ABSTRACT
Hippocampal gamma and theta oscillations are associated with mnemonic and navigational processes and adapt to changes in the behavioral state of an animal to optimize spatial information processing. It has been shown that locomotor activity modulates gamma and theta frequencies in rats, although how age alters this modulation has not been well studied. Here, we examine gamma and theta local-field potential and place cell activity in the hippocampus CA1 region of young and old male rats as they performed a spatial eye-blink conditioning task across 31 d. Although mean gamma frequency was similar in both groups, gamma frequency increased with running speed at a slower rate in old animals. By contrast, theta frequencies scaled with speed similarly in both groups but were lower across speeds in old animals. Although these frequencies scaled equally well with deceleration and speed, acceleration was less correlated with gamma frequency in both age groups. Additionally, spike phase-locking to gamma, but not theta, was greater in older animals. Finally, aged rats had reduced within-field firing rates but greater spatial information per spike within the field. These data support a strong relationship between locomotor behavior and local-field potential activity and suggest that age significantly affects this relationship. Furthermore, observed changes in CA1 place cell firing rates and information content lend support to the hypothesis that age may result in more general and context-invariant hippocampal representations over more detailed information. These results may explain the observation that older adults tend to recall the gist of an experience rather than the details.SIGNIFICANCE STATEMENT Hippocampal oscillations and place cell activity are sensitive to sensorimotor input generated from active locomotion, yet studies of aged hippocampal function often do not account for this. By considering locomotion and spatial location, we identify novel age-associated differences in the scaling of oscillatory activity with speed, spike-field coherence, spatial information content, and within-field firing rates of CA1 place cells. These results indicate that age has an impact on the relationship between locomotion and hippocampal oscillatory activity, perhaps indicative of alterations to afferent input. These data also support the hypothesis that aged hippocampal place cells, compared with young, may more often represent more general spatial information. If true, these results may help explain why older humans tend to recall less specific and more gist-like information.
Subject(s)
CA1 Region, Hippocampal , Place Cells , Animals , Male , Rats , Action Potentials , Hippocampus , Theta RhythmABSTRACT
Review, promotion, and tenure (RPT) processes at universities typically assess candidates along three dimensions: research, teaching, and service. In recent years, some have argued for the inclusion of a controversial fourth criterion: collegiality. While collegiality plays a role in the morale and effectiveness of academic departments, it is amorphic and difficult to assess, and could be misused to stifle dissent or enforce homogeneity. Despite this, some institutions have opted to include this additional element in their RPT documents and processes, but it is unknown the extent of this practice and how it varies across institution type and disciplinary units. This study is based on two sets of data: survey data collected as part of a project that explored the publishing decisions of faculty and how these related to perceived importance in RPT processes, and 864 RPT documents collected from 129 universities from the United States and Canada. We analysed these RPT documents to determine the degree to which collegiality and related terms are mentioned, if they are defined, and if and how they may be assessed during the RPT process. Results show that when collegiality and related terms appear in these documents they are most often just briefly mentioned. It is less common for collegiality and related terms to be defined or assessed in RPT documents. Although the terms are mentioned across all types of institutions, there is a statistically significant difference in how prevalent they are at each. Collegiality is more commonly mentioned in the documents of doctoral research-focused universities (60%), than of master's universities and colleges (31%) or baccalaureate colleges (15%). Results from the accompanying survey of faculty also support this finding: individuals from R-Types were more likely to perceive collegiality to be a factor in their RPT processes. We conclude that collegiality likely plays an important role in RPT processes, whether it is explicitly acknowledged in policies and guidelines or not, and point to several strategies in how it might be best incorporated in the assessment of academic careers.
