Effort-based decision making and motivational deficits in stroke patients

Motivational deficits in patients recovering from stroke are common and can reduce active participation in rehabilitation and thereby impede functional recovery. We investigated whether stroke patients with clinically reduced drive, initiation, and endurance during functional rehabilitative training (n = 30) display systematic alterations in effort-based decision making compared to age, sex, and severity-matched stroke patients (n = 30) whose drive appeared unaffected. Notably, the two groups did not differ in self-reported ratings of apathy and depression. However, on an effort-based decision-making task, stroke patients with clinically apparent drive impairment showed intact willingness to accept effort for reward, but were more likely to fail to execute the required effort compared to patients without apparent drive impairments. In other words, the decision behavioural assessment revealed that stroke patients that displayed reduced drive, initiation, and endurance during inpatient neurorehabilitation failed to persist in goal-directed effort production, even over very short periods. These findings indicate that reduced drive during rehabilitative therapy in post-stroke patients is not due to a diminished motivation to invest physical effort, but instead is related to a reduced persistence with effortful behaviour.

Stimulus awareness is necessary for both instrumental learning and instrumental responding to previously learned stimuli

Instrumental conditioning is a crucial part of adaptive behaviour, allowing agents to selectively interact with stimuli in their environment. Recent evidence suggests that instrumental conditioning cannot proceed without stimulus awareness. However, whether accurate unconscious instrumental responding can emerge from consciously acquired knowledge of the stimulus-action-outcome contingencies is unknown. We studied this question using instrumental trace conditioning, where participants learned to make approach/avoid decisions in two within-subject modes: conscious (stimuli in plain view) and unconscious (visually masked). Both tasks were followed by an unconscious-only instrumental performance task. We show that even when the contingencies are reliably learned in the conscious mode, participants fail to act upon them in the unconscious responding task. We also replicate the previous results that no instrumental learning occurs in the unconscious mode. Consequently, the absence of stimulus awareness not only precludes instrumental conditioning, but also precludes any kind of instrumental responding to already known stimuli. This suggests that instrumental behaviour is entirely supported by conscious awareness of the world, and corroborates the proposals that consciousness may be necessary for adaptive behaviours requiring selective action.

Tonic and phasic transcutaneous auricular vagus nerve stimulation (taVNS) both evoke rapid and transient pupil dilation

BACKGROUND

Transcutaneous auricular vagus nerve stimulation (tVNS or taVNS) is a non-invasive method of electrical stimulation of the afferent pathway of the vagus nerve, suggested to drive changes in putative physiological markers of noradrenergic activity, including pupil dilation.

OBJECTIVE

However, it is unknown whether different taVNS modes can map onto the phasic and tonic modes of noradrenergic activity. The effects of taVNS on pupil dilation in humans are inconsistent, largely due to differences in stimulation protocols. Here, we attempted to address these issues.

METHODS

We investigated pupil dilation under phasic (1 s) and tonic (30 s) taVNS, in a pre-registered, single-blind, sham-controlled, within-subject cross-over design, in the absence of a behavioural task.

RESULTS

Phasic taVNS induced a rapid increase in pupil size over baseline, significantly greater than under sham stimulation, which rapidly declined after stimulation offset. Tonic taVNS induced a similarly rapid (and larger than sham) increase in pupil size over baseline, returning to baseline within 5 s, despite the ongoing stimulation. Thus, both active and sham tonic modes closely resembled the phasic effect. There were no differences in tonic baseline pupil size, and no sustained effects of stimulation on tonic baseline pupil size.

CONCLUSIONS

These results suggest that both phasic- and tonic-like taVNS under the standard stimulation parameters may modulate primarily the phasic mode of noradrenergic activity, as indexed by evoked pupil dilation, over and above somatosensory effects. This result sheds light on the temporal profile of phasic and tonic stimulation, with implications for their applicability in further research.

Auditory inputs modulate intrinsic neuronal timescales during sleep

Functional magnetic resonance imaging (fMRI) studies have demonstrated that intrinsic neuronal timescales (INT) undergo modulation by external stimulation during consciousness. It remains unclear if INT keep the ability for significant stimulus-induced modulation during primary unconscious states, such as sleep. This fMRI analysis addresses this question via a dataset that comprises an awake resting-state plus rest and stimulus states during sleep. We analyzed INT measured via temporal autocorrelation supported by median frequency (MF) in the frequency-domain. Our results were replicated using a biophysical model. There were two main findings: (1) INT prolonged while MF decreased from the awake resting-state to the N2 resting-state, and (2) INT shortened while MF increased during the auditory stimulus in sleep. The biophysical model supported these results by demonstrating prolonged INT in slowed neuronal populations that simulate the sleep resting-state compared to an awake state. Conversely, under sine wave input simulating the stimulus state during sleep, the model's regions yielded shortened INT that returned to the awake resting-state level. Our results highlight that INT preserve reactivity to stimuli in states of unconsciousness like sleep, enhancing our understanding of unconscious brain dynamics and their reactivity to stimuli.

