Dataset Information

Analysis of human hippocampal volumetry in relation to pattern separation ability in healthy young subjects.

ABSTRACT:

Introduction

Hippocampal dentate gyrus related to pattern separation has attracted attention as an area for neurogenesis. However, the associations between the pattern separation and the volumes of hippocampal subfields in humans remain unknown.

Methods

58 young adults were examined the memory task (pattern separation, pattern completion) and the hippocampal volumes. Subjects were asked to determine whether the visual image is a new stimulus, or a similar but different stimulus (pattern separation), or the same stimulus (pattern completion), compared to preceding stimuli, and response time and correct response were measured. The volumes of the whole brain, hippocampus 6 subfields and perihippocampus 5 subfields, were measured using FreeSurfer 6.0.

Results

Negative associations between the pattern separation task and the volumes of whole brain areas were found in bilateral cerebellar cortex, fourth ventricle, left hippocampus, left thalamus, left ventral diencephalon, and brainstem. Simple linear regression analysis revealed a significant association with the left hippocampal-amygdaloid transition area only, while no significant associations were found in any of the subfield volumes when adjusted with covariates.

Conclusions

The principle "bigger is better"-an idea that the larger the volume the better the function-could not be applied to the relation between the pattern separation ability and the dentate gyrus.

SUBMITTER: Usugi R

PROVIDER: S-EPMC7749596 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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Publications

Analysis of human hippocampal volumetry in relation to pattern separation ability in healthy young subjects.

Usugi Ryoichi R Nishimura Masahiko M Ishiuchi Shogo S

Brain and behavior 20201023 12

<h4>Introduction</h4>Hippocampal dentate gyrus related to pattern separation has attracted attention as an area for neurogenesis. However, the associations between the pattern separation and the volumes of hippocampal subfields in humans remain unknown.<h4>Methods</h4>58 young adults were examined the memory task (pattern separation, pattern completion) and the hippocampal volumes. Subjects were asked to determine whether the visual image is a new stimulus, or a similar but different stimulus (p ...[more]

PMID: 33094927

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Project description:Adult hippocampal neurogenesis is a unique form of neural circuit plasticity that results in the generation of new neurons in the dentate gyrus throughout life. Neurons that arise in adults (adult-born neurons) show heightened synaptic plasticity during their maturation and can account for up to ten per cent of the entire granule cell population. Moreover, levels of adult hippocampal neurogenesis are increased by interventions that are associated with beneficial effects on cognition and mood, such as learning, environmental enrichment, exercise and chronic treatment with antidepressants. Together, these properties of adult neurogenesis indicate that this process could be harnessed to improve hippocampal functions. However, despite a substantial number of studies demonstrating that adult-born neurons are necessary for mediating specific cognitive functions, as well as some of the behavioural effects of antidepressants, it is unknown whether an increase in adult hippocampal neurogenesis is sufficient to improve cognition and mood. Here we show that inducible genetic expansion of the population of adult-born neurons through enhancing their survival improves performance in a specific cognitive task in which two similar contexts need to be distinguished. Mice with increased adult hippocampal neurogenesis show normal object recognition, spatial learning, contextual fear conditioning and extinction learning but are more efficient in differentiating between overlapping contextual representations, which is indicative of enhanced pattern separation. Furthermore, stimulation of adult hippocampal neurogenesis, when combined with an intervention such as voluntary exercise, produces a robust increase in exploratory behaviour. However, increasing adult hippocampal neurogenesis alone does not produce a behavioural response like that induced by anxiolytic agents or antidepressants. Together, our findings suggest that strategies that are designed to increase adult hippocampal neurogenesis specifically, by targeting the cell death of adult-born neurons or by other mechanisms, may have therapeutic potential for reversing impairments in pattern separation and dentate gyrus dysfunction such as those seen during normal ageing.

Project description:Pattern separation is a central concept in current theories of episodic memory: this computation is thought to support our ability to avoid confusion between similar memories by transforming similar cortical input patterns of neural activity into dissimilar output patterns before their long-term storage in the hippocampus. Because there are many ways one can define patterns of neuronal activity and the similarity between them, pattern separation could in theory be achieved through multiple coding strategies. Using our recently developed assay that evaluates pattern separation in isolated tissue by controlling and recording the input and output spike trains of single hippocampal neurons, we explored neural codes through which pattern separation is performed by systematic testing of different similarity metrics and various time resolutions. We discovered that granule cells, the projection neurons of the dentate gyrus, can exhibit both pattern separation and its opposite computation, pattern convergence, depending on the neural code considered and the statistical structure of the input patterns. Pattern separation is favored when inputs are highly similar, and is achieved through spike time reorganization at short time scales (< 100 ms) as well as through variations in firing rate and burstiness at longer time scales. These multiplexed forms of pattern separation are network phenomena, notably controlled by GABAergic inhibition, that involve many celltypes with input-output transformations that participate in pattern separation to different extents and with complementary neural codes: a rate code for dentate fast-spiking interneurons, a burstiness code for hilar mossy cells and a synchrony code at long time scales for CA3 pyramidal cells. Therefore, the isolated hippocampal circuit itself is capable of performing temporal pattern separation using multiplexed coding strategies that might be essential to optimally disambiguate multimodal mnemonic representations.

Dataset Information

Analysis of human hippocampal volumetry in relation to pattern separation ability in healthy young subjects.

Introduction

Methods

Results

Conclusions

Publications

Analysis of human hippocampal volumetry in relation to pattern separation ability in healthy young subjects.

Similar Datasets

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