Dependence of the transcranially induced silent period on the 'instruction set' and the individual reaction time

OBJECTIVES AND METHODS: We looked for influences of the experimental condition on the silent period (SP) from transcranial motor cortex stimulation and analyzed how the instruction given to the subject, as well as the individual reaction time, might affect the duration of the SP in the biceps brachii muscle. RESULTS: The duration of the SP was found to critically depend on the subject's voluntary reaction of the target muscle immediately after the stimulus. With low stimulus intensity and low background force, the duration of the silent period was significantly longer in 10 of 13 subjects (P = 0.002) when they were instructed to relax quickly after the stimulus rather than to maintain the the force at a constant level. A significant shortening of the SP (P = 0.02) was observed when the subjects were instructed to perform a rapid contraction of the target muscle in reaction to the cortical stimulus. With low stimulus intensity and high background force, the same influence of the instruction set was found in 6 of 13 subjects. When the subjects were left without precise instruction, the SP duration was unpredictable. In 10 subjects, the SP corresponded to that obtained with the instruction to maintain the force at a constant level. However, in 3 subjects it was prolonged to the value observed in the 'relax' instruction. With greater stimulus intensities, the effect of the instruction set on the SP duration was generally smaller. A significant prolongation was nevertheless found at low background forces with rapid relaxation (P < 0.001), and a significant shortening was found at high background forces with rapid contraction (P < 0.001) after the stimulus. The SP duration observed with 20% of maximal voluntary contraction (MVC) significantly correlated with the individual reaction time. No such correlation was found for the SP obtained with 80% MVC. The SP was slightly longer at 20% MVC, as compared to 80% MVC within each instruction group. This effect was significant (P < 0.05) at low stimulus intensities. CONCLUSIONS: Therefore, when assessing the SP duration for diagnostic purposes, not only the stimulus intensity but also the background force and the voluntary reaction must be standardized. Furthermore, great stimulus intensities and high background forces should be used to minimise the effects of instruction set and individual reaction time.     

Morphological changes in the central nervous system of animals depending on the dosage and time elapsed after exposure to low let radiation

Analytical review of the morphological investigations of cerebral cortex neurons of various animals shortly after exposure to X- and gamma-radiation was made. Considered were data of qualitative and quantitative analyses of dystrophic changes in neurons of the sensorimotor cortex of the large cerebral hemispheres of rats immediately and a long period since X-irradiation. Results of the quantitative analysis of structural disorders in the central nervous system neurons suggest radiation-produced damages early after exposure of animals to relatively low doses. Higher incidence of irreversible changes in neurons of the experimental animals, as compared with intact controls, was stimulated by the doses of no more than 0.25 to 1.0 Gy. The relative number of structural disorders in neurons and percentage of irreversibly impaired cells rose proportionally to the dose growth and further delay of the time of investigation. Possible mechanisms of delayed disorders that led to a massive building-up of the number of dystrophic neurons following 3 to 4 months post irradiation of rats are discussed.     

Variations with time and age in the risks of solid cancer incidence after radiation exposure in childhood

The Japanese atomic bomb survivor incidence data set and data on five other groups exposed to ionizing radiation in childhood are analysed and evidence found for a reduction in the radiation-induced relative risk of cancers other than leukaemia with increasing time since exposure. Overall, reductions of 5.7-6.1 per cent per year of time since exposure are indicated, depending on the time at which the reduction is presumed to start, and all the reductions are statistically significant at the 5 per cent level. There is no significant heterogeneity in the speed of the reductions in relative risk with time by cohort, by cancer type, sex, or age at exposure group. There is a significant reduction of relative risk with increasing age at exposure, but adjustment for age at exposure does not markedly affect the time trends of relative risk. For all of the groups considered, there is a statistically significant increase in the excess absolute risk with increasing time since exposure. However, by contrast with the relative homogeneity of the time trends of relative risk, there is statistically significant heterogeneity by cancer type within the Japanese cohort (P = 0.05) and between the cohorts (P < 0.0001) in the speed of increase of the excess absolute risk with time since exposure.     

Assessment of exposure rate and collective effective dose equivalent in the city of Baghdad due to natural gamma radiation

Exposure rate measurements in the city of Baghdad were initiated in June 1981. The average exposure rate, the average annual effective dose equivalent and the collective effective dose equivalent are assessed. The data are presented according to the eleven municipal divisions of the city. The average exposure rate was 6.9 microR h-1 and an average annual effective dose equivalent of 4.5 x 10(-4) Sv year-1. The collective effective dose equivalent is 1.81 x 10(3) man Sv year-1.     

