The cognitive neuroscience of sustained attention: where top-down meets bottom-up

Mild body cooling impairs attention via distraction from skin cooling

Many contemporary workers are routinely exposed to mild cold stress, which may compromise mental function and lead to accidents. A study investigated the effect of mild body cooling of 1.0 degree C rectal temperature (Tre) on vigilance (i.e. sustained attention) and the orienting of spatial attention (i.e. spatially selective processing of visual information). Vigilance and spatial attention tests were administered to 14 healthy males and six females at four stages (pre-immersion, deltaTre = 0, -0.5 and - 1.0 degree C ) of a gradual, head-out immersion cooling session (18-25 deltaC water), and in four time-matched stages of a contrast session, in which participants sat in an empty tub and no cooling took place. In the spatial attention test, target discrimination times were similar for all stages of the contrast session, but increased significantly in the cooling phase upon immersion (deltaTre = 0 degrees C), with no further increases at deltaTre = -0.5 and - 1.0 degree C. Despite global response slowing, cooling did not affect the normal pattern of spatial orienting. In the vigilance test, the variability of detection time was adversely affected in the cooling but not the contrast trials: variability increased at immersion but did not increase further with additional cooling. These findings suggest that attentional impairments are more closely linked to the distracting effects of cold skin temperature than decreases in body core temperature.

Regulation of cognitive resources during sustained attention and working memory in 10-year-olds and adults

We examined differences between 10-year-olds and young adults in resource recruitment and regulation during tasks of sustained attention and spatial working memory. We administered participants spatial 0- and 1-back tasks and used pupillary dilation as a measure of resource recruitment. Repeated administration of 0-back led to smaller pupillary dilations and greater response time (RT) variability, revealing a vigilance decrement. Effects of repeated administration of 0-back and differences between 0- and 1-back in d' and RTs were similar between ages. Results further suggested that the children may not have been as effective as adults in extracting frequency information. Thus, on simple tasks of sustained attention and working memory, children recruit resources in a manner similar to adults. Finally, d' was correlated with RT variability on both tasks at both ages, highlighting the role of attentional fluctuations on both tasks.

Physiological responses of 5-month-old infants to smiling and blank faces

Physiological responses (i.e., EEG, heart period, respiratory sinus arrhythmia (RSA)) were monitored in 5-month-old infants during the replacement of an adult's smiling (SF) with a blank face (BF) in a face-to-face setting. Affect, while the infant looked at and away from the adult's face during both conditions, was analyzed. Infants displayed neutral and some positive affect while looking at both SF and BF. RSA was quantified continuously during both conditions. RSA increased during BF relative to SF. EEG was quantified only while the infants were looking at the adult's face during both conditions. An increase in theta over multiple scalp areas (AF3,4; F7,8; FC3; T6) was observed during BF relative to SF. The data suggest that infant attention to BF and SF reflect different psychophysiological processes that can be indexed by RSA and scalp-recorded theta.

Mechanisms of working memory dysfunction after mild and moderate TBI: evidence from functional MRI and neurogenetics

Cognitive complaints are a frequent source of distress and disability after mild and moderate traumatic brain injury (TBI). While there are deficits in several cognitive domains, many aspects of these complaints and deficits suggest that problems in working memory (WM) play an important role. Functional imaging studies in healthy individuals have outlined the neural substrate of WM and have shown that regions important in WM circuitry overlap with regions commonly vulnerable to damage in TBI. Use of functional MRI (fMRI) in individuals with mild and moderate TBI suggests that they can have problems in the activation and allocation of WM, and several lines of evidence suggest that subtle alterations in central catecholaminergic sensitivity may underlie these problems. We review the evidence from fMRI and neurogenetic studies that support the role of catecholaminergic dysregulation in the etiology of WM complaints and deficits after mild and moderate TBI.

Neuronal correlates of signal detection in the posterior parietal cortex of rats performing a sustained attention task

The posterior parietal cortex (PPC) plays an integral role in visuospatial attention. Evidence suggests that neuronal activity in the PPC predicts the allocation of attention to stimuli. The present experiment tested the hypothesis that in rats performing a sustained attention task, the detection of signals, as opposed to missed signals, is associated with increased PPC unit activity. Single unit activity was recorded from the PPC of rats and analyzed individually and as a population vector for each recording session. A population of single units (28/111) showed significant activation evoked by signals on trials resulting in correct performance (hits). A smaller population of neurons (three/111) was activated on trials in which signals were not detected by the animals (misses). Analysis of populations of simultaneously recorded neurons indicated increased activation predicting signal detection; no population of neurons was activated on trials in which the animal incorrectly pressed the hit lever following nonsignals. The increased, hit-predicting activity was not modulated by signal duration or the presence of a visual distractor, although the distractor reduced the number of trials in which hit-predicting activity and subsequent correct detection occurred. These findings indicate that attentional signal processing in the PPC integrates successful detection of signals.

Phasic norepinephrine: a neural interrupt signal for unexpected events

Extensive animal studies indicate that the neuromodulator norepinephrine plays an important role in specific aspects of vigilance, attention and learning, putatively serving as a neural interrupt or reset function. The activity of norepinephrine-releasing neurons in the locus coeruleus during attentional tasks is modulated not only by the animal's level of engagement and the sensory inputs, but also by temporally rich aspects of internal decision-making processes. Here, we propose that it is unexpected changes in the world within the context of a task that activate the noradrenergic interrupt signal. We quantify this idea in a Bayesian model of a well-studied visual discrimination task, demonstrating that the model captures a rich repertoire of noradrenergic responses at the sub-second temporal resolution.

Effects of task difficulty and target likelihood in area V4 of macaque monkeys

Spatial attention improves performance at attended locations and correspondingly modulates firing rates of cortical neurons. The size of these behavioral and neuronal effects depends on the difficulty of the task performed at the attended location. Psychological theorists have attributed this to a tighter focus of a fixed amount of processing resource at the attended location, but the effects of task difficulty on the distribution of neuronal effects of attention across the visual field have not been fully explored. We trained rhesus monkeys to do a detection task in which difficulty and spatial attention were manipulated independently. Probe stimuli were used to measure behavioral performance in different conditions of attention and difficulty. Animals performed better at attended locations and this advantage increased with difficulty, consistent with data from human psychophysics. Neuronal modulation by spatial attention was larger with greater difficulty. In two animals, increasing difficulty caused a modest increase in neuronal responses to visual stimuli regardless of the locus of spatial attention. In a third animal, which was previously trained to ignore multiple distracting stimuli, increasing task difficulty increased responses at the focus of attention and suppressed responses away from the focus of attention. The results show that difficulty can modulate effects of spatial attention in V4; it can alter the distribution of sensory responses across the visual scene in ways that may depend on the subject's behavioral strategy.

