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Hippocampus Jun 2016To systematically review the characteristics, validity and outcome measures of tasks that have been described in the literature as assessing pattern separation and... (Review)
Review
To systematically review the characteristics, validity and outcome measures of tasks that have been described in the literature as assessing pattern separation and pattern completion in humans. Electronic databases were searched for articles. Parameters for task validity were obtained from two reviews that described optimal task design factors to evaluate pattern separation and pattern completion processes. These were that pattern separation should be tested during an encoding task using abstract, never-before-seen visual stimuli, and pattern completion during a retrieval task using partial cues; parametric alteration of the degree of interference of stimuli or degradation of cues should be used to generate a corresponding gradient in behavioral output; studies should explicitly identify the specific memory domain under investigation (sensory/perceptual, temporal, spatial, affect, response, or language) and account for the contribution of other potential attributes involved in performance of the task. A systematic, qualitative assessment of validity in relation to these parameters was performed, along with a review of general validity and task outcome measures. Sixty-two studies were included. The majority of studies investigated pattern separation and most tasks were performed on young, healthy adults. Pattern separation and pattern completion were most frequently tested during a retrieval task using familiar or recognizable visual stimuli and cues. Not all studies parametrically altered the degree of stimulus interference or cue degradation, or controlled for potential confounding factors. This review found evidence that some of the parameters for task validity have been followed in some human studies of pattern separation and pattern completion, but no study was judged to have adequately met all the parameters for task validity. The contribution of these parameters and other task design factors towards an optimal behavioral paradigm is discussed and recommendations for future research are made. © 2015 Wiley Periodicals, Inc.
Topics: Discrimination, Psychological; Hippocampus; Humans; Recognition, Psychology
PubMed: 26663362
DOI: 10.1002/hipo.22561 -
Pharmacology & Therapeutics Jun 2020The neurogenic hypothesis of depression states that adult hippocampal neurogenesis is disrupted by stress and depression and is recovered by chronic treatments with... (Meta-Analysis)
Meta-Analysis
The neurogenic hypothesis of depression states that adult hippocampal neurogenesis is disrupted by stress and depression and is recovered by chronic treatments with antidepressants. Indeed, chronic antidepressant treatments increased newborn neurons in the adult dentate gyrus in many early studies. However, conflicting findings appeared over time. Thus, our motivation to write this unbiased systematic review and meta-analysis was to answer the following question: can antidepressants reliably promote neurogenesis in adult hippocampus? A meta-analysis was performed on studies in naive rodents. Results indicated that increased neurogenesis is a more nuanced, compound-dependent action of antidepressants than a yes-or-no event. This nuanced notion can lead to a new understanding of the concepts of neurogenic-dependent and neurogenic-independent effects of antidepressants, which would be better described as effects "more-dependent" or "less-dependent" on hippocampal neurogenesis. Further studies are on the way to investigate the strength of the causal relationship between adult hippocampal neurogenesis and behavioural effects of antidepressants.
Topics: Age Factors; Animals; Antidepressive Agents; Behavior, Animal; Depression; Disease Models, Animal; Hippocampus; Mice; Neurogenesis; Rats
PubMed: 32109488
DOI: 10.1016/j.pharmthera.2020.107515 -
Neuropsychopharmacology Reports Dec 2018The hippocampus is considered a key region in schizophrenia pathophysiology, but the nature of hippocampal subregion abnormalities and how they contribute to disease...
AIM
The hippocampus is considered a key region in schizophrenia pathophysiology, but the nature of hippocampal subregion abnormalities and how they contribute to disease expression remain to be fully determined. This study reviews findings from schizophrenia hippocampal subregion volumetric and physiological imaging studies published within the last decade.
METHODS
The PubMed database was searched for publications on hippocampal subregion volume and physiology abnormalities in schizophrenia and their findings were reviewed.
RESULTS
The main replicated findings include smaller CA1 volumes and CA1 hyperactivation in schizophrenia, which may be predictive of conversion in individuals at clinical high risk of psychosis, smaller CA1 and CA4/DG volumes in first-episode schizophrenia, and more widespread smaller hippocampal subregion volumes with longer duration of illness. Several studies have reported relationships between hippocampal subregion volumes and declarative memory or symptom severity.
