An integrative theory of locus coeruleus-norepinephrine function: adaptive gain and optimal performance

Low arousal modulates visuospatial attention in three-dimensional virtual space

Clinical, experimental, and functional imaging studies suggest overlapping neuronal networks and functional interactions of alertness and visuospatial attention within the right hemisphere of the brain. To examine the interaction of arousal and visuospatial attention in peripersonal and extrapersonal virtual space, we tested 20 healthy male adults during 24 hr of sleep deprivation at four points during the night (9 p.m., 1 a.m., 5 a.m., and 9 a.m.). The main finding concerning covert orienting in a virtual environment is a highly significant slowing of reorientation toward the left visual hemifield in extrapersonal space due to decreased arousal. The results provide additional evidence for the proposed anatomical and functional overlap of the two attentional systems and indicate a modulation of visuospatial attention by the level of arousal in extrapersonal space.

Noradrenergic-glucocorticoid mechanisms in emotion-induced amnesia: from adaptation to disease

DISCUSSIONS

The interaction of emotion and episodic encoding has costs and benefits. These costs and benefits have been characterized in oddball experiments, where a violation of prevailing neutral context through aversive oddballs is associated with subsequent hypermnesia for the aversive oddball and peri-emotional amnesia for the neutral context. Both hypermnesia and peri-emotional amnesia are amygdala-dependent and vary as a function of noradrenergic-glucocorticoid input to the amygdala during emotional episodic encoding. Pharmacological enhancement of this input allows to model the maladaptive effects of emotion on episodic encoding. Extrapolation of these findings to conditions of emotional trauma suggests that disinhibited noradrenergic-glucocorticoid signaling could serve as a crucial etiological contributor to the pathogenesis of peri-traumatic amnesia (PTA) and post-traumatic stress disorder (PTSD).

CONCLUSIONS

Immediate pharmacological blockade of noradrenergic-glucocorticoid signaling might prove effective in the secondary prevention of PTA and PTSD.

Vestibular Stimulation for ADHD: randomized controlled trial of Comprehensive Motion Apparatus

OBJECTIVE

This research evaluates effects of vestibular stimulation by Comprehensive Motion Apparatus (CMA) in ADHD.

METHOD

Children ages 6 to 12 (48 boys, 5 girls) with ADHD were randomized to thrice-weekly 30-min treatments for 12 weeks with CMA, stimulating otoliths and semicircular canals, or a single-blind control of equal duration and intensity, each treatment followed by a 20-min typing tutorial.

RESULTS

In intent-to-treat analysis (n = 50), primary outcome improved significantly in both groups (p = .0001, d = 1.09 to 1.30), but treatment difference not significant (p = .7). Control children regressed by follow-up (difference p = .034, d = 0.65), but overall difference was not significant (p = .13, d = .47). No measure showed significant treatment differences at treatment end, but one did at follow-up. Children with IQ-achievement discrepancy > or = 1 SD showed significantly more CMA advantage on three measures.

CONCLUSION

This study illustrates the importance of a credible control condition of equal duration and intensity in trials of novel treatments. CMA treatment cannot be recommended for combined-type ADHD without learning disorder.

Noradrenergic neuromodulation of human attention for emotional and neutral stimuli

INTRODUCTION

Norepinephrine (NE) has a regulatory role in human attention.

OBJECTIVE

To examine its role in emotional modulation of attention, we used an attentional blink (AB) paradigm, in the context of psychopharmacological manipulation, where targets were either emotional or neutral items.

RESULTS AND DISCUSSION

We report behavioural evidence that beta-adrenergic blockade with propranolol impairs attention independent of target valence. Furthermore, this effect is centrally mediated as administration of the peripheral beta-adrenergic antagonist nadolol did not impair attention. By contrast, increasing NE tone, using the selective NE reuptake inhibitor reboxetine, improves detection of emotional stimuli.

CONCLUSION

In line with theoretical and animal models, these findings provide human behavioural evidence that the adrenergic system has a modulatory influence on selective attention that in some instances depends on item valence.

Reduced brainstem inhibition during anticipated pelvic visceral pain correlates with enhanced brain response to the visceral stimulus in women with irritable bowel syndrome

Cognitive factors such as fear of pain and symptom-related anxiety play an important role in chronic pain states. The current study sought to characterize abnormalities in preparatory brain response before aversive pelvic visceral distention in irritable bowel syndrome (IBS) patients and their possible relationship to the consequences of distention. The brain functional magnetic resonance imaging (fMRI) blood oxygen level-dependent (BOLD) response to anticipated and delivered mild and moderate rectal distention was recorded from 14 female IBS patients and 12 healthy controls. During cued anticipation of distention, activity decreased in the insula, supragenual anterior cingulate cortex (sACC), amygdala, and dorsal brainstem (DBS) of controls. IBS patients showed less anticipatory inactivation. Group differences were significant in the right posterior insula and bilateral DBS. Self-rated measures of negative affect during scanning were higher in patients than controls (p < 0.001), and the anticipatory BOLD decreases in DBS were inversely correlated with these ratings. During subsequent distention, both groups showed activity increases in insula, dorsal ACC, and DBS and decreases in the infragenual ACC. The increases were more extensive in patients, producing significant group differences in dorsal ACC and DBS. The amplitude of the anticipatory decrease in the pontine portion of DBS was associated with greater activation during distention in right orbitofrontal cortex and bilateral sACC. Both regions have been associated previously with corticolimbic inhibition and cognitive coping. Deficits in preparatory inhibition of DBS, including the locus ceruleus complex and parabrachial nuclei, may interfere with descending corticolimbic inhibition and contribute to enhanced brain responsiveness and perceptual sensitivity to visceral stimuli in IBS.

Pupil dilation reflects perceptual selection and predicts subsequent stability in perceptual rivalry

During sustained viewing of an ambiguous stimulus, an individual's perceptual experience will generally switch between the different possible alternatives rather than stay fixed on one interpretation (perceptual rivalry). Here, we measured pupil diameter while subjects viewed different ambiguous visual and auditory stimuli. For all stimuli tested, pupil diameter increased just before the reported perceptual switch and the relative amount of dilation before this switch was a significant predictor of the subsequent duration of perceptual stability. These results could not be explained by blink or eye-movement effects, the motor response or stimulus driven changes in retinal input. Because pupil dilation reflects levels of norepinephrine (NE) released from the locus coeruleus (LC), we interpret these results as suggestive that the LC-NE complex may play the same role in perceptual selection as in behavioral decision making.

