"Light Bulb Moment"

The ability to extract generalizable rules from specific experiences is a fundamental attribute of higher cognitive functioning. Rule-learning is a term that describes the phenomenon of learning how to learn (sometimes also termed meta-learning). Training rats in a particularly difficult olfactory discrimination (OD) task initiates a period of accelerated learning capabilities, manifested as a dramatic increase in their capacity to acquire memories for new odors once they have learned the first discrimination task, implying that rule learning has taken place. 

In the last three decades an increasing amount of evidence suggests that modifications in intrinsic neuronal excitability play a key role in learning. In particular, enhanced intrinsic neuronal excitability  enables neuronal ensembles to enter into a state which may be best termed "learning mode", by setting a time window in which activity-dependent synaptic modifications are more likely to occur, as neurons are more easily recruited into new memory traces. This state lasts for up to several days and its behavioral manifestation is enhanced learning capability of complex tasks.

At the cellular biophysical level, OD rule learning-induced enhanced excitability is mediated by long-term reduction in the amplitude of the post-burst after-hyperpolarization (AHP) in pyramidal neurons, thus enhancing the frequency of their repetitive spike firing. Such reduction results from reduced conductance of the intrinsic slow calcium-dependent potassium current (sIAHP). Activation of a specific kainate subtype glutamatergic receptor, GluK2, triggers the chain of events leading to OD rule learning by inducing the long-term reduction in the sIAHP. At the behavioral level, overexpression of GluK2 in the piriform cortex enhances OD rule learning, while GluK2 knockouts are unable to learn the rule. Thus, causal relations exist between enhanced intrinsic neuronal excitability and OD rule learning.

We hypothesis that a whole-network reduction of the post burst AHP is induced at a particular point in time during training for complex tasks, resulting in a "light bulb moment" (defined as "a moment when you suddenly realize something or have a good idea"), when the animal understands the rule. This leap in learning capability occurs after a relatively long training period and its hallmark is a synchronous change in most, if not all, excitatory neurons in the relevant neuronal network, as they all become more intrinsically excitable.

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Combine precise electrophysiological and imaging tools with genetic identification of active neurons, to study of the cellular and molecular mechanisms of this intriguing phenomenon.