Intermediately synchronised brain states optimise trade-off between subject specificity and predictive capacity

Functional connectivity (FC) refers to the statistical dependencies between activity of distinct brain areas. To study temporal fluctuations in FC within the duration of a functional magnetic resonance imaging (fMRI) scanning session, researchers have proposed the computation of an edge time series (ETS) and their derivatives. Evidence suggests that FC is driven by a few time points of high-amplitude co-fluctuation (HACF) in the ETS, which may also contribute disproportionately to interindividual differences. However, it remains unclear to what degree different time points actually contribute to brain-behaviour associations. Here, we systematically evaluate this question by assessing the predictive utility of FC estimates at different levels of co-fluctuation using machine learning (ML) approaches. We demonstrate that time points of lower and intermediate co-fluctuation levels provide overall highest subject specificity as well as highest predictive capacity of individual-level phenotypes.

Motor cortical signals reflecting decision making and action preparation

Decision making often requires accumulating evidence in favour of a particular option. When choices are expressed with a motor response, these actions are preceded by reductions in the power of oscillations in the alpha and beta range in motor cortices. For unimanual movements, these reductions are greater over the hemisphere contralateral to the response side. Such lateralizations are hypothesized to be an online index of the neural state of decisions as they develop over time of processing. In contrast, the lateralized readiness potential (LRP) is considered to selectively activate a response and appears shortly before the motor output. We investigated to what extent these neural signals reflect integration of decision evidence or more motor-related action preparation. Using two different experiments, we found that lateralization of alpha and beta power (APL and BPL, respectively) rapidly emerged after stimulus presentation, even when making an overt response was not yet possible. In contrast, we show that even after prolonged stimulus presentation, no LRP was present. Instead, the LRP emerged only after an imperative cue, prompting participants to indicate their choice. Furthermore, we could show that variations in sensory evidence strength modulate APL and BPL onset times, suggesting that integration of evidence is represented in these motor cortical signals. We conclude that APL and BPL reflect higher cognitive processes rather than pure action preparation, whereas LRP is more closely tied to motor performance. APL and BPL potentially encode decision information in motor areas serving the later preparation of overt decision output.

Reinstatement of Cortical Outcome Representations during Higher-Order Learning

Naturalistic learning scenarios are characterized by infrequent experience of external feedback to guide behavior. Higher-order learning mechanisms like second-order conditioning (SOC) may allow stimuli that were never experienced together with reinforcement to acquire motivational value. Despite its explanatory potential for real-world learning, surprisingly little is known about the neural mechanism underlying such associative transfer of value in SOC. Here, we used multivariate cross-session, cross-modality searchlight classification on functional magnetic resonance imaging data obtained from humans during SOC. We show that visual first-order conditioned stimuli (CS) reinstate cortical patterns representing previously paired gustatory outcomes in the lateral orbitofrontal cortex (OFC). During SOC, this OFC region showed increased functional covariation with amygdala, where neural pattern similarity between second-order CS and outcomes increased from early to late stages of SOC. Our data suggest a mechanism by which motivational value is conferred to stimuli that were never paired with reinforcement.

A causal role of estradiol in human reinforcement learning

The sex hormone estradiol is hypothesized to play a key role in human cognition, and reward processing specifically, via increased dopamine D1-receptor signalling. However, the effect of estradiol on reward processing in men has never been established. To fill this gap, we performed a double-blind placebo-controlled study in which men (N = 100) received either a single dose of estradiol (2 mg) or a placebo. Subjects performed a probabilistic reinforcement learning task where they had to choose between two options with varying reward probabilities to maximize monetary reward. Results showed that estradiol administration increased reward sensitivity compared to placebo. This effect was observed in subjects' choices, how much weight they assigned to their previous choices, and subjective reports about the reward probabilities. Furthermore, effects of estradiol were moderated by reward sensitivity, as measured through the BIS/BAS questionnaire. Using reinforcement learning models, we found that behavioral effects of estradiol were reflected in increased learning rates. These results demonstrate a causal role of estradiol within the framework of reinforcement learning, by enhancing reward sensitivity and learning. Furthermore, they provide preliminary evidence for dopamine-related genetic variants moderating the effect of estradiol on reward processing.