Effects of nucleus basalis magnocellularis stimulation on a socially transmitted food preference and c-Fos expression

Experiment 1 examined the effects of electrical stimulation of nucleus basalis magnocellularis (NBM) on a relational odor-association task--the social transmission of food preference (STFP). Rats were stimulated unilaterally in the NBM for 20 min (100 microA, 1 Hz) immediately before the social training. They were tested on their ability to remember preference for the trained food either immediately or following a 24-h delay. Stimulation of NBM improved retention regardless of delay, and additional behavioral measures (social interaction, motor activity, or exploration) did not account for such effects. Experiment 2 investigated brain regions activated after NBM electrical stimulation by examining the induction of c-Fos. This treatment led to bilateral increased c-Fos expression in prefrontal regions, such as orbitofrontal, prelimbic, and infralimbic cortices, and some hippocampal subregions (dorsal CA and ventral dentate gyrus). In contrast, no differences between groups in c-Fos expression were found in basolateral amygdala, dorsal dentate gyrus, ventral CA, or ventral subiculum. Present findings indicate that pretraining NBM electrical stimulation facilitates the acquisition of STFP, supporting a role of NBM in the early stages of memory formation, and suggest that the treatment might cause such effects by inducing neural changes, related to transcription factors such as c-Fos, in the prefrontal cortex or the hippocampal formation.

Synaptologic and fine structural features distinguishing a subset of basal forebrain cholinergic neurons embedded in the dense intrinsic fiber network of the caudal extended amygdala

Cholinergic basal forebrain neurons confined within the intrinsic connections of the extended amygdala in the caudal sublenticular region and anterior amygdaloid area (cSLR/AAA) differ from other basal forebrain cholinergic neurons in several morphological and neurochemical respects. These cSLR/AAA cholinergic neurons have been subjected to additional investigations described in this report. First, fibers traced anterogradely following injections of Phaseolus vulgaris-leucoagglutinin in the central amygdaloid nucleus were shown to contact cSLR/AAA cholinergic neurons and dendrites. Second, these neurons were shown to be contacted by numerous GABAergic boutons with symmetric synaptic specializations. Third, the numbers of synaptic densities of morphologically characterized symmetric contacts on the somata and proximal dendrites of cSLR/AAA cholinergic neurons were shown to significantly exceed those of extra-cSLR/AAA cholinergic neurons. Fourth, fine structural features distinguishing cSLR/AAA cholinergic neurons from other basal forebrain cholinergic neurons were revealed. Specifically, cSLR/AAA cholinergic neurons have less abundant cytoplasm and a less well-organized system of rough endoplasmic reticulum than their counterparts in other parts of the basal forebrain. Thus, morphologically and neurochemically distinct cSLR/AAA cholinergic neurons exhibit robust proximal inhibitory inputs, of which a significant number originate in the extended amygdala, while cholinergic neurons outside this region lack a substrate for strong proximal inhibitory input. The implications of these findings for interaction of fear, anxiety, and attention are considered.

White matter growth as a mechanism of cognitive development in children

We examined the functional role of white matter growth in cognitive development. Specifically, we used hierarchical regression analyses to test the unique contributions of age versus white matter integrity in accounting for the development of information processing speed. Diffusion tensor imaging was acquired for 17 children and adolescents (age range 6-17 years), with apparent diffusion coefficient (ADC) and fractional anisotropy (FA) calculated for 10 anatomically defined fiber pathways and 12 regions of hemispheric white matter. Measures of speeded visual-spatial searching, rapid picture naming, reaction time in a sustained attention task, and intelligence were administered. Age-related increases were evident across tasks, as well as for white matter integrity in hemispheric white matter. ADC was related to few measures. FA within multiple hemispheric compartments predicted rapid picture naming and standard error of reaction time in sustained attention, though it did not contribute significantly to the models after controlling for age. Independent of intelligence, visual-spatial searching was related to FA in a number of hemispheric regions. A novel finding was that only right frontal-parietal regions contributed uniquely beyond the effect of age in accounting for performance: age did not contribute to visual-spatial searching when FA within these regions was first included in the models. Considering we found that both FA in right frontal-parietal regions and speed of visual-spatial searching increased with age, our findings are consistent with the growth of regional white matter organization as playing an important role in increased speed of visual searching with age.

Effects of aging on transient and sustained successful memory encoding activity

Event-related fMRI studies have investigated age-related changes in encoding by identifying greater activity for items that are later remembered than for those that are forgotten (difference in memory, or Dm). The present study used hybrid blocked/event-related analyses to distinguish between transient Dm versus sustained Dm. Dm was identified as parametric increases in encoding activity as a function of a combined subsequent memory/confidence scale. Dm was measured in each trial (transient activity) and in blocks of eight trials (sustained activity). Transient Dm analyses showed age-related reductions in the left hippocampus but increases in left prefrontal cortex (PFC). Sustained Dm analyses showed age-related reductions in right PFC, but no region showing increased activity in older adults. These findings suggests that during semantic classification older adults show less spontaneous hippocampal-mediated encoding processes, but greater PFC-mediated semantic processes. Additionally, the decline in sustained Dm in PFC may involve age-related deficits in sustained attention that impact encoding processes. The results underscore the importance of investigating aging effects on both transient and sustained neural activity.

Investigating the enhancing effect of music on autobiographical memory in mild Alzheimer's disease

The enhancing effect of music on autobiographical memory recall in mild Alzheimer's disease individuals (n = 10; Mini-Mental State Examination score >17/30) and healthy elderly matched individuals (n = 10; Mini-Mental State Examination score 25-30) was investigated. Using a repeated-measures design, each participant was seen on two occasions: once in music condition (Vivaldi's 'Spring' movement from 'The Four Seasons') and once in silence condition, with order counterbalanced. Considerable improvement was found for Alzheimer individuals' recall on the Autobiographical Memory Interview in the music condition, with an interaction for condition by group (p < 0.005). There were no differences in terms of overall arousal using galvanic skin response recordings or attentional errors during the Sustained Attention to Response Task. A significant reduction in state anxiety was found on the State Trait Anxiety Inventory in the music condition (p < 0.001), suggesting anxiety reduction as a potential mechanism underlying the enhancing effect of music on autobiographical memory recall.

