and spatial navigation Neurons co-activated during learning also fire together during sleep. Quick replay of co-activated neurons Spatial navigation is a series of associative learning “episodes” played out over time Question 3 Organization Hippocampus in spatial navigation Hippocampus in long term memory formation Evidence at encoding and recall Neural mechanisms Relational memory  Hippocampus in Memory Encoding Encoding – forming a memory representation from incoming information At recall asked to say whether word was old or new (recognition) and if word had been in red or green (recall). People more likely to report old words as old and new words as new Question 4  Hippocampus in Memory Encoding Hippocampus shows greater activity at time of encoding for words that were correctly recalled than were forgotten. This activity related to actual recall (was the word red or green) rather than familiarity (old, new) Question 5 Hippocampus in Memory Encoding Scanned while watching “Curb Your Enthusiasm” Later, asked questions about specific segments of the episode  Hippocampus creating long term memories Xs are times there was a difference between remembered  Parahippocampus and forgotten was more active for scenes remembered scenes while watching them  Primary visual cortex– no effect. Question 6 Green – Onset of scene Hippocampus and Memory formation “What” information: from unimodal sensory regions of neocortex passing through perirhinal cortex. “Where” information: from cortical areas passing through posterior parts of parahippocampal cortex. “Where” and “What” project into entorhinal cortex but converge within hippocampus. Hippocampus binds information/stimuli that happen at the same time. Consolidation Theory – Systems Level Before Learning: After Learning: Hippocampus consolidates multiple representations across the cortex into a memory After consolidation, retrieving the memory does not require the hippocampus Organization Hippocampus in spatial navigation Hippocampus in long term memory formation Evidence at encoding and recall Neural mechanisms Relational memory Consolidation Theory – Cellular Long-term potentiation (LTP) or depression (LTD) Strengthens or weakens synaptic connection Baseline = 1 pulse LTP = burst of fast pulses LTD = slow pulses PSP = post-synaptic potentials Hippocampal neuron is more likely to fire after LTP and less likely to fire after LTD Question 7 Associative LTP: An Example of Hebbian Learning S1 S1 CA1 CA1 w1 cell cell w1 w2 w2  If strong (s1) input and two weak (w1,w2) inputs to same neuron, if w1 and s1 are active together, w1 connection is strengthened and w2 is not  3 rules of neuronal LTP:  Cooperativity – more than 1 input must be active at the same time  Associativity – weak with strong co-occur  Specificity – only that synapse potentiated Neurons that fire together, wire together Consolidation of Relational Memory Acquisition Hippocampus is part of network for developing associations between representations in different cortical areas. Accounts for: Role of MTL region in acquisition of new (declarative) memories Sparing of older memories that have already been formed Organization Hippocampus in spatial navigation Hippocampus in long term memory formation Evidence at encoding and recall Neural mechanisms Relational memory  Why are some memories formed by the hippocampus and others not? Explicit vs implicit?  Search for the T – raise your hand when you find it  Find the T L L L L L T L L L L L  Find the T L T L L L L L L L L L  Find the T L L L L L L L L L L T Clicker  Find the T L L L L L T L L L L L Notice anything about the last search? Relational memory If the T is red, it is always in the same place. Requires learning of the color, the letter, and the location together. Implicit task – people do not report noticing the red T is always in the same location If explicit vs implicit, hippocampal amnesics should be faster with the red T’s like control subjects If relational vs non-relational, hippocampal amnesics should not learn associations  RT decline assumed to reflect learning of shape discrimination Target is in a new location or the learned (old) location: Relational learning effect Dissociation of two types of implicit learning 1) Improved shape discrimination is normal 2) Relational learning is absent in amnesics even though it is non-declarative. Question 8 Computational differences between memories involving the hippocampus and those that do not require the hippocampus. Non-H Based Memory Hippocampus Memory unidimensional multidimensional (relational memory) limited neural extent representation of representation extend to multiple regions outside awareness accessible to awareness (but not required) Summary Hippocampus important for relating different aspects of an event and binding them together in space and time, regardless of whether they are conscious or unconscious Hippocampus forms memories but is not necessary for retrieval of those memories once they are consolidated