Music training is related to late ERP modulation and enhanced performance during Simon task but not Stroop task

Increasing evidence suggests that music training correlates with better performance in tasks measuring executive function components including inhibitory control, working memory and selective attention. The Stroop and Simon tasks measure responses to congruent and incongruent information reflecting cognitive conflict resolution. However, there are more reports of a music-training advantage in the Simon than the Stroop task. Reports indicate that these tasks may differ in the timing of conflict resolution: the Stroop task might involve early sensory stage conflict resolution, while the Simon task may do so at a later motor output planning stage. We hypothesize that musical experience relates to conflict resolution at the late motor output stage rather than the early sensory stage. Behavioral responses, and event-related potentials (ERP) were measured in participants with varying musical experience during these tasks. It was hypothesized that musical experience correlates with better performance in the Simon but not the Stroop task, reflected in ERP components in the later stage of motor output processing in the Simon task. Participants were classified into high- and low-music training groups based on the Goldsmith Musical Sophistication Index. Electrical brain activity was recorded while they completed visual Stroop and Simon tasks. The high-music training group outperformed the low-music training group on the Simon, but not the Stroop task. Mean amplitude difference (incongruent-congruent trials) was greater for the high-music training group at N100 for midline central (Cz) and posterior (Pz) sites in the Simon task and midline central (Cz) and frontal (Fz) sites in the Stroop task, and at N450 at Cz and Pz in the Simon task. N450 difference peaks occurred earlier in the high-music training group at Pz. Differences between the groups at N100 indicate that music training may be related to better sensory discrimination. These differences were not related to better behavioral performance. Differences in N450 responses between the groups, particularly in regions encompassing the motor and parietal cortices, suggest a role of music training in action selection during response conflict situations. Overall, this supports the hypothesis that music training selectively enhances cognitive conflict resolution during late motor output planning stages.

Effects of acute and long-term mindfulness on neural activity and the conflict resolution component of attention

Mindfulness practices have been linked to enhanced attention and conflict resolution abilities. While much research has focused on the long-term effects of mindfulness, the immediate impact of a single session has been less studied. This study recruited 20 experienced meditators and 20 novices and assigned them to a mindfulness or a control condition. They completed a Stroop Task to measure cognitive conflict resolution before and after the intervention, with brain activity monitored via functional near-infrared spectroscopy (fNIRS). Novices showed an age-related decline in conflict resolution ability, while experienced meditators didn't. Initially, both groups showed similar Stroop performance, but experienced meditators had greater brain activation in the left dorsolateral prefrontal cortex (DLPFC). Post-intervention, novices in the breath count task became more similar to experienced meditators in their neural activity during conflict resolution. Our findings indicate that long-term mindfulness experience may protect against age-related decline in cognitive conflict resolution speed, and may alter neural processing of cognitive conflict resolution.

Music Training, and the Ability of Musicians to Harmonize, Are Associated With Enhanced Planning and Problem-Solving

Music training is associated with enhanced executive function but little is known about the extent to which harmonic aspects of musical training are associated with components of executive function. In the current study, an array of cognitive tests associated with one or more components of executive function, was administered to young adult musicians and non-musicians. To investigate how harmonic aspects of musical training relate to executive function, a test of the ability to compose a four-part harmony was developed and administered to musicians. We tested the working hypothesis that musicians would outperform non-musicians on measures of executive function, and that among musicians, the ability to harmonize would correlate positively with measures of executive function. Results indicate that musicians outperformed non-musicians on the Tower of London task, a measure of planning and problem-solving. Group differences were not detected on tasks more selective for inhibitory control, conflict resolution, or working memory. Among musicians, scores on the harmony assessment were positively correlated with performance of the Tower of London task. Taken together, the current results support a strong relationship between musicianship and planning and problem solving abilities, and indicate that the ability to harmonize is associated with components of executive function contributing to planning and problem solving.

Music Training, Working Memory, and Neural Oscillations: A Review

This review focuses on reports that link music training to working memory and neural oscillations. Music training is increasingly associated with improvement in working memory, which is strongly related to both localized and distributed patterns of neural oscillations. Importantly, there is a small but growing number of reports of relationships between music training, working memory, and neural oscillations in adults. Taken together, these studies make important contributions to our understanding of the neural mechanisms that support effects of music training on behavioral measures of executive functions. In addition, they reveal gaps in our knowledge that hold promise for further investigation. The current review is divided into the main sections that follow: (1) discussion of behavioral measures of working memory, and effects of music training on working memory in adults; (2) relationships between music training and neural oscillations during temporal stages of working memory; (3) relationships between music training and working memory in children; (4) relationships between music training and working memory in older adults; and (5) effects of entrainment of neural oscillations on cognitive processing. We conclude that the study of neural oscillations is proving useful in elucidating the neural mechanisms of relationships between music training and the temporal stages of working memory. Moreover, a lifespan approach to these studies will likely reveal strategies to improve and maintain executive function during development and aging.

