1. Ch.8 Theta rhythm and bidirectional plasticity in the hippocampus
Population Coding
Ch.8 Theta rhythm and bidirectional plasticity in the hippocampus
Summarized by Ko Youngkil
2009/1/6

2. Content Summary Theta rhythm Theta rhythm’s effect Conclusion
Hippocampus activity
Long-term potentiation
Ca2+ Level
Conclusion

3. Summary
The phase of theta rhythm determines the direction of plastic changes for the entire population
The rate of learning is faster highest theta power
LTP when peak tetanus
LTD when trough tetanus
Theta rhythm determine the level of Ca2+
Peak tetanus
Trough tetanus

4. Theta rhythm Rhythmic local field potential Theta appeared Absence
Walked, ran, sniffed, oriented, reared, REM
Absence
Eating, drinking, grooming, slow wave sleep
Experiments with rodents

5. Hippocampus activity Without theta rhythm
Impairment in a spatial memory task
Spatial alternation
Delayed non-match to position
And so on.
Rabbits when the hippocampal EEG has the highest amount of theta power
Theta enables associations to form between place cells with adjoining fields

6. Long-term potentiation (1/2)
Long-lasting enhancement of synaptic excitability
Long-term depression
Long-lasting decrease in the size of evoked potentials
Lead to lasting morphological changes at the synapse that alter synapsis

7. Long-term potentiation (2/2)
LTP
induced when a tetanus in positive phase of theta
LDP
Tetanus in negative phase of theta
Theta provide selectively decrease or increase synaptic efficacy
Peak tetanus
Trough tetanus

8. Ca2+ Level Spike timing dependent plasticity (STDP)
Induce LTP
By influx of Ca2+
Levels of Ca2+ determine the directionality of plastic changes, so the phase of theta rhythm controls the directionality

9. Conclusion Hippocampus activity is tightly controlled by theta.
Synaptic modification is dependent on theta
Intracellular potentials and ion levels are regulated by theta.
Macroscopic, microscopic scales