Dreaming and awareness during dexmedetomidine- and propofol-induced unresponsiveness.

BACKGROUND: Experiences during anaesthetic-induced unresponsiveness have previously been investigated by interviews after recovery. To explore whether experiences occur during drug administration, we interviewed participants during target-controlled infusion (TCI) of dexmedetomidine or propofol and after recovery. METHODS: Healthy participants received dexmedetomidine (n=23) or propofol (n=24) in stepwise increments until loss of responsiveness (LOR1). During TCI we attempted to arouse them for interview (return of responsiveness, ROR1). After the interview, if unresponsiveness ensued with the same dose (LOR2), the procedure was repeated (ROR2). Finally, the concentration was increased 1.5-fold to achieve presumable loss of consciousness (LOC), infusion terminated, and the participants interviewed upon recovery (ROR3). An emotional sound stimulus was presented during LORs and LOC, and memory for stimuli was assessed with recognition task after recovery. Interview transcripts were content analysed. RESULTS: Of participants receiving dexmedetomidine, 18/23 were arousable from LOR1 and LOR2. Of participants receiving propofol, 10/24 were arousable from LOR1 and two of four were arousable from LOR2. Of 93 interviews performed, 84% included experiences from periods of unresponsiveness (dexmedetomidine 90%, propofol 74%). Internally generated experiences (dreaming) were present in 86% of reports from unresponsive periods, while externally generated experiences (awareness) were rare and linked to brief arousals. No within drug differences in the prevalence or content of experiences during infusion vs after recovery were observed, but participants receiving dexmedetomidine reported dreaming and awareness more often. Participants receiving dexmedetomidine recognised the emotional sounds better than participants receiving propofol (42% vs 15%), but none reported references to sounds spontaneously. CONCLUSION: Anaesthetic-induced unresponsiveness does not induce unconsciousness or necessarily even disconnectedness. CLINICAL TRIAL REGISTRATION: NCT01889004.

Spoken words are processed during dexmedetomidine-induced unresponsiveness.

BACKGROUND: Studying the effects of anaesthetic drugs on the processing of semantic stimuli could yield insights into how brain functions change in the transition from wakefulness to unresponsiveness. Here, we explored the N400 event-related potential during dexmedetomidine- and propofol-induced unresponsiveness. METHODS: Forty-seven healthy subjects were randomised to receive either dexmedetomidine (n=23) or propofol (n=24) in this open-label parallel-group study. Loss of responsiveness was achieved by stepwise increments of pseudo-steady-state plasma concentrations, and presumed loss of consciousness was induced using 1.5 times the concentration required for loss of responsiveness. Pre-recorded spoken sentences ending either with an expected (congruous) or an unexpected (incongruous) word were presented during unresponsiveness. The resulting electroencephalogram data were analysed for the presence of the N400 component, and for the N400 effect defined as the difference between the N400 components elicited by congruous and incongruous stimuli, in the time window 300-600 ms post-stimulus. Recognition of the presented stimuli was tested after recovery of responsiveness. RESULTS: The N400 effect was not observed during dexmedetomidine- or propofol-induced unresponsiveness. The N400 component, however, persisted during dexmedetomidine administration. The N400 component elicited by congruous stimuli during unresponsiveness in the dexmedetomidine group resembled the large component evoked by incongruous stimuli at the awake baseline. After recovery, no recognition of the stimuli heard during unresponsiveness occurred. CONCLUSIONS: Dexmedetomidine and propofol disrupt the discrimination of congruous and incongruous spoken sentences, and recognition memory at loss of responsiveness. However, the processing of words is partially preserved during dexmedetomidine-induced unresponsiveness. CLINICAL TRIAL REGISTRATION: NCT01889004.

Comparative effects of dexmedetomidine, propofol, sevoflurane, and S-ketamine on regional cerebral glucose metabolism in humans: a positron emission tomography study.