Performance monitoring local field potentials in the medial frontal cortex of primates: anterior cingulate cortex

We describe intracranial local field potentials (LFP) recorded in the anterior cingulate cortex (ACC) of macaque monkeys performing a saccade countermanding task. The most prominent feature at approximately 70% of sites was greater negative polarity after errors than after rewarded correct trials. This negative polarity was also evoked in unrewarded correct trials. The LFP evoked by the visual target was much less polarized, and the weak presaccadic modulation was insufficient to control the initiation of saccades. When saccades were cancelled, LFP modulation decreased slightly with the magnitude of response conflict that corresponds to the coactivation of gaze-shifting and -holding neurons estimated from the probability of canceling. However, response time adjustments on subsequent trials were not correlated with LFP polarity on individual trials. The results provide clear evidence that error- and feedback-related, but not conflict-related, signals are carried by the LFP in the macaque ACC. Finding performance monitoring field potentials in the ACC of macaque monkeys establishes a bridge between event-related potential and functional brain-imaging studies in humans and neurophysiology studies in non-human primates.

A neural network model of the Eriksen task: reduction, analysis, and data fitting

We analyze a neural network model of the Eriksen task: a two-alternative forced-choice task in which subjects must correctly identify a central stimulus and disregard flankers that may or may not be compatible with it. We linearize and decouple the model, deriving a reduced drift-diffusion process with variable drift rate that describes the accumulation of net evidence in favor of either alternative, and we use this to analytically describe how accuracy and response time data depend on model parameters. Such analyses both assist parameter tuning in network models and suggest explanations of changing drift rates in terms of attention. We compare our results with numerical simulations of the full nonlinear model and with empirical data and show good fits to both with fewer parameters.

Conflict monitoring and decision making: reconciling two perspectives on anterior cingulate function

According to one influential account, the anterior cingulate cortex (ACC) serves to monitor for conflicts in information processing. According to another influential account, the ACC monitors action outcomes and guides decision making. Both of these perspectives are supported by an abundance of data, making it untenable to reject one view in favor of the other. Instead, the apparent challenge is to discover how the two perspectives might fit together within a larger account. In the present article, we consider the prospects for such a reconciliation. Juxtaposing the conflict-monitoring and decision-making accounts suggests an extension of the conflict-monitoring theory, by which conflict would act as a teaching signal driving a form of avoidance learning. The effect of this mechanism would be to bias behavioral decision making toward cognitively efficient tasks and strategies. We discuss evidence favoring this proposal and present an initial computational model, which lays the foundation for further development.

Anterior cingulate cortex and conflict detection: an update of theory and data

The dorsal anterior cingulate cortex (ACC) and associated regions of the medial frontal wall have often been hypothesized to play an important role in cognitive control. We have proposed that the ACC's specific role in cognitive control is to detect conflict between simultaneously active, competing representations and to engage the dorsolateral prefrontal cortex (DLPFC) to resolve such conflict. Here we review some of the evidence supporting this theory, from event-related potential (ERP) and fMRI studies. We focus on data obtained from interference tasks, such as the Stroop task, and review the evidence that trial-to-trial changes in control engagement can be understood as driven by conflict detection; the data suggest that levels of activation of the ACC and the DLPFC in such tasks do indeed reflect conflict and control, respectively. We also discuss some discrepant results in the literature that highlight the need for future research.

Convergent regulation of locus coeruleus activity as an adaptive response to stress

Although hypothalamic-pituitary-adrenal axis activation is generally considered to be the hallmark of the stress response, many of the same stimuli that initiate this response also activate the locus coeruleus-norepinephrine system. Given its functional attributes, the parallel engagement of the locus coeruleus-norepinephrine system with the hypothalamic-pituitary-adrenal axis serves to coordinate endocrine and cognitive limbs of the stress response. The elucidation of stress-related afferents to the locus coeruleus and the electrophysiological characterization of these inputs are revealing how the activity of this system is fine-tuned by stressors to facilitate adaptive cognitive responses. Emerging from these studies, is a picture of complex interactions between the stress-related neuropeptide, corticotropin-releasing factor (CRF), endogenous opioids and the excitatory amino acid neurotransmitter, glutamate. The net effect of these interactions is to adjust the activity and reactivity of the locus coeruleus-norepinephrine system such that state of arousal and processing of sensory stimuli are modified to facilitate adaptive behavioral responses to stressors. This review begins with an introduction to the basic anatomical and physiological characteristics of locus coeruleus neurons. The concept that locus coeruleus neurons operate through two activity modes, i.e., tonic vs. phasic, that determine distinct behavioral strategies is emphasized in light of its relevance to stress. Anatomical and physiological evidence are then presented suggesting that interactions between stress-related neurotransmitters that converge on locus coeruleus neurons regulate shifts between these modes of discharge in response to the challenge of a stressor. This review focuses specifically on the locus coeruleus because it is the major source of norepinephrine to the forebrain and has been implicated in behavioral and cognitive aspects of stress responses.

Prefrontal acetylcholine release controls cue detection on multiple timescales

Cholinergic neurons originating from the basal forebrain innervate the entire cortical mantle. Choline-sensitive microelectrodes were used to measure the synaptic release of cortical acetylcholine (ACh) at a subsecond resolution in rats performing a task involving the detection of cues. Cues that were detected, defined behaviorally, evoked transient increases in cholinergic activity (at the scale of seconds) in the medial prefrontal cortex (mPFC), but not in a nonassociational control region (motor cortex). In trials involving missed cues, cholinergic transients were not observed. Cholinergic deafferentation of the mPFC, but not motor cortex, impaired cue detection. Furthermore, decreases and increases in precue cholinergic activity predicted subsequent cue detection or misses, respectively. Finally, cue-evoked cholinergic transients were superimposed over slower (at the timescale of minutes) changes in cholinergic activity. Cortical cholinergic neurotransmission is regulated on multiple timescales to mediate the detection of behaviorally significant cues and to support cognitive performance.

Increased task difficulty results in greater impact of noradrenergic modulation of cognitive flexibility

Previous research suggests that the noradrenergic system modulates certain types of cognitive flexibility. This study compared various doses of beta-adrenergic antagonists for their effect on cognitive flexibility in problem solving, and how task difficulty interacts with this effect, as well as the effect of beta-adrenergic antagonists on other tasks. Anagram task performance was compared in 72 subjects using a within-subject design for propranolol at 20 mg, 40 mg, 60 mg, and placebo in a double-blinded manner, and the effects of subject ability and task difficulty were examined. We also examined the effect of the 40 mg propranolol dose on a range of other tasks. Overall, more anagram problems were solved while on propranolol 40 mg than on placebo. Subjects least able to solve the problems benefited significantly from 40 mg of propranolol. Also, for all subjects the most difficult problems were solved more quickly with propranolol 40 mg than placebo. Benefits were also seen for word fluency and backward digit span. Therefore, noradrenergic modulation of cognitive flexibility is affected by how much difficulty the subject is encountering when searching for the solution, a pattern consistent with what might be expected in an effect on the search of the semantic and associative network.

