Inverted-U-shaped dopamine actions on human working memory and cognitive control

Brain dopamine (DA) has long been implicated in cognitive control processes, including working memory. However, the precise role of DA in cognition is not well-understood, partly because there is large variability in the response to dopaminergic drugs both across different behaviors and across different individuals. We review evidence from a series of studies with experimental animals, healthy humans, and patients with Parkinson's disease, which highlight two important factors that contribute to this large variability. First, the existence of an optimum DA level for cognitive function implicates the need to take into account baseline levels of DA when isolating the effects of DA. Second, cognitive control is a multifactorial phenomenon, requiring a dynamic balance between cognitive stability and cognitive flexibility. These distinct components might implicate the prefrontal cortex and the striatum, respectively. Manipulating DA will thus have paradoxical consequences for distinct cognitive control processes, depending on distinct basal or optimal levels of DA in different brain regions.

Genetic demonstration of a role for PKA in the late phase of LTP and in hippocampus-based long-term memory

To explore the role of protein kinase A (PKA) in the late phase of long-term potentiation (L-LTP) and memory, we generated transgenic mice that express R(AB), an inhibitory form of the regulatory subunit of PKA, only in the hippocampus and other forebrain regions by using the promoter from the gene encoding Ca2+/ calmodulin protein kinase IIalpha. In these R(AB) transgenic mice, hippocampal PKA activity was reduced, and L-LTP was significantly decreased in area CA1, without affecting basal synaptic transmission or the early phase of LTP. Moreover, the L-LTP deficit was paralleled by behavioral deficits in spatial memory and in long-term but not short-term memory for contextual fear conditioning. These deficits in long-term memory were similar to those produced by protein synthesis inhibition. Thus, PKA plays a critical role in the consolidation of long-term memory.

Neurobiology of executive functions: catecholamine influences on prefrontal cortical functions

The prefrontal cortex guides behaviors, thoughts, and feelings using representational knowledge, i.e., working memory. These fundamental cognitive abilities subserve the so-called executive functions: the ability to inhibit inappropriate behaviors and thoughts, regulate our attention, monitor our actions, and plan and organize for the future. Neuropsychological and imaging studies indicate that these prefrontal cortex functions are weaker in patients with attention-deficit/hyperactivity disorder and contribute substantially to attention-deficit/hyperactivity disorder symptomology. Research in animals indicates that the prefrontal cortex is very sensitive to its neurochemical environment and that small changes in catecholamine modulation of prefrontal cortex cells can have profound effects on the ability of the prefrontal cortex to guide behavior. Optimal levels of norepinephrine acting at postsynaptic alpha-2A-adrenoceptors and dopamine acting at D1 receptors are essential to prefrontal cortex function. Blockade of norepinephrine alpha-2-adrenoceptors in prefrontal cortex markedly impairs prefrontal cortex function and mimics most of the symptoms of attention-deficit/hyperactivity disorder, including impulsivity and locomotor hyperactivity. Conversely, stimulation of alpha-2-adrenoceptors in prefrontal cortex strengthens prefrontal cortex regulation of behavior and reduces distractibility. Most effective treatments for attention-deficit/hyperactivity disorder facilitate catecholamine transmission and likely have their therapeutic actions by optimizing catecholamine actions in prefrontal cortex.

Cellular and systems reconsolidation in the hippocampus

Cellular theories of memory consolidation posit that new memories require new protein synthesis in order to be stored. Systems consolidation theories posit that the hippocampus has a time-limited role in memory storage, after which the memory is independent of the hippocampus. Here, we show that intra-hippocampal infusions of the protein synthesis inhibitor anisomycin caused amnesia for a consolidated hippocampal-dependent contextual fear memory, but only if the memory was reactivated prior to infusion. The effect occurred even if reactivation was delayed for 45 days after training, a time when contextual memory is independent of the hippocampus. Indeed, reactivation of a hippocampus-independent memory caused the trace to again become hippocampus dependent, but only for 2 days rather than for weeks. Thus, hippocampal memories can undergo reconsolidation at both the cellular and systems levels.

Memory traces unbound

The idea that new memories are initially 'labile' and sensitive to disruption before becoming permanently stored in the wiring of the brain has been dogma for >100 years. Recently, we have revisited the hypothesis that reactivation of a consolidated memory can return it to a labile, sensitive state - in which it can be modified, strengthened, changed or even erased! The data generated from some of the best-described paradigms in memory research, in conjunction with powerful neurobiological technologies, have provided striking support for a very dynamic neurobiological basis of memory, which is beginning to overturn the old dogma.