INTRODUCTION: The highly selective α2-agonist dexmedetomidine has become a popular sedative for neurointensive care patients. However, earlier studies have raised concern that dexmedetomidine might reduce cerebral blood flow without a concomitant decrease in metabolism. Here, we compared the effects of dexmedetomidine on the regional cerebral metabolic rate of glucose (CMRglu) with three commonly used anaesthetic drugs at equi-sedative doses. METHODS: One hundred and sixty healthy male subjects were randomised to EC50 for verbal command of dexmedetomidine (1.5 ng ml-1; n=40), propofol (1.7 µg ml-1; n=40), sevoflurane (0.9% end-tidal; n=40) or S-ketamine (0.75 µg ml-1; n=20) or placebo (n=20). Anaesthetics were administered using target-controlled infusion or vapouriser with end-tidal monitoring. 18F-labelled fluorodeoxyglucose was administered 20 min after commencement of anaesthetic administration, and high-resolution positron emission tomography with arterial blood activity samples was used to quantify absolute CMRglu for whole brain and 15 brain regions. RESULTS: At the time of [F18]fluorodeoxyglucose injection, 55% of dexmedetomidine, 45% of propofol, 85% of sevoflurane, 45% of S-ketamine, and 0% of placebo subjects were unresponsive. Whole brain CMRglu was 63%, 71%, 71%, and 96% of placebo in the dexmedetomidine, propofol, sevoflurane, and S-ketamine groups, respectively (P<0.001 between the groups). The lowest CMRglu was observed in nearly all brain regions with dexmedetomidine (P<0.05 compared with all other groups). With S-ketamine, CMRglu did not differ from placebo. CONCLUSIONS: At equi-sedative doses in humans, potency in reducing CMRglu was dexmedetomidine>propofol>ketamine=placebo. These findings alleviate concerns for dexmedetomidine-induced vasoconstriction and cerebral ischaemia. CLINICAL TRIAL REGISTRATION: NCT02624401.

Recurrent dreams: Recurring threat simulations?

Zadra, Desjardins, and Marcotte (2006) have made a valuable contribution to the empirical testing of the Threat Simulation Theory (TST) (Revonsuo, 2000a) in recurrent dreams. For the most part, their results are in accordance with the theory, while some findings seem to conflict with the predictions of TST. In our commentary, we consider some alternative ways to interpret the results, and we conclude that many prominent features of most recurrent dreams seem to be manifestations of a threat simulation function, leading to repeated rehearsal of threat perception and avoidance, but a minority of recurrent dreams seem to have origins unrelated to threat simulation.

Visual object recognition in early Alzheimer's disease: deficits in semantic processing.

OBJECTIVES: The purpose of the present study was to divide visual object recognition into different stages and to reveal which of these stages are impaired in early Alzheimer's disease (AD). METHODS: Performance in object detection, familiarity detection, semantic name and word categorization, and identification with naming were studied by using two-choice reaction-time tasks. Ten patients with newly diagnosed AD and 14 healthy subjects were studied. RESULTS: Patients with early AD had impairments in several stages of the object recognition process. After controlling for the basic visuomotor slowness, they were as fast and as accurate as the controls in object detection, but had difficulties in all stages that required semantic processing. CONCLUSIONS: Semantic memory impairments contribute to the deficits in visual object recognition in early AD. Thus, the semantic memory deficit may be manifested in several ways in the difficulties that AD patients experience in everyday life.

Cognitive representations underlying the N400 priming effect.

The present study explored whether the N400 semantic priming effect is based on semantic similarity or lexical associations, or both. The event-related potentials showed N400 priming effects for both semantically similar and lexically associated word pairs in the 250-375 ms time-window. However, the effect lasted for a longer time for lexical associates, particularly in frontal and central electrode sites in the 375-500 ms time-window, suggesting that different types of processing may contribute to the N400 priming effects evoked by the two types of relationships.

Visual object recognition in multiple sclerosis.