Subject(s)
Faculty , Publishing , Canada , Humans , Policy , United States , UniversitiesABSTRACT
Using an online survey of academics at 55 randomly selected institutions across the US and Canada, we explore priorities for publishing decisions and their perceived importance within review, promotion, and tenure (RPT). We find that respondents most value journal readership, while they believe their peers most value prestige and related metrics such as impact factor when submitting their work for publication. Respondents indicated that total number of publications, number of publications per year, and journal name recognition were the most valued factors in RPT. Older and tenured respondents (most likely to serve on RPT committees) were less likely to value journal prestige and metrics for publishing, while untenured respondents were more likely to value these factors. These results suggest disconnects between what academics value versus what they think their peers value, and between the importance of journal prestige and metrics for tenured versus untenured faculty in publishing and RPT perceptions.
Subject(s)
Faculty/psychology , Publishing , Social Values , Universities , Canada , Humans , Motivation , Publications , Surveys and Questionnaires , United StatesABSTRACT
Hippocampal sharp-wave ripples are brief high-frequency (120-250 Hz) oscillatory events that support mnemonic processes during sleep and awake behavior. Although ripples occurring during sleep are believed to facilitate memory consolidation, waking ripples may also be involved in planning and memory retrieval. Recent work from our group determined that normal aging results in a significant reduction in the peak oscillatory frequency and rate-of-occurrence of ripples during sleep that may contribute to age-associated memory decline. It is unknown, however, how aging alters waking ripples. We investigated whether characteristics of waking ripples undergo age-dependent changes. Sharp-wave ripple events were recorded from the CA1 region of the hippocampus in old (n = 5) and young (n = 6) F344 male rats as they performed a place-dependent eyeblink conditioning task. Several novel observations emerged from this analysis. First, although aged rats expressed more waking ripples than young rats during track running and reward consumption, this effect was eliminated, and, in the case of track-running, reversed when time spent in each location was accounted for. Thus, aged rats emit more ripples, but young rats express a higher ripple rate. This likely results from reduced locomotor activity in aged animals. Furthermore, although ripple rates increased as young rats approached rewards, rates did not increase in aged rats, and rates in aged and young animals were not affected by eyeblink conditioning. Finally, although the oscillatory frequency of ripples was lower in aged animals during rest, frequencies in aged rats increased during behavior to levels indistinguishable from young rats. Given the involvement of waking ripples in memory retrieval, a possible consequence of slower movement speeds of aged animals is to provide more opportunity to replay task-relevant information and compensate for age-related declines in ripple rate during task performance.
Subject(s)
Aging/physiology , Brain Waves/physiology , Conditioning, Eyelid/physiology , Hippocampus/physiology , Memory/physiology , Wakefulness/physiology , Age Factors , Animals , Male , Motor Activity/physiology , Rats , Rats, Inbred F344ABSTRACT
We analyzed how often and in what ways the Journal Impact Factor (JIF) is currently used in review, promotion, and tenure (RPT) documents of a representative sample of universities from the United States and Canada. 40% of research-intensive institutions and 18% of master's institutions mentioned the JIF, or closely related terms. Of the institutions that mentioned the JIF, 87% supported its use in at least one of their RPT documents, 13% expressed caution about its use, and none heavily criticized it or prohibited its use. Furthermore, 63% of institutions that mentioned the JIF associated the metric with quality, 40% with impact, importance, or significance, and 20% with prestige, reputation, or status. We conclude that use of the JIF is encouraged in RPT evaluations, especially at research-intensive universities, and that there is work to be done to avoid the potential misuse of metrics like the JIF.
Subject(s)
Career Mobility , Journal Impact Factor , Research Personnel , Work Performance , Canada , Humans , United States , UniversitiesABSTRACT
Much of the work done by faculty at both public and private universities has significant public dimensions: it is often paid for by public funds; it is often aimed at serving the public good; and it is often subject to public evaluation. To understand how the public dimensions of faculty work are valued, we analyzed review, promotion, and tenure documents from a representative sample of 129 universities in the US and Canada. Terms and concepts related to public and community are mentioned in a large portion of documents, but mostly in ways that relate to service, which is an undervalued aspect of academic careers. Moreover, the documents make significant mention of traditional research outputs and citation-based metrics: however, such outputs and metrics reward faculty work targeted to academics, and often disregard the public dimensions. Institutions that seek to embody their public mission could therefore work towards changing how faculty work is assessed and incentivized.