Methylphenidate preferentially increases catecholamine neurotransmission within the prefrontal cortex at low doses that enhance cognitive function

BACKGROUND

Low doses of psychostimulants, such as methylphenidate (MPH), are widely used in the treatment of attention-deficit/hyperactivity disorder (ADHD). Surprisingly little is known about the neural mechanisms that underlie the behavioral/cognitive actions of these drugs. The prefrontal cortex (PFC) is implicated in ADHD. Moreover, dopamine (DA) and norepinephrine (NE) are important modulators of PFC-dependent cognition. To date, the actions of low-dose psychostimulants on PFC DA and NE neurotransmission are unknown.

METHODS

In vivo microdialysis was used to compare the effects of low-dose MPH on NE and DA efflux within the PFC and select subcortical fields in male rats. Doses used (oral, 2.0 mg/kg; intraperitoneal, .25-1.0 mg/kg) were first determined to produce clinically relevant plasma concentrations and to facilitate both PFC-dependent attention and working memory.

RESULTS

At low doses that improve PFC-dependent cognitive function and that are devoid of locomotor-activating effects, MPH substantially increases NE and DA efflux within the PFC. In contrast, outside the PFC these doses of MPH have minimal impact on NE and DA efflux.

CONCLUSIONS

The current observations suggest that the therapeutic actions of low-dose psychostimulants involve the preferential activation of catecholamine neurotransmission within the PFC.

Effects of neuromodulation in a cortical network model of object working memory dominated by recurrent inhibition

Experimental evidence suggests that the maintenance of an item in working memory is achieved through persistent activity in selective neural assemblies of the cortex. To understand the mechanisms underlying this phenomenon, it is essential to investigate how persistent activity is affected by external inputs or neuromodulation. We have addressed these questions using a recurrent network model of object working memory. Recurrence is dominated by inhibition, although persistent activity is generated through recurrent excitation in small subsets of excitatory neurons. Our main findings are as follows. (1) Because of the strong feedback inhibition, persistent activity shows an inverted U shape as a function of increased external drive to the network. (2) A transient external excitation can switch off a network from a selective persistent state to its spontaneous state. (3) The maintenance of the sample stimulus in working memory is not affected by intervening stimuli (distractors) during the delay period, provided the stimulation intensity is not large. On the other hand, if stimulation intensity is large enough, distractors disrupt sample-related persistent activity, and the network is able to maintain a memory only of the last shown stimulus. (4) A concerted modulation of GABA(A) and NMDA conductances leads to a decrease of spontaneous activity but an increase of persistent activity; the enhanced signal-to-noise ratio is shown to increase the resistance of the network to distractors. (5) Two mechanisms are identified that produce an inverted U shaped dependence of persistent activity on modulation. The present study therefore points to several mechanisms that enhance the signal-to-noise ratio in working memory states. These mechanisms could be implemented in the prefrontal cortex by dopaminergic projections from the midbrain.

Delay-dependent impairment of a matching-to-place task with chronic and intrahippocampal infusion of the NMDA-antagonist D-AP5

We investigated the role of NMDA receptors in memory encoding and retrieval. A delayed matching-to-place (DMP) paradigm in the watermaze was used to examine 1-trial spatial memory in rats. Over periods of up to 21 days, 4 daily trials were given to an escape platform hidden in a new location each day, with the memory interval (ITI) varying from 15 sec to 2 hours between trials 1 and 2, but always at 15 sec for the remaining ITIs. Using chronic i.c.v. infusions of D-AP5, acute intrahippocampal infusions, ibotenate hippocampus + dentate lesions and relevant aCSF or sham surgery control groups, we established: (1) the DMP task is hippocampal-dependent; (2) D-AP5 causes a delay-dependent impairment of memory in which the Groups x Delay interaction was significant on two separate measures of performance; (3) this memory impairment also occurs with acute intrahippocampal infusions; (4) the impairment occurs irrespective of whether the animals stay in or are removed from the training context during the memory delay interval; and (5) D-AP5 affects neither the retrieval of information about the spatial layout of the environment, nor memory of where the escape platform had been located on the last day before the start of chronic D-AP5 infusion. LTP in vivo in the dentate gyrus was blocked in the chronically-infused D-AP5 rats and HPLC measurements at sacrifice revealed appropriate intrahippocampal levels. Acute intrahippocampal infusion of radiolabelled D-AP5 revealed relatively restricted diffusion and was used to estimate whole-tissue hippocampal drug concentrations. These results indicate that (1) short-term memory for spatial information is independent of NMDA receptors; (2) the rapid consolidation of spatial information into long-term memory requires activation of hippocampal NMDA receptors; (3) NMDA receptors are not involved in memory retrieval; and (4) the delay-related effects of NMDA receptor antagonists on performance of this task cannot be explained in terms of sensorimotor disturbances. The findings relate to the idea that hippocampal synaptic plasticity is involved in event-memory (Morris and Frey, Phil Trans R Soc Lond B 1997;352:1489-1503) and to a computational model of one-trial DMP performance of Foster et al. (unpublished data).