CONCLUSIONS
Together these studies provide support for hippocampal formation circuitry models of schizophrenia. These initial findings must be taken with caution as the scientific community is actively working on hippocampal subregion method improvement and validation. Further improvements in our understanding of the nature of hippocampal formation subregion involvement in schizophrenia will require the collection of structural and physiological imaging data at submillimeter voxel resolution, standardization and agreement of atlases, adequate control for possible confounding factors, and multi-method validation of findings. Despite the need for cautionary interpretation of the initial findings, we believe that improved localization of hippocampal subregion abnormalities in schizophrenia holds promise for the identification of disease contributing mechanisms.
Topics: Hippocampus; Humans; Magnetic Resonance Imaging; Schizophrenia
PubMed: 30255629
DOI: 10.1002/npr2.12031 -
PloS One 2020Recent results have established that masticatory function plays a role not only in the balance of the stomatognathic system and in the central motor control, but also in...
Altered mastication adversely impacts morpho-functional features of the hippocampus: A systematic review on animal studies in three different experimental conditions involving the masticatory function.
Recent results have established that masticatory function plays a role not only in the balance of the stomatognathic system and in the central motor control, but also in the trophism of the hippocampus and in the cognitive activity. These implications have been shown in clinical studies and in animal researches as well, by means of histological, biochemical and behavioural techniques. This systematic review describes the effects of three forms of experimentally altered mastication, namely soft-diet feeding, molar extraction and bite-raising, on the trophism and function of the hippocampus in animal models. Through a systematic search of PubMed, Embase, Web of Science, Scopus, OpenGray and GrayMatters, 645 articles were identified, 33 full text articles were assessed for eligibility and 28 articles were included in the review process. The comprehensiveness of reporting was evaluated with the ARRIVE guidelines and the risk of bias with the SYRCLE RoB tool. The literature reviewed agrees that a disturbed mastication is significantly associated with a reduced number of hippocampal pyramidal neurons in Cornu Ammonis (CA)1 and CA3, downregulation of Brain Derived Neurotrophic Factor (BDNF), reduced synaptic activity, reduced neurogenesis in the Dentate Gyrus (DG), glial proliferation, and reduced performances in behavioural tests, indicating memory impairment and reduced spatial orientation. Moreover, while the bite-raised condition, characterized by occlusal instability, is known to be a source of stress, soft-diet feeding and molar extractions were not consistently associated with a stress response. More research is needed to clarify this topic. The emerging role of chewing in the preservation of hippocampal trophism, neurogenesis and synaptic activity is worthy of interest and may contribute to the study of neurodegenerative diseases in new and potentially relevant ways.
Topics: Animals; Cognition; Dentate Gyrus; Hippocampus; Humans; Mastication; Memory Disorders; Models, Animal; Neurogenesis; Neurons
PubMed: 32817680
DOI: 10.1371/journal.pone.0237872 -
Synapse (New York, N.Y.) Aug 2019Environmental enrichment (EE) can be related to changes in the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus of adult rodents. Exposure to EE...
BACKGROUND AND AIM
Environmental enrichment (EE) can be related to changes in the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus of adult rodents. Exposure to EE may also induce neurogenesis in the dentate gyrus (DG). The aim of this systematic review was to analyze the current literature on the correlation between neurogenesis and BDNF expression in the hippocampal DG region resulting from exposure to EE, which is associated with changes in memory, in rodents.
METHODS
Bibliographic searches of the Medline/PubMed and ScienceDirect databases were carried out, and 334 studies were found. A predefined protocol was used and registered on PROSPERO, and 32 studies were included for qualitative synthesis. The PRISMA was used to report this systematic review.
RESULTS
Most of the included studies showed that there is little evidence in the literature demonstrating that memory changes resulting from EE are dependent on BDNF expression and that there is an induction of neurogenesis in the hippocampal DG. However, the observed increase in molecular expression levels and cell proliferation is dependent on the age, the timing and duration of exposure to EE. Regarding the methodological quality of the studies, the majority presented a risk of bias due to the high variability in the age of the animals.
CONCLUSION
There are few studies in the literature that correlate the molecular and cellular mechanisms involved in neurogenesis in the hippocampal DG with BDNF expression in this region in rodents exposed to EE; however, there are other factors that can modulate this neurogenesis.
Topics: Animals; Brain-Derived Neurotrophic Factor; Environment; Hippocampus; Neurogenesis; Neuronal Plasticity
PubMed: 31056812
DOI: 10.1002/syn.22103