Subject(s)
Career Mobility , Faculty , Canada , Humans , UniversitiesABSTRACT
Review, promotion, and tenure (RPT) processes significantly affect how faculty direct their own career and scholarly progression. Although RPT practices vary between and within institutions, and affect various disciplines, ranks, institution types, genders, and ethnicity in different ways, some consistent themes emerge when investigating what faculty would like to change about RPT. For instance, over the last few decades, RPT processes have generally increased the value placed on research, at the expense of teaching and service, which often results in an incongruity between how faculty actually spend their time vs. what is considered in their evaluation. Another issue relates to publication practices: most agree RPT requirements should encourage peer-reviewed works of high quality, but in practice, the value of publications is often assessed using shortcuts such as the prestige of the publication venue, rather than on the quality and rigor of peer review of each individual item. Open access and online publishing have made these issues even murkier due to misconceptions about peer review practices and concerns about predatory online publishers, which leaves traditional publishing formats the most desired despite their restricted circulation. And, efforts to replace journal-level measures such as the impact factor with more precise article-level metrics (e.g., citation counts and altmetrics) have been slow to integrate with the RPT process. Questions remain as to whether, or how, RPT practices should be changed to better reflect faculty work patterns and reduce pressure to publish in only the most prestigious traditional formats. To determine the most useful way to change RPT, we need to assess further the needs and perceptions of faculty and administrators, and gain a better understanding of the level of influence of written RPT guidelines and policy in an often vague process that is meant to allow for flexibility in assessing individuals.
Subject(s)
Academic Success , Career Mobility , Faculty , Guidelines as Topic , Humans , Publications , Research , TeachingABSTRACT
UNLABELLED: Spatial and episodic memory performance declines with age, and the neural basis for this decline is not well understood. Sharp-wave ripples are brief (â¼70 ms) high-frequency oscillatory events generated in the hippocampus and are associated with the consolidation of spatial memories. Given the connection between ripple oscillations and memory consolidation, we investigated whether the structure of ripple oscillations and ripple-triggered patterns of single-unit activity are altered in aged rats. Local field and single-unit activity surrounding sharp-wave ripple events were examined in the CA1 region of the hippocampus of old (n = 5) and young (n = 6) F344 rats during periods of rest preceding and following performance on a place-dependent eyeblink-conditioning task. Neural responses in aged rats differed from responses in young rats in several ways. First, compared with young rats, the rate of ripple occurrence (ripple density) is reduced in aged rats during postbehavior rest. Second, mean ripple frequency during prebehavior and postbehavior rest is lower in aged animals (aged: 132 Hz; young: 146 Hz). Third, single neurons in aged animals responded more consistently from ripple to ripple. Fourth, variability in interspike intervals was greater in aged rats. Finally, neurons were tuned to a narrower range of phases of the ripple oscillation relative to young animals. Together, these results suggest that the CA1 network in aged animals has a reduced "vocabulary" of available representational states. SIGNIFICANCE STATEMENT: The hippocampus is a structure that is critical for the formation of episodic memories. Sharp-wave ripple events generated in the hippocampus have been implicated in memory consolidation processes critical to memory stabilization. We examine here whether these ripple oscillations are altered over the course of the life span, which could contribute to hippocampus-dependent memory deficits that occur during aging. This experiment used young and aged memory-impaired rats to examine age-related changes in ripple architecture, ripple-triggered spike variance, and spike-phase coherence. We found that there are, indeed, significant changes in characteristics of ripples in older animals that could impact consolidation processes and memory stabilization in the aged brain.
