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Biomedical subjects

R J Davidson

Publications and source records attributed to R J Davidson.

At least 91 records · Page 5Linked to original sources
PubMed1992

Lateralized effects of diazepam on frontal brain electrical asymmetries in rhesus monkeys.

A growing body of literature has documented the differential role of the frontal regions of the two cerebral hemispheres in certain positive and negative affective processes. This corpus of evidence has led to the hypothesis of a possible differential effect of diazepam on asymmetry of frontal activation. To examine this question, nine infant rhesus monkeys were tested on two occasions during which brain electrical activity was recorded from left and right frontal and parietal scalp regions. During one session, recordings were obtained under a baseline restraint condition and then after an injection of diazepam (1 mg/kg). In the other session, following the same baseline restraint condition, a vehicle injection was given. In response to diazepam, the animals showed an asymmetrical decrease in power in the 4-8 Hz frequency band, which was most pronounced in the left frontal region. No change in electroencephalogram (EEG) activity was observed in response to vehicle. Asymmetry in parietal EEG activity was also unchanged by diazepam. Diazepam also produced overall reductions in power across different frequency bands in both frontal and parietal regions. Good test-retest stability of EEG measures of activation asymmetry was also found between the two testing sessions separated by three months. The possible proximal cause of the asymmetrical change in frontal brain electrical activity in response to diazepam, as well as the implications of these findings for understanding the mechanism of action of benzodiazepines are discussed.

Animals↗
PubMed1992

Anterior brain electrical asymmetries in response to reward and punishment.

A variety of recent research indicates that when subjects are induced to experience certain negative emotions, there is greater suppression of alpha power in the right than left frontal region, while during the experience of positive emotion, alpha power asymmetry in this region shows the opposite pattern. We have conceptualized this asymmetry as reflecting specialization for approach and withdrawal processes in the left and right frontal regions, respectively. In this experiment, reward and punishment contingencies were directly manipulated to produce approach and withdrawal emotional states. In addition, subjects responded to imperative stimuli using either an approach response (finger press) or a withdrawal response (finger lift). EEG was recorded from multiple scalp locations. During the foreperiod prior to the response to the imperative stimuli, the EEG was extracted, Fourier-transformed and power computed in the theta, alpha and beta frequency bands. In addition, the contingent negative variation (CNV) was derived from the identical epoch. Reward trials were associated with greater left frontal alpha power suppression than punishment trials, while during the latter trials, there was greater right-sided frontal alpha power suppression than during reward trials. There was also some evidence to indicate that withdrawal responses were associated with greater right-sided alpha power suppression in the temporo-parietal region compared with approach responses. Power in the theta and beta bands did not systematically vary with condition. The CNV was larger during trials on which subjects responded quickly compared with slow trials, but did not differentiate between reward and punishment contingencies. The findings support the hypothesis that approach-related processes can be differentiated from withdrawal-related processes on the basis of asymmetrical shifts in alpha power in the frontal region. They also indicate that the CNV and spectral power estimates from the identical epochs reflect different neural processes.

Adolescent↗
PubMed1992

Anterior cerebral asymmetry and the nature of emotion.

This article presents an overview of the author's recent electrophysiological studies of anterior cerebral asymmetries related to emotion and affective style. A theoretical account is provided of the role of the two hemispheres in emotional processing. This account assigns a major role in approach- and withdrawal-related behavior to the left and right frontal and anterior temporal regions of two hemispheres, respectively. Individual differences in approach- and withdrawal-related emotional reactivity and temperament are associated with stable differences in baseline measures of activation asymmetry in these anterior regions. Phasic state changes in emotion result in shifts in anterior activation asymmetry which are superimposed upon these stable baseline differences. Future directions for research in this area are discussed.

Adult↗
PubMed1992

Muscle tension patterns during auditory attention.

Although there is much evidence demonstrating muscle tension changes during mental work, there are few data concerning muscle tension patterns during effortful attention to simple sensory stimuli. In the present study, sensory attention was evoked by a pitch discrimination task at three levels of difficulty, with a digit retention task administered for comparison. Twenty-four females each performed both tasks at all levels of difficulty, while the EKG, and the corrugator supercilii, frontalis, lip, jaw, chin, and forearm area EMG were recorded. As expected, heart rate decreased significantly with increasing difficulty of the pitch task. A pattern of facial EMG responses accompanied the pitch task, which included significant increases in corrugator and frontalis, and decreases in the jaw as a function of difficulty, and time within trials. The tension pattern observed during sensory intake is discussed in terms of its relation to emotional expressions and motor theories of attention.