Binge drinking in young adults: Data, definitions, and determinants

Binge drinking is an increasingly important topic in alcohol research, but the field lacks empirical cohesion and definitional precision. The present review summarizes findings and viewpoints from the scientific binge-drinking literature. Epidemiological studies quantify the seriousness of alcohol-related problems arising from binge drinking, with a growing incidence reported in college-age men over the last 2 years. Experimental studies have found neurocognitive deficits for frontal lobe processing and working memory operations in binge-drinking compared with nonbinge alcohol drinkers. The findings are organized with the goals of providing a useful binge-drinking definition in the context of the empirical results. Theoretical implications are discussed on how binge drinking may alter neurophysiological and neurocognitive function.

Ketamine anesthesia during the first week of life can cause long-lasting cognitive deficits in rhesus monkeys

Previously our laboratory has shown that ketamine exposure (24h of clinically relevant anesthesia) causes significant increases in neuronal cell death in perinatal rhesus monkeys. Sensitivity to this ketamine-induced neurotoxicity was observed on gestational days 120-123 (in utero exposure via maternal anesthesia) and on postnatal days (PNDs) 5-6, but not on PNDs 35-37. In the present study, six monkeys were exposed on PND 5 or 6 to intravenous ketamine anesthesia to maintain a light surgical plane for 24h and six control animals were unexposed. At 7 months of age all animals were weaned and began training to perform a series of cognitive function tasks as part of the National Center for Toxicological Research (NCTR) Operant Test Battery (OTB). The OTB tasks used here included those for assessing aspects of learning, motivation, color discrimination, and short-term memory. Subjects responded for banana-flavored food pellets by pressing response levers and press-plates during daily (M-F) test sessions (50 min) and were assigned training scores based upon their individual performance. As reported earlier (Paule et al., 2009) beginning around 10 months of age, control animals significantly outperformed (had higher training scores than) ketamine-exposed animals for approximately the next 10 months. For animals now over 3 and one-half years of age, the cognitive impairments continue to manifest in the ketamine-exposed group as poorer performance in the OTB learning and color and position discrimination tasks, as deficits in accuracy of task performance, but also in response speed. There are also apparent differences in the motivation of these animals which may be impacting OTB performance. These observations demonstrate that a single 24-h episode of ketamine anesthesia, occurring during a sensitive period of brain development, results in very long-lasting deficits in brain function in primates and provide proof-of-concept that general anesthesia during critical periods of brain development can result in subsequent functional deficits. Supported by NICHD, CDER/FDA and NCTR/FDA.

Layered reward signalling through octopamine and dopamine in Drosophila

Dopamine is synonymous with reward and motivation in mammals. However, only recently has dopamine been linked to motivated behaviour and rewarding reinforcement in fruitflies. Instead, octopamine has historically been considered to be the signal for reward in insects. Here we show, using temporal control of neural function in Drosophila, that only short-term appetitive memory is reinforced by octopamine. Moreover, octopamine-dependent memory formation requires signalling through dopamine neurons. Part of the octopamine signal requires the α-adrenergic-like OAMB receptor in an identified subset of mushroom-body-targeted dopamine neurons. Octopamine triggers an increase in intracellular calcium in these dopamine neurons, and their direct activation can substitute for sugar to form appetitive memory, even in flies lacking octopamine. Analysis of the β-adrenergic-like OCTβ2R receptor reveals that octopamine-dependent reinforcement also requires an interaction with dopamine neurons that control appetitive motivation. These data indicate that sweet taste engages a distributed octopamine signal that reinforces memory through discrete subsets of mushroom-body-targeted dopamine neurons. In addition, they reconcile previous findings with octopamine and dopamine and suggest that reinforcement systems in flies are more similar to mammals than previously thought.