Not giving up: Testosterone promotes persistence against a stronger opponent

Recent research suggests that when we lack a sense of control, we are prone to motivational failures and early quitting in competitions. Testosterone, on the other hand, is thought to boost competitiveness. Here we investigate the interaction between these factors, testing the testosterone's potential to enhance persistence in a competition against a stronger opponent, depending on experimentally manipulated perceived control. Healthy participants were administered a single dose of testosterone or placebo. They first underwent a task designed to either induce low or high perceived control and then entered a costly competition against a progressively stronger opponent that they could quit at any time. In the placebo group, men with low perceived control quitted twice as early as those with high perceived control. Testosterone countered this effect, making individuals with low control persist in the competition for as long as those with high perceived control, and did so also despite raising participants' explicit awareness of the opponents' advantage. This psychoendocrinological effect was not modulated by basal cortisol levels, CAG repeat polymorphism of the androgen receptor gene, or trait dominance. Our results provide the first causal evidence that testosterone promotes competitive persistence in humans and demonstrate that this effect depends on the psychological state elicited prior to the competition, broadening our understanding of the complex relationships between testosterone and social behaviors.

Dissociable roles of cortical excitation-inhibition balance during patch-leaving versus value-guided decisions

In a dynamic world, it is essential to decide when to leave an exploited resource. Such patch-leaving decisions involve balancing the cost of moving against the gain expected from the alternative patch. This contrasts with value-guided decisions that typically involve maximizing reward by selecting the current best option. Patterns of neuronal activity pertaining to patch-leaving decisions have been reported in dorsal anterior cingulate cortex (dACC), whereas competition via mutual inhibition in ventromedial prefrontal cortex (vmPFC) is thought to underlie value-guided choice. Here, we show that the balance between cortical excitation and inhibition (E/I balance), measured by the ratio of GABA and glutamate concentrations, plays a dissociable role for the two kinds of decisions. Patch-leaving decision behaviour relates to E/I balance in dACC. In contrast, value-guided decision-making relates to E/I balance in vmPFC. These results support mechanistic accounts of value-guided choice and provide evidence for a role of dACC E/I balance in patch-leaving decisions.

Dorsolateral Prefrontal Cortex Enables Updating of Established Memories

Updating established memories in light of new information is fundamental for memory to guide future behavior. However, little is known about the brain mechanisms by which existing memories can be updated. Here, we combined functional magnetic resonance imaging and multivariate representational similarity analysis to elucidate the neural mechanisms underlying the updating of consolidated memories. To this end, participants first learned face-city name pairs. Twenty-four hours later, while lying in the MRI scanner, participants were required to update some of these associations, but not others, and to encode entirely new pairs. Updating success was tested again 24 h later. Our results showed increased activity of the dorsolateral prefrontal cortex (dlPFC) specifically during the updating of existing associations that was significantly stronger than when simple retrieval or new encoding was required. The updating-related activity of the dlPFC and its functional connectivity with the hippocampus were directly linked to updating success. Furthermore, neural similarity for updated items was markedly higher in the dlPFC and this increase in dlPFC neural similarity distinguished individuals with high updating performance from those with low updating performance. Together, these findings suggest a key role of the dlPFC, presumably in interaction with the hippocampus, in the updating of established memories.

Decisions bias future choices by modifying hippocampal associative memories

Decision-making is guided by memories of option values. However, retrieving items from memory renders them malleable. Here, we show that merely retrieving values from memory and making a choice between options is sufficient both to induce changes to stimulus-reward associations in the hippocampus and to bias future decision-making. After allowing participants to make repeated choices between reward-conditioned stimuli, in the absence of any outcome, we observe that participants prefer stimuli they have previously chosen, and neglect previously unchosen stimuli, over otherwise identical-valued options. Using functional brain imaging, we show that decisions induce changes to hippocampal representations of stimulus-outcome associations. These changes are correlated with future decision biases. Our results indicate that choice-induced preference changes are partially driven by choice-induced modification of memory representations and suggest that merely making a choice - even without experiencing any outcomes - induces associative plasticity.

Learning relative values in the striatum induces violations of normative decision making

To decide optimally between available options, organisms need to learn the values associated with these options. Reinforcement learning models offer a powerful explanation of how these values are learnt from experience. However, human choices often violate normative principles. We suggest that seemingly counterintuitive decisions may arise as a natural consequence of the learning mechanisms deployed by humans. Here, using fMRI and a novel behavioural task, we show that, when suddenly switched to novel choice contexts, participants' choices are incongruent with values learnt by standard learning algorithms. Instead, behaviour is compatible with the decisions of an agent learning how good an option is relative to an option with which it had previously been paired. Striatal activity exhibits the characteristics of a prediction error used to update such relative option values. Our data suggest that choices can be biased by a tendency to learn option values with reference to the available alternatives.

