A specific role for the thalamus in mediating the interaction of attention and arousal in humans

Light as a modulator of cognitive brain function

Humans are a diurnal species usually exposed to light while engaged in cognitive tasks. Light not only guides performance on these tasks through vision but also exerts non-visual effects that are mediated in part by recently discovered retinal ganglion cells maximally sensitive to blue light. We review recent neuroimaging studies which demonstrate that the wavelength, duration and intensity of light exposure modulate brain responses to (non-visual) cognitive tasks. These responses to light are initially observed in alertness-related subcortical structures (hypothalamus, brainstem, thalamus) and limbic areas (amygdala and hippocampus), followed by modulations of activity in cortical areas, which can ultimately affect behaviour. Light emerges as an important modulator of brain function and cognition.

The neurophysiological bases of emotion: An fMRI study of the affective circumplex using emotion-denoting words

OBJECTIVE

We aimed to study the neural processing of emotion-denoting words based on a circumplex model of affect, which posits that all emotions can be described as a linear combination of two neurophysiological dimensions, valence and arousal. Based on the circumplex model, we predicted a linear relationship between neural activity and incremental changes in these two affective dimensions.

METHODS

Using functional magnetic resonance imaging, we assessed in 10 subjects the correlations of BOLD (blood oxygen level dependent) signal with ratings of valence and arousal during the presentation of emotion-denoting words.

RESULTS

Valence ratings correlated positively with neural activity in the left insular cortex and inversely with neural activity in the right dorsolateral prefrontal and precuneus cortices. The absolute value of valence ratings (reflecting the positive and negative extremes of valence) correlated positively with neural activity in the left dorsolateral and medial prefrontal cortex (PFC), dorsal anterior cingulate cortex, posterior cingulate cortex, and right dorsal PFC, and inversely with neural activity in the left medial temporal cortex and right amygdala. Arousal ratings and neural activity correlated positively in the left parahippocampus and dorsal anterior cingulate cortex, and inversely in the left dorsolateral PFC and dorsal cerebellum.

CONCLUSION

We found evidence for two neural networks subserving the affective dimensions of valence and arousal. These findings clarify inconsistencies from prior imaging studies of affect by suggesting that two underlying neurophysiological systems, valence and arousal, may subserve the processing of affective stimuli, consistent with the circumplex model of affect.

Late evening brain activation patterns and their relation to the internal biological time, melatonin, and homeostatic sleep debt

Sleep propensity increases sharply at night. Some evidence implicates the pineal hormone melatonin in this process. Using functional magnetic resonance imaging, brain activation during a visual search task was examined at 22:00 h (when endogenous melatonin levels normally increase). The relationships between brain activation, endogenous melatonin (measured in saliva), and self-reported fatigue were assessed. Finally, the effects of exogenous melatonin administered at 22:00 h were studied in a double blind, placebo-controlled crossover manner. We show that brain activation patterns as well as the response to exogenous melatonin significantly differ at night from those seen in afternoon hours. Thus, activation in the rostro-medial and lateral aspects of the occipital cortex and the thalamus diminished at 22:00 h. Activation in the right parietal cortex increased at night and correlated with individual fatigue levels, whereas exogenous melatonin given at 22:00 h reduced activation in this area. The right dorsolateral prefrontal cortex, an area considered to reflect homeostatic sleep debt, demonstrated increased activation at 22:00 h. Surprisingly, this increase correlated with endogenous melatonin. These results demonstrate and partially differentiate circadian effects (whether mediated by melatonin or not) and homeostatic sleep debt modulation of human brain activity associated with everyday fatigue at night.

Using computational cognitive modeling to predict dual-task performance with sleep deprivation

OBJECTIVE

The effects of fatigue on multiple-task performance were explored through computational cognitive modeling.

BACKGROUND

Fatigue typically has a negative impact on human performance. Biomathematical models exist that characterize the dynamics of human alertness, but the link between alertness and in situ performance on specific tasks is tenuous. Cognitive architectures offer a principled means of establishing that link.

METHOD

We implemented mechanisms for fatigue, which produce microlapses in cognitive processing, into an existing model, adaptive control of thought-rational, and validated the performance predictions with Bratzke, Rolke, Ulrich, and Peters' data on fatigue and multiple-task performance.

RESULTS

The microlapse model replicated the human performance results very well with zero free parameters, although the fit was improved when we allowed two individual differences parameters to vary.

CONCLUSION

Increased frequency of microlapses as a result of fatigue provides a parsimonious explanation for the impact of fatigue on dual-task performance and is consistent with previous research.

APPLICATION

Our results illustrate how using biomathematical models of fatigue in conjunction with a cognitive architecture can result in accurate predictions of the effects of fatigue on dual-task performance. Extending and generalizing this capability has potential utility in any safety-critical domain in which fatigue may affect performance.

Impairment of attentional networks after 1 night of sleep deprivation

Here, we assessed the effects of sleep deprivation (SD) on brain activation and performance to a parametric visual attention task. Fourteen healthy subjects underwent functional magnetic resonance imaging of ball-tracking tasks with graded levels of difficulty during rested wakefulness (RW) and after 1 night of SD. Self-reports of sleepiness were significantly higher and cognitive performance significantly lower for all levels of difficulty for SD than for RW. For both the RW and the SD sessions, task difficulty was associated with activation in parietal cortex and with deactivation in visual and insular cortices and cingulate gyrus but this pattern of activation/deactivation was significantly lower for SD than for RW. In addition, thalamic activation was higher for SD than for RW, and task difficulty was associated with increases in thalamic activation for the RW but not the SD condition. This suggests that thalamic resources, which under RW conditions are used to process increasingly complex tasks, are being used to maintain alertness with increasing levels of fatigue during SD. Thalamic activation was also inversely correlated with parietal and prefrontal activation. Thus, the thalamic hyperactivation during SD could underlie the reduced activation in parietal and blunted deactivation in cingulate cortices, impairing the attentional networks that are essential for accurate visuospatial attention performance.