Phosphorylation of tyrosine receptor kinase B in the dorsal striatum and dorsal hippocampus is associated with response learning in a water plus maze

The dorsal hippocampus and dorsal striatum have dissociable roles in learning and memory that are related to region-specific changes in proteins necessary for neuronal plasticity and memory formation. There is additional evidence that the hippocampus and striatum can interact during memory formation. Phosphorylation of tyrosine receptor kinase B is important for memory formation in the hippocampus, but whether or not it has a role in striatum-dependent learning, or in interactions between the hippocampus and striatum, has not been examined. In the present study, we tested the hypothesis that response training increases pTrkB in the dorsal striatum, but decreases pTrkB in dorsal hippocampus, due to an interaction between the systems during memory formation. Results show a significant decrease in pTrkB levels in the dorsal hippocampus of rats trained on the response task compared with swim controls. Response training did not increase pTrkB levels in the dorsal striatum. Positive correlations were found between response learning and the total area of cells expressing pTrkB in the dorsal striatum, while no correlations were found in swim controls. Our results partially support our hypothesis and indicate that response learning is associated with a decrease in hippocampal pTrkB, while phosphorylation of TrkB in the dorsal striatum remains constant. This indicates that suppression of hippocampal pTrkB during response learning may be involved in striatum-dependent memory formation. Additionally, our findings suggest that activation of TrkB in a sparse arrangement of cells may be associated with faster acquisition of a response task. (PsycINFO Database Record

Lentivirus-mediated chronic expression of dominant-negative CREB in the dorsal hippocampus impairs memory for place learning and contextual fear conditioning

Extensive research has shown that the transcription factor CREB has an important role during memory formation. In the present study, we tested a new method for chronic, stable expression of a dominant-negative form of CREB (mCREB) in the dorsal hippocampus using lentiviral vectors. In specific, we tested whether lentivirus-mediated chronic expression of mutant CREB impairs memory for two hippocampus-dependent tasks - place training in the water maze and contextual fear conditioning. Two weeks following intra-hippocampal infusion, experimental (mCREB) and control (LacZ and saline) rats were trained for 30 trials in one session on a place task in a water plus-maze and tested for an additional 30 trials on day 2 and on day 7. On day 8, all rats were trained on a contextual fear conditioning task and tested 24h later. For place learning, there was no difference between treatment groups on day 1, indicating that treatment with the lentiviral vectors did not alter performance or acquisition of the task. In comparisons with controls, mCREB-treated rats were not significantly impaired on day 2, overall, but they showed significant impairment on day 7. Contextual fear memory was impaired in mCREB-infused rats in comparison with controls. At the end of the experiment, total CREB and phosphorylated CREB protein were measured by western blot. Levels of total CREB were increased by approximately 40% among mCREB-treated rats in comparisons with controls, whereas levels of pCREB did not differ between groups, suggesting that the treatment caused significant expression of mCREB. In addition, mCREB infused rats showed a significant reduction in the pCREB to CREB ratio in comparison with controls, suggesting that the memory deficit seen in mCREB rats is most likely due to disruption of gene regulation caused by expression of mutant CREB. Taken together, the present results show that lentivirus expressing mCREB can be used to effectively alter CREB function within the hippocampus and that the treatment impairs memory for hippocampus-dependent tasks.

The orbitofrontal cortex is not necessary for acquisition or remote recall of socially transmitted food preferences

A role for prefrontal cortex has been proposed in systems consolidation of memory. The current study examined the effects of excitotoxic lesions of the orbitofrontal cortex (OFC) in rats on acquisition and remote recall of socially transmitted food preferences (STFP). Subjects received excitotoxic lesions of the OFC, and they were trained on two food preferences. They were tested 1h after the first training session to determine the effect of the lesion on acquisition. The following day, they were trained on a second preference and tested 10 days later to determine the effect of the lesion on remote recall. OFC lesions did not impair either STFP acquisition or remote recall in comparisons with sham-operated animals. In addition, a subset of animals underwent odor discrimination and reversal training. Consistent with previous reports, subjects with OFC lesions required more trials to reach criterion and made more errors during reversal training than did sham-operated animals. Taken together, the results of the present study indicate that the orbitofrontal cortex is not necessary for acquisition or systems consolidation of socially transmitted food preferences.

