EEG complexity and performance measures of creative thinking

The electroencephalogram (EEG) was used because of its dimensional complexity to establish a differentiation of divergent versus convergent thought, considered fundamental modes of cortical processing. In 28 men, the EEG was recorded while solving tasks of divergent and convergent thinking and during mental relaxation. The EEG during divergent thought was compared between subjects achieving high versus low performance scores on this type of task. The dimensional complexity of the EEG was greater during divergent thinking than during convergent thinking. While solving tasks of divergent thinking, subjects with high performance scores had a lower EEG dimension than did subjects with low scores, in particular over frontal cortical areas. The changes were not reflected in single frequency bands of conventional EEG analysis. Based on Hebb's view of neuron assemblies as functional processing units, the higher EEG complexity during divergent than convergent thinking could be the result of the concurrent activation of a greater number of independently oscillating processing units.

Transient-evoked otoacoustic emissions as a measure of noise-induced threshold shift

Otoacoustic emissions and behavioral hearing thresholds were measured before and after exposure to a 10-min, 105-dB SPL, half-octave band of noise centered at 1.414 kHz. Along a single recovery function, transient-evoked otoacoustic-emission (TEOAE) measurements made with 74-dB pSPL nonlinear click ensembles were alternated with a Bekesy threshold-tracking procedure. Each of the 14 participants with normal hearing underwent 2 hour-long temporary-threshold shift (TTS) sessions as well as 2 pretest sessions and a posttest session. The Bekesy test frequency was fixed at 2.0 kHz, whereas emissions were analyzed in half-octave bandwidths with center frequencies ranging from 0.707 to 5.656 kHz. Results showed that (a) the maximum temporary emission shifts (TES) were half to 1 octave above the exposure frequency; (b) the 4.7-dB average temporary emission shift magnitude at approximately 2 min postexposure was less than half of the 11.7-dB average TTS; (c) the average recovery times for emissions and hearing thresholds were similar (188 vs. 186 min); and (d) the average TTS magnitude along the recovery function was predictable from TES magnitude. It is concluded that both TEOAEs and Bekesy thresholds reveal the same aspects of postexposure inner-ear changes.

Acute effects of recombinant human interleukin-6 on endocrine and central nervous sleep functions in healthy men

Interleukin-6 (IL-6) is a proinflammatory cytokine that has been shown to mediate, in addition to immune reactions, various endocrine and central nervous components of the acute phase response. In this context, the present study aimed to specify the contributions of IL-6 to the regulation of pituitary-adrenal secretory activity and GH and TSH secretion, as well as to the regulation of central nervous sleep and mood in healthy men. Effects of a low dose of IL-6 (0.5 microgram/kg body weight) were assessed, inducing plasma IL-6 concentrations closely comparable with those typically observed after infectious challenge. Each of the 16 male subjects participated in two 14-h sessions (between 1800 and 0800 h), receiving either placebo or human recombinant IL-6 sc at 1900 h. Blood was collected repeatedly to determine plasma hormone levels, serum concentrations of cytokines, and C-reactive protein. Moreover, mood was assessed, and sleep recordings were obtained between 2300 and 0700 h. The cytokine induced a prolonged increased in plasma concentrations of ACTH and cortisol (P < 0.001), but led to a decrease in TSH concentrations (P < 0.01). In response to IL-6, subjects reported fatigue and felt more inactive and less capable of concentrating than after placebo. Sleep architecture was altered significantly by the cytokine. Slow-wave sleep was decreased during the first half and increased during the second half of sleep. Rapid eye movement sleep during the entire nocturnal sleep time was significantly decreased. After IL-6, body temperature rose slightly. C-reactive protein concentrations were dramatically increased 12.5 h after substance administration (P < 0.001). IL-6 did not affect serum concentrations of IL-2, IL-8, interferon-alpha, and interferon-gamma. The results underscore the importance of IL-6 in the cascade of cytokines for the neuroendocrine response during the acute phase reaction. In addition, IL-6 appears to be involved in changes of sleep and behavior accompanying infection and inflammatory disorders.