Deficits in tasks measuring visual processing have been earlier reported in studies of MS. Yet, the nature and severity of visual-processing deficits in MS remains unclear. We used a new method in order to measure the different stages of visual processing in object recognition: shape recognition, familiarity recognition, semantic categorization, and identification with naming. Six two-choice reaction-time tasks were presented to 30 MS patients and 15 healthy controls. The patients were divided into cognitively preserved and cognitively deteriorated study groups according to their cognitive status. The purpose was to find out whether deficits at specific stages of visual processing can be found in cognitively deteriorated MS patients. Cognitively deteriorated MS patients did not perform as well as cognitively preserved MS patients or healthy controls. They were slower already at the early stage of visual processing where discrimination of whole objects from scrambled ones was required. They also had higher error rates in tasks requiring object familiarity detection and object identification with naming. Thus, cognitively deteriorated MS patients had difficulties in visual shape recognition and semantic-lexical processing. However, variation of performances was large within both of the patient groups indicating that even patients without a generalized cognitive decline may have deficits in some stages of the visual processing. We suggest that because of the heterogeneity of the patients, every single case needs to be examined separately in order to identify the possible deficits in visual processing.

Anterior brain functions and hypnosis: a test of the frontal hypothesis.

Neuropsychological frontal lobe tests were used to compare individuals with high (n = 8) and low (n = 9) hypnotizability during both baseline and hypnosis conditions. Subjects were assessed on two hypnotic susceptibility scales and a test battery that included the Stroop test, word fluency to letter- and semantic-designated categories, tests of simple reaction time and choice reaction time, a vigilance task, and a questionnaire of 40 self-descriptive statements of focused attention. Effects for hypnotic susceptibility and hypnosis/control conditions were scant across the dependent variables. High hypnotizables scored higher on the questionnaire at baseline, and their performance on the word-fluency task during hypnosis was reduced to a greater extent than lows. Findings indicate that although the frontal area may play an important role regarding hypnotic response, the mechanisms seem to be much more complex than mere general inhibition.

GSM phone signal does not produce subjective symptoms.

The influence of pulsed radiofrequency (RF) electromagnetic fields of digital GSM mobile phones (902 MHz, 217 Hz pulse modulation) on subjective symptoms or sensations in healthy subjects were studied in two single-blind experiments. The duration of the RF exposure was about 60 min in Experiment 1 and 30 min in Experiment 2. Each subject rated symptoms or sensations in the beginning of the experimental session and at the end of both the exposure and the nonexposure conditions. The symptoms rated were headache, dizziness, fatigue, itching or tingling of the skin, redness on the skin, and sensations of warmth on the skin. The results did not reveal any differences between exposure and non-exposure conditions, suggesting that a 30-60 min exposure to this RF field does not produce subjective symptoms in humans.

Putting color back where it belongs.

I disagree with Ross about the location of colors: They are in the brain, not in the external world. It is difficult to deny that there are colors in our conscious visual experience, and if we take the causal theory of perception seriously, we cannot identify these colors with the beginning of the causal chain in perception (external objects in the distal stimulus field), but we must search for them at the end of the causal chain (in the brain). Several lines of compelling evidence from cognitive neuroscience (e.g., synesthesia, dreaming, and achromatopsia) demonstrate unambiguously that color is in the brain. Furthermore, it seems that Ross has failed to consider one substantial version of subjectivism in his article. This monistic approach to color and consciousness appears to be the least implausible alternative when we try to understand what colors are and where they reside.

Impairment of semantic knowledge in Parkinson disease.

