Neurocentre Magendie

Einar EINARSSON




Post-Doctorant

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Cursus:
PhD McGill University (2012)






7 publication(s) depuis Juin 2001:


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Abstract:
After acquisition, hippocampus-dependent memories undergo a systems consolidation process, during which they become independent of the hippocampus and dependent on the anterior cingulate cortex (ACC) for memory expression. However, consolidated remote memories can become transiently hippocampus-dependent again following memory reactivation. How this systems reconsolidation affects the role of the ACC in remote memory expression is not known. Using contextual fear conditioning, we show that the expression of 30-day-old remote memory can transiently be supported by either the ACC or the dorsal hippocampus following memory reactivation, and that the ACC specifically mediates expression of remote generalized contextual fear memory. We found that suppression of neural activity in the ACC with the AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) impaired the expression of remote, but not recent, contextual fear memory. Fear expression was not affected by this treatment if preceded by memory reactivation 6 h earlier, nor was it affected by suppression of neural activity in the dorsal hippocampus with the GABA-receptor agonist muscimol. However, simultaneous targeting of both the ACC and the dorsal hippocampus 6 h after memory reactivation disrupted contextual fear memory expression. Second, we observed that expression of a 30-day-old generalized contextual fear memory in a novel context was not affected by memory reactivation 6 h earlier. However, intra-ACC CNQX infusion before testing impaired contextual fear expression in the novel context, but not the original training context. Together, these data suggest that although the dorsal hippocampus may be recruited during systems reconsolidation, the ACC remains necessary for the expression of generalized contextual fear memory.Neuropsychopharmacology advance online publication, 3 September 2014; doi:10.1038/npp.2014.197.




14/06/2013 | Neuroscience   IF 3.2
Medial prefrontal cortex neuronal circuits in fear behavior
Courtin J, Bienvenu T, Einarsson EO, Herry C

Abstract:
he medial prefrontal cortex (mPFC) has emerged as a key structure involved in the modulation of fear behavior over the past few decades. Anatomical, functional and electrophysiological studies have begun to shed light on the precise mechanisms by which different prefrontal regions regulate the expression and inhibition of fear behavior. These studies have established a canonical view of mPFC functions during fear behavior with dorsal regions selectively involved in the expression of fear behavior and ventral regions linked to the inhibition of fear behavior. Although numerous reports support this view, recent data have refined this model and suggested that dorsal prefrontal regions might also play an important role in the encoding of fear behavior itself. The recent development of sophisticated approaches such as large scale neuronal recordings, simultaneous multisite recordings of spiking activity and local field potentials (LFPs) along with optogenetic approaches will facilitate the testing of these new hypotheses in the near future. Here we provide an extensive review of the literature on the role of mPFC in fear behavior and propose further directions to dissect the contribution of specific prefrontal neuronal elements and circuits in the regulation of fear behavior.




Abstract:
It has been suggested that memories become more stable and less susceptible to the disruption of reconsolidation over weeks after learning. Here, we test this by targeting the anterior cingulate cortex (ACC) and test its involvement in the formation, consolidation, and reconsolidation of recent and remote contextual fear memory. We found that inhibiting NMDAR-NR2B activity disrupts memory formation, and that infusion of the protein-synthesis inhibitor anisomycin impairs memory consolidation and reconsolidation of recent and remote memory. Our findings demonstrate for the first time that the ACC plays an important role in reconsolidation of contextual fear memory at recent and remote time points.




25/11/2011 | Hippocampus   IF 4.1
Periodically reactivated context memory retains its precision and dependence on the hippocampus.
de Oliveira Alvares L*, Einarsson EO*, Santana F, Crestani AP, Haubrich J, Cassini LF, Nader K, Quillfeldt JA

Abstract:
Hippocampus is hypothesized to play a temporary role in the retrieval of context memories. Similarly, previous studies have reported that the expression of context memories becomes more generalized as memory ages. We report, first, that contextual fear memory expression changes from being sensitive to dorsal hippocampus inactivation by muscimol at 2 days post-conditioning, to insensitive at 28 days, and second, that over the same period rats lose their ability to discriminate between a novel and conditioned context. Furthermore, we show thatrepeated brief memory reactivation sessions prevent memory from becoming both hippocampus-independent and generalized. (c) 2011 Wiley Periodicals, Inc.




03/2010 | Ann N Y Acad Sci   IF 2.7
Memory reconsolidation: an update.
Nader K, Einarsson EO

Abstract:
Memory consolidation refers to the stabilization that a new memory has to undergo in order to persist. Recently, this dominant view of memory has been challenged by renewed interest in reconsolidation, where consolidated memories return to a transient unstable state following their retrieval, from which they must again stabilize in order to persist. In this review, we discuss how reconsolidation is supported by the same line of evidence as consolidation and recent findings of boundary conditions of reconsolidation. Furthermore, we discuss how recent controversies on the nature of amnesia following challenges to reconsolidation are using the same paradigm that failed to resolve the nature of amnesia after challenges to consolidation; we also discuss a new paradigm that can lead to more fruitful ways of studying amnesia in general.




Abstract:
There are two research traditions on dynamic memory processes. In cognitive psychology, the malleable nature of long-term memory has been extensively documented. Distortions, such as the misinformation effect or hindsight bias, illustrate that memories can be easily changed, often without their owner taking notice. On the other hand, effects like hypermnesia demonstrate that memory might be more reliable than these distortions suggest. In the neuroscience field, similar observations were obtained mostly from animal studies. Research on memory consolidation suggested that memories become progressively resistant to amnesic treatments over time, but the reconsolidation phenomenon showed that this stability can be transiently lifted when these memories are reactivated, i.e., retrieved. Surprisingly, both research traditions have not taken much notice of each others' advances in understanding memory dynamics. We apply concepts developed in neuroscience to phenomena revealed in cognitive psychology to illustrate how these twins separated at birth may be reunited again.




06/2001 | laeknabladid   IF 0.3
[Home mechanical ventilation in Iceland.]
Kjartansson G, Ingadottir S, Halldorsdottir B, Gunnarsdottir A, Guethmundsson G, Einarsson EO, Gislason T

Abstract:
Objective: To describe the users of home mechanical ventilation treatment in Iceland. Material and methods: Records for all patients in Iceland using noninvasive ventilatory support at home on April 30th 1999 were analysed. Results: A total of 54 patients were using ventilatory support at home. There were 33 males and 21 females. The mean age for the group was 61 years. The mean treatment time was 3.5 years. The majority were using pressure controlled ventilators that were connected to a nose mask or full face mask. The most common reason for treatment was decreased respiratory muscle function. In 11 patients this was secondary to muscle- or neurological diseases, in nine from TBC sequelae and in six post polio or from idiopathic kyphoscoliosis. In addition there were 21 patients that had a combination of chronic obstructive pulmonary disease and sleep-related breathing disorder. Cheyne-Stoke breathing secondary to congestive heart failure was the reason for home ventilatory treatment in five males and two females. These patients had relatively normal spirometric and bloodgas results, which is in contrast to the rest of the group, where spirometric values were on the average less than 50% of predicted. Arterial blood gases commonly showed hypoxia and 16 of the patients had long-term oxygen therapy (over 16 hrs/day). Conclusions: Home ventilatory treatment has become part of medical treatment in Iceland and benefits patients with decreased ventilatory function, especially during sleep.