Short-term adaptation to a simple motor task: a physiological process preserved in multiple sclerosis

Short-term adaptation indicates the attenuation of the functional MRI (fMRI) response during repeated task execution. It is considered to be a physiological process, but it is unknown whether short-term adaptation changes significantly in patients with brain disorders, such as multiple sclerosis (MS). In order to investigate short-term adaptation during a repeated right-hand tapping task in both controls and in patients with MS, we analyzed the fMRI data collected in a large cohort of controls and MS patients who were recruited into a multi-centre European fMRI study. Four fMRI runs were acquired for each of the 55 controls and 56 MS patients at baseline and 33 controls and 26 MS patients at 1-year follow-up. The externally cued (1 Hz) right hand tapping movement was limited to 3 cm amplitude by using at all sites (7 at baseline and 6 at follow-up) identically manufactured wooden frames. No significant differences in cerebral activation were found between sites. Furthermore, our results showed linear response adaptation (i.e. reduced activation) from run 1 to run 4 (over a 25 minute period) in the primary motor area (contralateral more than ipsilateral), in the supplementary motor area and in the primary sensory cortex, sensory-motor cortex and cerebellum, bilaterally. This linear activation decay was the same in both control and patient groups, did not change between baseline and 1-year follow-up and was not influenced by the modest disease progression observed over 1 year. These findings confirm that the short-term adaptation to a simple motor task is a physiological process which is preserved in MS.

Subjective feeling of psychological fatigue is related to decreased reactivity in ventrolateral prefrontal cortex

The purpose of this study is to examine the relationship between subjective fatigue and brain function. Twenty-three healthy young volunteers participated in this study. Relationships were investigated between subjective fatigue assessed using visual-analogue scale (VAS) score and sleep duration, and cerebral cortex reactivity during a verbal fluency task by 52-channel near-infrared spectroscopy (NIRS). The VAS score negatively correlated with oxygenated hemoglobin concentration ([oxy-Hb]) increases in the bilateral channels over the regions from the ventrolateral part of the frontal lobe to the upper part of the temporal lobe during the verbal fluency task. Sleep duration in the previous night positively correlated with [oxy-Hb] increases in the bilateral channels over the dorsolateral prefrontal lobe also during the verbal fluency task. No significant correlations between the VAS score and sleep duration in the previous night with [oxy-Hb] increases were found during a control task, the left-finger-tapping task. The subjective feeling of psychological fatigue is related to decreased reactivities in the lateral frontal and superior temporal cortices and is unrelated to sleep duration in the previous night, which is reflected in the reactivity in the dorsolateral prefrontal cortices. These results suggest that transient hypofunction and persistent dysfunction in the lateral prefrontal and temporal lobes are among the brain substrates of fatigue. These also demonstrate the advantage of NIRS for investigating brain function during subjective phenomena such as fatigue because it enables examination in a natural setting.

The Human Thalamus is Crucially Involved in Executive Control Operations

The processing of executive control is thought to involve cortical as well as thalamic brain areas. However, the questions of how thalamic structures contribute to the control of behavior and how cortical versus thalamic processing is coordinated remain to be settled. We therefore aimed at specifying respective activations during the performance of a go/no-go task. To this end, an electroencephalogram was recorded simultaneously from scalp and thalamic electrodes in seven patients undergoing deep brain stimulation. Meanwhile, left- or right-directed precues were presented indicating with which index finger a button press should be putatively executed. Thereafter, 2 sec elapsed until a go or no-go stimulus determined if the prepared movement had to be performed or withheld. In fronto-central scalp as well as in thalamic recordings, event-related potentials upon go versus no-go instructions were expressed differentially. This task effect was unrelated to motor processes and emerged significantly prior at thalamic than at scalp level. Amplitude fluctuations of depth and scalp responses showed site- and task-dependent correlations, particularly between thalamic and no-go-related activities at frontal recording sites. We conclude that an early classification of go and no-go instructions is performed already thalamically. It further appears that this information is subsequently utilized by cortical areas engaged in the definite inhibition of the prepared action.

Arousal and attention: self-chosen stimulation optimizes cortical excitability and minimizes compensatory effort

Cortical excitability is assumed to depend on cortical arousal level in an inverted U-shaped fashion: Largest (optimal) excitability is usually associated with medium levels of arousal. It has been proposed that under conditions of low arousal, compensatory effort is exerted if attentional demands persist. People tend to avoid this resource-consuming top-down compensation by creating or selecting environmental conditions that provide sufficient bottom-up stimulation. These assumptions were tested in an attention-demanding dual-task situation: We combined a simulated driving task to induce three different arousal levels by varying stimulation (high vs. low vs. self-chosen) with a visual two-stimulus paradigm to assess cortical excitability by the initial contingent negative variation (iCNV) component of the event-related potential. Additionally, we analyzed the oscillatory power of the beta2 band of the electroencephalogram at anterior frontal sites, which is assumed to reflect low-arousal compensatory activity. The iCNV amplitude differed in all three arousal conditions as expected: It was highest in the condition of self-chosen stimulation and lowest in the low- and high-arousal conditions. Additionally, in the low-arousal condition, anterior frontal beta2 power was found to be significantly higher than in the other two conditions and correlated positively with subjective strain. This pattern of results suggests that subjects select medium levels of stimulation which optimize cortical excitability under attentional demand conditions. The elevated fronto-central beta2 power in the low-stimulation condition may indicate the involvement of the anterior cingulate cortex in compensating for reduced arousal by top-down stimulation of the noradrenergic arousal system.