BACKGROUND: Parkinson disease (PD) is commonly characterized by cognitive deterioration, but it is still unclear whether PD is associated with semantic impairments. OBJECTIVE: To evaluate semantic knowledge of concepts in patients with idiopathic PD, addressing concrete and abstract concepts, conceptual attributes, and conceptual relations. METHODS: Twelve patients with preserved cognitive status, 12 patients with mildly deteriorated cognitive status, and 12 control subjects were studied. The cognitive status of patients and controls was determined using detailed cognitive testing. Patients were participants in a university-based movement disorder program, and their PD diagnoses were clinically confirmed during long-term follow-up. The 2 patient groups were similar in age, level of education, disease duration, and parkinsonian disability. Patients were required to produce verbal descriptions of concrete and abstract concepts, to give ratings of the importance of concept attributes, and to assess and construct conceptual hierarchies. The description tasks included guiding questions, which were used if the spontaneous productions of the patients lacked any essentials expected in the answers. RESULTS: Patients with mild cognitive deterioration performed less well than the other groups in defining concrete and abstract concepts (P<.001 for both). External guidance did not help them markedly improve their performance. They also had difficulties in tasks calling for knowledge of the importance of given attributes to the concepts and in tasks demanding evaluation of hierarchical semantic relations between concepts (P<.001 for both). CONCLUSION: Semantic disruption is implied in idiopathic PD in association with incipient cognitive impairment.

Semantic priming by pictures and words in the cerebral hemispheres.

In order to determine whether pictures would act as more effective semantic primes than words in the right cerebral hemisphere, automatic semantic activation in intact hemispheres was studied with primed GO-NOGO lexical decision tasks by presenting word-word and picture-word pairs to the left visual field (right hemisphere) or to the right visual field (left hemisphere). Response times in Experiment 1 showed that categorically related targets (e.g., TABLE-BED) were primed only in the right visual field after both word and picture primes. Experiment 2 found that picture primes activated the representations of the corresponding written names in both visual fields. These observations suggest that the range of automatic semantic activation is larger in the left than in the right hemisphere. The results implicate that semantic categories may be organized in a different fashion in the left than the right hemisphere.

The effects of electromagnetic field emitted by GSM phones on working memory.

The influence of pulsed radiofrequency (RF) electromagnetic fields of digital GSM mobile phones on working memory in healthy subjects were studied. Memory load was varied from 0 to 3 items in an n-back task. Each subject was tested twice within a single session, with and without the RF exposure (902MHz, 217Hz). The RF field speeded up response times when the memory load was three items but no effects of RF were observed with lower loads. The results suggest that RF fields have a measurable effect on human cognitive performance and encourage further studies on the interactions of RF fields with brain function.

Effects of electromagnetic field emitted by cellular phones on the EEG during a memory task.

The effects of electromagnetic fields (EMF) emitted by cellular phones on the ERD/ERS of the 4-6 Hz, 6-8 Hz, 8-10 Hz and 10-12 Hz EEG frequency bands were studied in 16 normal subjects performing an auditory memory task. All subjects performed the memory task both with and without exposure to a digital 902 MHz EMF in counterbalanced order. The exposure to EMF significantly increased EEG power in the 8-10 Hz frequency band only. Nonetheless, the presence of EMF altered the ERD/ERS responses in all studied frequency bands as a function of time and memory task (encoding vs retrieval). Our results suggest that the exposure to EMF does not alter the resting EEG per se but modifies the brain responses significantly during a memory task.

Does P3 reflect attentional or memory performances, or cognition more generally?

The study evaluated the off-line relationship of attention, memory and other cognitive performances with the auditory event-related potentials P3 (P300) and N2. The sample comprised 200 middle-aged construction workers. Verbal, visuomotor and memory tests were administered. Attentional domains were examined using CogniSpeed software. Slowed reaction times in the test of sustained attention (vigilance) were associated with delayed P3 latency (p < 0.001) and decreased P3 amplitude (p = 0.005), as well as with delayed N2 latency (p < 0.001). Visuomotor slowing in Digit Symbol was also related to delayed P3 latency (p = 0.030) and decreased P3 amplitude (p = 0.014). In contrast, mild cognitive impairment, short- and long-term memory, and concentrating or sharing attention with high working memory demands were not related to P3. The results suggest that P3 is linked to attentional performance with low working memory demands rather than to effortful working memory updating, retrieval from memory stores, or mild cognitive impairment.