More attention must be paid: The neurobiology of attentional effort

Increases in attentional effort are defined as the motivated activation of attentional systems in response to detrimental challenges on attentional performance, such as the presentation of distractors, prolonged time-on-task, changing target stimulus characteristics and stimulus presentation parameters, circadian phase shifts, stress or sickness. Increases in attentional effort are motivated by the expected performance outcome; in the absence of such motivation, attentional performance continues to decline or may cease altogether. The beneficial effects of increased attentional effort are due in part to the activation of top-down mechanisms that act to optimize input detection and processing, thereby stabilizing or recovering attentional performance in response to challenges. Following a description of the psychological construct "attentional effort", evidence is reviewed indicating that increases in the activity of cortical cholinergic inputs represent a major component of the neuronal circuitry mediating increases in attentional effort. A neuronal model describes how error detection and reward loss, indicating declining performance, are integrated with motivational mechanisms on the basis of neuronal circuits between prefrontal/anterior cingulate and mesolimbic regions. The cortical cholinergic input system is activated by projections of mesolimbic structures to the basal forebrain cholinergic system. In prefrontal regions, increases in cholinergic activity are hypothesized to contribute to the activation of the anterior attention system and associated executive functions, particularly the top-down optimization of input processing in sensory regions. Moreover, and influenced in part by prefrontal projections to the basal forebrain, increases in cholinergic activity in sensory and other posterior cortical regions contribute directly to the modification of receptive field properties or the suppression of contextual information and, therefore, to the mediation of top-down effects. The definition of attentional effort as a cognitive incentive, and the description of a neuronal circuitry model that integrates brain systems involved in performance monitoring, the processing of incentives, activation of attention systems and modulation of input functions, suggest that 'attentional effort' represents a viable construct for cognitive neuroscience research.

Selective lesions of the nucleus basalis magnocellularis impair cognitive flexibility

The authors tested the hypothesis that the cholinergic nucleus basalis magnocellularis (NBM) is involved in solving problems requiring cognitive flexibility. Rats with 192 IgG-saporin lesions of the NBM were assessed for perseveration (i.e., cognitive inflexibility) in the serial reversal of an operant discrimination and during subsequent extinction testing. It was hypothesized that the NBM lesion and control groups would not differ in the acquisition of the initial, simple discrimination, because this task does not demand cognitive flexibility. In contrast, it was hypothesized that the NBM lesion group would show perseveration during serial reversal and extinction testing. Results generally supported these hypotheses, suggesting that the NBM plays an important role in mediating cognitive flexibility.

Sintomatologia depressiva, atenção sustentada e desempenho escolar em estudantes do ensino médio

A depressão inclui diversos sintomas cognitivos, tais como problemas de atenção que, por sua vez, podem prejudicar o desempenho escolar. De modo a verificar as relações entre essas variáveis, foram obtidas as notas escolares e aplicados o Teste de Atenção Concentrada e o Inventário de Depressão de Beck a 62 estudantes do ensino médio, de ambos os sexos, com idades entre 15 e 24 anos. Destes, 33,8% apresentaram sintomas depressivos, distribuídos entre os níveis leve e grave, sendo que as mulheres apresentaram maior severidade de sintomas que os homens. A severidade de sintomatologia depressiva mostrou-se negativamente correlacionada tanto com o desempenho escolar quanto com a qualidade da atenção. A comparação entre grupos com e sem sintomas de depressão revelaram que o primeiro apresentou desempenho escolar pior e déficit da atenção. Tais resultados corroboram a hipótese de relação entre depressão, atenção e desempenho escolar em alunos do Ensino Médio.

Neural response to sustained affective visual stimulation using an indirect task

Event-related potentials were recorded from 30 subjects using sustained stimulation and an indirect task, two strategies which facilitate affective responses that are complete and free of cognitive interference. Stimuli were of three types: pleasant, unpleasant and neutral. A three-phase pattern was found. The first phase, an amplitude increase in response to negative stimuli higher than to neutral and pleasant stimuli, was produced at 160 ms after stimulus onset, the prefrontal cortex being the origin of this phase. The second phase, characterized by maximal amplitudes in response to positive stimuli, was produced at 400 ms, originating in the visual cortex. Finally, the third phase, another amplitude increase in response to negative stimuli, was produced at 680 ms, and its source was located in the left precentral gyrus. Present data show that the cortical response to sustained emotional visual stimulation presented within indirect tasks provides information on attention-, motivation- and motor-related biases that complement information obtained under other experimental conditions.

Nicotinic modulation of neuronal networks: from receptors to cognition

RATIONALE

Nicotine affects many aspects of human cognition, including attention and memory. Activation of nicotinic acetylcholine receptors (nAChRs) in neuronal networks modulates activity and information processing during cognitive tasks, which can be observed in electroencephalograms (EEGs) and functional magnetic resonance imaging studies.

OBJECTIVES

In this review, we will address aspects of nAChR functioning as well as synaptic and cellular modulation important for nicotinic impact on neuronal networks that ultimately underlie its effects on cognition. Although we will focus on general mechanisms, an emphasis will be put on attention behavior and nicotinic modulation of prefrontal cortex. In addition, we will discuss how nicotinic effects at the neuronal level could be related to its effects on the cognitive level through the study of electrical oscillations as observed in EEGs and brain slices.

RESULTS/CONCLUSIONS

Very little is known about mechanisms of how nAChR activation leads to a modification of electrical oscillation frequencies in EEGs. The results of studies using pharmacological interventions and transgenic animals implicate some nAChR types in aspects of cognition, but neuronal mechanisms are only poorly understood. We are only beginning to understand how nAChR distribution in neuronal networks impacts network functioning. Unveiling receptor and neuronal mechanisms important for nicotinic modulation of cognition will be instrumental for treatments of human disorders in which cholinergic signaling have been implicated, such as schizophrenia, attention deficit/hyperactivity disorder, and addiction.

