M. A. Wilson and B. L. McNaughton Presented by: Katie Herdman, Monika Walerjan, Scott Good, Snir Seitelbach and David Dudar

Presentation Outline  Introduction  Hippocampus  Place Cells  Purpose of the Experiment  Methods  Apparatus  Data Analysis  Results  Findings  Inhibitory Interneurons  Repeat Trials  Discussion  Conclusions Katie Herdman

Hippocampus (HC)  HC role in memory encoding is extensively documented  HC has long been considered important for cognitive representations and associative memory  The notorious Morris Water Maze proved similar activation of the HC - Introduction - Methods - Results - Discussion Katie Herdman

Place Cells  HC is the home of “place cells”  Place Cells fire when the individual is in a physical environment that the cell is responsible for  Place cells require active movement through the environment - Introduction - Methods - Results - Discussion Katie Herdman

Purpose of the Experiment  To determine if cell population activity over brief intervals is a robust indicator of spatial location  To address the role of experience in the establishment of hippocampal spatial representations  To determine whether incorporation of new spatial information has any effect on previously stored information - Introduction - Methods - Results - Discussion Katie Herdman

Methods  3 rats implanted with microdrive arrays containing 12 four-channel recording electrodes (tetrodes)  Each tetrode resolves activity from 5-20 hippocampal neurons - Introduction - Methods - Results - Discussion Scott Good

The Apparatus  Rectangular box used, 124cm x 62cm x 62cm  Walls were covered with a variety of visual and tactile cues  Two areas, called Box A and Box B, were separated by a partition - Introduction - Methods - Results - Discussion Scott Good

The Apparatus ctd.  During test period, tetrodes recorded for 10 minutes while rats explored Box A  Partition was removed, neuronal recording during exploration of Box B - Introduction - Methods - Results - Discussion Scott Good

The Apparatus ctd.  Partition returned, recording continued for 10 minutes afterwards in Box A  Recordings were divided into appropriate phases; Introduction - Methods - Results - Discussion Scott Good

Data Analysis  The rats’ trajectories were plotted and computed  Each square represents spatial activation of one particular cell  Depending on what cells were activated, the experimenters could predict the location of the rats in the box - Introduction - Methods - Results - Discussion Scott Good

Findings  The longer the integration time, the less cells are needed to predict rats location accurately  Spatial representations involve many HC cells working together, rather than just one or two - Introduction - Methods - Results - Discussion Snir Seitelbach

Findings ctd.  Error estimating rat location was greater than 5cm due to intrinsic tracking error - Introduction - Methods - Results - Discussion Snir Seitelbach

Findings ctd.  Different place cells are activated during different situations  Inhibitory interneurons were activated, inhibited other hippocampal neurons  Inhibitory interneurons allow certain place cells to fire while inhibiting others, key role in forming spatial maps - Introduction - Methods - Results - Discussion Snir Seitelbach

Inhibitory Interneurons  When open to Box A and B, inhibitory interneurons were suppressed  Hypothesized to be synaptic modification to a new environment  Indicates necessity for HC place cells to gradually acquire cognitive representation - Introduction - Methods - Results - Discussion Snir Seitelbach

Effect of Experience  Little effect on firing of place cells  New spatial knowledge did not interfere with prior spatial knowledge - Introduction - Methods - Results - Discussion Snir Seitelbach

Conclusions - Introduction - Methods - Results - Discussion Snir Seitelbach  One can predict the location of the rats in a box based on firing of hippocampal place cells  New spatial representation expression improved rapidly with experience; the assumed synaptic modification mechanisms are rapid  Inhibitory interneuron suppression might facilitate the synaptic modification involved in encoding novel spatial information  Interference between new spatial information and prior spatial knowledge was very small

Significance  Complexity of hippocampus function and its general significance - Introduction - Methods - Results - Discussion Snir Seitelbach