Telencephalon: Neocortex

The neocortex is an ultracomplex, six-layered structure that develops from the dorsal palliai sector of the telencephalic hemispheres (Figs. 2.24, 2.25, 11.1). All mammals, including monotremes and marsupials, possess a neocortex, but in reptiles, i.e. the ancestors of mammals, only a three-layered neocortical primordium is present [509, 511]. The term neocortex refers to its late phylogenetic appearance, in comparison to the “palaeocortical” olfactory cortex and the “archicortical” hippocampal cortex, both of which are present in all amniotes [509].

Conflict-Triggered Goal Shielding

Action control in a changing environment requires that one shield current goals from distracting information (goal shielding) and at the same time monitor the environment for potentially significant stimuli that may afford a goal switch (background monitoring). Response conflicts modulate the balance between goal shielding and background monitoring, as indicated by reduced susceptibility to interference after response conflicts. Such conflict-adaptation effects have been attributed to enhanced recruitment of cognitive control on trials following conflicts. Here we show that conflict triggers increased goal shielding on the conflict trial itself. Subjects performed a spatial compatibility task during which they had to notice rare prospective memory cues. Such cues were overlooked more often on conflict trials than on nonconflict trials, a result indicating that shielding of the current goal and inhibition of distractors were increased on the current trial when it involved a response conflict. Thus, evidence for enhanced recruitment of control following conflict may partly reflect aftereffects of goal shielding on the conflict trial itself.

Evidence of temporal cortical dysfunction in rhesus monkeys following chronic cocaine self-administration

Cocaine abusers show impaired performance on cognitive tasks that engage prefrontal cortex. These deficits may contribute to impaired control and relapse in abusers. Understanding the neuronal substrates that lead to these deficits requires animal models that are relevant to the human condition. However, to date, models have mostly focused on behaviors mediated by subcortical systems. Here we evaluated the impact of long-term self-administration of cocaine in the rhesus monkey on cognitive performance. Tests included stimulus discrimination (SD)/reversal and delayed alternation tasks. The chronic cocaine animals showed marked deficits in ability to organize their behavior for maximal reward. This was demonstrated by an increased time needed to acquire SDs. Deficits were also indicated by an increased time to initially learn the delayed alternation task, and to adapt strategies for bypassing a reliance on working memory to respond accurately. Working memory per se (delay dependent performance) was not affected by chronic self-administration. This pattern of cognitive deficits suggests dysfunction that extends beyond localized prefrontal cortical areas. In particular, it appears that temporal cortical function is also compromised. This agrees with other recent clinical and preclinical findings, and suggests further study into addiction related dysfunction across more widespread cortical networks is warranted.

Noradrenergic modulation of arousal

Through a highly divergent efferent projection system, the locus coeruleus-noradrenergic system supplies norepinephrine throughout the central nervous system. State-dependent neuronal discharge activity of locus coeruleus neurons has long-suggested a role of this system in the induction of an alert waking state. More recent work supports this hypothesis, demonstrating robust wake-promoting actions of the locus coeruleus-noradrenergic system. Norepinephrine enhances arousal, in part, via actions of beta- and alpha1-receptors located within multiple subcortical structures, including the general regions of the medial septal area and the medial preoptic areas. Recent anatomical studies suggest that arousal-enhancing actions of norepinephrine are not limited to the locus coeruleus system and likely include the A1 and A2 noradrenergic cell groups. Thus, noradrenergic modulation of arousal state involves multiple noradrenergic systems acting within multiple subcortical regions. Pharmacological studies indicate that the combined actions of these systems are necessary for the sustained maintenance of arousal levels associated with spontaneous waking. Enhanced arousal state is a prominent aspect of both stress and psychostimulant drug action and evidence indicates that noradrenergic systems likely play an important role in both stress-related and psychostimulant-induced arousal. These and other observations suggest that the dysregulation of noradrenergic neurotransmission could well contribute to the dysregulation of arousal associated with a variety of behavioral disorders including insomnia and stress-related disorders.

Brain responses to violet, blue, and green monochromatic light exposures in humans: prominent role of blue light and the brainstem

Background

Relatively long duration retinal light exposure elicits nonvisual responses in humans, including modulation of alertness and cognition. These responses are thought to be mediated in part by melanopsin-expressing retinal ganglion cells which are more sensitive to blue light than violet or green light. The contribution of the melanopsin system and the brain mechanisms involved in the establishment of such responses to light remain to be established.

Methodology/Principal Findings

We exposed 15 participants to short duration (50 s) monochromatic violet (430 nm), blue (473 nm), and green (527 nm) light exposures of equal photon flux (10¹³ph/cm²/s) while they were performing a working memory task in fMRI. At light onset, blue light, as compared to green light, increased activity in the left hippocampus, left thalamus, and right amygdala. During the task, blue light, as compared to violet light, increased activity in the left middle frontal gyrus, left thalamus and a bilateral area of the brainstem consistent with activation of the locus coeruleus.

Conclusion/Significance

These results support a prominent contribution of melanopsin-expressing retinal ganglion cells to brain responses to light within the very first seconds of an exposure. The results also demonstrate the implication of the brainstem in mediating these responses in humans and speak for a broad involvement of light in the regulation of brain function.

Towards an executive without a homunculus: computational models of the prefrontal cortex/basal ganglia system

The prefrontal cortex (PFC) has long been thought to serve as an 'executive' that controls the selection of actions and cognitive functions more generally. However, the mechanistic basis of this executive function has not been clearly specified often amounting to a homunculus. This paper reviews recent attempts to deconstruct this homunculus by elucidating the precise computational and neural mechanisms underlying the executive functions of the PFC. The overall approach builds upon existing mechanistic models of the basal ganglia (BG) and frontal systems known to play a critical role in motor control and action selection, where the BG provide a 'Go' versus 'NoGo' modulation of frontal action representations. In our model, the BG modulate working memory representations in prefrontal areas to support more abstract executive functions. We have developed a computational model of this system that is capable of developing human-like performance on working memory and executive control tasks through trial-and-error learning. This learning is based on reinforcement learning mechanisms associated with the midbrain dopaminergic system and its activation via the BG and amygdala. Finally, we briefly describe various empirical tests of this framework.

Understanding decision-making deficits in neurological conditions: insights from models of natural action selection

Models of natural action selection implicate fronto-striatal circuits in both motor and cognitive 'actions'. Dysfunction of these circuits leads to decision-making deficits in various populations. We review how computational models provide insights into the mechanistic basis for these deficits in Parkinson's patients and those with ventromedial frontal damage. We then consider implications of the models for understanding behaviour and cognition in attention-deficit/hyperactivity disorder (ADHD). Incorporation of cortical noradrenaline function into the model improves action selection in noisy environments and accounts for response variability in ADHD. We close with more general clinical implications.