Subject(s)
Aging/physiology , CA1 Region, Hippocampal/physiology , Evoked Potentials , Neurons/physiology , Animals , Blinking , CA1 Region, Hippocampal/cytology , CA1 Region, Hippocampal/growth & development , Conditioning, Classical , Male , Memory , Neurons/classification , Rats , Rats, Inbred F344 , Reaction TimeABSTRACT
Distinct ensembles of hippocampal cells can be active in numerous contexts, but specific "cognitive maps" tend to be retrieved on repeat visits to the same place. During aging, the reliability of map retrieval in CA1 networks is reduced; this provides a unique opportunity to investigate correlations between inconsistent activity patterns in circuits hypothesized to enable context encoding and hippocampus-dependent learning ability. Here, CA1 pyramidal cells were recorded in six young and six old rats, while memory for specific locations was probed using a place-dependent eyeblink conditioning task. Rats were conditioned twice daily for 31 days, during which a total of 8259 and 7042 cells were recorded from young and old rats, respectively. Spontaneous remapping, a change in location of the majority of place fields between two consecutive sessions in the same environment, was observed in two young rats and four old rats during this task, but only after at least 13 days of training. Under these conditions the altered network representation did not result in loss of spatial accuracy of the blink, and in fact those rats with the best place conditioning remapped the most, whereas those with the best memory in a spatial water maze task remapped the least. These results suggest that when the hippocampal representation for a particular context is weak or unstable, such as can occur in senescence, extra-hippocampal systems that mediate alternate learning strategies are more likely to dominate behavior.
Subject(s)
Brain Mapping , Hippocampus/physiology , Learning/physiology , Aging/psychology , Algorithms , Animals , CA1 Region, Hippocampal/physiology , Conditioning, Eyelid/physiology , Electromyography , Electrophysiological Phenomena , Hippocampus/growth & development , Male , Maze Learning/physiology , Memory/physiology , Orientation/physiology , Psychomotor Performance/physiology , Rats , Rats, Inbred F344ABSTRACT
Age-related cognitive and behavioral slowing may be caused by changes in the speed of neural signaling or by changes in the number of signaling steps necessary to achieve a given function. In the mammalian cortex, neural communication is organized by a 30-100 Hz "gamma" oscillation. There is a putative link between the gamma frequency and the speed of processing in a neural network: the dynamics of pyramidal neuron membrane time constants suggest that synaptic integration is framed by the gamma cycle, and pharmacological slowing of gamma also slows reaction times on behavioral tasks. The present experiments identify reductions in a robust 40-70 Hz gamma oscillation in the aged rat medial frontal cortex. The reductions were observed in the form of local field potentials, later peaks in fast-spiking neuron autocorrelations, and delays in the spiking of inhibitory neurons following local excitatory signals. Gamma frequency did not vary with movement speed, but rats with slower gamma also moved more slowly. Gamma frequency age differences were not observed in hippocampus. Hippocampal CA1 fast-spiking neurons exhibited interspike intervals consistent with a fast (70-100 Hz) gamma frequency, a pattern maintained across theta phases and theta frequencies independent of fluctuations in the average firing rates of the neurons. We propose that an average lengthening of the cortical 15-25 ms gamma cycle is one factor contributing to age-related slowing and that future attempts to offset cognitive declines will find a target in the response of fast-spiking inhibitory neurons to excitatory inputs.
Subject(s)
Aging/physiology , Behavior, Animal/physiology , Electroencephalography , Prefrontal Cortex/physiology , Rest/physiology , Animals , CA1 Region, Hippocampal/physiology , Decision Making/physiology , Electrodes, Implanted , Evoked Potentials/physiology , Hippocampus/physiology , Male , Rats , Theta Rhythm/physiologyABSTRACT
During aging, many experience a decline in cognitive function that includes memory loss. The encoding of long-term memories depends on new protein synthesis, and this is also reduced during aging. Thus, it is possible that changes in the regulation of protein synthesis contribute to the memory impairments observed in older animals. Several lines of evidence support this hypothesis. For instance, protein synthesis is required for a longer period following learning to establish long-term memory in aged rodents. Also, under some conditions, synaptic activity or pharmacological activation can induce de novo protein synthesis and lasting changes in synaptic transmission in aged, but not young, rodents; the opposite results can be observed in other conditions. These changes in plasticity likely play a role in manifesting the altered place field properties observed in awake and behaving aged rats. The collective evidence suggests a link between memory loss and the regulation of protein synthesis in senescence. In fact, pharmaceuticals that target the signaling pathways required for induction of protein synthesis have improved memory, synaptic plasticity, and place cell properties in aged animals. We suggest that a better understanding of the mechanisms that lead to different protein expression patterns in the neural circuits that change as a function of age will enable the development of more effective therapeutic treatments for memory loss.