Transfection of mutant CREB in the striatum, but not the hippocampus, impairs long-term memory for response learning

Extensive research has shown that the striatum is necessary for response learning. We reported previously that rats using a response strategy to solve a cross maze task showed sustained phosphorylation of striatal CREB [Colombo, P. J., Brightwell, J. J., & Countryman, R. A. (2003). Cognitive strategy-specific increases in phosphorylated cAMP response element-binding protein and c-Fos in the hippocampus and dorsal striatum. Journal of Neuroscience, 23(8), 3547-3554], a transcription factor implicated in long-term memory formation. In the current study, we used viral vector-mediated gene transfer to test the hypothesis that CREB function in the dorsolateral striatum is necessary for the formation of long-term memory for a response strategy. In addition, we tested the hypothesis that the striatum and the hippocampus interact in a cooperative or competitive manner during memory formation. CREB function was blocked in the dorsolateral striatum by overexpression of a mutant form of CREB in which Ser133 was replaced with Ala (HSV-mCREB). CREB function was increased or decreased in the dorsal hippocampus by overexpressing wild-type CREB (HSV-CREB) or mutant CREB. Rats were trained to make a consistent turning response in one session to a criterion of 9 out of 10 correct trials in a water version of the cross maze. Experimental subjects and controls were trained 3 days following infusion into the hippocampus or striatum and tested for memory of the strategy 6 days later. There were no significant differences between treatment groups in acquisition of the task. At test, controls showed significant savings whereas rats infused with HSV-mCREB in the striatum did not. Rats receiving intrahippocampal overexpression of HSV-CREB, HSV-mCREB, or vehicle all showed significant savings between training and test. The present results show that long-term memory of a response strategy requires CREB function in the dorsolateral striatum and is independent of CREB function in the dorsal hippocampus.

Time-courses of Fos expression in rat hippocampus and neocortex following acquisition and recall of a socially transmitted food preference

The present study examined expression of the immediate-early gene, c-Fos, following acquisition, 48-h (recent) recall, and 1-week (remote) recall of a socially transmitted food preference (STFP) in multiple brain regions implicated in learning and memory. In comparisons with controls, trained Long-Evans rats had increased Fos immunoreactivity in the ventral hippocampus following acquisition and recent recall. In the parahippocampal cortices, Fos was increased in the lateral entorhinal cortex after acquisition. In the orbitofrontal cortex, increased Fos immunoreactivity was observed in the lateral orbital cortex following both recent and remote recall and in the ventral orbital cortex following remote recall, indicating a role for the orbitofrontal cortex in the remote recall of STFP memory. In contrast, in the medial prefrontal cortex, increased Fos-ir was found following acquisition in the prelimbic cortex and following recent recall in the prelimbic and infralimbic cortices. No differences in Fos expression were found between trained rats and controls in the dorsal hippocampus, posterior parietal cortex, or amygdala. The present findings support a time-limited role of the hippocampus in the acquisition and recall of STFP memory and implicate neocortical regions involved in STFP acquisition, recent, and remote recall.

Long-term memory for place learning is facilitated by expression of cAMP response element-binding protein in the dorsal hippocampus

Extensive research has shown that the hippocampus is necessary for consolidation of long-term spatial memory in rodents. We reported previously that rats using a place strategy to solve a cross maze task showed sustained phosphorylation of hippocampus cyclic AMP response element-binding protein (CREB), a transcription factor implicated in long-term memory formation. In the current study, we used viral vector-mediated gene transfer to test the hypothesis that formation of long-term memory for place learning can be facilitated by increasing levels of CREB in the dorsal hippocampus. Three days after intrahippocampus infusion, experimental (HSV-CREB) and control (HSV-LacZ; saline) rats were trained during a single session on a place task in a water cross maze. Rats were tested for memory 5 d later. Rats in all groups showed short-term memory, and there were no significant differences among treatment groups during acquisition. However, only HSV-CREB-infused rats showed significant savings between training and test, while HSV-LacZ- and saline-treated rats did not. Quantitative Western blotting confirmed that levels of dorsal hippocampus CREB were increased during training in rats infused with HSV-CREB in comparisons with controls. The present results show that formation of long-term memory can be facilitated by increasing levels of hippocampus CREB protein.