Reward-Guided Learning with and without Causal Attribution

When an organism receives a reward, it is crucial to know which of many candidate actions caused this reward. However, recent work suggests that learning is possible even when this most fundamental assumption is not met. We used novel reward-guided learning paradigms in two fMRI studies to show that humans deploy separable learning mechanisms that operate in parallel. While behavior was dominated by precise contingent learning, it also revealed hallmarks of noncontingent learning strategies. These learning mechanisms were separable behaviorally and neurally. Lateral orbitofrontal cortex supported contingent learning and reflected contingencies between outcomes and their causal choices. Amygdala responses around reward times related to statistical patterns of learning. Time-based heuristic mechanisms were related to activity in sensorimotor corticostriatal circuitry. Our data point to the existence of several learning mechanisms in the human brain, of which only one relies on applying known rules about the causal structure of the task.

Impulsivity and predictive control are associated with suboptimal action-selection and action-value learning in regular gamblers

Heightened impulsivity and cognitive biases are risk factors for gambling problems. However, little is known about precisely how these factors increase the risks of gambling-related harm in vulnerable individuals. Here, we modelled the behaviour of eighty-seven community-recruited regular, but not clinically problematic, gamblers during a binary-choice reinforcement-learning game, to characterise the relationships between impulsivity, cognitive biases, and the capacity to make optimal action selections and learn about action-values. Impulsive gamblers showed diminished use of an optimal (Bayesian-derived) probability estimate when selecting between candidate actions, and showed slower learning rates and enhanced non-linear probability weighting while learning action values. Critically, gamblers who believed that it is possible to predict winning outcomes (as 'predictive control') failed to use the game's reinforcement history to guide their action selections. Extensive evidence attests to the ease with which gamblers can erroneously perceive structure in the reinforcement history of games when there is none. Our findings demonstrate that the generic and specific risk factors of impulsivity and cognitive biases can interfere with the capacity of some gamblers to utilise structure when it is available in the reinforcement history of games, potentially increasing their risks of sustaining gambling-related harms.

Acetylcholine mediates behavioral and neural post-error control

Humans often commit errors when they are distracted by irrelevant information and no longer focus on what is relevant to the task at hand. Adjustments following errors are essential for optimizing goal achievement. The posterior medial frontal cortex (pMFC), a key area for monitoring errors, has been shown to trigger such post-error adjustments by modulating activity in visual cortical areas. However, the mechanisms by which pMFC controls sensory cortices are unknown. We provide evidence for a mechanism based on pMFC-induced recruitment of cholinergic projections to task-relevant sensory areas. Using fMRI in healthy volunteers, we found that error-related pMFC activity predicted subsequent adjustments in task-relevant visual brain areas. In particular, following an error, activity increased in those visual cortical areas involved in processing task-relevant stimulus features, whereas activity decreased in areas representing irrelevant, distracting features. Following treatment with the muscarinic acetylcholine receptor antagonist biperiden, activity in visual areas was no longer under control of error-related pMFC activity. This was paralleled by abolished post-error behavioral adjustments under biperiden. Our results reveal a prominent role of acetylcholine in cognitive control that has not been recognized thus far. Regaining optimal performance after errors critically depends on top-down control of perception driven by the pMFC and mediated by acetylcholine. This may explain the lack of adaptivity in conditions with reduced availability of cortical acetylcholine, such as Alzheimer's disease.

Dual serotonergic signals: a key to understanding paradoxical effects?

Neuroscientists have been puzzled by the fact that acute administration of a selective serotonin reuptake inhibitor (SSRI) produces results that are, at times, compatible with either decreases or increases in serotonergic neurotransmission. Furthermore, the underlying cause of the delayed onset of antidepressant effects of SSRI treatment has remained obscure. It has recently been reported that serotonergic raphe neurons co-release glutamate and that serotonergic and glutamatergic components constitute a dual signal with behaviorally distinct effects. We discuss the consequences of these novel findings and propose a framework for understanding the controversial effects of acute SSRI administration. Furthermore, we suggest that the delayed remedial onset of SSRI treatment could be explained by an initial reduction of the glutamatergic component of the dual serotonergic signal.