Increased capacity and density of choline transporters situated in synaptic membranes of the right medial prefrontal cortex of attentional task-performing rats

Cholinergic neurons innervating the cortex have been conceptualized as a major component of the attention system of the brain. Because of recent evidence indicating plastic mechanisms regulating choline transporter (CHT)-mediated high-affinity choline uptake, which is the rate-limiting step of acetylcholine synthesis, the present experiment determined the capacity of cholinergic terminals to transport choline, and the proportion of choline transporters localized in the membrane of synaptic terminals, in several brain regions of rats performing a cognitive vigilance task (CVT) and a simple reaction time task (SRTT) and nonperforming (NP) rats. Compared with evidence from NP rats, increased choline transporter capacity [as indicated by maximum transporter velocity (Vmax)] and an increased density of CHTs situated in synaptic plasma membrane, relative to intracellular locations, were observed in the medial prefrontal cortex of the right but not left hemisphere of CVT-performing animals. Furthermore, right medial prefrontal Vmax values of CVT-performing rats correlated positively and left medial Vmax values correlated negatively with the animals' performance in signal trials. Measures of CHT function in the brains of SRTT-performing animals did not differ significantly from those in NP rats. The present data support the hypothesis that an increased capacity of choline transporters in the right medial prefrontal cortex, primarily attributable to increased trafficking of transporters from intracellular compartments to the terminal membrane, represents a cellular mechanism contributing to the mediation of attentional performance.

NMDA and dopamine interactions in the nucleus accumbens modulate cortical acetylcholine release

The nucleus accumbens (NAC) plays a key role in directing appropriate motor output following the presentation of behaviorally relevant stimuli. As such, we postulate that accumbens efferents also participate in the modulation of neuronal circuits regulating attentional processes directed toward the identification and selection of these stimuli. In this study, N-methyl-d-aspartate (NMDA) and D1 ligands were perfused into the shell region of the NAC of awake rats. Cortical cholinergic transmission, a mediator of attentional processes, was measured via microdialysis probes inserted into the prefrontal cortex (PFC). NMDA perfusions (150 or 250 microm) into NAC resulted in significant increases in acetylcholine (ACh) efflux in PFC (150-200% above baseline levels). Co-administration of the D1 antagonist SCH-23390 (150 microm) markedly attenuated (by approx. 70%) ACh efflux following perfusions of 150 microm NMDA but not following 250 microm NMDA, suggesting that D1 receptor activity contributes to the ability of the lower but not the higher concentration of NMDA to increase cortical ACh release. Collectively, these data reveal a positive modulation of NMDA receptors by D1 receptors in NAC that is expressed trans-synaptically at the level of cortical transmission. This modulation may underlie the coordinated linking of attentional processes and motor output following exposure to salient and behaviorally relevant stimuli.

Mental chronometry of target detection: human thalamus leads cortex

Attentive monitoring of environmental stimuli is most fundamental for rapid target detection. The aim of this study was to assess the timing of thalamic versus cortical processes involved in this cognitive operation. To this end, simultaneous depth and scalp EEG was recorded in eight patients with essential tremor, undergoing thalamic deep brain stimulation (DBS), when the DBS electrodes could be accessed via their temporarily externalized leads. The patients performed an oddball task consisting of 300 presentations of one frequent and two rare visual cues, appearing in randomized order. One of the rare cues was defined as a target, the occurrences of which had to be indicated by a button press (motor condition) or silently counted (non-motor condition). At the scalp and the thalamus, event-related potentials (ERP) were largest upon target presentation, with peak latencies in the time domain of classical P300 responses. Remarkably, target-specific thalamic ERP emerged significantly prior to scalp P300. Furthermore, whereas scalp ERP had a higher amplitude upon rare than upon frequent non-target signals, thalamic ERP were independent of stimulus probability. This pattern was identified during motor and non-motor task execution. We conclude that the human thalamus specifically supports the early recognition of target events and can widely distribute this label through its divergent cortical projections.

Long-term effects of immunotoxic cholinergic lesions in the septum on acquisition of the cone-field task and noncognitive measures in rats

In rats, nonspecific mechanical or neurotoxic lesions of the septum impair spatial memory in, e.g., Morris water- and radial-maze tasks. Unfortunately, the lack of specificity of such lesions limits inferences about the role of the cholinergic hippocampal projections in spatial cognition. We therefore tested the effects of septal lesions produced by 192 IgG-saporin in rats, which is highly selective for basal forebrain cholinergic neurons, on home cage activity, noncognitive tests (modified Irwin test, open field and forced swimming tests, and various sensorimotor tasks), and the cone-field spatial learning task. The immunotoxic lesion reduced acetylcholine (ACh) levels in the septum (-61%) and hippocampus (>-75%). Rats with lesions showed mild home-cage hyperactivity at 4 weeks postlesion, but no noncognitive deficits at 13 weeks postsurgery. In the cone-field task, rats with septal lesions made more working- and reference-memory errors than the controls, but acquisition curves were parallel in both groups. The speed of visiting cones was faster in the rats with lesions, indicative of disturbed attention or increased motivation. These data support the growing evidence that involvement of the septohippocampal cholinergic system in spatial learning and memory may have been overestimated in studies that used lesions with poor selectivity.

The modulatory effects of nicotine on parietal cortex activity in a cued target detection task depend on cue reliability

This functional magnetic resonance imaging study investigates the effects of nicotine in a cued target detection task when changing cue reliability. Fifteen non-smoking volunteers were studied under placebo and nicotine (Nicorette polacrilex gum 1 and 2 mg). Validly and invalidly cued trials were arranged in blocks with high, middle and low cue reliability. Two effects of nicotine were investigated: its influence on i) parietal cortex activity underlying the processing of invalid vs. valid trials (i.e. validity effect) and ii) neural activity in the context of low, middle and high informative value of the cue (i.e. cue reliability effect). Nicotine did not affect behavioral performance. However, nicotine reduced the difference in the blood oxygenation level dependent (BOLD) signal between invalid and valid trials in the right intraparietal sulcus. The reduction of parietal activity in invalid trials was smaller in the low cue reliability condition. The same posterior parietal region exhibited a nicotinic modulation of BOLD activity in valid trials which was dependent on cue reliability: Nicotine specifically enhanced the neural activity during valid trials in the context of low cue reliability, i.e. when subjects are already in a state of low certainty. We speculate that the right intraparietal sulcus might be part of two networks working in parallel: one responsible for reorienting attention and the other for the cholinergic modulation of cue reliability. By reducing the use of the cue, nicotine modulates parietal activity related to reorienting attention in conditions with higher cue certainty. On the other hand, nicotine increases parietal activity in states of low certainty. This enhanced activation might influence brain regions, such as the posterior cingulate, directly involved in the processing of cue reliability.

