In the past Sheri J.Y. Mizumori has collaborated on articles with Wambura C. Fobbs and Oxana Eschenko. One of their most recent publications is Research paperInvestigations into the neuropharmacological basis of temporal stages of memory formation in mice trained in an active avoidance task. Which was published in journal Behavioural Brain Research.

More information about Sheri J.Y. Mizumori research including statistics on their citations can be found on their Copernicus Academic profile page.

Sheri J.Y. Mizumori's Articles: (6)

Research paperInvestigations into the neuropharmacological basis of temporal stages of memory formation in mice trained in an active avoidance task

AbstractThe memorial effects of glutamate, LaCl3, ouabain, or anisomycin injection around the time of active avoidance training in mice were assessed in this study. Based on the Gibbs and Ng hypothesis of memory formation in chicks (Biobehav. Rev., 1 [1977] 113–136), it was predicted that these pharmacological agents would not only induce significant amnesia but, more specifically, short duration memory should be selectively impaired by glutamate and LaCl3, intermediate duration memory should be impaired by ouabain, and anisomycin should affect only long-lasting memories. Results of the experiments described below indicate these drugs are potent inhibitors of memory formation in rodents. In addition, LaCl3-induced amnesia was fully prevented by CaCl2. However, the mechanism by which glutamate and ouabain affected memory may not be exactly as described by Gibbs and Ng: γ-d-glutamylglycine and diphenylhydantoin did not completely prevent glutamate- and ouabain-induced amnesias, respectively. Finally, all amnestic agents induced amnesia that developed within minutes of training, and the time course of development of amnesia for each drug could not be distinguished from one another. These data are discussed in terms of their implications for the Gibbs and Ng model of memory formation.

Brief communicationEffects of dietary choline on memory and brain chemistry in aged mice

AbstractThe purpose of this study was to investigate in more detail the characteristics of the age-related extension of the retrograde amnesia gradient previously demonstrated in a passive avoidance task [6]. In Experiment 1, it was found that while 2–3 month old mice were susceptible to the amnesic effects of anisomycin (ANI) only when given prior to 15 min post-training, memory of 14–16 month old mice was susceptible to disruption when ANI was given as late as 20 min post-training, and retention of 17–20 month old mice was impaired when ANI was injected even as late as 30 min after training. Experiment 2 examined whether the age-related change in susceptibility to the effects of ANI could be ameliorated by chronic pretreatment with a choline-enriched diet. Results showed that ANI injected 20 min after training did not induce amnesia in choline treated mice (14.5 month old), but did induce amnesia when injected 15 min post training. Subsequent assay of choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) activity showed that choline treatment significantly reduced ChAT activity but did not affect TH activity. It appears that dietary choline treatment can render new long-term memories less susceptible to disruption following training.

Chapter Nine - Cost–Benefit Decision Circuitry: Proposed Modulatory Role for Acetylcholine

AbstractIn order to select which action should be taken, an animal must weigh the costs and benefits of possible outcomes associate with each action. Such decisions, called cost–benefit decisions, likely involve several cognitive processes (including memory) and a vast neural circuitry. Rodent models have allowed research to begin to probe the neural basis of three forms of cost–benefit decision making: effort-, delay-, and risk-based decision making. In this review, we detail the current understanding of the functional circuits that subserve each form of decision making. We highlight the extensive literature by detailing the ability of dopamine to influence decisions by modulating structures within these circuits. Since acetylcholine projects to all of the same important structures, we propose several ways in which the cholinergic system may play a local modulatory role that will allow it to shape these behaviors. A greater understanding of the contribution of the cholinergic system to cost–benefit decisions will permit us to better link the decision and memory processes, and this will help us to better understand and/or treat individuals with deficits in a number of higher cognitive functions including decision making, learning, memory, and language.

Memory influences on hippocampal and striatal neural codes: Effects of a shift between task rules