Consciousness and cerebral baseline activity fluctuations

The origin of within-subject variability in perceptual experiments is poorly understood. We here review evidence that baseline brain activity in the areas involved in sensory perception predict subsequent variations in sensory awareness. We place these findings in light of recent findings on the architecture of spontaneous BOLD fluctuations in the awake human brain, and discuss the possible origins of the observed baseline brain activity fluctuations.

Does hormone therapy affect attention and memory in sleep-deprived women?

OBJECTIVES

To evaluate whether hormone therapy (HT) modifies cognitive performance during sleep deprivation in postmenopausal women. Comparison was made with a group of young women.

METHODS

Participants included 26 postmenopausal women (age 58-72 years, 16 HT users, 10 non-users), 11 young women (age 20-26 years). They spent four consecutive nights in the sleep laboratory. Cognitive tests of attention, working memory, and verbal episodic memory were carried out after the baseline night, 25-h sleep deprivation, and recovery night.

RESULTS

Sleep deprivation impaired performance in all groups. It was manifested either as delayed practice effect or deteriorated performance (p < 0.05). In simple reaction time and 10-choice reaction time, non-users and young maintained their performance, whereas HT users suffered a minor impairment (p < 0.01). In other measurements, there was no interaction of group and condition. In 10-choice reaction time and vigilance, postmenopausal women made fewer errors and omissions than the young (p < 0.05). For most tasks, all groups showed improvement after one recovery night.

CONCLUSIONS

HT had a minor adverse effect on cognitive performance during sleep deprivation. Attention and memory deteriorated similarly in postmenopausal and young women, despite the lower initial performance level of postmenopausal women. One night of sleep ensured recovery in most tasks.

Sleep deprivation and vigilant attention

Sleep deprivation severely compromises the ability of human beings to respond to stimuli in a timely fashion. These deficits have been attributed in large part to failures of vigilant attention, which many theorists believe forms the bedrock of the other more complex components of cognition. One of the leading paradigms used as an assay of vigilant attention is the psychomotor vigilance test (PVT), a high signal-load reaction-time test that is extremely sensitive to sleep deprivation. Over the last twenty years, four dominant findings have emerged from the use of this paradigm. First, sleep deprivation results in an overall slowing of responses. Second, sleep deprivation increases the propensity of individuals to lapse for lengthy periods (>500 ms), as well as make errors of commission. Third, sleep deprivation enhances the time-on-task effect within each test bout. Finally, PVT results during extended periods of wakefulness reveal the presence of interacting circadian and homeostatic sleep drives. A theme that links these findings is the interplay of "top-down" and "bottom-up" attention in producing the unstable and unpredictable patterns of behavior that are the hallmark of the sleep-deprived state.

Imaging the placebo response: a neurofunctional review

An emerging literature has started to document the neuronal changes associated with the placebo phenomenon. This has altered placebo from being considered a nuisance factor in clinical research to a target of scientific investigation per se. This paper reviews the neuroimaging literature on the placebo effect, and illustrates how imaging tools can improve current understanding of brain mechanisms underlying the placebo response. Imaging studies provide evidence of specific, predictable and replicable patterns of neural changes associated with placebo administration. In general, placebo responses seem mediated by "top-down" processes dependent on frontal cortical areas that generate and maintain cognitive expectancies. Dopaminergic reward pathways may underlie these expectancies. Placebo-induced clinical benefits also involve disorder-specific neuronal responses, yielding neurofunctional or neurochemical alterations similar to those produced by pharmacological treatments.

Sustained attention and serotonin: a pharmaco-fMRI study

OBJECTIVE

Evidence suggests that stimulation of serotonergic function in healthy humans causes an impairment of sustained attention. The present study assessed the influence of increased serotonin levels on brain areas involved in sustained attention.

METHODS

Ten healthy volunteers (5 females, 5 males) received the selective serotonin reuptake inhibitor (SSRI) escitalopram (20 mg) and placebo in a balanced, double blind, two-way crossover design. Participants performed the Mackworth Clock Test to measure sustained attention during functional MRI measurements at 3 Tesla. Subjective measurements after pharmacological manipulation were conducted with the Bond and Lader Questionnaire.

RESULTS

Independent of treatment, brain areas associated with task performance on a sustained attention task were activated, including right prefrontal and parietal areas. After escitalopram administration, less activation was shown in the caudate nucleus, thalamus, and frontal areas. No effect of escitalopram was shown on behavioral data although subjective measurements showed decreased alertness after escitalopram.

CONCLUSIONS

The results of the current pharmaco-functional magnetic resonance imaging (fMRI) study give a first indication of involvement of serotonin in sustained attention through modulating activation of selective brain areas including the thalamus and caudate nucleus. Possibly, these areas are involved in a subcortical network for sustained attention, but further research is necessary.

The effects of total sleep deprivation on bayesian updating

Subjects performed a decision task (Grether, 1980) in both a well-rested and experimentally sleep-deprived state. We found two main results: 1) final choice accuracy was unaffected by sleep deprivation, and yet 2) the estimated decision model differed significantly following sleep-deprivation. Following sleep deprivation, subjects placed significantly less weight on new information in forming their beliefs. Because the altered decision process still maintains decision accuracy, it may suggest that increased accident and error rates attributed to reduced sleep in modern society stem from reduced auxiliary function performance (e.g., slowed reaction time, reduced motor skills) or other components of decision making, rather than the inability to integrate multiple pieces of information.