Acoustic Stimulation↗
PubMed1992

Individual differences in anterior brain asymmetry and fundamental dimensions of emotion.

This research assessed whether individual differences in anterior brain asymmetry are linked to differences in basic dimensions of emotion. In each of 2 experimental sessions, separated by 3 weeks, resting electroencephalogram (EEG) activity was recorded from female adults during 8 60-s baselines. Mean alpha power asymmetry across both sessions was extracted in mid-frontal and anterior temporal sites. Across both regions, groups demonstrating stable and extreme relative left anterior activation reported increased generalized positive affect (PA) and decreased generalized negative affect (NA) compared with groups demonstrating stable and extreme relative right anterior activation. Additional correlational analyses revealed robust relations between anterior asymmetry and PA and NA, particularly among subjects who demonstrated stable patterns of EEG activation over time. Anterior asymmetry was unrelated to individual differences in generalized reactivity.

Adolescent↗
PubMed1992

In-vitro activity of streptogramin RP 59500 against staphylococci, including bactericidal kinetic studies.

The in-vitro activity of RP 59500 and comparative agents was determined against 270 clinical isolates of the genus Staphylococcus. MICs were performed by micro-dilution dilution. MIC90 and MBC90 (mg/L) of RP 59500 were as follows: oxacillin-sensitive Staphylococcus aureus (0.5/0.5), oxacillin-resistant S. aureus (0.5/0.5), oxacillin-sensitive Staphylococcus epidermidis (0.5/0.5), oxacillin-resistant S. epidermidis (0.25/0.25), oxacillin-resistant Staphylococcus hominis (1.0/1.0), oxacillin-resistant Staphylococcus haemolyticus (1.0/1.0), oxacillin-sensitive Staphylococcus saprophyticus (1.0/1.0). Killing kinetic methods were used to assess the bactericidal activity of inhibitory (1 x, 2 x MIC) concentrations of RP 59500 in comparison with that of vancomycin (1 x, 2 x MIC) and oxacillin (1 x, 2 x MIC) against 20 strains of oxacillin-sensitive and -resistant S. aureus and S. epidermidis. RP 59500 was as active as vancomycin, displaying rapid bactericidal activity against the majority of strains tested and reducing initial inoculum counts by greater than 99.9% in 2-12 h. Regrowth was seen with some S. epidermidis strains after 12-24 h.

Drug Resistance, Microbial↗
PubMed1992

Psychometric properties of resting anterior EEG asymmetry: temporal stability and internal consistency.

We examined whether resting anterior electroencephalographic (EEG) asymmetry in the alpha frequency band has psychometric properties that would be expected of a measure assessing individual differences. In each of two experimental sessions, separated by three weeks, resting EEG in midfrontal and anterior temporal sites was recorded from 85 female adults during eight 60-s baselines. Resting alpha asymmetry demonstrated acceptable test-retest stability and excellent internal consistency reliability. Analyses including other frequency bands indicated that degree of stability varied somewhat as a function of band and region. In addition, asymmetry was less stable than absolute power. Discussion focuses on the implications of the present findings for the measurement and conceptualization of resting anterior asymmetry.

Adult↗
PubMed1992

Hematological status of male runners in relation to the extent of physical training.

Blood biochemical indices of iron status were measured in venous blood from 20 runners and 6 control subjects. All subjects were male, ages 20 to 40 years, and stable with regard to body weight and degree of physical activity. Dietary analysis was undertaken using a 7-day weighed food intake. There was no evidence of iron deficiency: hemoglobin concentrations and serum ferritin levels were within the normal population range for all individuals. However, serum ferritin was negatively correlated with the amount of training. Daily iron intake appeared to be adequate; iron intake was correlated with protein intake but not related to training or energy intake. Serum ferritin, an indicator of iron status, was significantly correlated with vitamin C intake but not iron intake. Serum transferrin concentration was higher in the group of athletes undertaking a high weekly training load compared with the control subjects, suggesting an alteration in iron metabolism although there was no evidence of increased erythropoiesis. The biological significance of this is unclear.