Dopamine binds to alpha(2)-adrenergic receptors in the song control system of zebra finches (Taeniopygia guttata)

A commonly held view is that dopamine exerts its effects via binding to D1- and D2-dopaminergic receptors. However, recent data have emerged supporting the existence of a direct interaction of dopamine with adrenergic but this interaction has been poorly investigated. In this study, the pharmacological basis of possible in vivo interactions between dopamine and alpha(2)-adrenergic receptors was investigated in zebra finches. A binding competition study showed that dopamine displaces the binding of the alpha(2)-adrenergic ligand, [(3)H]RX821002, in the brain. The affinity of dopamine for the adrenergic sites does not differ between the sexes and is 10- to 28-fold lower than that for norepinephrine. To assess the anatomical distribution of this interaction, binding competitions were performed on brain slices incubated in 5nM [(3)H]RX821002 in the absence of any competitor or in the presence of norepinephrine [0.1microM] or dopamine [1microM]. Both norepinephrine and dopamine displaced the binding of the radioligand though to a different extent in most of the regions studied (e.g., area X, the lateral part of the magnocellular nucleus of anterior nidopallium, HVC, arcopallium dorsale, ventral tegmental area and substantia grisea centralis) but not in the robust nucleus of the arcopallium. Together these data provide evidence for a direct interaction between dopamine and adrenergic receptors in songbird brains albeit with regional variation.

Arousal and the pupil: why diazepam-induced sedation is not accompanied by miosis

RATIONALE

There is a close relationship between arousal and pupil diameter, decrease in the level of arousal being accompanied by constriction of the pupil (miosis), probably reflecting the attenuation of sympathetic outflow as sedation sets in. Paradoxically, sedation induced by benzodiazepines is not accompanied by miosis.

OBJECTIVE

The objective of this study was to examine the hypothesis that diazepam may attenuate both the sympathetic and the opposing parasympathetic outflow to the iris, which may mask the miosis. Dapiprazole (sympatholytic) and tropicamide (parasympatholytic) were applied topically, together with the cold pressor test (CPT), to manipulate the sympathetic/parasympathetic balance.

MATERIALS AND METHODS

Sixteen healthy male volunteers participated in four weekly sessions according to a balanced double-blind protocol. Diazepam 10 mg (two sessions) and placebo (two sessions), associated with either 0.01% tropicamide or 0.5% dapiprazole eyedrops, were administered orally. Pupil diameter, light and darkness reflexes and pupillary sleepiness waves were recorded with infrared video pupillometry, alertness was measured by critical flicker fusion frequency (CFFF) and visual analogue scales (VAS), blood pressure and heart rate by conventional methods. CPT was applied after post-treatment testing. Data were analysed by analysis of variance, with multiple comparisons.

RESULTS

Diazepam caused sedation (reduction in VAS alertness scores and CFFF, increase in sleepiness waves), dapiprazole had a sympatholytic and tropicamide a parasympatholytic effect on the pupil. Diazepam had no effect on pupil diameter and reflexes or their modifications by the antagonists. CPT increased pupil diameter, blood pressure and heart rate, and the increase only in systolic blood pressure was attenuated by diazepam.

CONCLUSIONS

Diazepam-induced sedation is not accompanied by any change in either the sympathetic or parasympathetic influence on the iris.

Behavior-dependent modulation of hippocampal EEG activity by the selective norepinephrine reuptake inhibitor reboxetine in rats

Both active wakefulness and rapid eye movement sleep (REM) give rise to rhythmic synchronized hippocampal field oscillations, known as theta activity. Antidepressant drugs, including norepinephrine re-uptake inhibitors are proven to diminish REM sleep, and REM sleep-related hippocampal theta oscillation. Since reboxetine, a highly selective norepinephrine re-uptake inhibitor has been shown to block REM sleep, but induce or facilitate hippocampal theta activity in anesthetized rats, the current study investigated the effects of reboxetine on stage- and behavior dependent theta activity. Polysomnographic recordings, which included hippocampal field potentials at the hippocampal fissure, were carried out in rats for 8 h during the light phase of the circadian cycle. Theta rhythm was analyzed during three different behavioral conditions: REM sleep, during motor activity in a familiar environment, and during exploration in a novel environment. We found that, compared with REM sleep, theta power was relatively low during periods of active wakefulness when the animal was in the familiar home cage, but considerably increased during exploration in a novel environment. Reboxetine suppressed sleep and thus abolished REM sleep-related hippocampal theta rhythm, attenuated theta in the familiar environment, and significantly enhanced theta oscillations associated with exploratory behavior. Our findings demonstrate a state- and behavior-dependent modulation of hippocampal theta activity by reboxetine, providing further evidence for a prominent role of norepinephrine in arousal and focused or selective attention.

alpha2-Noradrenergic receptors activation enhances excitability and synaptic integration in rat prefrontal cortex pyramidal neurons via inhibition of HCN currents

Stimulation of alpha(2)-noradrenergic (NA) receptors within the PFC improves working memory performance. This improvement is accompanied by a selective increase in the activity of PFC neurons during delay periods, although the cellular mechanisms responsible for this enhanced response are largely unknown. Here we used current and voltage clamp recordings to characterize the response of layer V-VI PFC pyramidal neurons to alpha(2)-NA receptor stimulation. alpha(2)-NA receptor activation produced a small hyperpolarization of the resting membrane potential, which was accompanied by an increase in input resistance and evoked firing. Voltage clamp analysis demonstrated that alpha(2)-NA receptor stimulation inhibited a caesium and ZD7288-sensitive hyperpolarization-activated (HCN) inward current. Suppression of HCN current by alpha(2)-NA stimulation was not dependent on adenylate cyclase but instead required activation of a PLC-PKC linked signalling pathway. Similar to direct blockade of HCN channels, alpha(2)-NA receptor stimulation produced a significant enhancement in temporal summation during trains of distally evoked EPSPs. These dual effects of alpha(2)-NA receptor stimulation - membrane hyperpolarization and enhanced temporal integration - together produce an increase in the overall gain of the response of PFC pyramidal neurons to excitatory synaptic input. The net effect is the suppression of isolated excitatory inputs while enhancing the response to a coherent burst of synaptic activity.

Neurocognitive components of the behavioral inhibition and activation systems: implications for theories of self-regulation

We examined the neurocognitive correlates of the Behavioral Inhibition and Behavioral Activation Systems (BIS/BAS) in an effort to clarify ambiguities concerning interpretations of BIS as reflecting inhibition versus avoidance. We hypothesized that self-reported BIS should relate to neural mechanisms associated with conflict monitoring, whereas self-reported BAS should be associated with neural correlates of approach motivation. Consistent with these predictions, higher self-reported BIS was uniquely related to the N2 event-related potential on No-Go trials of a Go/No-Go task, linking BIS with conflict monitoring and sensitivity to No-Go cues. Higher BAS was uniquely related to greater left-sided baseline frontal cortical asymmetry associated with approach orientation. Implications for theories of self-regulation involving conflict monitoring, cognitive control, and approach/avoidance motivation are discussed.

Emotion-induced retrograde amnesia varies as a function of noradrenergic-glucocorticoid activity

RATIONALE

Privileged episodic encoding of an aversive event often comes at a cost of neutral events flanking the aversive event, resulting in decreased episodic memory for these neutral events. This peri-emotional amnesia is amygdala-dependent and varies as a function of norepinephrine activity. However, less is known about the amnesiogenic potential of cortisol.