Effects of 902 MHz electromagnetic field emitted by cellular telephones on response times in humans.

The present study examined possible influences of a 902 MHz electromagnetic field emitted by cellular telephones on cognitive functioning in 48 healthy humans. A battery of 12 reaction time tasks was performed twice by each participant in a counterbalanced order: once with and once without the exposure to the field. The results showed that the exposure to the electromagnetic field speeded up response times in simple reaction time and vigilance tasks and that the cognitive time needed in a mental arithmetics task was decreased. The results suggest that exposure to the electromagnetic field emitted by cellular telephones may have a facilitatory effect on brain functioning, especially in tasks requiring attention and manipulation of information in working memory.

The reinterpretation of dreams: an evolutionary hypothesis of the function of dreaming.

Several theories claim that dreaming is a random by-product of REM sleep physiology and that it does not serve any natural function. Phenomenal dream content, however, is not as disorganized as such views imply. The form and content of dreams is not random but organized and selective: during dreaming, the brain constructs a complex model of the world in which certain types of elements, when compared to waking life, are underrepresented whereas others are over represented. Furthermore, dream content is consistently and powerfully modulated by certain types of waking experiences. On the basis of this evidence, I put forward the hypothesis that the biological function of dreaming is to simulate threatening events, and to rehearse threat perception and threat avoidance. To evaluate this hypothesis, we need to consider the original evolutionary context of dreaming and the possible traces it has left in the dream content of the present human population. In the ancestral environment human life was short and full of threats. Any behavioral advantage in dealing with highly dangerous events would have increased the probability of reproductive success. A dream-production mechanism that tends to select threatening waking events and simulate them over and over again in various combinations would have been valuable for the development and maintenance of threat-avoidance skills. Empirical evidence from normative dream content, children's dreams, recurrent dreams, nightmares, post traumatic dreams, and the dreams of hunter-gatherers indicates that our dream-production mechanisms are in fact specialized in the simulation of threatening events, and thus provides support to the threat simulation hypothesis of the function of dreaming.

Effects of electromagnetic fields emitted by cellular phones on the electroencephalogram during a visual working memory task.

PURPOSE: To examine the effects of electromagnetic fields (EMF) emitted by cellular phones on the event-related desynchronization/synchronization (ERD/ERS) responses of the 4-6, 6-8, 8-10 and 10-12Hz EEG frequency bands during cognitive processing. MATERIALS AND METHODS: Twenty-four subjects performed a visual sequential letter task (n-back task) with three different working memory load conditions: zero, one and two items. All subjects performed the memory task both with and without exposure to a digital 902 MHz EMF in counterbalanced order. RESULTS: The presence of EMF altered the ERD/ERS responses in the 6-8 and 8-10 Hz frequency bands but only when examined as a function of memory load and depending also on whether the presented stimulus was a target or not. CONCLUSIONS: The results suggest that the exposure to EMF modulates the responses of EEG oscillatory activity approximately 8 Hz specifically during cognitive processes.

Binding and the phenomenal unity of consciousness.

The binding problem is frequently discussed in consciousness research. However, it is by no means clear what the problem is supposed to be and how exactly it relates to consciousness. In the present paper the nature of the binding problem is clarified by distinguishing between different formulations of the problem. Some of them make no mention of consciousness, whereas others are directly related to aspects of phenomenal experience. Certain formulations of the binding problem are closely connected to the classical philosophical problem of the unity of consciousness and the currently fashionable search for the neural correlates of consciousness. Nonetheless, only a part of the current empirical research on binding is directly relevant to the study of consciousness. The main message of the present paper is that the science of consciousness needs to establish a clear theoretical view of the relation between binding and consciousness and to encourage further empirical work that builds on such a theoretical foundation.