Systems level modeling of a neuronal network subserving intrinsic alertness

Cognitive control of alertness in unwarned situations (intrinsic alertness) relies on a predominantly right hemisphere cortical and subcortical network. In a previous functional activation study, we have demonstrated that this network comprises the anterior cingulate gyrus, the dorsolateral and polar frontal as well as the inferior parietal cortex, the thalamus and ponto-mesencephalic parts of the brain stem. The aim of this study was to study effective connectivity of this network by employing structural equation modeling. Fifteen right-handed male subjects participated in the PET study. The functional network showed stronger connectivity in the right hemisphere. Furthermore, there were strong effective connections between thalamus and brainstem on the one hand and between thalamus and anterior cingulate on the other. Our results suggest that the anterior cingulate functions as the central coordinating structure for the right hemispheric neural network of intrinsic alertness and that the anterior cingulate gyrus is modulated mainly by prefrontal and parietal cortex.

Volatile anesthetics disrupt frontal-posterior recurrent information transfer at gamma frequencies in rat

We seek to understand neural correlates of anesthetic-induced unconsciousness. We hypothesize that cortical integration of sensory information may underlie conscious perception and may be disrupted by anesthetics. A critical role in frontal-posterior interactions has been proposed, and gamma (20-60 Hz) oscillations have also been assigned an essential role in consciousness. Here we investigated whether general anesthetics may interfere with the exchange of information encoded in gamma oscillations between frontal and posterior cortices. Bipolar electrodes for recording of event-related potentials (ERP) were chronically implanted in the primary visual cortex, parietal association and frontal association cortices of six rats. Sixty light flashes were presented every 5s, and ERPs were recorded at increasing concentrations of halothane or isoflurane (0-2%). Information exchange was estimated by transfer entropy, a novel measure of directional information transfer. Transfer entropy was calculated from 1-s wavelet-transformed ERPs. We found that (1) feedforward transfer entropy (FF-TE) and feedback transfer entropy (FB-TE) were balanced in conscious-sedated state; (2) anesthetics at concentrations producing unconsciousness augmented both FF-TE and FB-TE at 30 Hz but reduced them at 50 Hz; (3) reduction at 50 Hz was more pronounced for FB-TE, especially between frontal and posterior regions; (4) at high concentrations, both FF-TE and FB-TE at all frequencies were at or below conscious-sedated baseline. Our findings suggest that inhalational anesthetics preferentially impair frontal-posterior FB information transfer at high gamma frequencies consistent with the postulated role of frontal-posterior interactions in consciousness.

Spectral integration in auditory cortex: mechanisms and modulation

Auditory cortex contributes to the processing and perception of spectrotemporally complex stimuli. However, the mechanisms by which this is accomplished are not well understood. In this review, we examine evidence that single cortical neurons receive input covering much of the audible spectrum. We then propose an anatomical framework by which spectral information converges on single neurons in primary auditory cortex, via a combination of thalamocortical and intracortical "horizontal" pathways. By its nature, the framework confers sensitivity to specific, spectrotemporally complex stimuli. Finally, to address how spectral integration can be regulated, we show how one neuromodulator, acetylcholine, could act within the hypothesized framework to alter integration in single neurons. The results of these studies promote a cellular understanding of information processing in auditory cortex.

Perfusion functional MRI reveals cerebral blood flow pattern under psychological stress

Despite the prevalence of stress in everyday life and its impact on happiness, health, and cognition, little is known about the neural substrate of the experience of everyday stress in humans. We use a quantitative and noninvasive neuroimaging technique, arterial spin-labeling perfusion MRI, to measure cerebral blood flow (CBF) changes associated with mild to moderate stress induced by a mental arithmetic task with performance monitoring. Elicitation of stress was verified by self-report of stress and emotional state and measures of heart rate and salivary-cortisol level. The change in CBF induced by the stress task was positively correlated with subjective stress rating in the ventral right prefrontal cortex (RPFC) and left insula/putamen area. The ventral RPFC along with right insula/putamen and anterior cingulate showed sustained activation after task completion in subjects reporting a high stress level during arithmetic tasks. Additionally, variations of baseline CBF in the ventral RPFC and right orbitofrontal cortex were found to correlate with changes in salivary-cortisol level and heart rate caused by undergoing stress tasks. We further demonstrated that the observed right prefrontal activation could not be attributed to increased cognitive demand accompanying stress tasks and extended beyond neural pathways associated with negative emotions. Our results provide neuroimaging evidence that psychological stress induces negative emotion and vigilance and that the ventral RPFC plays a key role in the central stress response.

Sustained attention in mild Alzheimer's disease

The vigilance decrement in perceptual sensitivity was examined in 10 patients with mild Alzheimer's disease (AD) and 20 age-matched controls. A visual high-event rate digit-discrimination task lasting 7.2 min. (six 1.2 min blocks) was presented at different levels of stimulus degradation. Previous studies have shown that sensitivity decrements (d') over time at high-stimulus degradation result from demands on effortful processing. For all degradation levels, the overall level of vigilance (d') was lower in AD patients than in controls. All participants showed sensitivity decrement over blocks, with greater decrement at higher degradation levels. AD patients exhibited greater sensitivity decrement over time at the highest degradation level they all could perform relative to control participants. There were no concomitant changes in either response bias (C) or response times. The results indicate that mild AD patients have overall lower levels of vigilance under conditions that require both automatic and effortful processing. Mild AD patients also exhibit a deficit in the maintenance of vigilance over time under effortful processing conditions. Although the sample of AD patients was small, results further suggest that both possible and probable AD patients had greater sensitivity decrement over time at the highest degradation level than did control participants, but only probable AD patients had lower overall levels of vigilance. In the possible AD patients as a group, the decrement in vigilance occurred in the absence of concurrent deficits on standard attentional tasks, such as the Stroop and Trail Making tests, suggesting that deficits in vigilance over time may appear earlier than deficits in selective attention.