OBJECTIVE

We used a strategy of pharmacologically potentiating cortisol and norepinephrine activity to probe the putative neurochemical substrates of peri-emotional amnesia.

MATERIALS AND METHODS

Fifty-four healthy individuals participated in a randomized double-blind placebo-controlled study. Within the experimental context of an established peri-emotional amnesia paradigm, we tested the amnesiogenic potential of hydrocortisone (30 mg p.o.) in the presence or absence of the norepinephrine-reuptake inhibitor reboxetine (4 mg p.o.).

RESULTS

Under dual challenge conditions, we observed a linear dose-response relationship in the magnitude and duration of emotion-induced retrograde amnesia.

CONCLUSIONS

Our results are consistent with a phenotypic expression of retrograde amnesia varying as a function of norepinephrine and cortisol coactivation during episodic encoding of aversive events. Our study demonstrates that the adverse cognitive and behavioral sequelae of aversive emotion can be experimentally modeled by a pharmacological manipulation of its putative neurochemical substrates.

The effect of propranolol on cognitive flexibility and memory in acute cocaine withdrawal

Upregulated noradrenergic activity occurs early in cocaine withdrawal. Our previous work revealed impaired cognitive flexibility in acute cocaine withdrawal, a cognitive domain that appears to be modulated by noradrenergic activity. Therefore, we wished to determine the effect of beta-adrenergic antagonists on cognitive performance in acute cocaine withdrawal. Eleven subjects acutely withdrawing from cocaine were tested in this pilot study on tasks of cognitive flexibility as well as word fluency, attention, verbal memory, and spatial memory, off and on propranolol in a double-blinded manner. Propranolol significantly benefited certain aspects of cognitive flexibility in acute cocaine withdrawal, and improved some measures of verbal fluency and verbal recall. Cocaine withdrawal treatment is characterized by high failure rates. Further research is needed to determine the role this finding of a reversible cognitive impairment in cocaine withdrawal has in treatment.

Updating P300: an integrative theory of P3a and P3b

The empirical and theoretical development of the P300 event-related brain potential (ERP) is reviewed by considering factors that contribute to its amplitude, latency, and general characteristics. The neuropsychological origins of the P3a and P3b subcomponents are detailed, and how target/standard discrimination difficulty modulates scalp topography is discussed. The neural loci of P3a and P3b generation are outlined, and a cognitive model is proffered: P3a originates from stimulus-driven frontal attention mechanisms during task processing, whereas P3b originates from temporal-parietal activity associated with attention and appears related to subsequent memory processing. Neurotransmitter actions associating P3a to frontal/dopaminergic and P3b to parietal/norepinephrine pathways are highlighted. Neuroinhibition is suggested as an overarching theoretical mechanism for P300, which is elicited when stimulus detection engages memory operations.

Mapping brain c-Fos immunoreactivity after insulin-induced voluntary lard intake: insulin- and lard-associated patterns

In addition to the inhibitory role of central insulin on food intake, insulin also acts to promote lard intake. We investigated the neural pathways involved in this facet of insulin action. Insulin or saline was infused into either the superior mesenteric or right external jugular veins of streptozotocin-diabetic rodents with elevated steady-state circulating corticosterone concentrations. After postsurgical recovery, rats were offered the choice of chow or lard to eat. Irrespective of the site of venous infusion, insulin increased lard and decreased chow intake. After 4 days, lard was removed for 8 h. On return for 1 h, only insulin infused into the superior mesenteric vein resulted in lard intake. This facilitated distinction between the effects of circulating insulin concentrations (similar in the two insulin-infused groups) and lard ingestion on the patterns of c-Fos(+) cells in the brain, termed insulin- and lard-associated patterns, respectively. Insulin-associated changes in c-Fos(+) cell numbers were evident in the arcuate nucleus, bed nucleus of the stria terminalis and substantia nigra pars compacta, concomitant with elevated leptin levels and reduced chow intake. Lard-associated changes in c-Fos(+) cell numbers were observed in the nucleus of the tractus solitarius, lateral parabrachial nucleus, central nucleus of the amygdala, ventral tegmental area, nucleus accumbens shell and the prefrontal cortex, and were associated with lower levels of triglycerides and free fatty acids. The anterior paraventricular thalamic nucleus exhibited both patterns. These data collectively fit into a framework for food intake and reward and provide targets for pharmacological manipulation to influence the choice of food intake.

Dissociable but inter-related systems of cognitive control and reward during decision making: Evidence from pupillometry and event-related fMRI

Decision making involves the allocation of cognitive resources in response to expectations and feedback. Here we explored how frontal networks respond in a gambling paradigm in which uncertainty was manipulated to increase demands for cognitive control. In one experiment, pupil diameter covaried with uncertainty during decision making and with the degree to which subsequent outcomes violated reward expectations. In a second experiment, fMRI showed that both uncertainty and unexpected outcomes modulated activation in a network of frontal regions. Thus, the frontal network supports multiple phases of the decision-making process including information regarding reward uncertainty and reward outcome. In contrast, striatal activation only tracked reward delivery, suggesting a distinct reward pathway that might, under certain circumstances, oppose the frontal network. These results are consistent with the interpretation that reward signals may bias recruitment of frontal networks that are linked to allocation of cognitive resources.

Temporal filtering of reward signals in the dorsal anterior cingulate cortex during a mixed-strategy game

The process of decision making in humans and other animals is adaptive and can be tuned through experience so as to optimize the outcomes of their choices in a dynamic environment. Previous studies have demonstrated that the anterior cingulate cortex plays an important role in updating the animal's behavioral strategies when the action outcome contingencies change. Moreover, neurons in the anterior cingulate cortex often encode the signals related to expected or actual reward. We investigated whether reward-related activity in the anterior cingulate cortex is affected by the animal's previous reward history. This was tested in rhesus monkeys trained to make binary choices in a computer-simulated competitive zero-sum game. The animal's choice behavior was relatively close to the optimal strategy but also revealed small systematic biases that are consistent with the use of a reinforcement learning algorithm. In addition, the activity of neurons in the dorsal anterior cingulate cortex that was related to the reward received by the animal in a given trial often was modulated by the rewards in the previous trials. Some of these neurons encoded the rate of rewards in previous trials, whereas others displayed activity modulations more closely related to the reward prediction errors. In contrast, signals related to the animal's choices were represented only weakly in this cortical area. These results suggest that neurons in the dorsal anterior cingulate cortex might be involved in the subjective evaluation of choice outcomes based on the animal's reward history.