NMDA receptors regulate developmental gap junction uncoupling via CREB signaling

Signaling through gap junctions (electrical synapses) is important in the development of the mammalian central nervous system. Abundant between neurons during postnatal development, gap junction coupling subsequently decreases and remains low in the adult, confined to specific subsets of neurons. Here we report that developmental uncoupling of gap junctions in the rat hypothalamus in vivo and in vitro is associated with a decrease in connexin 36 (Cx36) protein expression. Both developmental gap junction uncoupling and Cx36 downregulation are prevented by the blockade of NMDA glutamate receptors, action potentials and the calcium-cyclic AMP response element binding protein (CREB), and are accelerated by CREB overexpression. Developmental gap junction uncoupling and Cx36 downregulation are not affected by blockade of non-NMDA glutamate receptors, and do not occur in hypothalamic neurons from NMDA receptor subunit 1 (NMDAR1) knockout mice. These results demonstrate that NMDA receptor activity contributes to the developmental uncoupling of gap junctions via CREB-dependent downregulation of Cx36.

Hippocampal c-fos is necessary for long-term memory of a socially transmitted food preference

The present article examined the requirement of hippocampal c-Fos for learning a socially transmitted food preference (STFP). We reported previously that expression of the c-Fos protein is increased in the dorsal and ventral hippocampus of rats trained on the STFP (Countryman, Orlowski, Brightwell, Oskowitz, & Colombo, 2005). Pretraining intrahippocampal antisense to the immediate early gene c-fos was administered to adult male Long-Evans rats to determine if c-fos expression is necessary for either short- or long-term memory for STFP. Guide cannulae were implanted bilaterally into the dorsal hippocampus. Antisense oligodeoxynucleotides (ODNs) were administered unilaterally either 6.5, 8.5, 10.5, or 12.5 h prior to STFP training while either sense ODNs or saline were infused into the opposite hemisphere. Immunocytochemistry was performed, and cells showing c-Fos immunoreactivity (ir) were counted from the antisense-treated hemisphere and compared to cell counts from the control hemisphere. The results indicated significant suppression of learning-induced c-Fos protein at the 8.5 and 10.5 infusion-train intervals. Additional rats were implanted with cannulae into the dorsal and ventral hippocampus, and antisense ODNs, sense ODNs, or saline were administered bilaterally 8.5h prior to training. Rats were tested immediately and 14 days after training. Rats in all groups showed a significant preference for the demonstrated food at the short-term memory test. At the long-term memory test, however, rats infused with c-fos antisense showed no preference for the demonstrated food whereas rats infused with either sense or saline maintained their preference. The present findings suggest that c-fos is necessary for consolidation of non-spatial hippocampal-dependent memory.

CREB phosphorylation and c-Fos expression in the hippocampus of rats during acquisition and recall of a socially transmitted food preference

In the present study, phosphorylation of cAMP-response element binding protein (pCREB) and expression of c-Fos were measured in the dorsal and ventral hippocampus, as well as in a control region, the retrosplenial cortex, of rats following acquisition and recall of a socially transmitted food preference (STFP). Behavioral analyses revealed that STFP-trained rats showed a stronger preference for the demonstrated food than did rats in social-control or odor-control conditions. Rats in a social + odor control condition displayed an intermediate preference that was not significantly different from either STFP-trained rats or the social- or odor-controls. Immunocytochemical analyses revealed increased pCREB-immunoreactivity (ir) in the ventral hippocampus of STFP-trained rats in comparisons with rats in all three control conditions and increased pCREB-ir in the dorsal hippocampus in comparisons with the social- and odor-control conditions. In contrast, c-Fos-ir was greater in the dorsal hippocampus of STFP-trained rats in comparisons with all three control conditions and greater in the ventral hippocampus than rats in the social- and odor-control conditions. Comparisons of pCREB-ir and c-Fos-ir were made also between STFP-trained rats and social-controls following either acquisition or a 48-h recall test. c-Fos-ir was greater in STFP-trained rats after both acquisition and recall, whereas pCREB was greater after recall only. There were no differences in either c-Fos-ir or pCREB-ir in comparisons between trained and control rats in the retrosplenial cortex. The current results indicate that the activity of transcription factors in the hippocampus is related to both acquisition and retention of a socially transmitted food preference.

Learning-induced activation of transcription factors among multiple memory systems

Experimental evidence for multiple memory systems grew initially from reports that integrity of the medial temporal lobes is necessary for some, but not all, types of memory formation. A primary inference from many studies of multiple memory systems is that they operate independently during encoding, storage, and retrieval of information. An accumulation of recent evidence, however, suggests that multiple memory systems may interact under some conditions. At the cellular level of analysis, it is accepted widely that protein synthesis is necessary for the formation of long-term memory and recent efforts have focused on the mechanisms by which learning-induced gene transcription and translation are regulated. The present review examines learning-induced activation of transcription factors among multiple memory systems. The results indicate that studies of transcriptional regulation, in conjunction with other experimental approaches, can provide complementary lines of evidence to further understanding of the extent to which multiple memory systems are independent or interactive.