Decomposing interference during Stroop performance into different conflict factors: an event-related fMRI study

In the current event-related functional magnetic resonance imaging (fMRI) study, we sought to trace back Stroop-interference to circumscribed properties of task-irrelevant word information - response-incompatibility, semantic incongruency and task-reference - that we conceive as conflict factors. Thereby, we particularly wanted to disentangle intermingled contributions of semantic conflict and response conflict to the overall Stroop-interference effect. To delineate neural substrates of single factors, we referred to the logics of cognitive subtraction and cognitive conjunction. Moreover, in a second step, we conducted correlation analyses to determine the relationship between neural activations and behavioral interference costs (i.e., conflict-related reaction time (RT) slowing) so as to further elucidate the functional role of the respective brain regions in conflict processing. Response-incompatibility was associated with activation in the left premotor cortex which can be interpreted as indicating motor competition or conflict, i.e., the presence of competing response tendencies. Accordingly, this activation was positively correlated with behavioral conflict costs. Semantic incongruency exhibited specific activation in the anterior cingulate cortex (ACC), the bilateral insula, and thalamus as well as in left somatosensory cortex. As supported by the consistent negative correlation with behavioral conflict costs, these activations most probably reflect strengthened control efforts to overcome interference and to ensure adequate task performance. Finally, task-reference elicited activation in the left temporo-polar cortex (TPC) and the right medial superior as well as in left rostroventral prefrontal cortex (rvPFC, sub-threshold activation). As strongly supported by prior studies' findings, this neural activation pattern may underlie residual semantic processing of the task-irrelevant word information.

Does caffeine modulate verbal working memory processes? An fMRI study

To assess the effect of caffeine on the functional MRI signal during a 2-back verbal working memory task, we examined blood oxygenation level-dependent regional brain activity in 15 healthy right-handed males. The subjects, all moderate caffeine consumers, underwent two scanning sessions on a 1.5-T MR-Scanner separated by a 24- to 48-h interval. Each participant received either placebo or 100 mg caffeine 20 min prior to the performance of the working memory task in blinded crossover fashion. The study was implemented as a blocked-design. Analysis was performed using SPM2. In both conditions, the characteristic working memory network of frontoparietal cortical activation including the precuneus and the anterior cingulate could be shown. In comparison to placebo, caffeine caused an increased response in the bilateral medial frontopolar cortex (BA 10), extending to the right anterior cingulate cortex (BA 32). These results suggest that caffeine modulates neuronal activity as evidenced by fMRI signal changes in a network of brain areas associated with executive and attentional functions during working memory processes.

Baseline brain activity fluctuations predict somatosensory perception in humans

In perceptual experiments, within-individual fluctuations in perception are observed across multiple presentations of the same stimuli, a phenomenon that remains only partially understood. Here, by means of thulium-yttrium/aluminum-garnet laser and event-related functional MRI, we tested whether variability in perception of identical stimuli relates to differences in prestimulus, baseline brain activity. Results indicate a positive relationship between conscious perception of low-intensity somatosensory stimuli and immediately preceding levels of baseline activity in medial thalamus and the lateral frontoparietal network, respectively, which are thought to relate to vigilance and "external monitoring." Conversely, there was a negative correlation between subsequent reporting of conscious perception and baseline activity in a set of regions encompassing posterior cingulate/precuneus and temporoparietal cortices, possibly relating to introspection and self-oriented processes. At nociceptive levels of stimulation, pain-intensity ratings positively correlated with baseline fluctuations in anterior cingulate cortex in an area known to be involved in the affective dimension of pain. These results suggest that baseline brain-activity fluctuations may profoundly modify our conscious perception of the external world.

Neurophysiological correlates of sleepiness: A combined TMS and EEG study

Changes of cortical and corticospinal excitability as a function of sleep deprivation have been studied, using EEG power maps and several TMS measures in 33 normal subjects before and after a 40-h sleep deprivation (SD). The effects of SD were independently assessed by subjective and EEG measures of sleepiness, the latter being represented in terms of cortical maps for different frequency bands. Short intracortical facilitation (SICF) and inhibition (SICI) were measured by the paired-pulse TMS technique with different inter-stimulus intervals. Besides standardized motor threshold (MT), lower threshold (LT) and upper threshold (UT) were also determined. Subjective sleepiness severely increased as a consequence of SD, paralleled by a drastic decrease of alertness. EEG topography showed large increases in delta and theta activity, mainly evident at fronto-central areas. Standard MTs, as well as LTs and UTs, all increased as a consequence of SD. SICF also showed a significant increase as compared to pre-deprivation values, but only in females. The increase of theta activity was strongly associated in the left frontal and prefrontal cortex to a smaller decrease of corticospinal excitability, expressed by MTs, and a larger increase of intracortical facilitation, expressed by SICF. TMS and EEG measures converge in indicating that SD has severe effects on both cortical and corticospinal excitability, as shown respectively by the increases of slow-frequency EEG power and MTs. The SICF enhancement in females and the results of the combined topographical analysis of EEG and TMS changes are coherent with the hypothesis that cortical TMS-evoked responses are higher as a consequence of a longer wakefulness. However, the lack of an increase in cortical excitability after prolonged wakefulness in males suggests some caution in the generalization of these effects, that deserve further investigation.

Functional microstates within human REM sleep: first evidence from fMRI of a thalamocortical network specific for phasic REM periods

High thalamocortical neuronal activity characterizes both, wakefulness and rapid eye movement (REM) sleep, but apparently this network fulfills other roles than processing external information during REM sleep. To investigate thalamic and cortical reactivity during human REM sleep, we used functional magnetic resonance imaging with simultaneous polysomnographic recordings while applying acoustic stimulation. Our observations indicate two distinct functional substates within general REM sleep. Acoustic stimulation elicited a residual activation of the auditory cortex during tonic REM sleep background without rapid eye movements. By contrast, periods containing bursts of phasic activity such as rapid eye movements appear characterized by a lack of reactivity to sensory stimuli. We report a thalamocortical network including limbic and parahippocampal areas specifically active during phasic REM periods. Thus, REM sleep has to be subdivided into tonic REM sleep with residual alertness, and phasic REM sleep with the brain acting as a functionally isolated and closed intrinsic loop.