Lesions of the dorsal noradrenergic bundle impair attentional set-shifting in the rat

Rats with medial prefrontal cortex (mPFC) lesions are impaired in attentional set-shifting, when it is required to shift to a previously irrelevant perceptual dimension. The main source of noradrenergic input to the mPFC is from the locus coeruleus via the dorsal noradrenergic ascending bundle (DNAB). This study examined the effects of selective cortical noradrenaline depletion following 6-hydroxydopamine-induced lesions of the DNAB on attentional set-shifting and other aspects of discrimination learning and performance. Rats learned to dig in baited bowls, and then acquired discriminations based on one of two aspects of a bowl--odour or digging medium. The task tested acquisition of novel discriminations (both intra- and extra-dimensional) and reversal learning when contingencies were reversed with the same stimuli. At the conclusion of testing, the DNAB-lesioned rats were shown to have a selective depletion of noradrenaline of approximately 70% within the mPFC (cingulate and prelimbic cortex subregions), with no other significant changes in dopamine or 5-hydroxytryptamine. Rats required more trials to learn new discriminations when attentional shifting was required [extra-dimensional (ED)-shift]. Rats with dorsal noradrenergic ascending bundle (DNAB) lesions were impaired in novel acquisitions when an ED-shift was required, but were unimpaired in reversal learning and other aspects of discrimination learning, relative to controls. These data are consistent with other evidence implicating noradrenaline (NA) in attentional set-shifting, and contrast with effects of manipulations of 5-hydroxytryptamine (5-HT) and acetylcholine within the medial prefrontal cortex (mPFC). The findings are also relevant to recent theorizing about the functions of the coeruleo-cortical noradrenergic system.

Regulation of the norepinephrine transporter by alpha-synuclein-mediated interactions with microtubules

alpha-Synuclein (alpha-Syn) regulates catecholaminergic neurotransmission. We demonstrate that alpha-Syn regulates the activity and surface expression of the norepinephrine transporter (NET), depending on its expression levels. In cells co-transfected with NET and low amounts of alpha-Syn, NET activity and cell surface expression were increased and protein interactions with alpha-Syn decreased, compared with cells transfected with NET alone. Converse effects were observed at higher levels of alpha-Syn expression. Treatment with nocodazole and other microtubule (MT) destabilizers abolished the expression-dependent bimodal regulation of NET by alpha-Syn. At low alpha-Syn levels, nocodazole had no effect on NET surface expression or protein interactions, while inducing increases in these measures at higher levels. Cells that were transfected with NET alone displayed no sensitivity to nocodazole, indicating that alpha-Syn expression was necessary for the MT-dependent changes in NET activity. MT destabilizers also caused a significant increase in [(3)H]-NE uptake in brainstem primary neurons and synaptosomes from the frontal cortex, but not striatal synaptosomes. These findings suggest that the surface localization and activity of NET is modulated by alpha-Syn in a manner that is both dependent on interactions with the MT cytoskeleton and varies across brain regions.

Glutamate receptor subunit expression in the rhesus macaque locus coeruleus

The locus coeruleus (LC) is a major noradrenergic brain nucleus that regulates states of arousal, optimizes task-oriented decision making, and may also play an important role in modulating the activity of the reproductive neuroendocrine axis. Rodent studies have shown that the LC is responsive to glutamate receptor agonists, and that it expresses various glutamate receptor subunits. However, glutamate receptor subunit expression has not been extensively examined in the primate LC. We previously demonstrated expression of the NR1 NMDA glutamate receptor subunit in the rhesus macaque LC and now extend this work by also examining the expression of non-NMDA (AMPA and kainate) ionotropic glutamate receptor subunits. Using in situ hybridization histochemistry and immunohistochemistry, we confirmed the presence of the obligatory NR1 subunit in the LC. In addition, we demonstrated expression of the AMPA glutamate receptor subunits GluR1, GluR2, and GluR3. More extensive receptor profiling, using rhesus monkey gene microarrays (Affymetrix GeneChip), further corroborated the histological findings and showed expression of mRNA encoding ionotropic glutamate receptor subunits NR2A, NR2D, GluR4, and GluR6, as well as the metabotropic glutamate receptor subunits mGluR1, mGluR3, mGluR4, mGluR5, and mGluR7. These data provide a foundation for future examination of how changes in glutamate receptor composition contribute to the control of primate physiology.

Genetic contribution to the P3 in young and middle-aged adults

Previous studies in young and adolescent twins suggested substantial genetic contributions to the amplitude and latency of the P3 evoked by targets in an oddball paradigm. Here we examined whether these findings can be generalized to adult samples. A total of 651 twins and siblings from 292 families participated in a visual oddball task. In half of the subjects the age centered around 26 (young adult cohort), in the other half the age centered around 49 (middle-aged adult cohort). P3 peak amplitude and latency were scored for 3 midline leads Pz, Cz, and Fz. No cohort differences in heritability were found. P3 amplitude (approximately 50%) and latency (approximately 45%) were moderately heritable for the 3 leads. A single genetic factor influenced latency at all electrodes, suggesting a single P3 timing mechanism. Specific genetic factors influenced amplitude at each lead, suggesting local modulation of the P3 once triggered. Genetic analysis of the full event-related potential waveform showed that P3 heritability barely changes from about 100 ms before to 100 ms after the peak. Age differences are restricted to differences in means and variances, but the proportion of genetic variance as part of the total variance of midline P3 amplitude and latency does not change from young to middle-aged adulthood.

Learning the value of information in an uncertain world

Our decisions are guided by outcomes that are associated with decisions made in the past. However, the amount of influence each past outcome has on our next decision remains unclear. To ensure optimal decision-making, the weight given to decision outcomes should reflect their salience in predicting future outcomes, and this salience should be modulated by the volatility of the reward environment. We show that human subjects assess volatility in an optimal manner and adjust decision-making accordingly. This optimal estimate of volatility is reflected in the fMRI signal in the anterior cingulate cortex (ACC) when each trial outcome is observed. When a new piece of information is witnessed, activity levels reflect its salience for predicting future outcomes. Furthermore, variations in this ACC signal across the population predict variations in subject learning rates. Our results provide a formal account of how we weigh our different experiences in guiding our future actions.

From the Golgi–Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: Wiring and volume transmission

After Golgi-Cajal mapped neural circuits, the discovery and mapping of the central monoamine neurons opened up for a new understanding of interneuronal communication by indicating that another form of communication exists. For instance, it was found that dopamine may be released as a prolactin inhibitory factor from the median eminence, indicating an alternative mode of dopamine communication in the brain. Subsequently, the analysis of the locus coeruleus noradrenaline neurons demonstrated a novel type of lower brainstem neuron that monosynaptically and globally innervated the entire CNS. Furthermore, the ascending raphe serotonin neuron systems were found to globally innervate the forebrain with few synapses, and where deficits in serotonergic function appeared to play a major role in depression. We propose that serotonin reuptake inhibitors may produce antidepressant effects through increasing serotonergic neurotrophism in serotonin nerve cells and their targets by transactivation of receptor tyrosine kinases (RTK), involving direct or indirect receptor/RTK interactions. Early chemical neuroanatomical work on the monoamine neurons, involving primitive nervous systems and analysis of peptide neurons, indicated the existence of alternative modes of communication apart from synaptic transmission. In 1986, Agnati and Fuxe introduced the theory of two main types of intercellular communication in the brain: wiring and volume transmission (WT and VT). Synchronization of phasic activity in the monoamine cell clusters through electrotonic coupling and synaptic transmission (WT) enables optimal VT of monoamines in the target regions. Experimental work suggests an integration of WT and VT signals via receptor-receptor interactions, and a new theory of receptor-connexin interactions in electrical and mixed synapses is introduced. Consequently, a new model of brain function must be built, in which communication includes both WT and VT and receptor-receptor interactions in the integration of signals. This will lead to the unified execution of information handling and trophism for optimal brain function and survival.