Catecholamine influences on dorsolateral prefrontal cortical networks

The symptoms of attention-deficit/hyperactivity disorder (ADHD) involve impairments in prefrontal cortical top-down regulation of attention and behavior. All current pharmacological treatments for ADHD facilitate catecholamine transmission, and basic research suggests that these compounds have prominent actions in the prefrontal cortex (PFC). The dorsolateral PFC is especially sensitive to levels of norepinephrine and dopamine, whereby either too little or too much markedly impairs PFC function. Recent physiological studies have shown that norepinephrine strengthens PFC network connectivity and maintains persistent firing during a working memory task through stimulation of postsynaptic α(2A)-adrenoceptors on PFC neurons. Conversely, dopamine acts at D1 receptors to narrow spatial tuning, sculpting network inputs to decrease noise (i.e., stabilization of the representation). The stimulant medications and atomoxetine appear to enhance PFC function by indirectly increasing these catecholamine actions through blockade of norepinephrine and/or dopamine transporters. In contrast, guanfacine mimics the enhancing effects of norepinephrine at postsynaptic α(2A)-receptors in the PFC, strengthening network connectivity. Stronger PFC regulation of attention, behavior, and emotion likely contributes to the therapeutic effects of these medications for the treatment of ADHD.

Physostigmine: improvement of long-term memory processes in normal humans

Nineteen normal male subjects received 1.0 milligram of physostigmine or 1.0 milligram of saline by a slow intravenous infusion on two nonconsecutive days. Physostigmine significantly enhanced storage of information into long-term memory. Retrieval of information from long-term memory was also improved. Short-term memory processes were not significantly altered by physostigmine.

Working memory is more sensitive than declarative memory to the acute effects of corticosteroids: a dose-response study in humans

The effects of various doses (40 microg/kg/hr, 300 microg/kg/hr, 600 microg/kg/hr or placebo) of hydrocortisone on tasks assessing working and declarative memory function were measured in 4 groups of 10 young men. During the infusion, participants were given an item-recognition working memory task, a paired-associate declarative memory task, and a continuous performance task used to control possible concomitant effects of corticosteroids on vigilance. The results revealed significant acute effects of the highest dose of hydrocortisone on working memory function, without any significant effect on declarative memory function or arousal-vigilance performance. These results suggest that working memory is more sensitive than declarative memory to the acute elevations of corticosteroids, which could explain the detrimental effects of corticosteroids on acquisition and consolidation of information, as reported in the literature.

Attention and executive functions in remitted major depression patients

BACKGROUND

Although deficits in attention and executive functions in patients with Major Depressive Disorder (MDD) are well confirmed [Veiel, H.O.F., 1997. A preliminary profile of neuropsychological deficits associated with major depression. Journal of Clinical and Experimental Neuropsychology 19, 587-603.]. The database regarding the relationship between impairments and the duration of disease or the number of episodes is inconsistent. Furthermore, the role of long-term cognitive impairments in MDD during remitted state is not well understood [Elliott, R., 2002. The neuropsychological profile in primary depression. Taylor and Francis, London, pp. 273-293.]. There is consequently a lack of studies accounting for different courses of illness in the euthymic state and considering the influence of possible attentional deficits on executive performance.

METHODS

40 euthymic patients with MDD diagnosis according to DSM-IV (20 patients with 1-2 episodes and 20 severe depressives with at least three episodes) as well as 20 healthy controls matched for education and age were administered three tests for attention (attentional shift, Stroop task, sustained attention) and three for executive functions (BADS, word fluency, memory span). The methods selected were theory based with regard to an involvement of frontal-subcortical networks in MDD, attention, and executive functions, respectively.

RESULTS

Euthymic patients with MDD showed deficits in all tests related to attentional and executive functions compared to healthy controls. The patient groups did not differ with regard to attentional performance. Executive functions in severe depressives were more impaired than in mild depressives.

LIMITATIONS

Differing performances of the patient groups in the subtests of the executive test battery (BADS) can only be interpreted to a limited extent.

CONCLUSIONS

The results support the assumption that deficits in attention and executive functions in MDD show an increase in trait character and executive function during chronic course. Implications for differential diagnosis and cognitive psychotherapy are discussed.