EEG-Based Lapse Detection With High Temporal Resolution

A warning system capable of reliably detecting lapses in responsiveness (lapses) has the potential to prevent many fatal accidents. We have developed a system capable of detecting lapses in real-time with second-scale temporal resolution. Data was from 15 subjects performing a visuomotor tracking task for two 1-hour sessions with concurrent electroencephalogram (EEG) and facial video recordings. The detector uses a neural network with normalized EEG log-power spectrum inputs from two bipolar EEG derivations, though we also considered a multichannel detector. Lapses, identified using a combination of video rating and tracking behavior, were used to train our detector. We compared detectors employing tapped delay-line linear perceptron, tapped delay-line multilayer perceptron (TDL-MLP), and long short-term memory (LSTM) recurrent neural networks operating continuously at 1 Hz. Using estimates of EEG log-power spectra from up to 4 s prior to a lapse improved detection compared with only using the most recent estimate. We report the first application of a LSTM to an EEG analysis problem. LSTM performance was equivalent to the best TDL-MLP network but did not require an input buffer. Overall performance was satisfactory with area under the curve from receiver operating characteristic analysis of 0.84 +/- 0.02 (mean +/- SE) and area under the precision-recall curve of 0.41 +/- 0.08.

Effects of sleep deprivation on neural functioning: an integrative review

Sleep deprivation has a broad variety of effects on human performance and neural functioning that manifest themselves at different levels of description. On a macroscopic level, sleep deprivation mainly affects executive functions, especially in novel tasks. Macroscopic and mesoscopic effects of sleep deprivation on brain activity include reduced cortical responsiveness to incoming stimuli, reflecting reduced attention. On a microscopic level, sleep deprivation is associated with increased levels of adenosine, a neuromodulator that has a general inhibitory effect on neural activity. The inhibition of cholinergic nuclei appears particularly relevant, as the associated decrease in cortical acetylcholine seems to cause effects of sleep deprivation on macroscopic brain activity. In general, however, the relationships between the neural effects of sleep deprivation across observation scales are poorly understood and uncovering these relationships should be a primary target in future research.

Neuro-optometric diagnosis, treatment and rehabilitation following traumatic brain injuries: a brief overview

Traumatic brain injury (TBI) commonly impacts on the connections and interactions between signals from sensory, cognitive, motor and emotional systems and signals transmitted via both visual and non-visual retinal fiber pathways. The non-visual retinal pathways are actively involved in aspects of living, such as spatial orientation, auditory localization, circadian rhythm and motor function. Non-visual retinal signal processing and linkage dysfunctions require more than specialized neuro-ophthalmologic or traditional eye care evaluation. Neuro-optometric techniques, such as discussed herein, are necessary to test the complex, often overlooked interrelationships among these systems. As part of a multi-disciplinary approach, neuro-optometric intervention is an essential consideration for the optimal diagnosis, treatment and rehabilitation following a TBI.

Reduced thalamic volume in first-episode non-affective psychosis: correlations with clinical variables, symptomatology and cognitive functioning

Structural studies have inconsistently shown the presence of thalamic volume differences in patients with schizophrenia. However, only a few studies have examined the relation between thalamic structure and clinical and cognitive variables in early phases of the illness. Thalamic volumes in right-handed minimally treated first episode patients with non-affective psychosis (N=61) relative to those of right-handed healthy comparison subjects (N=40) were measured. Thalamic volumes in the right and left hemispheres and total thalamic volume were automatically segmented and analyzed using BRAINS2. Analysis of covariance was used to control for intracranial volume. Clinical symptoms were assessed by total scores of BPRS, SAPS and SANS. The relationship between three cognitive dimensions (verbal learning and memory, speed processing/executive functioning and sustained attention/vigilance), and thalamic volume was evaluated. The impact of the duration of untreated illness, untreated psychosis and prodrome period in thalamic morphometry was also explored. Right, left, and total thalamic volumes of the patients with non-affective psychosis were significantly smaller than those of the healthy subjects. Larger thalamic volumes were associated with an earlier age of onset, a poorer cognitive functioning and a more severe negative symptomatology. Thalamic volumetric differences between patients with non-affective psychosis and healthy controls are already present at early phases of the illness. However, further investigations are warranted to fully clarify the relationship between those structural anomalies and clinical and cognitive outcomes.

Low-resolution brain electromagnetic tomography (LORETA) identifies brain regions linked to psychometric performance under modafinil in narcolepsy

Low-resolution brain electromagnetic tomography (LORETA) showed a functional deterioration of the fronto-temporo-parietal network of the right hemispheric vigilance system in narcolepsy and a therapeutic effect of modafinil. The aim of this study was to determine the effects of modafinil on cognitive and thymopsychic variables in patients with narcolepsy and investigate whether neurophysiological vigilance changes correlate with cognitive and subjective vigilance alterations at the behavioral level. In a double-blind, placebo-controlled crossover design, EEG-LORETA and psychometric data were obtained during midmorning hours in 15 narcoleptics before and after 3 weeks of placebo or 400 mg modafinil. Cognitive investigations included the Pauli Test and complex reaction time. Thymopsychic/psychophysiological evaluation comprised drive, mood, affectivity, wakefulness, depression, anxiety, the Symptom Checklist 90 and critical flicker frequency. The Multiple Sleep Latency Test (MSLT) and the Epworth Sleepiness Scale (ESS) were performed too. Cognitive performance (Pauli Test) was significantly better after modafinil than after placebo. Concerning reaction time and thymopsychic variables, no significant differences were observed. Correlation analyses revealed that a decrease in prefrontal delta, theta and alpha-1 power correlated with an improvement in cognitive performance. Moreover, drowsiness was positively correlated with theta power in parietal and medial prefrontal regions and beta-1 and beta-2 power in occipital regions. A less significant correlation was observed between midmorning EEG LORETA and the MSLT; between EEG LORETA and the ESS, the correlation was even weaker. In conclusion, modafinil did not influence thymopsychic variables in narcolepsy, but it significantly improved cognitive performance, which may be related to medial prefrontal activity processes identified by LORETA.