Scalp recorded direct current brain potentials during human sleep

The direct current (DC) potential recorded from the scalp of awake humans has been considered a reflection of general changes in cortical excitability. This study examined DC potential shifts in humans during a night of continuous sleep. Standard polysomnographic recordings and skin temperature were measured simultaneously. Contrary to expectations, average DC potential level indicated higher negativity during nonrapid eye movement (NREM) sleep than REM sleep and wakefulness. Moreover, a dynamic regulation of the DC potential level was revealed in association with the NREM-REM sleep cycle comprising four successive phases: (i) a steep 'NREM-transition-negative shift' during the initial 10-15 min of the NREM sleep period; (ii) a more subtle 'NREM-positive slope' during the subsequent NREM sleep period; (iii) a steep 'REM-transition-positive shift' starting shortly prior to the REM sleep period, and (iv) a 'REM-negative slope', characterizing the remaining greater part of the REM sleep period. DC potential changes were only weakly related to changes in slow-wave activity (r2 < 0.18). The NREM-negative slope and REM-positive slope could reflect, respectively, gradually increasing and decreasing cortical excitability resulting from widespread changes in the depolarization of apical dendrites. In contrast, the NREM-transition-negative shift and the REM-transition-positive shift may reflect the progression and retrogression, respectively, of a long-lasting hyperpolarization in deeply lying neurons.

Adrenocorticotropin widens the focus of attention in humans. A nonliner electroencephalographic analysis

OBJECTIVE

This study examined the effects of ACTH 4-10, a fragment of adrenocorticotropin (ACTH) with known central nervous system (CNS) activity, on the dimensional complexity of the ongoing electroencephalographic (EEG) activity. Stressful stimuli cause ACTH to be released from the pituitary, and as a neuropeptide ACTH may concurrently exert adaptive influences on the brain's processing of these stimuli. Previous studies have indicated an impairing influence of ACTH on selective attention.

METHODS

Dimensional complexity of the EEG, which indexes the brain's way of stimulus processing, was evaluated while subjects performed tasks with different attention demands. Sixteen healthy men (23 to 33 years) were tested once after placebo and another time after administration of ACTH 4-10 (1.25 mg intravenously (i.v.), 30 minutes before testing). The EEG was recorded while subjects were presented with a dichotic listening task (consisting of the concurrent presentation of tone pips to the left and right ear). Subjects either a) listened to pips in both ears (divided attention), or b) listened selectively to pips in one ear (selective attention), or c) ignored all pips.

RESULTS

Dimensional complexity of the EEG was higher during divided than selective attention. ACTH significantly increased the EEG complexity during selective attention, in particular over the midfrontal cortex (Fz, Cz).

CONCLUSIONS

The effects support the view of a de-focusing action of ACTH during selective attention that could serve to improve the organism's adaptation to stress stimuli.

The significance of fibres found in head hair

The incidence of four common fibres in the head hair of 100 individuals has been established. A total of 37 matching fibres were found in the hair of 22 people with a maximum of five fibres on any one head. Two subjects had fibres matching two sources in their hair.

Slow wave sleep drives inhibition of pituitary-adrenal secretion in humans

During the first half of nocturnal sleep, the secretory response of the pituitary-adrenal axis to either CRH or vasopressin (VP) administration is reduced. Two experiments were performed aiming (i) to investigate the impact of sleep on the response to a combined CRH/VP administration and (ii) to specify the onset of sleep associated pituitary-adrenal suppression and its relation to specific sleep stages. In experiment I, we compared the effect of simultaneous administration of VP (0.5 IU i.v., within 6 min) and CRH (50 micrograms bolus i.v., in the third min of VP infusion) on the secretion of ACTH, cortisol and GH in healthy men during the first nocturnal epoch of slow wave sleep (SWS) and during nocturnal wakefulness. The increase of ACTH and cortisol concentrations after combined VP/CRH administration was distinctly higher during wakefulness than sleep (P < 0.01). In experiment II, CRH (30 micrograms/h, after an initial bolus of 30 micrograms) was continuously infused in 7 healthy men on 2 nights. On one of the nights, the men were allowed to sleep (between 23.00 h and 05.00 h) after a 3-h period of wakefulness, on the other night they stayed awake throughout the experiment. In both conditions, CRH enhanced ACTH/cortisol plasma levels. Compared with concentrations during continuous wakefulness, sleep and in particular SWS was associated with a suppression of ACTH/cortisol levels (P < 0.05). The findings further support an inhibitory influence of early nocturnal sleep on pituitary-adrenal activity. The effect appears to be strongest during SWS and is probably mediated via hypothalamic secretion of a release inhibiting factor of ACTH.