ABSTRACT
Long-term potentiation (LTP), an activity-dependent enhancement of synaptic strength, and memory can be influenced by neuromodulatory transmitters such as norepinephrine (NE) and also by genetic background. beta-Adrenergic receptor activation can facilitate the expression of hippocampal CA1 LTP induced by weak stimulus patterns, but its influence on LTP induced by stronger stimulus patterns is unclear. We examined neural NE and dopamine (DA) levels, beta-adrenergic receptor expression and hippocampal LTP in genetically diverse inbred mouse strains. Brain tissue levels of NE were significantly lower in strains 129S1/SvImJ (129), BALB/cByJ (BALB) and C3H/HeJ (C3H) than in C57BL/6NCrlBR (B6). Western blot analysis showed that hippocampal beta(1)-adrenergic receptor expression was similar in strains B6, 129 and C3H, but was increased in BALB. LTP was induced in area CA1 of hippocampal slices by four trains of high-frequency stimulation (HFS) of the Schaeffer collaterals in the four inbred strains. Two hours after induction, LTP was significantly reduced in strains 129, BALB and C3H compared to B6, correlating with neural NE levels. We rescued hippocampal LTP in strains 129, BALB and C3H to levels seen in B6 by bath application of 1 microm isoproterenol, a beta-adrenergic receptor agonist, during HFS. Propranolol, a beta-adrenergic receptor antagonist, blocked this rescue in 129, BALB and C3H but did not affect LTP in strain B6. Thus, although this form of multitrain LTP does not rely on beta-adrenergic receptor activation, our data show that pharmacological activation of beta-adrenergic receptors during multiple trains of HFS can rescue CA1 LTP in genetically diverse strains with impaired LTP.
Subject(s)
Hippocampus/physiopathology , Long-Term Potentiation/physiology , Receptors, Adrenergic, beta/genetics , Receptors, Adrenergic, beta/metabolism , Adrenergic beta-Antagonists/pharmacology , Animals , Blotting, Western/methods , Brain Chemistry/drug effects , Brain Chemistry/physiology , Brain Chemistry/radiation effects , Chromatography, High Pressure Liquid/methods , Dopamine/metabolism , Dose-Response Relationship, Radiation , Electric Stimulation/methods , Hippocampus/injuries , Long-Term Potentiation/drug effects , Mice , Mice, Inbred Strains , Norepinephrine/genetics , Norepinephrine/metabolism , Propranolol/pharmacology , Species SpecificityABSTRACT
Inbred mouse strains have different genetic backgrounds that can result in impairments of synaptic plasticity and memory. They are valuable models for probing the mechanisms of memory impairments. We examined fear memory in several inbred strains, along with synaptic plasticity that may underlie fear memory. Long-term potentiation (LTP) is a form of activity-dependent synaptic plasticity that is a candidate cellular mechanism for some forms of learning and memory. Strains with impaired contextual or cued fear memory may have selective LTP deficits in different hippocampal subregions, or in the amygdala. We measured fear memory and its extinction in five inbred strains: C57BL/6NCrlBR (B6), A/J, BALB/cByJ (BALB), C57BL/10J (B10), and SM/J (SM). We also measured LTP in the basolateral amygdala and in the hippocampal Schaeffer collateral-commissural (SC) and medial perforant pathways (MPP). All strains exhibited intact contextual fear memory 24 h post-training, but cued fear memory was impaired in strains A/J, BALB, and SM. At 1 h post-training, both contextual and cued fear memory deficits were more widespread: all strains except for B6 and B10 showed impairments of both types of memory. Contextual fear extinction was impaired in BALB and SM. We found that amygdalar LTP was reduced in strains A/J and BALB, but SC LTP was intact in all strains (except for a selective multi-train LTP impairment in BALB). MPPLTP was similar in all five strains. Thus, reduced amygdalar LTP is correlated with impaired cued fear memory in strains A/J and BALB. Also, hippocampal SC LTP is more strongly correlated with 24-h (long-term) than with 1-h (short-term) contextual fear memory. In this first conjoint study of amygdala-dependent memory and amygdalar LTP in inbred mice, we identified specific hippocampal and amygdalar LTP deficits that correlate with fear memory impairments. These deficits should be considered when selecting inbred strains for genetic modification.