Hippocampal overexpression of mutant creb blocks long-term, but not short-term memory for a socially transmitted food preference

Phosphorylation of the transcription factor CREB on Ser133 is implicated in the establishment of long-term memory for hippocampus-dependent tasks, including spatial learning and contextual fear conditioning. We reported previously that training on a hippocampus-dependent social transmission of food preference (STFP) task increases CREB phosphorylation in the hippocampus of trained rats in comparisons with controls. In the current study, we tested the hypothesis that CREB function is necessary for long-term memory for STFP using herpes simplex viral (HSV) vector-mediated gene transfer. Rats received intrahippocampal infusions of HSV-mCREB (a mutant form of CREB, in which Ser133 has been replaced with Ala), HSV-LacZ, or saline, and were trained 3 d later. Rats were tested for food preference (demonstrated vs. novel foods) immediately (short-term test) and 11 d (long-term test) after training. Rats in all treatment groups showed a significant preference for the demonstrated food at the short-term memory test. At the long-term memory test, however, the percentage of demonstrated food eaten by mCREB-treated rats was significantly less than that eaten by the LacZ- or saline-treated rats. Quantitative Western blotting confirmed that mCREB-infused rats had significantly more hippocampal CREB protein than controls during training. The present results show that hippocampal CREB function is necessary for long-term, but not short-term memory for STFP.

Hippocampal CREB1 but not CREB2 is decreased in aged rats with spatial memory impairments

Recent evidence has shown that abnormal signal transduction is related to non-pathological memory impairment among aged subjects. Members of the CREB family of transcription factors contain enhancers (i.e., CREB1) and repressors (i.e., CREB2) of transcription and interact with numerous signaling proteins to mediate the transition from short-term to long-term memory. In this study, quantitative Western blotting was used to determine the levels of CREB1 and CREB2 in homogenates from hippocampi of individual 6- and 24-month-old male Long-Evans rats trained first on a place-learning task in the Morris water maze, then on a transfer task. Based on spatial memory performance, aged rats were characterized into two groups; aged-unimpaired rats (AU) had scores within the range of the young (Y) and aged-impaired rats (AI) fell outside of that range. Overall, CREB1 protein was significantly lower in aged rats in comparison with young rats. Aposteriori analysis showed that this difference was due to a significant decrease in CREB1 levels among aged-impaired rats, whereas aged-unimpaired rats had CREB1 levels comparable to young rats. There was no significant change in levels of CREB2 protein between young and aged rats. These results show that the dysregulation of CREB1 protein may contribute to the spatial memory deficits observed among some aged subjects.

Cognitive strategy-specific increases in phosphorylated cAMP response element-binding protein and c-Fos in the hippocampus and dorsal striatum

Extensive research has shown that the hippocampus and striatum have dissociable roles in memory and are necessary for "place" and "response" learning, respectively. In the present study, rats were trained on a cross maze task that could be solved by either a place or a response strategy, and the strategy used was determined by a probe trial. Phosphorylated cAMP response element-binding protein (pCREB) and c-Fos immunoreactivity (IR) were measured in the hippocampus and striatum either immediately or 1 hr after cross maze training. Immediately after training, pCREB-IR and c-Fos-IR were significantly higher in the hippocampus and striatum of trained rats than in control rats matched for motor activity, but the increase was independent of the strategy revealed at probe. One hour after training, however, pCREB-IR and c-Fos-IR were sustained in the hippocampal pyramidal and granule cell layers of place learners but returned to basal levels among response learners. In addition, pCREB-IR was sustained in the dorsomedial and dorsolateral striatum of response learners but returned to basal levels among place learners. There were no differences between place and response learners in c-Fos-IR in the striatum at either time point. The present results indicate that cross maze training causes an initial activation of transcription factors in both the hippocampus and striatum. Formation of memory for a place strategy, however, is related to sustained phosphorylation of CREB and expression of c-Fos for at least 1 hr in the hippocampus, whereas formation of memory for a response strategy is related to phosphorylation of CREB in the striatum.