Effect of negative middle-ear pressure on transient-evoked otoacoustic emissions

OBJECTIVE

The purpose of the study was to illustrate the effect of negative middle-ear pressure (MEP) on both the stimulus and response of transient-evoked otoacoustic emissions (TEOAEs) and the effect of compensating for negative pressure in the middle ear by pneumatically introducing pressure into the ear canal. Simulation of negative MEP by introducing positive pressure into the ear canal also was examined.

DESIGN

TEOAEs were measured over 6 mo in a subject who frequently had negative MEP out to -150 daPa. Compensation was done for MEPs of -105, -135, and -165 daPa. Simulation of negative pressure was done for these same pressures. The effect of a pressure differential across the eardrum on the stimulus spectrum was measured at 100, 200, and 300 daPa. All measurements were made on the same subject.

RESULTS

Small amounts of negative MEP significantly affected both stimulus and response spectra. The simulated negative MEP approximated actual MEP at MEPs of -105 and -135 daPa. At -165 daPa, a divergence between the two spectra occurred below 2.0 kHz. Compensation for negative MEP by pneumatically introducing pressure into the ear canal essentially returned both spectra to that seen when the MEP was close to ambient pressure, at least for frequencies above 1.5 to 2.0 kHz. At lower frequencies, compensation resulted in increased TEOAE amplitude relative to the amplitude at ambient pressure.

CONCLUSIONS

Small amounts of negative MEP may affect TEOAE spectra and potentially influence the reliability of the test. For long-term monitoring of TEOAEs, MEPs either should be near ambient pressure or should be compensated for by an equivalent pressure in the ear canal.

Effect of step size on clinical and adaptive 2IFC procedures in quiet and in a noise background

Audibility thresholds for a 1000-Hz sinusoid were measured with a standard clinical (CLIN) procedure and a two-interval, forced-choice (2IFC) adaptive procedure bracketing 79% correct. Both used 2- and 5-dB step sizes in quiet and in a continuous, broadband noise background. Clinical thresholds were from 2 to 4 dB higher than 2IFC thresholds, depending on the condition. Step size had a larger effect on the CLIN thresholds than the 2IFC thresholds. For the CLIN procedure, thresholds with a 2-dB step size were 1.4 dB lower than with a 5-dB step size. For the 2IFC procedure, thresholds with a 2-dB step size were 0.8 dB higher than with a 5-dB step size. Reliability, as measured by the intrasubject standard deviation, was better for the 2IFC than for the CLIN procedure and better in noise than in quiet. Reliability was unaffected by step size. Adding extra trials to the 2IFC adaptive track decreased the variability across threshold estimates, but more for the noise background than the quiet background. The efficiency of the 2IFC procedure was fairly constant across track length in noise, but decreased for longer track lengths in quiet. In both quiet and noise backgrounds, CLIN procedures were much more efficient than 2IFC procedures.

Research initiatives at the University of Toronto Environmental Hypersensitivity Research Unit

The Environmental Hypersensitivity Research Unit at the University of Toronto is following a research strategy to develop and evaluate diagnostic methods for environmental hypersensitivity. These methods will be used to identify cases for inclusion in studies of disease etiology and therapy. The Research Unit has actively sought consultation and collaboration with researchers at the University of Toronto, clinicians from a variety of specialties, and patients. It is hoped that such a multidisciplinary approach will lead to the generation and testing of innovative hypothesis with rigorous methodology and, ultimately, to increased understanding of the complex conditions known as environmental hypersensitivity.