Dissociable contributions of ventromedial prefrontal and posterior parietal cortex to value-guided choice

Two long-standing traditions have highlighted cortical decision mechanisms in the parietal and prefrontal cortices of primates, but it has not been clear how these processes differ, or when each cortical region may influence behaviour. Recent data from ventromedial prefrontal cortex (vmPFC) and posterior parietal cortex (PPC) have suggested one possible axis on which the two decision processes might be delineated. Fast decisions may be resolved primarily by parietal mechanisms, whereas decisions made without time pressure may rely on prefrontal mechanisms. Here, we report direct evidence for such dissociation. During decisions under time pressure, a value comparison process was evident in PPC, but not in vmPFC. Value-related activity was still found in vmPFC under time pressure. However, vmPFC represented overall input value rather than compared output value. In contrast, when decisions were made without time pressure, vmPFC transitioned to encode a value comparison while value-related parameters were entirely absent from PPC. Furthermore, under time pressure, decision performance was primarily governed by PPC, while it was dominated by vmPFC at longer decision times. These data demonstrate that parallel cortical mechanisms may resolve the same choices in differing circumstances, and offer an explanation of the diverse neural signals reported in vmPFC and PPC during value-guided choice.

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Value parameter represented in ventromedial PFC depends on available decision time.

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Under time pressure, vmPFC activity represents overall input value.

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Without time pressure, vmPFC transitions to encode a value comparison.

Neurophysiology of performance monitoring and adaptive behavior

Successful goal-directed behavior requires not only correct action selection, planning, and execution but also the ability to flexibly adapt behavior when performance problems occur or the environment changes. A prerequisite for determining the necessity, type, and magnitude of adjustments is to continuously monitor the course and outcome of one's actions. Feedback-control loops correcting deviations from intended states constitute a basic functional principle of adaptation at all levels of the nervous system. Here, we review the neurophysiology of evaluating action course and outcome with respect to their valence, i.e., reward and punishment, and initiating short- and long-term adaptations, learning, and decisions. Based on studies in humans and other mammals, we outline the physiological principles of performance monitoring and subsequent cognitive, motivational, autonomic, and behavioral adaptation and link them to the underlying neuroanatomy, neurochemistry, psychological theories, and computational models. We provide an overview of invasive and noninvasive systemic measures, such as electrophysiological, neuroimaging, and lesion data. We describe how a wide network of brain areas encompassing frontal cortices, basal ganglia, thalamus, and monoaminergic brain stem nuclei detects and evaluates deviations of actual from predicted states indicating changed action costs or outcomes. This information is used to learn and update stimulus and action values, guide action selection, and recruit adaptive mechanisms that compensate errors and optimize goal achievement.

A mechanism for value-guided choice based on the excitation-inhibition balance in prefrontal cortex

Although the ventromedial prefrontal cortex (vmPFC) has long been implicated in reward-guided decision making, its exact role in this process has remained an unresolved issue. Here we show that, in accordance with models of decision making, vmPFC concentrations of GABA and glutamate in human volunteers predict both behavioral performance and the dynamics of a neural value comparison signal. These data provide evidence for a neural competition mechanism in vmPFC that supports value-guided choice.

Neurokinin3 receptor modulation of the behavioral and neurochemical effects of cocaine in rats and monkeys

Neurokinin3 (NK3) receptors and their endogenous ligands (e.g. the neuropeptide substance P and its C-terminal fragment) have been implicated in psychomotor activity and reinforcement mechanisms. We review here recent findings on the involvement of NK3 receptors in the behavioral and neurochemical effects of cocaine. Although NK3 receptors can modulate dopamine (DA) activity in the brain, recent results suggest that this modulation does not occur during spontaneous behavioral activity. However, NK3 receptors play a role in the regulation of cocaine-induced DA responses in the nucleus accumbens core and shell subregions. NK3 receptor agonism as well as antagonism potentiate cocaine's effects on nucleus accumbens DA subregions specifically, and modulate the acute behavioral effects of cocaine in rats and non-human primates (Callithrix penicillata). However, conditioned place preference studies in rats have, so far, failed to provide evidence for an involvement of NK3 receptors in the reinforcing effects of cocaine.