Adult↗
PubMed1992

Effect of pooled human cerebrospinal fluid on the postantibiotic effects of cefotaxime, ciprofloxacin, and gentamicin against Escherichia coli.

The killing and postantibiotic effects (PAE) of cefotaxime, ciprofloxacin, and gentamicin against Escherichia coli were determined in Mueller-Hinton broth (MHB) and pooled human cerebrospinal fluid (CSF). MICs performed in MHB and CSF were within one dilution for all antimicrobial agent-organism combinations. At two times the MIC, CSF significantly (P less than 0.05) increased the duration of the PAE compared with MHB when cefotaxime, ciprofloxacin, and gentamicin were used against all strains tested. This effect occurred despite similar reductions in bacterial growth in both fluids after the 2-h antimicrobial agent exposure. We conclude that pooled human CSF markedly increases the PAE of cefotaxime, ciprofloxacin, and gentamicin against E. coli compared with MHB, without affecting bacterial killing.

Cefotaxime↗
PubMed1992

Antimicrobial activity of subinhibitory concentrations of ciprofloxacin against Pseudomonas aeruginosa as determined by the killing curve method and the postantibiotic effect.

This investigation used the postantibiotic effect (PAE) and killing curves to examine the antimicrobial activity of subinhibitory (1/8x, 1/4x and 1/2x MIC) and inhibitory (1x MIC) concentrations of ciprofloxacin against mucoid (M) and nonmucoid (NM) urinary isolates of Pseudomonas aeruginosa. Subinhibitory concentrations (1/8x, 1/4x and 1/2x MIC) of ciprofloxacin produced PAEs with no difference between M and NM strains. For NM strains, those with low MICs (< or = 1.0 mg/l) to ciprofloxacin produced significantly longer PAEs than isolates with high MICs (> 1 mg/l). Killing curve studies demonstrated that subinhibitory concentrations of ciprofloxacin produce little effect (1/8x MIC) or stasis (1/4x and 1/2x MIC) of growth for several hours. Only 1x MIC was bactericidal for several strains. At 1/2x and 1x MIC, bacterial inhibition was greater against NM versus M isolates. The M phenotype of P. aeruginosa reduces killing by ciprofloxacin but not the PAE.

Ciprofloxacin↗
PubMed1992

A new alpha chain variant, Hb Turriff [alpha 99(G6)Lys----Glu]: the interference of abnormal hemoglobins in Hb A1c determination.

Hb Turriff is a new hemoglobin variant which we have identified in a diabetic individual. During the determination of Hb A1c by high performance liquid chromatography, an inappropriately elevated result was found to be due to the abnormal hemoglobin chromatographing with the Hb A1c fraction. This new hemoglobin variant, Hb Turriff [alpha 99(G6)Lys----Glu], is not associated with any hematological disturbance, and family investigations indicate that it has arisen as a de novo mutation.

Adult↗
PubMed1991

Left frontal hypoactivation in depression.

Baseline resting electroencephalogram activity was recorded with 3 different reference montages from 15 clinically depressed and 13 control subjects. Power in all frequency bands was extracted by fast Fourier transformation. There was a significant Group X Hemisphere interaction in the mid-frontal region, for the alpha band power only. Depressed subjects had less left-sided activation (i.e., more alpha activity) than did normal control subjects. This pattern of diminished left-sided frontal activation is interpreted as indicating a deficit in approach mechanisms in depressed subjects.

Adult↗
PubMed1991

Frontal brain asymmetry and immune function.

The relation between brain activity and the immune system was evaluated by assessing immune responses in 20 healthy women who manifested extreme differences in the asymmetry of frontal cortex activation. One group showed extreme and stable left frontal activation; the other group showed extreme and stable right frontal activation. As predicted, women with extreme right frontal activation had significantly lower levels of natural killer cell activity (at effector:target cell ratios of 33:1 and 11:1) than did left frontally activated individuals. This difference did not extend to two other immune measures, lymphocyte proliferation and T-cell subsets. However, higher immunoglobulin levels of the M class were observed in the right frontal group. In this study, the immune patterns could not be accounted for by plasma cortisol levels, anxiety- and depression-related symptomatology, or recent health histories. These findings support the hypothesis that there is a specific association between frontal brain asymmetry and certain immune responses.

Adolescent↗