Kinetics of removal and reappearance of non-transferrin-bound plasma iron with deferoxamine therapy

The rapidity and duration of the response of non-transferrin-bound iron (NTBPI) to chelation therapy are largely unknown and have important implications for the design of optimal chelation regimens. Methodology was developed to measure simultaneously NTBPI, deferoxamine (DFO), and its major metabolite. NTBPI was present in all but 2 of 28 thalassaemia major (TM) patients who had received conventional subcutaneous DFO the previous night, suggesting a short duration of NTBPI clearance by DFO. The detailed kinetics of NTBPI were therefore studied in response to intravenous DFO at 50 mg/kg/27 h for 48 hours and compared in 17 regularly transfused TM and 8 untransfused thalassaemia intermedia (TI) patients to determine the influence of hypertransfusion and iron overload on NTBPI response. Before DFO infusion, NTBPI was present in all patients and was significantly higher in TI (4.52 +/- 0.53 mumol/L) than TM (2.92 +/- 0.03 mumol/L; P = .03). NTBPI values in TM correlated with transferrin saturation (r = .6, P = .03) but not with serum ferritin. Removal of NTBPI by intravenous DFO is in a biphasic manner. The initial rapid rate constant (alpha) was similar in TI (1.5 hour-1) and TM (1.6 hour-1), but the subsequent beta phase was slower (0.04 hour-1) in TI when compared with TM (0.4 hour-1, P = .002). Detectable NTBPI persisted during the beta phase, particularly in TI, despite an excess of plasma DFO also being present (steady state 8 mumol/L). On cessation of DFO infusion, NTBPI reappearance was rapid; the kinetics also being biphasic. The rapid initial rate constant (alpha = 2.5 hour-1) lasted less than 30 minutes and was approximately equal to the summation of the initial rate constant for removal of DFO (1.8 hour-1) and its major metabolite (0.6 hour-1). This was followed by a slower return to pretreatment levels, usually between 6 and 12 hours, which was faster in TI than in TM. This marked NTBPI lability supports the use of continuous rather than intermittent DFO in high risk patients.

Event-related gamma band activity during passive and active oddball tasks

The EEG was recorded during passive listening and active attending to tone pips of an oddball stimulus sequence, and the time course of event-related gamma band activity (30-60 Hz) was compared with event-related potential (ERP) components. In the conventional frequency range (0.1-4.3 Hz) mismatch negativity (MMN) was produced in the passive listening condition. Concurrent with MMN, the power of event-related gamma activity to the deviant stimulus was higher than gamma activity elicited by the preceding standard stimulus. The transition from the N2b to the P3 wave, produced during active attention, was associated with a decrease in gamma band power upon the deviant tone. The results show the differential generation of gamma band power depending on preattentive and attentive stimulus processing.

Reliability of transient-evoked otoacoustic emissions

OBJECTIVE

This investigation addressed four factors affecting transient-evoked otoacoustic emission (TEOAE) reliability: 1) The effect of evoking-stimulus level, 2) the effect of analyzing bandwidth, 3) the effect of slight-mild hearing loss, and 4) the effect of variability in the stimulus spectrum.

DESIGN

TEOAEs at 80, 74, 68, and 62 dB pSPL evoking-stimulus levels were measured in 25 ears spanning a range of hearing levels from normal to mild hearing loss for a minimum of 10 test sessions. Reliability was assessed for 1/6-, 1/3-, 1/2-, and 1-octave analyzing bandwidths.

RESULTS

Evoking-stimulus level, hearing loss, and center frequency did not significantly affect reliability. With decreasing analyzing bandwidth, reliability decreased. Intrasubject test-retest standard deviations were 1.2 dB for a broadband analyzing bandwidth and 1.4, 1.5, 1.6, and 1.8 dB for 1-, 1/2-, 1/3-, and 1/6-octave analyzing bandwidths, respectively. Stimulus variability within narrower bandwidths was of sufficient magnitude to influence test-retest reliability, and attempts to correct for the variations in stimulus spectrum were unsuccessful. Slopes of the input-output functions differed across frequencies, with shallower slopes at higher frequencies.