Subject(s)
Amygdala/physiopathology , Fear/physiology , Genetic Predisposition to Disease/genetics , Long-Term Potentiation/physiology , Memory Disorders/physiopathology , Animals , Disease Models, Animal , Extinction, Psychological/physiology , Female , Hippocampus/physiopathology , Memory/physiology , Memory Disorders/genetics , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Perforant Pathway/physiopathology , Species Specificity , Synaptic Transmission/physiologyABSTRACT
Inbred mouse strains have different genetic backgrounds that likely influence memory and long-term potentiation (LTP). LTP, a form of synaptic plasticity, is a candidate cellular mechanism for some forms of learning and memory. Strains with impaired fear memory may have selective LTP deficits in different hippocampal subregions or in the amygdala. The authors assessed fear memory in 4 inbred strains: C57BL/6NCrlBR (B6), 129S1/SvImJ (129), C3H/HeJ (C3H), and DBA/2J (D2). The authors also measured LTP in the hippocampal Schaeffer collateral (SC) and medial perforant pathways (MPP) and in the basolateral amygdala. Contextual and cued fear memory, and SC and amygdalar LTP, were intact in B6 and 129, but all were impaired in C3H and D2. MPP LTP was similar in all 4 strains. Thus, SC, but not MPP, LTP correlates with hippocampus-dependent contextual memory expression, and amygdalar LTP correlates with amygdala-dependent cued memory expression, in these inbred strains.
Subject(s)
Amygdala/physiology , Fear , Hippocampus/physiology , Long-Term Potentiation/genetics , Memory/physiology , Amygdala/pathology , Animals , Female , Hippocampus/pathology , Mice , Mice, Inbred StrainsABSTRACT
The hippocampus is critical for forming new long-term memories, but the contributions of the hippocampal commissure (HC) to memory function and hippocampal synaptic plasticity are unclear. To shed light on this issue, we characterized behavioral memory and hippocampal synaptic plasticity in two inbred mouse strains. BALB/cWah1 mice display a range of corpus callosal defects and an intact HC, whereas 9XCA/Wah mice exhibit a complete absence of corpus callosum and a greatly reduced HC. No differences between strains were found in long-term potentiation (LTP) within two synaptic pathways in hippocampal slices. However, paired-pulse facilitation was deficient in area CA1 of slices from 9XCA/Wah, and it was rescued by decreasing extracellular [Ca2+], suggesting that presynaptic calcium dynamics may be altered in this strain. In addition, contextual fear extinction was impaired in 9XCA/Wah mice, but performance on cued fear extinction and on 24 hr memory tests for cued and contextual fear conditioning were not significantly different between strains. Thus, an intact HC is critical for normal extinction of contextual fear. Intact interhemispheric connectivity is not required for acquisition or expression of cued and contextual fear conditioning. LTP was normal in slices from mice that lacked an intact HC, and this was correlated with normal performance on fear conditioning tests. In contrast, impaired short-term synaptic plasticity was correlated with defective contextual memory extinction in mice lacking an intact HC. Thus, the HC in mice is vital for particular aspects of memory function and for short-term synaptic modification in specific hippocampal circuits.