Comparison of diphenhydramine and modafinil on arousal and autonomic functions in healthy volunteers

Arousal is regulated by the interplay between wakefulness- and sleep-promoting nuclei. Major wakefulness-promoting nuclei are the histaminergic tuberomamillary nucleus (TMN) of the hypothalamus and the noradrenergic locus coeruleus (LC) of the pons, which also play a role in autonomic regulation. First generation antihistamines, such as diphenhydramine, are likely to cause sedation by blocking excitatory H1 histamine receptors in the cerebral cortex, and the anti-narcolepsy drug modafinil may promote wakefulness by activating the locus coeruleus. We compared the effects of single doses of diphenhydramine (75 mg) and modafinil (200 mg) on arousal and autonomic functions in 16 healthy male volunteers, using a placebo-controlled, balanced, double-blind design. Arousal was assessed by critical flicker fusion frequency (CFFF), visual analogue scales (VAS) and pupillary fatigue waves (Pupillographic Sleepiness Test (PST)). Autonomic functions measured included resting pupil diameter, light and darkness reflex responses, blood pressure, heart rate and salivation. Data were analysed with ANOVA, with multiple comparisons. Diphenhydramine had sedative effects as shown by reductions in CFFF, VAS alertness ratings and increases of the indices of pupillary fatigue. Modafinil had alerting effects as indicated by reductions in the measures of pupillary fatigue. Comparison of pre-post medication changes in pupil diameter showed a decrease after diphenhydramine and an increase after modafinil. Diphenhydramine reduced salivation, and modafinil increased systolic blood pressure. In conclusion, diphenhydramine and modafinil evoked opposite effects on arousal and sympathetic functions, which are likely to reflect their interaction with the central histaminergic and noradrenergic systems. Hyposalivation by diphenhydramine is likely to be due to its additional anticholinergic property.

Effects of the noradrenergic agonist clonidine on temporal and spatial attention

RATIONALE

Recent theories posit an important role for the noradrenergic system in attentional selection in the temporal domain. In contrast, the spatially diffuse topographical projections of the noradrenergic system are inconsistent with a direct role in spatial selection.

OBJECTIVES

To test the hypotheses that pharmacological attenuation of central noradrenergic activity should (1) impair performance on the attentional blink task, a task requiring the selection of targets in a rapid serial visual stream of stimuli; and (2) leave intact the efficiency of the search for a target in a two-dimensional visuospatial stimulus array.

MATERIALS AND METHODS

Thirty-two healthy adult human subjects performed an attentional blink task and a visual search task in a double-blind, placebo-controlled, between-subject study investigating the effects of the alpha2 adrenoceptor agonist clonidine (150 microg, oral dose).

RESULTS

No differential effects of clonidine vs placebo were found on the attentional blink performance. Clonidine slowed overall reaction times in the visual search task but did not impair the efficiency of the visual search.

CONCLUSIONS

The attentional blink results are inconsistent with recent theories about the role of the noradrenergic system in temporal filtering and in mediating the attentional blink. This discrepancy between theory and data is discussed in detail. The visual search results, in combination with previous findings, suggest that the noradrenergic system is not directly involved in spatial attention processes but instead can modulate these processes in an indirect fashion.

Clorgyline-induced modification of behavioral sensitization to quinpirole: effects on local cerebral glucose utilization

Sensitization refers to augmented behavioral responses produced by repeated, intermittent injections of dopaminergic psychostimulants. The locomotor manifestations observed after a sensitizing course of quinpirole, a D(2)/D(3) dopamine agonist, can be modified by the MAO(A) inhibitor clorgyline, by a mechanism apparently unrelated to its actions on MAO(A). Alterations in regional neuronal activity produced by quinpirole in quinpirole-sensitized rats with or without clorgyline pretreatment were assessed based on LCGU using the [(14)C]-2-deoxyglucose (2-DG) method. Adult, male Long-Evans rats (180-200 g, n=9-10/group) were subjected to an injection of either clorgyline (1.0 mg/kg, s.c.) or saline 90 min prior to an injection of quinpirole (0.5 mg/kg, s.c.) or saline, 1 set of injections administered every 3rd day for 10 sets. The 2-DG procedure was initiated 60 min after an 11th set of injections in freely moving rats. LCGU was determined by quantitative autoradiography. LCGU was decreased in a number of limbic (nucleus accumbens and ventral pallidum) and cortical (medial/ventral orbital and infralimbic) regions and in the raphe magnus nucleus in quinpirole-sensitized rats (P<0.05 vs. saline-saline). Quinpirole-sensitized rats pretreated with clorgyline had similar alterations in LCGU, but LCGU was higher in the locus coeruleus compared to quinpirole alone (P<0.05), was not decreased in the raphe magnus nucleus, and was decreased in the piriform cortex and septum. This implicates altered activity of the noradrenergic, serotonergic, olfactory, and limbic systems in the modified behavioral response to quinpirole with clorgyline pretreatment.

Identification of connexin36 in gap junctions between neurons in rodent locus coeruleus

Locus coeruleus neurons are strongly coupled during early postnatal development, and it has been proposed that these neurons are linked by extraordinarily abundant gap junctions consisting of connexin32 (Cx32) and connexin26 (Cx26), and that those same connexins abundantly link neurons to astrocytes. Based on the controversial nature of those claims, immunofluorescence imaging and freeze-fracture replica immunogold labeling were used to re-investigate the abundance and connexin composition of neuronal and glial gap junctions in developing and adult rat and mouse locus coeruleus. In early postnatal development, connexin36 (Cx36) and connexin43 (Cx43) immunofluorescent puncta were densely distributed in the locus coeruleus, whereas Cx32 and Cx26 were not detected. By freeze-fracture replica immunogold labeling, Cx36 was found in ultrastructurally-defined neuronal gap junctions, whereas Cx32 and Cx26 were not detected in neurons and only rarely detected in glia. In 28-day postnatal (adult) rat locus coeruleus, immunofluorescence labeling for Cx26 was always co-localized with the glial gap junction marker Cx43; Cx32 was associated with the oligodendrocyte marker 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase); and Cx36 was never co-localized with Cx26, Cx32 or Cx43. Ultrastructurally, Cx36 was localized to gap junctions between neurons, whereas Cx32 was detected only in oligodendrocyte gap junctions; and Cx26 was found only rarely in astrocyte junctions but abundantly in pia mater. Thus, in developing and adult locus coeruleus, neuronal gap junctions contain Cx36 but do not contain detectable Cx32 or Cx26, suggesting that the locus coeruleus has the same cell-type specificity of connexin expression as observed ultrastructurally in other regions of the CNS. Moreover, in both developing and adult locus coeruleus, no evidence was found for gap junctions or connexins linking neurons with astrocytes or oligodendrocytes, indicating that neurons in this nucleus are not linked to the pan-glial syncytium by Cx32- or Cx26-containing gap junctions or by abundant free connexons composed of those connexins.