Individual differences in spatial memory among aged rats are related to hippocampal PKCgamma immunoreactivity

We reported previously that the extent of spatial memory impairment among aged rats was correlated positively with levels of protein kinase Cgamma in hippocampal homogenates measured by quantitative Western blotting (Colombo et al., 1997). In the current study, immunocytochemistry was used to test whether the relationship between elevated PKC-gamma and memory impairment among aged rats could be localized further within regions of the hippocampus. Six- and 24-month-old male Long-Evans rats were first trained in the water maze on a standard place-learning task and then trained 2 weeks later on a transfer task designed for rapid acquisition. In comparison with young rats, aged rats with impaired spatial memory had increased PKCgamma-immunoreactivity (PKCgamma-ir) in CA1 of the hippocampus, but not the dentate gyrus. In addition, PKCgamma-ir in CA1 was correlated positively with spatial memory impairment among aged rats on the standard place-learning and the transfer training tasks. The current results are consistent with our previous report of PKCgamma in hippocampal homogenates, and show further that the relationships between PKCgamma-ir and memory impairments among aged rats are most evident in area CA1. Thus age-related impairments of spatial memory, as well as deficits in the flexible use of previously acquired information, may result from dysregulation of PKCgamma.

Kappa opioid receptor activity modulates memory for peck-avoidance training in the 2-day-old chick

To examine the role of kappa opioid receptors in memory formation, 2-day-old chicks were injected intracerebrally with either the endogenous opioid peptide dynorphin(1-13), the highly kappa selective agonist U-50,488 or the kappa selective antagonist nor-binaltorphimine (nor-BNI), given one-trial peck-avoidance training, and tested 24 h later. Dynorphin(1-13) impaired memory in a dose dependent manner at 24 h test. Injection of U-50,488 caused a biphasic dose-dependent effect on memory; low doses caused a trend toward enhanced memory and high doses caused significant impairment. Conversely, injection of low doses of nor-BNI caused a trend toward memory impairment, and higher doses caused significant memory enhancement. The results indicate that memory formation for one-trial peck-avoidance training may be modulated by kappa opioid receptor activity.

Metabotropic glutamate receptor-mediated hippocampal phosphoinositide turnover is blunted in spatial learning-impaired aged rats

Maximal phosphoinositide (PI) turnover was examined in the hippocampus of young and aged Long-Evans rats that were behaviorally characterized for spatial learning in the Morris water maze. The type 1 metabotropic glutamate receptor (mGluR) agonist 1S,3R ACPD was used to stimulate PI turnover and to determine the E(MAX) for each rat. Protein levels in hippocampus for type 1 mGluRs, Galphaq11, and phospholipase Cbeta-1 (PLCbeta-1) were also measured by quantitative Western blotting. The results show that PI turnover mediated by the mGluRs was blunted in the aged rats. The magnitude of the decrement in PI turnover was also significantly correlated with age-related spatial memory decline. The decrease in mGluR-mediated PI turnover occurred without changes in the protein level of either the mGluRs or the G-protein coupled to those receptors, Galphaq11. A significant decrease in the immunoreactivity of PLCbeta-1, however, was observed in the hippocampus of aged rats; PLCbeta-1 immunoreactivity was significantly correlated with spatial learning only when the young and aged rats were considered together. The decrement in mGluR-mediated signal transduction in the hippocampus that is related to cognitive impairment in aging may be attributable, at least in part, to a deficiency in the enzyme PLCbeta-1. That deficiency may also contribute to a blunted response in muscarinic stimulation of hippocampal PI turnover that we previously found in this same study population. An age-related alteration in this signal transduction system may provide a functional basis for cognitive decline independent of any loss of neurons in the hippocampus.

Individual differences in spatial memory and striatal ChAT activity among young and aged rats

Individual differences in spatial memory among young and aged rats were assessed using memory tasks related to integrity of the hippocampus and the neostriatum. Relationships were then examined between measures of spatial memory and regional choline acetyltransferase (ChAT) activity, a marker for cholinergic integrity. Twenty-four-month-old Long-Evans rats were impaired in comparisons with 6-month-old rats on measures of place learning, working memory, reference memory, and perseveration in water-maze tasks. Aged rats that were impaired on one measure of memory, however, were not necessarily impaired on other measures. ChAT activity in the ventromedial and dorsolateral neostriatum of aged rats was significantly reduced in comparisons with young rats whereas no difference was found in the hippocampus. Aged rats with the most ChAT activity in the anterior ventromedial neostriatum performed best on the place-learning and reference memory tasks but also made the most perseverative errors on the working memory task. In addition, young and aged rats with the most ChAT activity in the anterior dorsolateral neostriatum were those with the least accurate working memory. No relationships were found between ChAT activity in the hippocampus and spatial memory. Thus age-related memory impairment has components that can be segregated by measuring relationships between cholinergic integrity in subregions of the anterior neostriatum and memory tasks with different strategic requirements.

