Neurobiology of learning and memory
-
Neurobiol Learn Mem · Oct 2014
A critical role of glutamate transporter type 3 in the learning and memory of mice.
Hippocampus-dependent learning and memory are associated with trafficking of excitatory amino acid transporter type 3 (EAAT3) to the plasma membrane. To assess whether this trafficking is an intrinsic component of the biochemical responses underlying learning and memory, 7- to 9-week old male EAAT3 knockout mice and CD-1 wild-type mice were subjected to fear conditioning. Their hippocampal CA1 regions, amygdalae and entorhinal cortices were harvested before, or 30 min or 3 h after the fear conditioning stimulation. ⋯ These biochemical responses were attenuated in the EAAT3 knockout mice. These results suggest that EAAT3 plays a critical role in learning and memory. Our results also provide initial evidence that EAAT3 may have receptor-like functions to participate in the biochemical reactions underlying learning and memory.
-
Neurobiol Learn Mem · Oct 2014
Exercise reduces diet-induced cognitive decline and increases hippocampal brain-derived neurotrophic factor in CA3 neurons.
Previous studies have shown that a western diet impairs, whereas physical exercise enhances hippocampus-dependent learning and memory. Both diet and exercise influence expression of hippocampal brain-derived neurotrophic factor (BDNF), which is associated with improved cognition. We hypothesized that exercise reverses diet-induced cognitive decline while increasing hippocampal BDNF. ⋯ These data suggest that exercise improves memory retrieval, particularly with respect to avoiding aversive stimuli, and may be beneficial in protecting against diet induced cognitive decline, likely via elevated BDNF in neurons of the CA3 region.
-
Neurobiol Learn Mem · Sep 2014
Human fear extinction and return of fear using reconsolidation update mechanisms: the contribution of on-line expectancy ratings.
Disruption of the reconsolidation of conditioned fear memories has been suggested as a non-pharmacological means of preventing the return of learned fear in human populations. A reconsolidation update paradigm was developed in which a reconsolidation window is opened by a single isolated retrieval trial of a previously reinforced CS+ which is then followed by Extinction Training within that window. However, follow-up studies in humans using multi-methods fear conditioning indices (e.g., fear-potentiated startle, skin conductance, US-expectancy) have failed to replicate the retrieval+extinction effects. ⋯ Participants were fear conditioned to two visual cue CS+'s, one of which was presented as a single, isolated retrieval trial before Extinction Training and one that was extinguished as usual. The results show that the inclusion of US-expectancy measures strengthens the CS-US association to provide enhanced fear conditioning and maintenance of fear memories over the experimental sessions. In addition, in the groups that used on-line US-expectancy measures, the retrieval+extinction procedure reduced reinstatement of fear-potentiated startle to both previously reinforced CS+'s, as compared to the extinction as usual group.
-
Neurobiol Learn Mem · Sep 2014
Extinction in multiple virtual reality contexts diminishes fear reinstatement in humans.
Although conditioned fear can be effectively extinguished by unreinforced exposure to a threat cue, fear responses tend to return when the cue is encountered some time after extinction (spontaneous recovery), in a novel environment (renewal), or following presentation of an aversive stimulus (reinstatement). As extinction represents a context-dependent form of new learning, one possible strategy to circumvent the return of fear is to conduct extinction across several environments. Here, we tested the effectiveness of multiple context extinction in a two-day fear conditioning experiment using 3-D virtual reality technology to create immersive, ecologically-valid context changes. ⋯ Extinction in multiple contexts attenuated reinstatement of fear but did not reduce spontaneous recovery. Results from fear renewal were tendential. Our findings suggest that multi-context extinction can reduce fear relapse following an aversive event--an event that often induces return of fear in real-world settings--and provides empirical support for conducting exposure-based clinical treatments across a variety of environments.
-
Neurobiol Learn Mem · Sep 2014
Dispositional cognitive reappraisal modulates the neural correlates of fear acquisition and extinction.
Adverse learning experiences play a significant role in the etiology of anxiety disorders. However, not all individuals experiencing negative events develop heightened anxiety. This is possibly due to individual differences in the regulation of negative emotions associated with these negative events. ⋯ In addition, reduced recovery of conditioned arousal, reduced anterior cingulate and dorsomedial prefrontal cortex activation and enhanced ventromedial prefrontal cortex activation during extinction recall was observed in individuals with higher cognitive reappraisal scores. The results indicate that dispositional cognitive reappraisal modulates subjective and neural correlates of fear conditioning, probably leading to reduced acquisition and stronger extinction learning and recall. These results point to the important role of dispositional cognitive reappraisal in the development and modification of conditioned emotional responses and might further improve our understanding of anxiety disorders.