Sleep deprivation: Impact on cognitive performance

Today, prolonged wakefulness is a widespread phenomenon. Nevertheless, in the field of sleep and wakefulness, several unanswered questions remain. Prolonged wakefulness can be due to acute total sleep deprivation (SD) or to chronic partial sleep restriction. Although the latter is more common in everyday life, the effects of total SD have been examined more thoroughly. Both total and partial SD induce adverse changes in cognitive performance. First and foremost, total SD impairs attention and working memory, but it also affects other functions, such as long-term memory and decision-making. Partial SD is found to influence attention, especially vigilance. Studies on its effects on more demanding cognitive functions are lacking. Coping with SD depends on several factors, especially aging and gender. Also interindividual differences in responses are substantial. In addition to coping with SD, recovering from it also deserves attention. Cognitive recovery processes, although insufficiently studied, seem to be more demanding in partial sleep restriction than in total SD.

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.

A review of neuroimaging studies in PTSD: heterogeneity of response to symptom provocation

Different experiential, psychophysiological, and neurobiological responses to traumatic symptom provocation in posttraumatic stress disorder (PTSD) have been reported in the literature. Two subtypes of trauma response have been hypothesized, one characterized predominantly by hyperarousal and the other primarily dissociative, each one representing unique pathways to chronic stress-related psychopathology. Recent PTSD neuroimaging findings in our own laboratory support this notion and are consistent with the view that grouping all PTSD subjects, regardless of their different symptom patterns, in the same diagnostic category may interfere with our understanding of posttrauma psychopathology. This review will integrate findings of different experiential, psychophysiological, and neurobiological responses to traumatic symptom provocation with the clinical symptomatology and the neurobiology of PTSD.

Frontal lobe metabolic decreases with sleep deprivation not totally reversed by recovery sleep

We studied the effects of total sleep deprivation and recovery sleep in normal subjects using position emission tomography with 18F-deoxyglycose. Sleep deprivation resulted in a significant decrease in relative metabolism of the frontal cortex, thalamus, and striatum. Recovery sleep was found to have only a partial restorative effect on frontal lobe function with minimal reversal of subcortical deficits. Sleep may be especially important for maintenance of frontal lobe activity.

Energetical bases of extraversion: Effort, arousal, EEG, and performance

This study investigates an extension of H.J. Eysenck's [Eysenck, H.J., 1967. The Biological Basis of Personality. Charles C. Thomas, Springfield, IL] arousal theory of extraversion, incorporating an effort system as a control system for different aspects of arousal. Extraverts were expected to have lower levels of reticocortical arousal than introverts, to invest more effort, and to have lower task performance in a monotonous vigilance task. In a 40-min vigilance task, participants had to react to the shorter of two 1 kHz tones presented binaurally at an event rate of 200 per 10 min. Spontaneous EEG, event-related potential, and performance data of 40 extremely introverted and 41 extremely extraverted students were available for statistical analysis. A tendency for lower arousal levels of extraverts (alpha 2 band), the expected higher effort investment (P300) and a lower performance (hits) of extraverts were found.

Thalamocortical circuits: fMRI assessment of the pulvinar and medial dorsal nucleus in normal volunteers

This fMRI study investigates the activation of the thalamic nuclei in a spatial focusing-of-attention task previously shown to activate the pulvinar with FDG-PET and assesses the connectivity of the thalamic nuclei with cortical areas. Normal right-handed subjects (eight men, eight women, average age=32 years) viewed four types of stimuli positioned to the right or left of the central fixation point (left hemifield-large letter, left hemifield-small letter display with flanking letters; right hemifield-large letter, right hemifield-small letter display with flankers). BOLD responses to small letters surrounded by flankers were compared with responses to large isolated letters. To examine maximum functional regional connectivity, we modeled "subject" as a random effect and attained fixed effect parameter estimates and t-statistics for functional connectivity between each of the thalamic nuclei (pulvinar, medial dorsal, and anterior) as the seed region and each non-seed voxel. Greater BOLD activation for letters surrounded by flankers than for large letters was observed in the pulvinar as anticipated and was also marked in the medial dorsal nucleus (MDN), anterior and superior cingulate (BA24 and BA24'), dorsolateral prefrontal cortex, and frontal operculum and insula. For the MDN, maximal functional connectivity was with the dorsolateral prefrontal cortex; correlations with left superior temporal, parietal, posterior frontal, and occipital regions were also observed. For the pulvinar, maximal functional connectivity was with parietal BA39; for anterior thalamus, with anterior cingulate.