Microsphere embolism-induced cortical cholinergic deafferentation and impairments in attentional performance

Ischemic events have been hypothesized to play a critical role on the pathogenesis of dementia and the acceleration of cognitive impairments. This experiment was designed to determine the consequences of microvascular ischemia on the cortical cholinergic input system and associated attention capacities. Injections of microspheres ( approximately 50 microm diameter; approximately 5000 microspheres/100 microL) into the right common carotid artery of rats served as a model of microvascular ischemia and resulted in decreases in the density of cholinergic fibers in the ipsilateral medial prefrontal cortex and frontoparietal areas. Furthermore, dense astrogliosis, indicated by glial fibrillary acidic protein (GFAP) immunohistochemistry, was observed in the globus pallidus, including the areas of origin of cholinergic projections to the cortex. Fluoro-Jade B staining indicated that loss of neurons in the cortex was restricted to areas of microsphere-induced infarcts. Attentional performance was assessed using an operant sustained attention task; performance in this task was previously demonstrated to reflect the integrity and activity of the cortical cholinergic input system. Embolized animals' performance was characterized by a decrease in the animals' ability to detect signals. Their performance in non-signal trials remained unaffected. The residual density of cholinergic axons in prefrontal and frontoparietal areas correlated with the animals' performance. The present data support the hypothesis that microvascular ischemia results in loss of cortical cholinergic inputs and impairs associated attentional performance. Microsphere embolism represents a useful animal model for studying the role of interactions between microvascular disorder and impaired forebrain cholinergic neurotransmission in the manifestation of cognitive impairments.

Preparation for speeded action as a psychophysiological concept

Mental preparation aids performance and induces multiple physiological changes that should inform concepts of preparation. To date, however, these changes have been interpreted as being due to a global preparatory process (e.g., attention or alertness). The authors review psychophysiological and performance investigations of preparation. Concepts of the central regulation of action offer an integrative framework for understanding the psychophysiology of preparation. If people process multiple streams of information concurrently, then preparatory processing requires a form of supervisory attention- central regulation to maintain unity of action. This concept is consistent with existing psychophysiological results and links them to current views of information processing. Conversely, psychophysiological measures may provide indices to test concepts within theories of the central regulation of action.

Necker cube reversals during long-term EEG recordings: sub-bands of alpha activity

Reversible figures, such as the Necker cube, make up a well-known class of visual phenomena in which an invariant stimulus pattern gives rise to at least two different perceptual interpretations. A better understanding of the neurophysiological processes underlying perceptual reversals might help to disentangle bottom-up from top-down influences on multistable perception. Recently, we reported alpha activity decrease during multistable visual perception. The aim of the present study was to define more specifically the functional roles of the EEG alpha band during the perception of Necker cube reversals by subdividing the extended alpha band into three sub-bands (lower-1 alpha, lower-2 alpha, upper alpha). We employed a long-term recording condition, during which 10 healthy participants observed the Necker cube for approximately 60 min and responded by pressing a button to any perceived reversal. The results showed a reversal induced alpha desynchronization for the lower alpha bands, with the lower-2 alpha desynchronization differing across the time course of the experiment. The upper alpha band demonstrated no reliable effects. It is concluded that the lower-1 alpha desynchronization reflects an automatic arousal reaction which triggers attentional processing in a bottom-up manner, whereas the lower-2 alpha desynchronization is related to attentional processes that are achieved by top-down control with limited resources. The lack of reliable effects in the upper alpha band is presumably due to the relatively low semantic task demands in figure reversal.

Prefrontal cortical modulation of acetylcholine release in posterior parietal cortex

Attentional processing is a crucial early stage in cognition and is subject to "top-down" regulation by prefrontal cortex (PFC). Top-down regulation involves modification of input processing in cortical and subcortical areas, including the posterior parietal cortex (PPC). Cortical cholinergic inputs, originating from the basal forebrain cholinergic system, have been demonstrated to mediate important aspects of attentional processing. The present study investigated the ability of cholinergic and glutamatergic transmission within PFC to regulate acetylcholine (ACh) release in PPC. The first set of experiments demonstrated increases in ACh efflux in PPC following AMPA administration into the PFC. These increases were antagonized by co-administration of the AMPA receptor antagonist DNQX into the PFC. The second set of experiments demonstrated that administration of carbachol, but not nicotine, into the PFC also increased ACh efflux in PPC. The effects of carbachol were attenuated by co-administration (into PFC) of a muscarinic antagonist (atropine) and partially attenuated by the nicotine antagonist mecamylamine and DNQX. Perfusion of carbachol, nicotine, or AMPA into the PPC did not affect PFC ACh efflux, suggesting that these cortical interactions are not bi-directional. These studies demonstrate the capacity of the PFC to regulate ACh release in the PPC via glutamatergic and cholinergic prefrontal mechanisms. Prefrontal regulation of ACh release elsewhere in the cortex is hypothesized to contribute to the cognitive optimization of input processing.

Effects of excitotoxic thalamic intralaminar nuclei lesions on attention and working memory

In rats, lesions of the thalamic intralaminar nuclei (ILn) impair measures of working memory, but it is unclear whether alterations of attention contribute to the mnemonic deficits. The present experiment tested the effects of ILn lesions on a two-lever attention task that required discrimination of visual signals and non-signals. Rats were trained presurgically in the task and then received sham surgery or infusions of n-methyl-d-aspartate (NMDA) into the ILn to induce excitotoxic lesions. ILn lesions transiently decreased accurate detection of signals. ILn lesions also increased omissions. Compared to sham-lesioned rats, ILn-lesioned animals were not differentially affected when task demands were increased by presenting a visual distracter. Finally, a retention interval was incorporated into the task to assess whether the lesions affected acquisition of a working memory version of this behavioral paradigm. Unlike sham-lesioned animals, ILn-lesioned rats did not demonstrate a significant improvement in signal detection when a retention interval was introduced. The transient lesion-induced deficits in the attention task suggest that, in rats, the ILn may contribute to aspects of attentional processing, but through neural re-organization or activity in other regions, there is compensation for the loss of ILn functioning. The ILn appear to be necessary for maintaining performance when working memory demands are increased.

