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Muscimol infused into the entorhinal cortex prior to training blocks the involvement of this area in post-training
P. Williner1, M. Bianchin, R. Walz
1Department of Psychology, University College of Swansea, Singleton Park, Swansea SA2 8PP, UK.
Abstract:
Muscimol infusions into the entorhinal cortex (ERC) have previously been reported to impair the retention of passive avoidance learning, but only when infusions were delayed until 90min after training. In the present study, three experiments were carried out to examine further the effects of muscimol infusions into the ERC prior to training. In Experiment 1, muscimol infusions prior to training had no effect on retention, confirming earlier findings, but blocked the amnestic effect of a second muscimol infusion 90min post-training. In Experiment 2, muscimol infusions prior to training blocked the improvement of retention normally seen following a second training trial 2h after the first. In Experiment 3, the technique of summation of performance across training trials was used to confirm that the direct effects of muscimol infusions lasted less than 2h. The results indicate that the GABA-ergic mechanism in the ERC is normally involved in the formation of memory for passive avoidance, but if the ERC is inactivated at the time of training, memory formation is diverted to other structures, which appear less capable of integrating consecutive memories across time.
Insights
Inactivating the entorhinal cortex (ERC) before training prevents memory formation in that area, diverting it elsewhere. This suggests the ERC is crucial for integrating memories over time.
Area of Science:
- Neuroscience
- Cognitive Science
- Memory Research
Background:
- Previous studies indicated entorhinal cortex (ERC) muscimol infusions impaired passive avoidance learning retention when delayed post-training.
- The role of the ERC during the initial learning phase remained unclear.
Purpose of the Study:
- To investigate the effects of muscimol infusions into the ERC immediately prior to passive avoidance training.
- To determine if ERC inactivation during training impacts memory consolidation and temporal integration.
Main Methods:
- Administered muscimol, a GABA-ergic agonist, into the ERC before training in three experiments.
- Assessed retention of passive avoidance learning.
- Utilized summation of performance across training trials to estimate drug effect duration.
Main Results:
- Pre-training ERC muscimol infusions did not impair retention but blocked the amnesic effect of post-training infusions.
- Pre-training ERC inactivation prevented the retention improvement typically seen after a second training trial.
- The direct effects of muscimol infusions in the ERC lasted less than 2 hours.
Conclusions:
- The GABA-ergic mechanism in the ERC is essential for normal memory formation in passive avoidance learning.
- Inactivating the ERC during training diverts memory formation to other brain structures.
- These alternative structures are less efficient at integrating sequential memories over time.