Hormone treatment gives no benefit against cognitive changes caused by acute sleep deprivation in postmenopausal women

The objective was to evaluate whether hormone therapy (HT) gives any benefit against the possible impairment of cognitive performance when challenged by acute sleep deprivation. Twenty postmenopausal women volunteered (age range 59-72 years, mean=64.4 years, SD=4.4): 10 HT users and 10 nonusers. Eleven young women served as a control group for the cognitive age effect (age range 20-26 years, mean age 23.1 years, SD=1.6). The subjects spent four consecutive nights at the sleep laboratory and were exposed to acute sleep deprivation of 40 h. Measures of attention (reaction speed and vigilance), alertness, and mood were administered every 2 h during the daytime and every hour during the sleep deprivation night. Postmenopausal women performed slower than young controls, whereas young controls made more errors. In HT users, the recovery night did not fully restore the performance in the simple and two-choice reaction time tasks, but in nonusers it did so. Sleep deprivation had a detrimental, yet reversible effect on vigilance in all groups. In all groups, sleepiness started to increase after 15 h of sleep deprivation and remained elevated in the morning after the recovery night. Prolonged wakefulness or HT had no effect on mood. In conclusion, sleep deprivation impaired cognitive performance in postmenopausal as well as young women. Postmenopausal women kept up their performance at the expense of reaction speed and young women at the expense of accuracy. One night was not enough for HT users to recover from sleep deprivation. Thus, HT gave no benefit in maintaining the attention and alertness during sleep deprivation.

Cerebral glucose metabolism change in patients with complex regional pain syndrome: a PET study

PURPOSE

The aim of this study was to examine abnormalities of the central nervous system in patients with chronic pain who were diagnosed with complex regional pain syndrome (CRPS).

MATERIALS AND METHODS

Brain activity was assessed using (18)F-fluorodeoxyglucose positron emission tomography. The data collected from 18 patients were compared with data obtained from 13 normal age-matched controls.

RESULTS

Our results showed that glucose metabolism was bilaterally increased in the secondary somatosensory cortex, mid-anterior cingulated cortex (ACC) or posterior cingulated cortex (PCC) (or both), parietal cortex, posterior parietal cortex (PPC), and cerebellum as well as in the right posterior insula and right thalamus in our patients. In contrast, glucose metabolism was reduced contralaterally in the dorsal prefrontal cortex and primary motor cortex. Glucose metabolism was bilaterally elevated in the mid-ACC/PCC and the PPC, which correlated with pain duration.

CONCLUSION

These data suggested that glucose metabolism in the brains of patients with CRPS changes dramatically at each location. In particular, glucose metabolism was increased in the areas concerned with somatosensory perception, possibly due to continuous painful stimulation.

Increased brain activation during verbal learning in obstructive sleep apnea

This study examined the cerebral response to a verbal learning (VL) task in obstructive sleep apnea (OSA) patients. Twelve OSA patients and 12 controls were studied with functional magnetic resonance imaging (FMRI). As hypothesized, VL performance was similar for both groups, but OSA patients showed increased brain activation in several brain regions. These regions included bilateral inferior frontal and middle frontal gyri, cingulate gyrus, areas at the junction of the inferior parietal and superior temporal lobes, thalamus, and cerebellum. Better free recall performance in the OSA group was related to increased cerebral responses within the left inferior frontal gyrus and left supramarginal area. Recall was negatively related to activation within the left inferior parietal lobe. The findings support the predictions that intact performance in OSA patients is associated with increased cerebral response. Recruitment of additional brain regions to participate in VL performance in OSA patients likely represents an adaptive compensatory recruitment response, similar to that observed in young adults following total sleep deprivation and in healthy older adults. These data, and those of the only other FMRI study in OSA, suggest that individuals with OSA show characteristic differences in the BOLD signal response to cognitive challenges. Including subjects with untreated OSA in neuroimaging studies may potentially influence the results by altering individual and group level activation patterns. Given this, future neuroimaging studies may want to be aware of this potential confound.

Total sleep deprivation effect on disengagement of spatial attention as assessed by saccadic eye movements

OBJECTIVE

Previous research has shown that total sleep deprivation (TSD) of short duration (one night) affects performance to some cognitive tasks subserved by a fronto-parietal network. The aim of our study was to assess the effects of TSD on visuo-spatial attention, which is a cognitive task involving this network. Specifically, the disengagement of spatial attention was investigated with gap and overlap paradigms of saccadic eye movements.

METHODS

Ten healthy young male subjects performed the two tasks the morning after a normal night and after a TSD night. The study was conducted using a balanced, crossover design.

RESULTS

TSD significantly increased the gap effect (difference of latency between overlap and gap).

CONCLUSIONS

This result can be interpreted as an impaired disengagement of attention after TSD. As the peak velocity, which is an indicator of alertness, was not altered by TSD, the impairment in the disengagement of spatial attention does not result from a decrease in alertness.

SIGNIFICANCE

This study shows that saccadic eye movements enable studying alertness and disengagement of spatial attention simultaneously. The idea that specific brain areas are affected by TSD is confirmed by our results.

Attention deficit disorders: are we barking up the wrong tree?

Attention deficit disorder (AAD) and attention deficit/hyperactivity disorder (ADHD) are very frequent and protean developmental disorders without a definite biologic marker. This review proposes a framework to understand the enlarged spectrum of its manifestations based on current knowledge of the mechanisms underlying arousal and attention variations during sleep/wake cycle. The neuro-modulation's pivotal role in this process as well as in the fine tuning of synaptic architecture during development must be taken into account when trying to understand the marked fuzziness of the symptoms and the very high prevalence of reported co-morbidities. The series of related interactions includes a cyclic deactivation of the dorso-lateral portion of the prefrontal cortex (DLPFC) during sleep, suspending executive functions, co-occurring with rhythmic periods of decreased noradrenergic tonus. A protracted unbalance in modulation, with catecholaminergic relative deficiency, could explain less-than-optimum waking DLPFC activation and the most important manifestations of ADD. Beside the well documented dopaminergic effects of stimulant medication used in ADD and ADHD, a more important role must be assigned to noradrenaline (NA). At this light hyperactivity and impulsivity are less important dimensions. Rather, an attention deficit spectrum disorder should probably be regarded as a complication of a core defect in prefrontal cortex dependent inhibitory control, underlying inattention.