The effects of nicotine on attention, information processing, and short-term memory in patients with dementia of the Alzheimer type

Nicotine in patients with dementia of the Alzheimer type (DAT) produced a significant and marked improvement in discriminative sensitivity and reaction times on a computerised test of attention and information processing. Nicotine also improved the ability of DAT patients to detect a flickering light in a critical flicker fusion test. These results suggest that nicotine may be acting on cortical mechanisms involved in visual perception and attention, and support the hypothesis that acetylcholine transmission modulates vigilance and discrimination. Nicotine may therefore be of some value in treating deficits in attention and information processing in DAT patients.

Estradiol enhances learning and memory in a spatial memory task and effects levels of monoaminergic neurotransmitters

The effects of chronic estrogen treatment on radial arm maze performance and on levels of central monoaminergic and amino acid neurotransmitters were examined in ovariectomized (Ovx) rats. In an eight arms baited paradigm, choice accuracy was enhanced following 12 days but not 3 days of treatment. In addition, performance during acquisition of the eight arms baited maze task was better in estrogen-treated Ovx rats than in Ovx rats. Performance of treated rats was also enhanced in win-shift trials conducted 12 days postestrogen treatment. Working, reference, and working-reference memory was examined when four of the eight arms were baited, and only working memory was improved by estrogen and only after long-term treatment. Activity of Ovx rats on an open field, crossings and rearings, was increased at 5 but not at 35 days following estrogen treatment. In medial prefrontal cortex, levels of NE, DA, and 5-HT were decreased but glutamate and GABA levels were not affected following chronic estrogen treatment. Basal forebrain nuclei also showed changes in monoamines following estrogen. Hippocampal subfields showed no effects of estrogen treatment on monoaminergic or amino acid transmitters. Levels of GABA were increased in the vertical diagonal bands following chronic estrogen. Results show that estrogen enhances learning/memory on a task utilizing spatial memory. Effects in Ovx rats appear to require the chronic (several days) presence of estrogen. Changes in activity of both monoaminergic and amino acid transmitters in the frontal cortex and basal forebrain may contribute to enhancing effects of estrogen on learning/memory.

A mechanistic account of striatal dopamine function in human cognition: Psychopharmacological studies with cabergoline and haloperidol

The authors test a neurocomputational model of dopamine function in cognition by administering to healthy participants low doses of D2 agents cabergoline and haloperidol. The model suggests that DA dynamically modulates the balance of Go and No-Go basal ganglia pathways during cognitive learning and performance. Cabergoline impaired, while haloperidol enhanced, Go learning from positive reinforcement, consistent with presynaptic drug effects. Cabergoline also caused an overall bias toward Go responding, consistent with postsynaptic action. These same effects extended to working memory and attentional domains, supporting the idea that the basal ganglia/dopamine system modulates the updating of prefrontal representations. Drug effects interacted with baseline working memory span in all tasks. Taken together, the results support a unified account of the role of dopamine in modulating cognitive processes that depend on the basal ganglia.

Effects of caffeine, sleep loss, and stress on cognitive performance and mood during U.S. Navy SEAL training. Sea-Air-Land

RATIONALE

When humans are acutely exposed to multiple stressors, cognitive performance is substantially degraded. Few practical strategies are available to sustain performance under such conditions.

OBJECTIVE

This study examined whether moderate doses of caffeine would reduce adverse effects of sleep deprivation and exposure to severe environmental and operational stress on cognitive performance.

METHODS

Volunteers were 68 U.S. Navy Sea-Air-Land (SEAL) trainees, randomly assigned to receive either 100, 200, or 300 mg caffeine or placebo in capsule form after 72 h of sleep deprivation and continuous exposure to other stressors. Cognitive tests administered included scanning visual vigilance, four-choice visual reaction time, a matching-to-sample working memory task and a repeated acquisition test of motor learning and memory. Mood state, marksmanship, and saliva caffeine were also assessed. Testing was conducted 1 and 8 h after treatment.

RESULTS

Sleep deprivation and environmental stress adversely affected performance and mood. Caffeine, in a dose-dependent manner, mitigated many adverse effects of exposure to multiple stressors. Caffeine (200 and 300 mg) significantly improved visual vigilance, choice reaction time, repeated acquisition, self-reported fatigue and sleepiness with the greatest effects on tests of vigilance, reaction time, and alertness. Marksmanship, a task that requires fine motor coordination and steadiness, was not affected by caffeine. The greatest effects of caffeine were present 1 h post-administration, but significant effects persisted for 8 h.