Estradiol modulates brainstem catecholaminergic cell groups and projections to the auditory forebrain in a female songbird

In songbirds, hearing conspecific song induces robust expression of the immediate early gene zenk in the auditory forebrain. This genomic response to song is well characterized in males and females of many species, and is highly selective for behaviorally relevant song. In white-throated sparrows, the selectivity of the zenk response requires breeding levels of estradiol; we previously showed that in non-breeding females with low levels of plasma estradiol, the zenk response to hearing song is no different than the response to hearing frequency-matched tones. Here, we investigated the role of brainstem catecholaminergic cells groups, which project to the forebrain, in estradiol-dependent selectivity. First, we hypothesized that estradiol treatment affects catecholaminergic innervation of the auditory forebrain as well as its possible sources in the brainstem. Immunohistochemical staining of tyrosine hydroxylase revealed that estradiol treatment significantly increased the density of catecholaminergic innervation of the auditory forebrain as well as the number of catecholaminergic cells in the locus coeruleus (A6) and the ventral tegmental area (A10), both of which are known to contain estrogen receptors in songbirds. Second, we hypothesized that during song perception, catecholaminergic cell groups of the brainstem actively participate in auditory selectivity via estrogen-dependent changes in activity. We found that hearing songs did not induce the expression of zenk, a putative marker of activity, within catecholaminergic neurons in any of the cell groups quantified. Together, our results suggest that estradiol induces changes in brainstem catecholaminergic cell groups that may play a neuromodulatory role in behavioral and auditory selectivity.

Testing computational models of dopamine and noradrenaline dysfunction in attention deficit/hyperactivity disorder

We test our neurocomputational model of fronto-striatal dopamine (DA) and noradrenaline (NA) function for understanding cognitive and motivational deficits in attention deficit/hyperactivity disorder (ADHD). Our model predicts that low striatal DA levels in ADHD should lead to deficits in 'Go' learning from positive reinforcement, which should be alleviated by stimulant medications, as observed with DA manipulations in other populations. Indeed, while nonmedicated adult ADHD participants were impaired at both positive (Go) and negative (NoGo) reinforcement learning, only the former deficits were ameliorated by medication. We also found evidence for our model's extension of the same striatal DA mechanisms to working memory, via interactions with prefrontal cortex. In a modified AX-continuous performance task, ADHD participants showed reduced sensitivity to working memory contextual information, despite no global performance deficits, and were more susceptible to the influence of distractor stimuli presented during the delay. These effects were reversed with stimulant medications. Moreover, the tendency for medications to improve Go relative to NoGo reinforcement learning was predictive of their improvement in working memory in distracting conditions, suggestive of common DA mechanisms and supporting a unified account of DA function in ADHD. However, other ADHD effects such as erratic trial-to-trial switching and reaction time variability are not accounted for by model DA mechanisms, and are instead consistent with cortical noradrenergic dysfunction and associated computational models. Accordingly, putative NA deficits were correlated with each other and independent of putative DA-related deficits. Taken together, our results demonstrate the usefulness of computational approaches for understanding cognitive deficits in ADHD.

Enhanced emotion-induced amnesia in borderline personality disorder

BACKGROUND

Current biological concepts of borderline personality disorder (BPD) emphasize the interference of emotional hyperarousal and cognitive functions. A prototypical example is episodic memory. Pre-clinical investigations of emotion-episodic memory interactions have shown specific retrograde and anterograde episodic memory changes in response to emotional stimuli. These changes are amygdala dependent and vary as a function of emotional arousal and valence.

METHOD

To determine whether there is amygdala hyper-responsiveness to emotional stimuli as the underlying pathological substrate of cognitive dysfunction in BPD, 16 unmedicated female patients with BPD were tested on the behavioural indices of emotion-induced amnesia and hypermnesia established in 16 healthy controls.

RESULTS

BPD patients displayed enhanced retrograde and anterograde amnesia in response to presentation of negative stimuli, while positive stimuli elicited no episodic memory-modulating effects.

CONCLUSION

These findings suggest that an amygdala hyper-responsiveness to negative stimuli may serve as a crucial aetiological contributor to emotion-induced cognitive dysfunction in BPD.

There and back again: a tale of norepinephrine and drug addiction

Fueled by anatomical, electrophysiological, and pharmacological analyses of endogenous brain reward systems, norepinephrine (NE) was identified as a key mediator of both natural and drug-induced reward in the late 1960s and early 1970s. However, reward experiments from the mid-1970s that could distinguish between the noradrenergic and dopaminergic systems resulted in the prevailing view that dopamine (DA) was the primary 'reward transmitter' (a belief holding some sway still today), thereby pushing NE into the background. Most damaging to the NE hypothesis of reward were studies demonstrating that NE receptor antagonists and NE reuptake inhibitors failed to impact drug self-administration. In recent years new tools, such as genetically engineered mice, and new experimental paradigms, such as reinstatement of drug seeking following withdrawal, have propelled NE back into the awareness of addiction researchers. Of particular interest is disulfiram, an inhibitor of the NE biosynthetic enzyme dopamine beta-hydroxylase, which has demonstrated promising efficacy in the treatment of cocaine dependence in preliminary clinical trials. The purpose of this review is to synthesize the new data linking NE to critical aspects of DA signaling and drug addiction, with a focus on psychostimulants (eg, cocaine), opiates (eg, morphine), and alcohol.

A reciprocal relationship between bottom-up trace strength and the attentional blink bottleneck: relating the LC-NE and ST(2) models

There is considerable current interest in neural modeling of the attentional blink phenomenon. Two prominent models of this task are the Simultaneous Type Serial Token (ST(2)) model and the Locus Coeruleus-Norepinephrine (LC-NE) model. The former of these generates a broad spectrum of behavioral data, while the latter provides a neurophysiologically detailed account. This paper explores the relationship between these two approaches. Specifically, we consider the spectrum of empirical phenomena that the two models generate, particularly emphasizing the need to generate a reciprocal relationship between bottom-up trace strength and the blink bottleneck. Then we discuss the implications of using ST(2) token mechanisms in the LC-NE setting.