AbstractInteractions with neocortical memory systems may facilitate flexible information processing by hippocampus. We sought direct evidence for such memory influences by recording hippocampal neural responses to a change in cognitive strategy. Well-trained rats switched (within a single recording session) between the use of place and response strategies to solve a plus maze task. Maze and extramaze environments were constant throughout testing. Place fields demonstrated (in-field) firing rate and location-based reorganization [Leutgeb, S., Leutgeb, J. K., Barnes, C. A., Moser, E. I., McNaughton, B. L., & Moser, M. B. (2005). Independent codes for spatial and episodic memory in hippocampal neuronal ensembles. Science, 309, 619–623] after a task switch, suggesting that hippocampus encoded each phase of testing as a different context, or episode. The task switch also resulted in qualitative and quantitative changes to discharge that were correlated with an animal’s velocity or acceleration of movement. Thus, the effects of a strategy switch extended beyond the spatial domain, and the movement correlates were not passive reflections of the current behavioral state. To determine whether hippocampal neural responses were unique, striatal place and movement-correlated neurons were simultaneously recorded with hippocampal neurons. Striatal place and movement cells exhibited a response profile that was similar, but not identical, to that observed for hippocampus after a strategy switch. Thus, retrieval of a different memory led both neural systems to represent a different context. However, hippocampus may play a special (though not exclusive) role in flexible spatial processing since correlated firing amongst cell pairs was highest when rats successfully switched between two spatial tasks. Correlated firing by striatal cell pairs increased following any strategy switch, supporting the view that striatum codes change in reinforcement contingencies.

Immediate early gene activation in hippocampus and dorsal striatum: Effects of explicit place and response training

AbstractEvidence from lesion, electrophysiological, and neuroimaging studies support the hypothesis that the hippocampus and dorsal striatum process afferent inputs in such a way that each structure regulates expression of different behaviors in learning and memory. The present study sought to determine whether rats explicitly trained to perform one of two different learning strategies, spatial or response, would display disparate immediate early gene activation in hippocampus and striatum. c-Fos and Zif268 immunoreactivity (IR) was measured in both hippocampus and striatum 30 or 90 min following criterial performance on a standard plus-maze task (place learners) or a modified T-maze task (response learners). Place and response learning differentially affected c-Fos-IR in striatum but not hippocampus. Specifically, explicit response learning induced greater c-Fos-IR activation in two subregions of the dorsal striatum. This increased c-Fos-IR was dependent upon the number of trials performed prior to reaching behavioral criterion and accuracy of performance during post-testing probe trials. Quantification of Zif268-IR in both hippocampus and striatum failed to distinguish between place and response learners. The changes in c-Fos-IR occurred 30 min, but not 90 min, post-testing. The synthesis of c-Fos early in testing could reflect the recruitment of key structures in learning. Consequently, animals that were able to learn the response task efficiently displayed greater amounts of c-Fos-IR in dorsal striatum.

A role for the lateral dorsal tegmentum in memory and decision neural circuitry

AbstractA role for the hippocampus in memory is clear, although the mechanism for its contribution remains a matter of debate. Converging evidence suggests that hippocampus evaluates the extent to which context-defining features of events occur as expected. The consequence of mismatches, or prediction error, signals from hippocampus is discussed in terms of its impact on neural circuitry that evaluates the significance of prediction errors: Ventral tegmental area (VTA) dopamine cells burst fire to rewards or cues that predict rewards (Schultz, Dayan, & Montague, 1997). Although the lateral dorsal tegmentum (LDTg) importantly controls dopamine cell burst firing (Lodge & Grace, 2006) the behavioral significance of the LDTg control is not known. Therefore, we evaluated LDTg functional activity as rats performed a spatial memory task that generates task-dependent reward codes in VTA (Jo, Lee, & Mizumori, 2013; Puryear, Kim, & Mizumori, 2010) and another VTA afferent, the pedunculopontine nucleus (PPTg, Norton, Jo, Clark, Taylor, & Mizumori, 2011). Reversible inactivation of the LDTg significantly impaired choice accuracy. LDTg neurons coded primarily egocentric information in the form of movement velocity, turning behaviors, and behaviors leading up to expected reward locations. A subset of the velocity-tuned LDTg cells also showed high frequency bursts shortly before or after reward encounters, after which they showed tonic elevated firing during consumption of small, but not large, rewards. Cells that fired before reward encounters showed stronger correlations with velocity as rats moved toward, rather than away from, rewarded sites. LDTg neural activity was more strongly regulated by egocentric behaviors than that observed for PPTg or VTA cells that were recorded by Puryear et al. and Norton et al. While PPTg activity was uniquely sensitive to ongoing sensory input, all three regions encoded reward magnitude (although in different ways), reward expectation, and reward encounters. Only VTA encoded reward prediction errors. LDTg may inform VTA about learned goal-directed movement that reflects the current motivational state, and this in turn may guide VTA determination of expected subjective goal values. When combined it is clear the LDTg and PPTg provide only a portion of the information that dopamine cells need to assess the value of prediction errors, a process that is essential to future adaptive decisions and switches of cognitive (i.e. memorial) strategies and behavioral responses.

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