CONCLUSIONS

Even in the most adverse circumstances, moderate doses of caffeine can improve cognitive function, including vigilance, learning, memory, and mood state. When cognitive performance is critical and must be maintained during exposure to severe stress, administration of caffeine may provide a significant advantage. A dose of 200 mg appears to be optimal under such conditions.

Caffeine protects Alzheimer's mice against cognitive impairment and reduces brain beta-amyloid production

A recent epidemiological study suggested that higher caffeine intake over decades reduces the risk of Alzheimer's disease (AD). The present study sought to determine any long-term protective effects of dietary caffeine intake in a controlled longitudinal study involving AD transgenic mice. Caffeine (an adenosine receptor antagonist) was added to the drinking water of amyloid precursor protein, Swedish mutation (APPsw) transgenic (Tg) mice between 4 and 9 months of age, with behavioral testing done during the final 6 weeks of treatment. The average daily intake of caffeine per mouse (1.5 mg) was the human equivalent of 500 mg caffeine, the amount typically found in five cups of coffee per day. Across multiple cognitive tasks of spatial learning/reference memory, working memory, and recognition/identification, Tg mice given caffeine performed significantly better than Tg control mice and similar to non-transgenic controls. In both behaviorally-tested and aged Tg mice, long-term caffeine administration resulted in lower hippocampal beta-amyloid (Abeta) levels. Expression of both Presenilin 1 (PS1) and beta-secretase (BACE) was reduced in caffeine-treated Tg mice, indicating decreased Abeta production as a likely mechanism of caffeine's cognitive protection. The ability of caffeine to reduce Abeta production was confirmed in SweAPP N2a neuronal cultures, wherein concentration-dependent decreases in both Abeta1-40 and Abeta1-42 were observed. Although adenosine A(1) or A(2A) receptor densities in cortex or hippocampus were not affected by caffeine treatment, brain adenosine levels in Tg mice were restored back to normal by dietary caffeine and could be involved in the cognitive protection provided by caffeine. Our data demonstrate that moderate daily intake of caffeine may delay or reduce the risk of AD.

Initial phase 2 trial of a nicotinic agonist in schizophrenia

OBJECTIVE

Nicotinic acetylcholine receptors are possible therapeutic targets for schizophrenia, as shown by neurobiological and molecular evidence for deficiencies in expression of alpha(7)-nicotinic receptors. Patients' heavy smoking suggests attempted self-medication through this mechanism. The agent 3-(2,4-dimethoxybenzylidene) anabaseine (DMXB-A) is a partial alpha(7)-nicotinic agonist and can be taken orally. A phase 1 trial showed evidence for cognitive enhancement in schizophrenia.

METHOD

Thirty-one subjects with schizophrenia received DMXB-A at two different doses and placebo for periods of 4 weeks in a three-arm, two-site, double-blind, crossover phase 2 trial. The MATRICS Consensus Cognitive Battery assessed cognitive effects, and the Scale for the Assessment of Negative Symptoms (SANS) and Brief Psychiatric Rating Scale (BPRS) assessed clinical effects. Subjects continued their current antipsychotic drug during the trial and were nonsmokers.

RESULTS

There were no significant differences in the MATRICS cognitive measures between DMXB-A and placebo over the three treatment arms, but the patients experienced significant improvement at the higher DMXB-A dose on the SANS total score and nearly significant improvement on the BPRS total score. Improvement was most notable on the SANS anhedonia and alogia subscales. Examination of the first treatment arm showed effects of DMXB-A on the attention/vigilance and working memory MATRICS domains, compared to baseline. Five subjects developed mild tremor, and nearly half had mild nausea while taking DMXB-A.

CONCLUSION

DMXB-A, a nicotinic agonist that activates alpha(7)-nicotinic receptors, improved clinical ratings of negative symptoms that are generally resistant to treatment with dopamine antagonist antipsychotic drugs. The clinical utility of this treatment is not yet determined.