Spatial memory is related to hippocampal subcellular concentrations of calcium-dependent protein kinase C isoforms in young and aged rats

Relationships were examined between spatial learning and hippocampal concentrations of the alpha, beta2, and gamma isoforms of protein kinase C (PKC), an enzyme implicated in neuronal plasticity and memory formation. Concentrations of PKC were determined for individual 6-month-old (n = 13) and 24-month-old (n = 27) male Long-Evans rats trained in the water maze on a standard place-learning task and a transfer task designed for rapid acquisition. The results showed significant relationships between spatial learning and the amount of PKC among individual subjects, and those relationships differed according to age, isoform, and subcellular fraction. Among 6-month-old rats, those with the best spatial memory were those with the highest concentrations of PKCgamma in the particulate fraction and of PKCbeta2 in the soluble fraction. Aged rats had increased hippocampal PKCgamma concentrations in both subcellular fractions in comparison with young rats, and memory impairment was correlated with higher PKCgamma concentrations in the soluble fraction. No age difference or correlations with behavior were found for concentrations of PKCgamma in a comparison structure, the neostriatum, or for PKCalpha in the hippocampus. Relationships between spatial learning and hippocampal concentrations of calcium-dependent PKC are isoform-specific. Moreover, age-related spatial memory impairment is associated with altered subcellular concentrations of PKCgamma and may be indicative of deficient signal transduction and neuronal plasticity in the hippocampal formation.

Evidence for localized and discrete roles for enkephalins during memory formation in the chick

This study examined effects on memory formation produced by [Leu]enkephalin and [Met]enkephalin administration in 2 regions of the 2-day-old chick brain involved in memory formation: the intermediate medial hyperstriatum ventrale (IMHV) and the lobus parolfactorius (LPO). Basal concentrations of endogenous [Leu]enkephalin and [Met]enkephalin were determined for 5 brain regions, and effects of 1-trial peck-avoidance training on enkephalin concentrations were examined in the IMHV and LPO. [Leu]enkephalin was amnestic when administered in the IMHV but not in the LPO. In contrast, [Met]enkephalin may be amnestic when administered in the LPO but not in the IMHV. Training decreased [Met]enkephalin concentration in the LPO but not in the IMHV. Training had no effect on [Leu]enkephalin concentration in either the IMHV or the LPO. Thus, amnestic effects of [Leu]- or [Met]enkephalin administration are brain-region specific. Regional activity of endogenous [Met]enkephalin during memory formation is consistent with localized amnestic effects produced by [Met]enkephalin administration.

Evidence for localized and discrete roles for enkephalins during memory formation in the chick

This study examined effects on memory formation produced by [Leu]enkephalin and [Met]enkephalin administration in 2 regions of the 2-day-old chick brain involved in memory formation: the intermediate medial hyperstriatum ventrale (IMHV) and the lobus parolfactorius (LPO). Basal concentrations of endogenous [Leu]enkephalin and [Met]enkephalin were determined for 5 brain regions, and effects of 1-trial peck-avoidance training on enkephalin concentrations were examined in the IMHV and LPO. [Leu]enkephalin was amnestic when administered in the IMHV but not in the LPO. In contrast, [Met]enkephalin may be amnestic when administered in the LPO but not in the IMHV. Training decreased [Met]enkephalin concentration in the LPO but not in the IMHV. Training had no effect on [Leu]enkephalin concentration in either the IMHV or the LPO. Thus, amnestic effects of [Leu]- or [Met]enkephalin administration are brain-region specific. Regional activity of endogenous [Met]enkephalin during memory formation is consistent with localized amnestic effects produced by [Met]enkephalin administration.

Ageing: the cholinergic hypothesis of cognitive decline

The concept that memory loss in ageing might be attributable to deficiencies in cholinergic function was first proposed two decades ago. This proposal gained additional definition when pathology was found in the basal forebrain cholinergic system of patients with Alzheimer's disease, and substantial deterioration of these neurons was detected in several animal models of ageing. A recently developed method for selectively removing basal forebrain cholinergic neurons using an immunotoxin provides a powerful tool for examining the function of the basal forebrain cholinergic system. This review will address new information that has come from this approach, with an emphasis on understanding the contribution of basal forebrain cholinergic neurons to age-related cognitive impairment.

