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Sensitization and hippocampal type 2 theta in the rat
R S Sainsbury1, J L Harris, G L Rowland
1Department of Psychology, University of Calgary, Alberta, Canada.
Physiology & Behavior
|January 1, 1987
Summary
Inescapable shocks increase type 2 theta in rats, a brainwave linked to alert immobility. This suggests that a high arousal state, not conditioning, is necessary for producing type 2 theta.
Area of Science:
- Neuroscience
- Behavioral Neuroscience
- Electrophysiology
Background:
- Two types of hippocampal theta activity, Type 1 and Type 2, are documented across species.
- Type 1 theta is associated with voluntary movement, while Type 2 theta occurs during alert immobility.
- Type 2 theta is less common in rats but observed during conditioning.
Purpose of the Study:
- To investigate the relationship between Type 2 theta and inescapable shock.
- To examine how varying temporal characteristics of conditioning stimuli (CS) affect Type 2 theta production.
- To test the hypothesis that arousal is a precursor to Type 2 theta.
Main Methods:
- Rats were subjected to three conditioning paradigms: delay, trace, and random.
- Type 2 theta production was recorded and analyzed in relation to shock frequency and conditioning stimuli.
- The effect of previously neutral sensory stimulation post-conditioning was also assessed.
Main Results:
- Type 2 theta production increased with the number of inescapable shocks over time.
- No significant differences in Type 2 theta were observed during CS presentations or inter-stimulus intervals across groups.
- Previously neutral stimuli elicited Type 2 theta after conditioning, indicating sensitization.
Conclusions:
- Inescapable shock leads to a heightened arousal state in rats.
- This arousal state sensitizes rats to produce Type 2 theta.
- Arousal, rather than specific conditioning parameters, appears necessary for Type 2 theta production.