Effects of acute subcutaneous nicotine on attention, information processing and short-term memory in Alzheimer's disease

This single-blind, placebo controlled study reports on the effects of administering three acute doses of nicotine (0.4, 0.6 and 0.8 mg) subcutaneously to a group of Alzheimer's disease (DAT) patients (n = 22), young adult controls (n = 24), and normal aged controls (n = 24). The study extends our previous findings obtained using smaller groups of subjects. Drug effects were examined on three computerised tests: the first measuring rapid visual information processing, sustained visual attention and reaction time (RVIP task); a delayed response matching to location-order task measuring sustained visual attention and visual short-term memory (DRMLO task); and a finger tapping test measuring simple reaction time (FT task). The critical flicker fusion test (CFF) was used as a measure of perception and the WAIS digit span forwards (DS), of auditory short-term memory. Tests were graded in difficulty, titrated to avoid floor and ceiling effects so that meaningful, direct comparisons between groups could be made. Nicotine significantly improved sustained visual attention (in both RVIP and DRMLO tasks), reaction time (in both FT and RVIP tasks), and perception (CFF task--both ascending and descending thresholds). Nicotine administration did not improve auditory and visual short-term memory. There were no consistent, overall patterns of difference in performance between smokers and non-smokers in the control groups, or between males and females in any group. Despite the absence of change in memory functioning, these results demonstrate that DAT patients have significant perceptual and visual attentional deficits which are improved by nicotine administration.(ABSTRACT TRUNCATED AT 250 WORDS)

The amnesic action of benzodiazepines in man

A qualitative description of the amnesia produced by the benzodiazepines in man is presented. The benzodiazepines exert their greatest effects in tests of long-term episodic memory in which they cause a dose-related impairment in the acquisition of new information, do not appear to affect retention and may facilitate retrieval. Benzodiazepines do not appear to impair semantic memory or the acquisition of skills. Although state-dependent learning may be observed with benzodiazepine treatment it is a small effect and cannot account for most of the observed impairments. The amnesia appears to be characteristic of all benzodiazepines and may be related to the sedative action of these compounds but evidence on the latter point is inconclusive. The importance of the amnesic action in a population of clinically anxious outpatients taking benzodiazepines over an extended period remains to be investigated. The benzodiazepines may provide the cognitive psychologist with a useful tool to investigate the mechanisms of normal memory.

Dopaminergic modulation of high-level cognition in Parkinson's disease: the role of the prefrontal cortex revealed by PET

This study examined the effects of L-dopa medication in patients with Parkinson's disease on cortical and subcortical blood flow changes during two tasks known to involve frontostriatal circuitry. Eleven patients with Parkinson's disease were scanned on two occasions, one ON L-dopa medication and one OFF L-dopa medication, during performance of the Tower of London planning task and a related test that emphasized aspects of spatial working memory. L-dopa-induced decreases were observed in the right dorsolateral prefrontal cortex during performance of both the planning and the spatial working memory tasks compared with the visuomotor control task. Conversely, L-dopa-induced blood flow increases were observed in the right occipital lobe during the memory task relative to the control task. Data from age-matched healthy volunteers demonstrated that L-dopa effectively normalized blood flow in these regions in the patient group. Moreover, a significant correlation was found between L-dopa-induced, planning related blood flow decreases in the right dorsolateral prefrontal cortex and L-dopa-induced changes in performance on the planning task. These data suggest that L-dopa ameliorates high-level cognitive deficits in Parkinson's disease by inducing relative blood flow changes in the right dorsolateral prefrontal cortex.

Air pollution impairs cognition, provokes depressive-like behaviors and alters hippocampal cytokine expression and morphology

Particulate matter air pollution is a pervasive global risk factor implicated in the genesis of pulmonary and cardiovascular disease. Although the effects of prolonged exposure to air pollution are well characterized with respect to pulmonary and cardiovascular function, comparatively little is known about the impact of particulate matter on affective and cognitive processes. The central nervous system may be adversely affected by activation of reactive oxygen species and pro-inflammatory pathways that accompany particulate matter pollution. Thus, we investigated whether long-term exposure to ambient fine airborne particulate matter (<2.5 μm (PM(2.5))) affects cognition, affective responses, hippocampal inflammatory cytokines and neuronal morphology. Male mice were exposed to either PM(2.5) or filtered air (FA) for 10 months. PM(2.5) mice displayed more depressive-like responses and impairments in spatial learning and memory as compared with mice exposed to FA. Hippocampal pro-inflammatory cytokine expression was elevated among PM(2.5) mice. Apical dendritic spine density and dendritic branching were decreased in the hippocampal CA1 and CA3 regions, respectively, of PM(2.5) mice. Taken together, these data suggest that long-term exposure to particulate air pollution levels typical of exposure in major cities around the globe can alter affective responses and impair cognition.