Unraveling the attentional functions of cortical cholinergic inputs: interactions between signal-driven and cognitive modulation of signal detection

Neurophysiological studies demonstrated that increases in cholinergic transmission in sensory areas enhance the cortical processing of thalamic inputs. Cholinergic activity also suppresses the retrieval of internal associations, thereby further promoting sensory input processing. Behavioral studies documented the role of cortical cholinergic inputs in attentional functions and capacities by demonstrating, for example, that the integrity of the cortical cholinergic input system is necessary for attentional performance, and that the activity of cortical cholinergic inputs is selectively enhanced during attentional performance. This review aims at integrating the neurophysiological and behavioral evidence on the functions of cortical cholinergic inputs and hypothesizes that the cortical cholinergic input system generally acts to optimize the processing of signals in attention-demanding contexts. Such signals 'recruit', via activation of basal forebrain corticopetal cholinergic projections, the cortical attention systems and thereby amplify the processing of attention-demanding signals (termed 'signal-driven cholinergic modulation of detection'). The activity of corticopetal cholinergic projections is also modulated by direct prefrontal projections to the basal forebrain and, indirectly, to cholinergic terminals elsewhere in the cortex; thus, cortical cholinergic inputs are also involved in the mediation of top-down effects, such as the knowledge-based augmentation of detection (see Footnote 1) of signals and the filtering of irrelevant information (termed 'cognitive cholinergic modulation of detection'). Thus, depending on the quality of signals and task characteristics, cortical cholinergic activity reflects the combined effects of signal-driven and cognitive modulation of detection. This hypothesis begins to explain signal intensity or duration-dependent performance in attention tasks, the distinct effects of cortex-wide versus prefrontal cholinergic deafferentation on attention performance, and it generates specific predictions concerning cortical acetylcholine (ACh) release in attention task-performing animals. Finally, the consequences of abnormalities in the regulation of cortical cholinergic inputs for the manifestation of the symptoms of major neuropsychiatric disorders are conceptualized in terms of dysregulation in the signal-driven and cognitive cholinergic modulation of detection processes.

Background gamma rhythmicity and attention in cortical local circuits: a computational study

We describe a simple computational model, based on generic features of cortical local circuits, that links cholinergic neuromodulation, gamma rhythmicity, and attentional selection. We propose that cholinergic modulation, by reducing adaptation currents in principal cells, induces a transition from asynchronous spontaneous activity to a "background" gamma rhythm (resembling the persistent gamma rhythms evoked in vitro by cholinergic agonists) in which individual principal cells participate infrequently and irregularly. We suggest that such rhythms accompany states of preparatory attention or vigilance and report simulations demonstrating that their presence can amplify stimulus-specific responses and enhance stimulus competition within a local circuit.

Nicotinic-serotonergic drug interactions and attentional performance in rats

RATIONALE

Both central serotonergic and nicotinic systems play important roles in a variety of neurobehavioral functions; however, the interactions of these two systems have not been fully characterized. The current study served to determine the impact of a relatively selective 5-HT2A receptor antagonist, ketanserin, on attentional function in rats and the interactions of ketanserin with nicotine administration.

METHODS

A standard operant visual signal detection task was used to assess sustained attention. In expt 1, adult female Sprague-Dawley rats (n = 39) were injected subcutaneously (SC) with a dose range of ketanserin (0, 0.25, 0.5 and 1 mg/kg). In expt 2, the interactions of acute ketanserin (0, 1 and 2 mg/kg, SC) and acute nicotine (0, 25 and 50 microg/kg, SC) were assessed. In expt 3, the interaction of acute ketanserin (0, 1 and 2 mg/kg, SC) and chronic nicotine (5 mg/kg per day, SC for 4 weeks via osmotic pump) was characterized. Using an operant visual signal detection task, three possible outcomes (dependent variables) were measured in each trial: percent hit, percent correct rejection, and response omissions.

RESULTS

Ketanserin, when given alone, did not have a significant effect on either percent hit or percent correct rejection. Acute administration of 25 microg/kg nicotine significantly improved percent hit (i.e. improvement in choice accuracy), an effect that was reversed by acute administration of 1 mg/kg ketanserin. Chronic nicotine infusion for 28 consecutive days significantly increased percent correct rejection (i.e. improvement in choice accuracy) without development of tolerance, an effect which was reversed by an acute dose of 2 mg/kg ketanserin.

CONCLUSIONS

These data suggest a functional interaction between nicotine and 5-HT2A receptor antagonist ketanserin.

Extraversion and cortical activation during memory performance

In this study we analyzed the influence of the personality dimension extraversion-introversion (E) on the level and topographical distribution of cortical activation. In 62 participants (32 introverts and 30 extraverts), we measured the extent of Event-Related Desynchronization (ERD) in the EEG during performance of a short-term memory (i.e., temporary maintenance of information) and a more complex working memory task (i.e., temporary maintenance and active manipulation of information). The results indicate that during performance of both tasks, introverts display a larger amount of ERD than extraverted individuals. Moreover, the present E effects largely match previous studies as to the restriction of these effects to lower EEG frequency ranges (approx. 4-8 Hz). Topographical analyses show that the E effects are primarily present over (right-hemispheric) frontal and parietal regions of the cerebral cortex.

Stimulation of cortical acetylcholine release by orexin A

The basal forebrain cholinergic system is a critical component of the neurobiological substrates underlying attentional function. Orexin neurons are important for arousal and maintenance of wakefulness and are found in the area of the hypothalamus previously shown to project to the basal forebrain. We used dual-probe in vivo microdialysis in rats to test the hypothesis that orexin A (OxA) increases cortical acetylcholine (ACh) release. Intrabasalis administration of OxA (0, 0.1, 10.0 microM via reverse dialysis) dose-dependently increased ACh release within the prefrontal cortex (PFC). In a separate group of animals, local (intra-PFC) administration of OxA via reverse dialysis was found to have no significant effect on ACh release. In order to obtain anatomical corroboration of the basal forebrain as a site of orexin modulation of corticopetal cholinergic activity, we used immunohistochemistry to examine the relationship between orexin fibers and cholinergic neurons in the basal forebrain. We observed widespread distribution of orexin-immunoreactive fibers in cholinergic regions of the basal forebrain, particularly in more rostral areas where frequent instances of apparent appositional contact were observed between orexin fibers and choline acetyltransferase-positive cell bodies. Collectively, these data suggest that orexin projections to the basal forebrain form an important link between hypothalamic arousal and forebrain attentional systems.

Nicotine modulates reorienting of visuospatial attention and neural activity in human parietal cortex

Prior studies in animals and humans indicate that reorienting of visuospatial attention is modulated by the cholinergic agonist nicotine. We have previously identified neural correlates of alerting and reorienting attention in humans and found that the parietal cortex is specifically involved in reorienting. This study investigates whether the alerting and reorienting systems, especially in the parietal cortex, are modulated by nicotine. We used event-related functional magnetic resonance imaging (fMRI) and studied 15 nonsmoking volunteers under placebo and nicotine (NICORETTE) polacrilex gum 1 and 2 mg). Subjects performed a cued target detection task with four different types of randomly intermixed trials (no, neutral, valid, and invalid cue trials). Alerting was captured by comparing BOLD activity and reaction times (RTs) in neutrally cued trials with no cue trials. Reorienting was isolated by comparing invalidly with validly cued trials. On the behavioral level, nicotine affected reorienting of attention by speeding RTs in invalidly cued trials; alerting was not affected by nicotine. Neurally, however, nicotine modulated both attentional systems. Pharmacologic effects on alerting-related brain activity were mainly evident as modulation of BOLD responses in the right angular gyrus and right middle frontal gyrus due to a reduction of neural activity in no cue trials. In the reorienting system, effects of nicotine were mainly evident in the left intraparietal sulcus and precuneus and due to a reduction of neural activity in invalidly cued trials. We conclude that nicotine enhances reorienting of attention in visuospatial tasks and that one behavioral correlate of speeded RTs is reduced parietal activity.