INTEGRATIVE ASSESSMENT OF BRAIN FUNCTION IN PTSD: BRAIN STABILITY AND WORKING MEMORY

Posttraumatic Stress Disorder (PTSD) is characterized by symptoms of hyperarousal, avoidance and intrusive trauma-related memories and deficits in everyday memory and attention. Separate studies in PTSD have found abnormalities in electroencephalogram EEG, in event-related potential (ERP) and behavioral measures of working memory and attention. The present study seeks to determine whether these abnormalities are related and the extent to which they share this relationship with clinical symptoms. EEG data were collected during an eyes-open paradigm and a one-back working memory task. Behavioral and clinical data (CAPS) were also collected. The PTSD group showed signs of altered cortical arousal as indexed by reduced alpha power and an increased theta/alpha ratio, and clinical and physiological measures of arousal were found to be related. The normal relationship between theta power and ERP indices of working memory was not affected in PTSD, with both sets of measures reduced in the disordered group. Medication appeared to underpin a number of abnormal parameters, including P3 amplitude to targets and the accuracy, though not speed, of target detection. The present study helps to overcome a limitation of earlier studies that assess such parameters independently in different groups of patients that vary in factors such as comorbidity, medication status, gender and symptom profile. The present study begins to shed light on the relationship between these measures and suggests that abnormalities in brain working memory may be linked to underlying abnormalities in brain stability.

Acute opioid effects on human brain as revealed by functional magnetic resonance imaging

Functional magnetic resonance imaging has been widely used to study brain activation induced either by specific sensory stimulation or motor or cognitive task performance. We demonstrate that functional magnetic resonance imaging can provide information of brain regions involved in opioid-induced central nervous system effects. The reproducibility of the responses in the predefined regions of interest was confirmed by repeated boluses of ultra-short acting mu-opioid receptor agonist remifentanil and saline. We report spatially and temporally detailed information after remifentanil administration. Areas rich in mu-opioid receptors showed strong activations, whereas primary somatosensory cortex that has the lowest density of mu-opioid receptors showed negligible activation. The cingulate, orbitofrontal, posterior parietal and insular cortices, and amygdala showed activation, which was temporally closely related to most subjective sensations that were strongest at 80 to 90 s after drug administration. These areas belong to a circuitry that modulates the affective experience of sensory 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.

Compensatory recruitment after sleep deprivation and the relationship with performance

This study examined the effects of total sleep deprivation (TSD) on cerebral responses to a verbal learning task with two levels of word difficulty. A total of 32 subjects were studied with functional magnetic resonance imaging (FMRI) after normal sleep and following 36 h of TSD. Cerebral responses to EASY words were identical on both nights, but several brain regions showed increased activation to HARD words following TSD compared with following a normal night of sleep (NORM). These regions included bilateral inferior frontal gyrus, bilateral dorsolateral prefrontal cortex, and bilateral inferior parietal lobe. Better free recall performance on the HARD words after TSD was related to increased cerebral responses within the left inferior and superior parietal lobes and left inferior frontal gyrus. Recall was negatively related to activation within the right inferior frontal gyrus. Overall, the findings support the predictions of the compensatory recruitment hypothesis that task demands influence both the likelihood and location of increased cerebral activation during task performance following TSD, and refine that hypothesis by identifying a specific task demand that plays a role. The performance relationships suggest increased activation may be both beneficial (compensatory) and interfere with task performance, depending on the brain regions involved.

Functional brain imaging of a complex navigation task following one night of total sleep deprivation: a preliminary study

Several neuroimaging studies have demonstrated compensatory cerebral responses consequent to sleep deprivation (SD), but all have focused on simple tasks with limited behavioral response options. We assessed the cerebral effects associated with SD during the performance of a complex, open-ended, dual-joystick, 3D navigation task (simulated orbital docking) in a cross-over protocol, with counterbalanced orders of normal sleep (NS) and a single night of total SD (approximately 27 h). Behavioral performance on multiple measures was comparable in the two sleep conditions. Functional magnetic resonance imaging revealed multiple compensatory SD > NS cerebral responses, including the posterior superior temporal sulcus [Brodmann area (BA) 39/22/37], prefrontal cortex (BA 9), lateral temporal cortex (BA 22/21), and right substantia nigra. Right posterior cingulate cortex (BA 31) exhibited NS > SD activity. Our findings extend the compensatory cerebral response hypothesis to complex, open-ended tasks.

Arousal and consumer in-store behavior

From a psychophysiological point of view, arousal is a fundamental feature of behavior. As reported in different empirical studies based on insights from theories of consumer behavior, store atmosphere should evoke phasic arousal reactions to attract consumers. Most of these empirical investigations used verbal scales to measure consumers' perceived phasic arousal at the point-of-sale (POS). However, the validity of verbal arousal measurement is questioned; self-reporting methods only allow a time-lagged measurement. Furthermore, the selection of inappropriate items to represent perceived arousal is criticized, and verbal reports require some form of cognitive evaluation of perceived arousal by the individual, who might (in a non-measurement condition) not even be aware of the arousal. By contrast, phasic electrodermal reaction (EDR) has proven to be the most appropriate and valid indicator for measuring arousal [W. Boucsein, Physiologische Grundlagen und Messmethoden der dermalen Aktivität. In: F. Rösler (Ed.), Enzyklopädie der Psychologie, Bereich Psychophysiologie, Band 1: Grundlagen and Methoden der Psychophysiologie, Kapitel, Vol. 7, Hogrefe, Göttingen, 2001, pp. 551-623] that could be relevant to behavior. EDR can be recorded simultaneously to the perception of stimuli. Furthermore, telemetric online device can be used, which enables physiological arousal measurement while participants can move freely through the store and perform the assigned task in the experiments. The present paper delivers insights on arousal theory and results from empirical studies using EDR to measure arousal at the POS.