Neurokinin 3 receptor activation potentiates the psychomotor and nucleus accumbens dopamine response to cocaine, but not its place conditioning effects

Neurokinin(3) receptors (NK(3)-Rs) have been implicated in psychomotor activity and reinforcement mechanisms. Recently, we showed that NK(3)-R antagonism blocked the psychostimulant properties of cocaine both in rats and in primates. Here, using in vivo microdialysis in the nucleus accumbens (NAc) of freely moving rats, we investigated the effect of the NK(3)-R agonist senktide (0.2 and 0.4 mg/kg s.c.) on the cocaine-evoked increase in dopamine. Cocaine (10 mg/kg i.p.) increased dopamine levels to 404 and 480% of baseline in the core and shell of the NAc, respectively. Pretreatment with senktide at a dose of 0.2 mg/kg potentiated this effect to 666 (core) and 869% (shell) of baseline, without having any effect on dopamine when given alone. Behavioural measurements revealed that 0.2 mg/kg senktide also potentiated the cocaine-induced increase in horizontal and vertical activity. Senktide alone induced a short-lasting increase in activity that was not accompanied by any alterations of the neurochemical parameters. In conditioned place preference (CPP) experiments, senktide pretreatment did not alter CPP induced by cocaine (5 and 10 mg/kg i.p.), and had no effect when given alone. Likewise, cocaine-conditioned locomotor activity was not affected by the NK(3)-R agonist. However, as in the microdialysis studies, cocaine-induced (5 and 10 mg/kg i.p.) hyperactivity was potentiated by senktide, and there was evidence for a facilitation of sensitization to the hyperlocomotor effects of cocaine by senktide. These data provide evidence that NK(3)-Rs are involved in the control of the hyperlocomotor and NAc DA response to cocaine, but not in cocaine-induced CPP.

Neurokinin receptor antagonism attenuates cocaine's behavioural activating effects yet potentiates its dopamine-enhancing action in the nucleus accumbens core

Several lines of evidence indicate a role for neurokinin3 receptors (NK3-Rs) in behavioural activation and mechanisms governing reinforcement processes. In this study we investigated the effect of pretreatment with the NK3-R antagonist, SR142801, (0.2 and 2.0 mg/kg) on the cocaine-induced (10.0 mg/kg i.p.) increase in extracellular dopaminergic activity in the nucleus accumbens (NAc). In vivo microdialysis in the NAc of freely moving rats showed that cocaine increased concentrations of dopamine (DA) to approximately 350% in the core and approximately 450% in the shell. Pre-treatment with SR142801 significantly potentiated this effect in the core (to approximately 550%), whereas this effect was not found in the shell. We also investigated the effects of NK3-Rs antagonism on cocaine-induced hyperactivity and conditioned place preference. SR142801 blocked the hyperactivity, but neither the conditioned place preference nor the conditioned locomotor activity induced by cocaine, although there was a slight tendency towards a reduced place preference. When given alone, SR142801 had no effects on behaviour or extracellular dopamine concentrations in any of the structures investigated. These data provide evidence for a contribution of NK3-Rs in the acute behavioural and neurochemical effects of cocaine, involving dopaminergic activity in the core of the nucleus accumbens.

Interaction of the tachykinin NK3 receptor agonist senktide with behavioral effects of cocaine in marmosets (Callithrix penicillata)

Brain neuropeptide transmitters of the tachykinin family are involved in the organization of many behaviors. However, little is known about their contribution to the behavioral effects of drugs of abuse. Recently, antagonism of the tachykinin NK3-receptor (NK3-R), one of the three tachykinin receptors in the brain, was shown to attenuate the acute and chronic behavioral effects of cocaine in rats and the acute effects in non-human primates. In order to expand these findings we investigated the effects of the NK3-R agonist, succinyl-[Asp6, Me-Phe8]SP(6-11) (senktide), on the acute behavioral effects of cocaine in marmoset monkeys (Callithrix penicillata) using a figure-eight maze procedure. Animals were pretreated with senktide (0, 0.1, 0.2, 0.4 mg/kg, s.c.), and received either a treatment with cocaine (10 mg/kg) or saline (i.p.). Cocaine increased locomotor activity and the duration of aerial scanning behavior, but reduced exploratory activity, bodycare activity, the frequency of aerial scanning, and terrestrial glance behavior. Senktide blocked the effects of cocaine on locomotor activity, but enhanced the cocaine effects on exploratory activity, aerial scanning frequency, and terrestrial glance behavior. Senktide alone did not significantly influence monkey behavior in this study. These data expand previous findings suggesting a complex role of the NK3-R in the acute behavioral effects of cocaine in non-human primates.