Short-term, intermediate-term, and long-term memories

This paper focuses on the temporal dimension of memory formation and storage. Is the usual two-fold separation between short-term memory (STM) and long-term memory (LTM) sufficient to encompass all the phenomena of memory? The traditional view is that STM grades into LTM. Evidence for an intermediate-term memory (ITM) has been proposed by some investigators. We have used both rats and chicks to investigate the stages of memory formation. In this paper, the advantages of chicks for this type of research are briefly discussed. Using a paradigm that produces weak training, the retention function for control chicks appears to be made up of four successive components which we have interpreted as representing the memory buffer, STM, ITM, and LTM. In experiments using a variety of kinase inhibitors, we have obtained evidence that ITM and LTM depend on different classes of protein kinase activities. Agents that act on calcium/calmodulin kinase cause amnesia in the ITM range--15 to 30 min post-training. Another class of inhibitors act on one or more of the kinases PKA, PKC, or PKG and cause amnesia by 60 min post-training, so we interpret this group of inhibitors as inhibiting the formation of LTM. However, the three-stage model of memory may be over-simple. For example some agents including [Leu]enkephalin and MK801 cause amnesia 4 or more h after training.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynorphin(1-13) impairs memory formation for aversive and appetitive learning in chicks

The opioid peptide dynorphin(1-13) impairs memory formation in chicks (5). We examined whether this occurs for both aversively and appetitively motivated learning. Four-day-old chicks were injected with dynorphin(1-13) into the intermediate medial hyperstriatum ventrale and trained on either a peck avoidance (PA) or an appetitive discrimination (AD) task; 2-day-old chicks were trained on PA. In 2-day-old chicks, dynorphin was amnestic for PA at 0.01, 0.03, or 0.1 mM. In 4-day-old chicks, dynorphin impaired memory formation for PA at 0.1 mM, and for AD training at 0.03 mM. Thus, similar doses of dynorphin impair memory formation for both appetitive and aversive conditioning.

Allocentric spatial and tactile memory impairments in rats with dorsal caudate lesions are affected by preoperative behavioral training

Rats with caudate lesions and pretrained for 36 trials demonstrated impaired performance on the "reference memory" or invariant aspect of a 12-arm radial maze and normal performance on the "working memory" or variable aspect of the maze. Rats with caudate lesions and no pretraining were also impaired on an invariant tactile discrimination in a T maze, but they were not impaired on the variable goal-arm choice of the T maze. More extensive preoperative training ameliorated behavioral deficits of rats with caudate lesions in the T maze and radial arm maze. Results showed that behavioral impairment after damage to the caudate is not restricted to egocentric tasks as previously suggested, but the caudate seems to be involved in the initial acquisition of information that is invariant over many trials.

Preoperative training modifies radial maze performance in rats with ischemic hippocampal injury

Rats exposed to 30 minutes of four-vessel occlusion reliably develop severe bilateral CA1 hippocampal injury; under certain conditions of radial maze training, such rats perform the reference memory component as well as controls yet perform the working memory component worse than controls. Reference memory is thought to depend on invariable and working memory on variable spatial information. We assessed the effect of training before ischemia. In Experiment 1, rats trained for 36 trials on 12-arm radial mazes before ischemia demonstrated a persistent impairment on the working memory task but eventually performed the reference memory task comparable to controls. Ischemic rats made more working memory errors as the number of choices increased. This pattern of working memory errors was similar to that in controls except, as expected, ischemic rats made many more errors. In Experiment 2, training for 80 trials before ischemia in rats decreased the severity of both the working and the reference memory impairment. Ischemia did not affect motor behavior in either experiment. These results characterize the working memory deficit in ischemic rats and demonstrate the importance of experimental factors, particularly in the design of treatment strategies to reduce functional impairments caused by ischemia.

Allocentric spatial and tactile memory impairments in rats with dorsal caudate lesions are affected by preoperative behavioral training

Rats with caudate lesions and pretrained for 36 trials demonstrated impaired performance on the "reference memory" or invariant aspect of a 12-arm radial maze and normal performance on the "working memory" or variable aspect of the maze. Rats with caudate lesions and no pretraining were also impaired on an invariant tactile discrimination in a T maze, but they were not impaired on the variable goal-arm choice of the T maze. More extensive preoperative training ameliorated behavioral deficits of rats with caudate lesions in the T maze and radial arm maze. Results showed that behavioral impairment after damage to the caudate is not restricted to egocentric tasks as previously suggested, but the caudate seems to be involved in the initial acquisition of information that is invariant over many trials.