Neurobiology of learning and memory
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Neurobiol Learn Mem · Sep 2013
Gamma band plasticity in sensory cortex is a signature of the strongest memory rather than memory of the training stimulus.
Gamma oscillations (∼30-120Hz) are considered to be a reflection of coordinated neuronal activity, linked to processes underlying synaptic integration and plasticity. Increases in gamma power within the cerebral cortex have been found during many cognitive processes such as attention, learning, memory and problem solving in both humans and animals. However, the specificity of gamma to the detailed contents of memory remains largely unknown. ⋯ A stronger relationship was found between increased gamma power and the frequency with the strongest memory (peak of the difference between individual post- and pre-training FGGs) vs. behavioral responses to the CS training frequency. No such relationship was found for the theta/alpha band (4-15 Hz). These findings indicate that the strength of specific increased neuronal synchronization within primary sensory cortical fields can determine the specific contents of memory.
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Eye-blink conditioning (EBC) is a form of associative learning that depends on the cerebellum. Previous reports suggested that sensory cortex is necessary for trace EBC but not for delay EBC. The trace and delay EBC procedures used in these studies differed by the presence or absence of a temporal gap between the end of the conditioned stimulus and the onset of the unconditioned stimulus (trace interval) and in the interval between the onset of the CS and the US (inter-stimulus interval, ISI). ⋯ In Experiment 3, unilateral inactivation of the visual cortex impaired long-delay EBC but had no effect on trace EBC. The results indicate that the visual cortex facilitates EBC with relatively long ISIs, regardless of whether there is a trace interval or not. Moreover, the ipsilateral projections from the visual cortex to the pontine nuclei are sufficient for modulating long-delay EBC, whereas trace EBC involves bilateral visual cortical interactions with forebrain systems including the hippocampus and prefrontal cortex.
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Neurobiol Learn Mem · Jul 2013
ADRA2B genotype modulates effects of acute psychosocial stress on emotional memory retrieval in healthy young men.
Previous studies have shown that acute psychosocial stress impairs retrieval of declarative memory with emotional material being especially sensitive to this effect. A functional deletion variant of the ADRA2B gene encoding the α2B-adrenergic receptor has been shown to increase emotional memory and neural activity in the amygdala. We investigated the effects of acute psychosocial stress and the ADRA2B allele on recognition memory for emotional and neutral faces. ⋯ Carriers of the ADRA2B functional deletion variant showed an impaired recognition and slower retrieval of neutral faces under stress. Further, they were significantly slower in retrieving fearful faces in the control condition. The findings indicate that a genetic variation of the noradrenergic system may preserve emotional faces from stress-induced memory impairments seen for neutral faces and heighten reactivity to emotional stimuli under control conditions.
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Neurobiol Learn Mem · May 2013
Sodium butyrate-induced histone acetylation strengthens the expression of cocaine-associated contextual memory.
The conditioned place preference (CPP) paradigm entails Pavlovian conditioning and allows evaluating the acquisition and extinction of drug-associated memory. Epigenetic regulation of chromatin structure by acetylation and deacetylation of histone proteins is critical for formation of long-term memory (LTM). We have recently shown that a single administration of the histone deacetylase (HDAC) inhibitor sodium butyrate (NaB) facilitated extinction of fear-associated memory in mice. ⋯ Subjects that were conditioned by escalating schedule of cocaine and subsequently received repeated injections of NaB during daily reexposure to nonreinforced context showed either enhancement or no effect on place preference. Acute administration of NaB (1.2g/kg) to naïve mice resulted in marked increase in acetylation of histone H3 lysine 14 (H3K14) and histone H4 lysine 8 (H4K8) in hippocampus but not amygdala. Results suggest that regardless of the scheduling of either cocaine or NaB administration, NaB-induced histone hyperacetylation in the hippocampus may strengthen cocaine-associated contextual memory.
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Neurobiol Learn Mem · May 2013
Systemic administrations of β-estradiol alleviate both conditioned and sensitized fear responses in an ovariectomized rat model of post-traumatic stress disorder.
Although no single widely accepted animal model of PTSD has been established to date, the single prolonged stress (SPS) animal model has been partially validated as a model for PTSD. SPS rats mimic the pathophysiological abnormalities and behavioral characteristics of PTSD, such as enhanced fear response to the traumatic cue (conditioned fear response) and hyper arousal (the sensitized fear response). In the present study we are looking at PTSD-like symptoms in rats. ⋯ Findings indicated that rats who received electric shock the day after SPS exhibited both enhanced conditioned and sensitized fear responses in comparison to the control group. β-estradiol in 45μg/kg dose could reduce both types of fear responses. β-estradiol exert an inhibitory influence on contextual fear conditioning (hippocampal-dependent) and on sensitized fear conditioning (amygdala-dependent). Single injection of this dose is enough for CFR alleviation but at least twice injections are necessary to reduce sensitized fear response. Overall our data demonstrate that multiple injections of β-estradiol, dose dependently, could alleviate both SPS induced conditioned and sensitized fear responses, as signs of PTSD.