CONCLUSIONS

In general, TEOAE amplitude is highly reliable. For those individuals in this study who were more variable, the variability was at low frequencies or across the entire frequency spectrum. For clinical applications, the choice of analyzing bandwidth should be based on consideration of both frequency specificity (where narrow analyzing bandwidths are optimal) and reliability (where wide analyzing bandwidths are optimal).

Efficacy and potency of antivenoms in neutralizing the procoagulant effects of Australian snake venoms in dog and human plasma

The efficacy and potency of Commonwealth Serum Laboratories (CSL) snake antivenoms in neutralizing the procoagulant action of Australian snake venoms was studied in vitro. The procoagulant action of venoms from Tiger, Brown and Taipan Snakes were measured in pooled canine or pooled human plasma. Mixtures of the venoms and their appropriate antivenoms, ranging from 0.1 to 15 times the recommended neutralizing dose of antivenom were then added to pooled canine or pooled human plasma and the efficacy and potency of the antivenoms in preventing the procoagulant action was measured. Neutralization was achieved by the addition of the appropriate antivenom in concentrations of 0.5 (Taipan), 10 (Tiger), 10 (Gwardar), 15 (Dugite) and an estimated 20 (Common Brown) times the dose expected. Similar results were obtained in canine and human plasma. The potency of Tiger and especially Brown Snake antivenom is substantially lower (10-20 times) than that predicted by CSL. These findings support an increase in the dose of antivenom to be used for the treatment of Tiger and especially Brown Snake envenomation complicated by coagulopathy. The in vitro canine model may be suitable for studying the procoagulant effects of Australian snake venoms.

Enhanced dynamic complexity in the human EEG during creative thinking

This study shows that divergent thinking, considered the general process underlying creative production, can be distinguished from convergent, analytical thought based on the dimensional complexity of ongoing electroencephalographic (EEG) activity. EEG complexity over the central and posterior cortex was higher while subjects solved tasks of divergent than convergent thinking, and also higher than during mental relaxation. Over the frontal cortex, EEG complexity was comparable during divergent thinking and mental relaxation, but reduced during convergent thinking. Results indicate that the basic process underlying the generation of novel ideas expresses itself in a strong increase in the EEG's complexity, reflecting higher degrees of freedom in the competitive interactions among cortical neuron assemblies. Frontocortical EEG complexity being comparable with that during mental relaxation, speaks for a loosened attentional control during creative thinking.

Greater efficacy of episodic than continuous growth hormone-releasing hormone (GHRH) administration in promoting slow-wave sleep (SWS)

It has been suggested that growth hormone (GH)-releasing hormone (GHRH) stimulates the surge in GH and enhances slow-wave sleep (SWS), two phenomena that characterize the beginning of nocturnal sleep. However, in human studies the effects of systemic GHRH administration on sleep were not consistent. This may reflect the differential influence of administration procedures being episodic in one of the above studies, but either a continuous infusion or a single bolus in the others. The present study in healthy volunteers compared changes in nocturnal sleep following 200 micrograms GHRH administered iv either episodically (4 boluses of 50 micrograms each at 2200, 2300, 2400, and 0100 h) or as a continuous infusion (57 micrograms/h between 2130 and 0100 h). Time spent in stage 4 of SWS on nights of episodic GHRH administration significantly exceeded that on nights of continuous GHRH administration (P < 0.01). Compared with a placebo condition, episodic administration of GHRH enhanced SWS (P < 0.01) and rapid eye movement (REM) sleep (P < 0.05) and diminished time spent in wakefulness and sleep stage 1 (P < 0.05). Effects of continuous GHRH infusion on sleep generally remained insignificant compared with placebo. Plasma GH concentrations were enhanced during both conditions of GHRH administration (P < 0.01), with the increase following episodic administration slightly exceeding that during continuous infusion (P < 0.05). The results support a greater physiological efficacy of episodic GHRH stimulation in promoting sleep.

