2017-05-27
Every learning event is embedded in a context, but not always can we subsequently recall this context. Why is context sometimes an integral part of the memory and sometimes not? A good way of studying this is to concentrate on extinction learning. Here, it is assumed that context is not learned for initial acquisition but perfectly learned for the extinction period. While the neuronal mechanisms underlying contextual control of extinction are well known, the mechanisms of (non)learning during acquisition are mostly unknown. Here, we tested the hypothesis that shifting attention to critical cues is less likely during acquisition than during extinction and that this is the reason why context is less learned during acquisition than during extinction. We further assumed that these attentional mechanisms are controlled by activation of glutamatergic NMDA-receptors at prefrontal level. Thus, we antagonized NMDA receptors with AP5 in the pigeon nidopallium caudolaterale (NCL), the functional analogue of mammalian prefrontal cortex, during the concomitant acquisition and extinction of conditioned responding to two different stimuli. Indeed, NMDA receptor blockade resulted in an impairment of extinction learning, but left the acquisition of responses to a novel stimulus unaffected. Critically, when responses were tested in a different context in the retrieval phase, we observed that NMDA receptor blockade led to the abolishment of contextual control over acquisition performance. Thus, learning without functional NMDA receptors in NCL possibly results in a loss of contextual gain on the learned association, possibly via the modulation of attentional mechanisms. To come back to our initial question of why we sometimes learn the context and sometimes not: It depends on how much our attention is switched to the context during learning. If we pay attention, NMDA receptors at prefrontal level play a key role.
Every learning event is embedded in a context, but not always can we subsequently recall this context. Why is context sometimes an integral part of the memory and sometimes not? A good way of studying this is to concentrate on extinction learning. Here, it is assumed that context is not learned for initial acquisition but perfectly learned for the extinction period. While the neuronal mechanisms underlying contextual control of extinction are well known, the mechanisms of (non)learning during acquisition are mostly unknown. Here, we tested the hypothesis that shifting attention to critical cues is less likely during acquisition than during extinction and that this is the reason why context is less learned during acquisition than during extinction. We further assumed that these attentional mechanisms are controlled by activation of glutamatergic NMDA-receptors at prefrontal level. Thus, we antagonized NMDA receptors with AP5 in the pigeon nidopallium caudolaterale (NCL), the functional analogue of mammalian prefrontal cortex, during the concomitant acquisition and extinction of conditioned responding to two different stimuli. Indeed, NMDA receptor blockade resulted in an impairment of extinction learning, but left the acquisition of responses to a novel stimulus unaffected. Critically, when responses were tested in a different context in the retrieval phase, we observed that NMDA receptor blockade led to the abolishment of contextual control over acquisition performance. Thus, learning without functional NMDA receptors in NCL possibly results in a loss of contextual gain on the learned association, possibly via the modulation of attentional mechanisms. To come back to our initial question of why we sometimes learn the context and sometimes not: It depends on how much our attention is switched to the context during learning. If we pay attention, NMDA receptors at prefrontal level play a key role.
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