Removal of cholinergic input to perirhinal cortex disrupts object recognition but not spatial working memory in the rat

The perirhinal cortex of the temporal lobe has a crucial role in object recognition memory. Cholinergic transmission within perirhinal cortex also seems to be important for this function, as the muscarinic receptor antagonist scopolamine disrupts object recognition performance when administered systemically or directly into perirhinal cortex. In the present study, we directly assessed the contribution of cholinergic basal forebrain input to perirhinal cortex in object recognition. Selective bilateral removal of the cholinergic basal forebrain inputs to perirhinal cortex was accomplished by injecting the immunotoxin 192 IgG-saporin directly into perirhinal cortex in rats. These animals were significantly impaired relative to vehicle-injected controls in a spontaneous object recognition task despite intact spatial alternation performance. These results are consistent with recent reports of object recognition impairment following acute cholinergic receptor blockade and extend these findings by demonstrating that chronic removal of cholinergic basal forebrain input to an otherwise intact perirhinal cortex causes a severe object recognition deficit similar to that associated with more extensive cell body lesions of perirhinal cortex.

Cortical response to subjectively unconscious danger

Cortical involvement in the evolution-favored automatic reaction to danger was studied. Electrical neural activity was recorded from 31 subjects, reporting fear of spiders, at 60 scalp locations. Visual stimuli containing spiders (negative elements) or, alternatively, nonnegative elements were presented to subjects, though they were unaware of their presence: a concurrent visual detection task using consciously perceived targets was administered. Spatial and temporal principal component analyses were employed to define and quantify, in a reliable manner, the main components of the neuroelectrical response to unconscious stimuli, and a source localization algorithm provided information on their neural origin. Results indicated that around 150 ms after stimulus onset, ventromedial prefrontal areas previously reported as responding rapidly to danger-related (conscious) stimuli were activated by unconsciously perceived spiders more markedly than by nonnegative unconscious stimuli. Subsequently, around 500 ms after stimulus onset, activation of the posterior cingulate and visual association cortices increased in this same direction. These data support previous results indicating that the ventromedial prefrontal cortex is involved in the top-down regulation of attention (through its capability to modulate the activity of posterior cortices in charge of visual processing) and that it automatically facilitates danger processing.

Neurocognitive mechanisms underlying the experience of flow

Recent theoretical and empirical work in cognitive science and neuroscience is brought into contact with the concept of the flow experience. After a brief exposition of brain function, the explicit-implicit distinction is applied to the effortless information processing that is so characteristic of the flow state. The explicit system is associated with the higher cognitive functions of the frontal lobe and medial temporal lobe structures and has evolved to increase cognitive flexibility. In contrast, the implicit system is associated with the skill-based knowledge supported primarily by the basal ganglia and has the advantage of being more efficient. From the analysis of this flexibility/efficiency trade-off emerges a thesis that identifies the flow state as a period during which a highly practiced skill that is represented in the implicit system's knowledge base is implemented without interference from the explicit system. It is proposed that a necessary prerequisite to the experience of flow is a state of transient hypofrontality that enables the temporary suppression of the analytical and meta-conscious capacities of the explicit system. Examining sensory-motor integration skills that seem to typify flow such as athletic performance, writing, and free-jazz improvisation, the new framework clarifies how this concept relates to creativity and opens new avenues of research.

Activity of neurons in the basal magnocellular nucleus during performance of an operant task

Spike activity was studied in 95 neurons in the basal magnocellular nucleus in rabbits during spontaneous behavior and during performance of a conditioned operant response. Nearly half the neurons (48.4%) showed significant (p < 0.05) negative correlations between spontaneous discharges and the power of the frontal lobe EEG delta rhythm; most of these cells could be identified as cholinergic projection neurons. Neurons of this group had predominantly excitatory responses to the conditioned stimulus during performance of the operant task, while the responses to the conditioned stimulus of presumptively non-cholinergic neurons, not projecting to the cortex, were mainly inhibitory. The activatory responses of neurons in the basal magnocellular nucleus to the conditioned stimulus were markedly stronger while the animals performed the operant response as compared with performances in which there was no response to the conditioned stimulus. These results provide evidence that the basal magnocellular nucleus supports the level of waking and attending required for performance of operant conditioned reflex activity.

Cue reactivity in nicotine and tobacco dependence: a “multiple-action” model of nicotine as a primary reinforcement and as an enhancer of the effects of smoking-associated stimuli

The present paper proposes a model for the identification and the validation of brain processes and mechanisms underlying smokers' cue reactivity. Smoking behaviour is maintained by the reinforcing properties of nicotine, but it was also proposed that nicotine enhances the conditioned value of smoking and nicotine-associated stimuli. In fact, it is widely reported that the exposure of smokers to smoking/nicotine-associated stimuli induces cue reactivity, which is a vast array of physiological, psychological and behavioural responses. Imaging studies are revealing neuroanatomical correlates of cue reactivity in brain areas involved in motivational, emotional, cognitive processes and in their integration. Behavioural studies in laboratory animal models have shown analogies between the effects of nicotine-associated stimuli and cue reactivity effects in smokers. Lesion and mapping studies with nicotine reported brain activation patterns in cortico-limbic areas similarly to those obtained with imaging studies in humans. Although only limited studies have been done with nicotine-associated stimuli in animals, the identification of molecular mechanisms underlying other drugs of abuse-associated cue effect may help to propose potential common molecular mechanisms for nicotine cues. These findings suggest that smoking/nicotine-associated stimuli are processed at two levels: (i), bottom-up, automatic processing in a parallel fashion through ascendant pathways, to activate attentional functions; (ii), top-down, in a serial fashion from cortical areas, to modulate sensory inputs and motor control. It appears that nicotine increase information processing at both levels so as to establish and to amplify the conditioned value of smoking cues.