Slow potential shifts at sleep--wake transitions and shifts between NREM and REM sleep

Scalp-recorded direct current (DC) potentials and their topographical distribution (F3, F4, C3, C4 and Pz) were investigated at the transition from wakefulness to sleep, and during NREM-REM sleep and REM-NREM sleep transitions in 11 healthy men during normal sleep. Changes in endexpiratory CO2 partial pressure (ETCO2), scalp temperature and polysomnographic data were simultaneously measured. The transition to sleep was associated with a negative potential shift reaching significance bilaterally at frontal and central sites 5 to 10 minutes after sleep onset (p < 0.05). Largest shifts were found at frontal locations 10 to 15 minutes after sleep onset averaging (mean +/- SEM) -512 +/- 103 mu V. Negative DC potential shifts also occurred at the transitions from NREM to REM sleep and from REM to NREM sleep, but were, however, less pronounced. The negative DC shift at NREM-REM sleep transitions preceded the REM sleep onset (assessed conventionally by polysomnographic criteria) by about 1.5 minutes. Changes in temperature, ETCO2 and eye movements were ruled out as factors significantly contributing to the generation of these shifts. Assuming a neuronal origin of the DC potential, the negative shifts at the wake--sleep transition and between NREM and REM sleep suggest a temporary phase of increased cortical excitability.

Effect of glycerol on intracellular virus survival: implications for the clinical use of glycerol-preserved cadaver skin

Glycerol has long been used for the preservation of skin allografts. The antimicrobial activity of glycerol has not been fully documented. This paper reports the results of an investigation of a model studying the effect of glycerol on the inactivation of intracellular viruses. Two viruses--herpes simplex type I (HSV-1) and poliovirus--were cultured within human dermal fibroblasts. These intracellular viruses were incubated with 50 per cent, 85 per cent and 98 per cent glycerol at 4 degrees C and 20 degrees C for 4 weeks. Each week, the cultures in glycerol and controls in fibroblast maintenance medium were assayed for virus infectivity by examining the ability of harvested viruses to infect further fibroblasts. At 4 degrees C, 85 per cent glycerol could not fully inactivate intracellular HSV-I or poliovirus even after 4 weeks; 98 per cent glycerol inactivated intracellular HSV-I (after 3 weeks) but could not fully inactivate intracellular poliovirus after 4 weeks. At 20 degrees C, 85 per cent glycerol inactivated intracellular HSV-I (within 1 week) but could not fully inactivate intracellular poliovirus after 4 weeks; 98 per cent glycerol inactivated intracellular HSV-I (within 1 week) and inactivated intracellular poliovirus (after 2 weeks). It is suggested that, on the basis of this study, glycerol can reduce intracellular virus infectivity but that its effects are very dependent on concentration, time and temperature such that we would recommend that allograft skin be exposed to 98 per cent glycerol for a minimum of at least 4 weeks at a minimum temperature of 20 degrees C before clinical use.

Scalp recorded direct current potential shifts associated with the transition to sleep in man

Cortical direct current (DC) potentials are considered to reflect the state of cortical excitability which may change characteristically from wakefulness to sleep. The present experiments examined changes in the scalp recorded DC potential in 10 healthy humans at the transition from wakefulness to nocturnal sleep. For each subject, DC recordings obtained from Cz were evaluated for a 15 min pre-sleep onset interval and for a 20 min post-sleep onset interval, on 2 separate nights. Sleep stages were determined from standard sleep recordings. The transition from wakefulness to sleep coincided with a significant (P < 0.05) shift in the DC potential of negative polarity. Maximum negative potentials of (mean +/- S.E.M.) 500 +/- 130 microV (first night) and of 760 +/- 200 microV (second night) were reached at the end of the 20 min post-sleep onset interval. A number of possible technical and biological artifacts were controlled. It is reasonable to assume that the slow negative shift of the DC potential at the transition from wakefulness to sleep reflects increased cortical excitability. Whether the negative potential shift pertains during sleep, or is of transient nature and closely linked to the process of falling asleep, remains to be clarified.