The tachykinin NK3 receptor antagonist SR142801 blocks the behavioral effects of cocaine in marmoset monkeys

Brain neuropeptide transmitters of the tachykinin family are involved in the organization of many behaviors. However, little is known about their contribution to the behavioral effects of drugs of abuse. Recently, the tachykinin NK3 receptor, one of the three tachykinin receptors in the brain, was shown to attenuate the acute and chronic behavioral effects of cocaine in rats. In order to test if these findings can be generalized to primates we investigated the role of the tachykinin NK3 receptor in the acute behavioral effects of cocaine in marmoset monkeys (Callithrix penicillata) using a figure-eight maze procedure. Animals were pretreated with the tachykinin NK3 receptor antagonist, (R)-(N)-[1-[3-[1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl]propyl]-4-phenylpiperidin-4-yl]-N-methylacetamide (SR142801; 0, 0.02, 0.2, 2.0 mg/kg, i.p.), and received either a treatment with cocaine (10 mg/kg, i.p) or saline (i.p.). Cocaine increased locomotor activity and aerial glance behavior, but reduced exploratory and bodycare activities, scent marking and terrestrial scanning behavior. A sensitivity analysis revealed that two responder types can be differentiated in relation to the occurrence of a hyperlocomotor response to cocaine. SR142801 blocked the actions of cocaine on several behaviors dose-dependently for each responder type, respectively. There was no effect of SR142801 alone on any behavior measured. These data suggest that the tachykinin NK3 receptor contributes to the individual behavioral response to cocaine in marmoset monkeys. Having no behavioral effects on its own, but blocking the cocaine effects, might suggest the tachykinin NK3 receptor antagonist, SR142801, as a potential treatment of cocaine addiction in humans.

Correlations between hypothalamus-pituitary-adrenal axis parameters depend on age and learning capacity

Glucocorticoid hormones are released after activation of the hypothalamus-pituitary-adrenal (HPA) axis and in the brain can modulate synaptic plasticity and memory formation. Clear individual differences in spatial learning and memory in the water maze allowed classification of groups of young (3 months) and aged (24 months) male Wistar rats as superior and inferior learners. We tested 1) whether measures of HPA activity are associated with cognitive functions and aging and 2) whether correlations of these measures depend on age and learning performance. Basal ACTH, but not corticosterone, was increased in aged rats, with the stress-induced ACTH response exaggerated in aged-inferior learners. Aged-superior learners had lower expression of glucocorticoid receptor and CRH mRNA in the parvocellular paraventricular nucleus of the hypothalamus compared with all other groups. Hippocampal mineralocorticoid receptor and glucocorticoid receptor mRNAs differed modestly between groups, but steroid receptor coactivator and heat-shock-protein 90 mRNAs were not different. Strikingly, correlations between HPA axis markers were dependent on grouping animals according to learning performance or age. CRH mRNA correlated with ACTH only in aged animals. Parvocellular arginine vasopressin mRNA was negatively correlated to basal corticosterone, except in aged-inferior learners. Corticosteroid receptor mRNA expression showed a number of correlations with other HPA axis regulators specifically in superior learners. In summary, the relationships between HPA axis markers differ for subgroups of animals. These distinct interdependencies may reflect adjusted set-points of the HPA axis, resulting in adaptation (or maladaptation) to the environment and, possibly, an age-independent determination of learning ability.

Aged and Adult Rats Compared in Acquisition and Extinction of Escape From the Water Maze: Focus on Individual Differences

Individual differences in water maze and open-field performance of aged and adult rats were compared in a cross-sectional study. Three- and 24-month-old rats were classified into superior, moderate, and inferior groups on the basis of escape latencies during hidden platform acquisition and were compared regarding water maze acquisition and extinction, and open-field behavior. Unexpectedly, subgroup differences were invariant across age: The inferior and superior maze learners differed in (a) thigmotactic swimming during water maze acquisition and extinction and (b) open-field rearings. Thus, although aging has a detrimental effect on water maze acquisition and extinction, the degree of impairment might be partly determined by individual novelty-induced rearing activity and thigmotactic swimming at adult ages.

Neurokinin-1 receptor antagonism by SR140333: enhanced in vivo ACh in the hippocampus and promnestic post-trial effects

Substance P (SP) has memory-promoting, reinforcing and anxiolytic-like effects when applied systemically or centrally. Such effects may be mediated by the neurokinin-1 (NK-1) receptor, since SP preferentially binds to this receptor. We measured the effects of a selective non-peptide NK-1 receptor antagonist, SR140333 (1, 3 and 9 mg/kg i.p.) on ACh levels in frontal cortex, amygdala and hippocampus by microdialysis and HPLC. Levels of ACh in the hippocampus increased dose-dependently immediately after treatment. The same doses of SR140333 given post-trial had minor facilitative effects on inhibitory avoidance learning and open-field habituation, but did not have reinforcing effects in a conditioned place preference (CPP) task. The selective action of NK-1 receptor antagonism on hippocampal ACh may be related to its positive influence on learning.

Cocaine-induced ???active immobility??? and its modulation by the serotonin1A receptor

'Active immobility' (AI) is an independent behaviour that can be characterized by behavioural immobility, an increased muscular rigidity and the sustaining of an unusual posture. In previous studies with cocaine we observed, concomitant with hyperlocomotion and increased rearing activity, an increase in AI in well-habituated animals, which may constitute another 'positive' acute effect of cocaine on behaviour. The contribution of the serotonergic (5-HT) system to AI is well established. However, little information exists about the contribution of particular 5-HT-receptor subtypes. In order to examine a possible role of the 5-HT1A receptor on this effect of cocaine, we systematically re-analysed four previous experiments in well-habituated animals and one in little-habituated animals, focusing on the acute behavioural effects of cocaine on AI. We found that, in well-habituated animals, cocaine at a medium dose (10 mg/kg, i.p.) induces AI behaviour, which, however, does not correlate with cocaine effects on locomotion, rearing or grooming behaviour. However, there was no effect of cocaine (1, 5 or 15 mg/kg, i.p.) on AI in little-habituated animals. The 5-HT1A-receptor antagonist, WAY 100635 [N-[2-(4-2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide trihydrochloride] (0.4 mg/kg, i.p.), potentiated cocaine-induced AI in well-habituated animals, while the 5-HT1A-receptor agonist, 8-OH-DPAT (0.2 mg/kg, i.p.), attenuated it. The local application of 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin] into the nucleus accumbens (0, 1, 10 micromol/l) or hippocampus (0, 0.1, 1, 10 micromol/l) modulated cocaine-induced AI in a complex way. These results showed that cocaine induces AI at a medium dose in well-habituated but not in little-habituated animals. The cocaine-induced AI in well-habituated animals can be potentiated by systemic 5-HT1A-receptor antagonism and attenuated by 5-HT1A-receptor agonism. Two experiments with local activation of postsynaptic 5-HT1A receptors revealed that both nucleus accumbens and hippocampal 5-HT1A-receptor populations are involved in the expression of cocaine-induced AI.

Cocaine increases serotonergic activity in the hippocampus and nucleus accumbens in vivo: 5-HT1a-receptor antagonism blocks behavioral but potentiates serotonergic activation

The hippocampus is an important mediator of learning and reinforcement, but its role in cocaine effects has received little attention. Neuronal activity in the hippocampus and the nucleus accumbens (Nac) depend on serotonergic (5-HT) transmission. Here we describe for the first time a cocaine-induced increase in 5-HT concentration in the hippocampus and the Nac parallel to behavioral activation. In addition, pretreatment with the 5-HT(1A)-receptor antagonist WAY 100635 blocked the behavioral activation after cocaine while potentiating the 5-HT increase in the hippocampus and the Nac. In vivo microdialysis was used in behaving rats to measure extracellular concentration of 5-HT in the hippocampus and the Nac. Four groups of animals received one of the following drug combinations: WAY 100635 (0.4 mg/kg) and cocaine (10 mg/kg), saline and cocaine (10 mg/kg), WAY 100635 (0.4 mg/kg) and saline, or saline and saline. The injections were administered i.p. and spaced 30 min apart. It was found that 1.) cocaine, at a dose that activates behavior, increases 5-HT levels in the hippocampus and in the Nac, and 2.) 5-HT(1A)-receptor antagonism can cause a dissociation of the hippocampal and Nac 5-HT activity from behavioral activation after cocaine. These results are discussed within the framework of the hippocampal-accumbens projection and its contribution to behavioral activity. They suggest that the hippocampus may have a role in mediating the behavioral and neurochemical effects of cocaine.

[Spontaneous perforation of the esophagus (Boerhaave syndrome)]

It is reported on 2 patients with spontaneous perforation of the oesophagus (Boerhaave's syndrome). The picture of the disease is rare. Possible causes, symptomatology, diagnosis, differential diagnosis and therapy are described. Severe thoracic pains, which in most cases appear after vomiting, are in the foreground. Evident for the disease is the escape of the contrast medium in esophagography. The lethality is 30%. Prerequisite for better results of the treatment is a rapid diagnosis and early surgical approach.

[Acute hemopericardium--a rare intraoperative complication of cardiac pacemaker therapy]

During the observation period from 1977 to 1985 in altogether 1,520 cardiac pacemaker operations 7 perforations of the myocardium with haemodynamic effect on the cardiac function were treated. In the light of the own experiences of the operative surroundings and the results the pericardiotomy is regarded as method of choice. If in the implantation of a cardiac pacemaker an acute deterioration of the general condition of the patient develops, one should at first think of the possibility of the tamponade of the pericardium. Only by active approach (pericardiotomy or puncture) the patient's life can be preserved.