First analysis of mortality and occupational radiation exposure based on the National Dose Registry of Canada

A cohort mortality study of occupational radiation exposure was conducted using the records of the National Dose Registry of Canada. The cohort consisted of 206,620 individuals monitored for radiation exposure between 1951 and 1983 with mortality follow-up through December 31, 1987. A total of 5,426 deaths were identified by computerized record linkage with the Canadian Mortality Data Base. The standardized mortality ratio for all causes of death was 0.61 for both sexes combined. However, trends of increasing mortality with cumulative exposure to whole body radiation were noted for all causes of death in both males and females. In males, cancer mortality appeared to increase with cumulative exposure to radiation, without any clear relation to specific cancers. Unexplained trends of increasing mortality due to cardiovascular diseases (males and females) and accidents (males only) were also noted. The excess relative risk for both sexes, estimated to be 3.0% per 10 mSv (90% confidence interval 1.1-4.8) for all cancers combined, is within the range of risk estimates previously reported in the literature.     

The influence of extended posthatch holding time and placement density on broiler performance

Extended posthatch holding (in the hatcher) has been reported to dehydrate chicks, reduce broiler performance, and depress immune response. Nevertheless, some commercial hatcheries are increasing incubation time in an attempt to minimize possible bacterial contamination of incompletely healed navels. The objectives of this study were to determine the effects of posthatch holding on broiler performance and the effects of bird density and additive stress on performance and immune response. Twelve hundred broiler eggs (58 to 70 g) were incubated. Chicks were removed from the hatcher after 528 h of incubation, banded, and weighed. Half of the chicks were returned to the hatcher for an additional 24 h (HELD). Both hatcher treatments were placed at two densities (.07 and .12 m2 per bird). Individual BW were taken at 21 and 43 d of placement and 43 d of age. The HELD chicks weighed significantly less than controls at time of placement. At 21 d postplacement the HELD broilers were significantly heavier than controls, but were similar by 43 d. Total feed conversion was not affected in the HELD treatment, but birds in the .07 m2 per bird density were less efficient in terms of total feed conversion. Chick holding time and density seemed to affect antibody titers at 5 wk. Although holding chicks in the hatcher for 24 h did not clinically dehydrate chicks or affect performance, it decreased immune response. In addition to less efficient growth, birds in the more crowded pens had depressed immune response.     

The effectiveness and safety of low dose pravastatin in elderly hypertensive hypercholesterolemic subjects on antihypertensive therapy

To evaluate the efficacy and safety of low dose (10 mg) pravastatin in hypercholesterolemic, hypertensive elderly subjects undergoing antihypertensive treatment, a randomized, double-blind, placebo-controlled 6-month trial was conducted. The subjects had a total plasma cholesterol of at least 250 mg/dL and had been, for at least 3 months, consuming a standard lipid-lowering diet (American Heart Association Step 1 Diet). Sixty elderly hypertensive patients randomly received placebo (n = 30) or pravastatin (n = 30) treatment. The dosage consisted of 10 mg of pravastatin daily during the 6-month trial. Over that period, in the pravastatin group, plasma levels of total cholesterol and LDL-cholesterol significantly (P < .01) dropped (-20% and -25%, respectively) compared to the placebo group. The plasma level of HDL-cholesterol increased (+5%) while triglycerides slightly decreased (-8%) (P < .05). No serious side effects occurred, and pravastatin was generally tolerated. Fasting hyperinsulinemia (11.0 +/- 0.8 v 9.3 +/- 0.7 microU/mL; P = .06) also improved, although not significantly, after 6 months of pravastatin therapy. Results from this study confirmed that a low dose (10 mg) of pravastatin daily is a safe and effective method of reducing plasma total and LDL-cholesterol in hypercholesterolemic, hypertensive elderly patients who are on concurrent antihypertensive drug therapy.     

The effect of aversive stimuli on reaction time in schizophrenia.

"… the experiment was to assess the motivational role of aversive stimuli in modifying the performance of normal and… schizophrenic… males… [on] a visual reaction time task… . During… [one] series Ss responded under… experimental conditions… [part of which] involved the use of intense noise as an aversive stimulus. None of the experimental conditions appreciably altered the performance of normal Ss. However, schizophrenic Ss performing under… [conditions involving noise] displayed greater improvement than control Ss." 22 refs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of long-term UV radiation exposure on the skin autonomous microflora and on body nonspecific resistance

Hairless mice of strain HRS were exposed to vertical UV-B-irradiation (280-320 nm) at daily doses of 1 or 2 kJ/m2 (biologically effective doses 200 and 400 J/m2) five days a week for 13 and 6 weeks. As the length of exposure increased, the abundance of automicroflora of the dorsal skin first decreased, then exceeded the control value, was normalized, and remained at the normal level until the end of the experiment. The rates of effect appearance and disappearance, just as its amplitude, increased with the daily doses. No changes were found in resistance to staphylococcal alpha-toxin after its post-irradiation intraperitoneal injection.     

The effects of competition on reaction time and palmar skin conductance.

"Ninety-two Ss were tested on reaction time tasks under normal and competitive conditions. The speed of the simple reaction and of the discriminative reaction increased under the competitive condition… . Under the competitive condition, the level of palmar skin conductance increased and self-rated alertness increased, but these measures were not related to the decrease in reaction time. Thus the speed of performance and some measures of the level of motivation both increased in a competitive situation, but there was no evidence… for a causal relationship between them." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The impact of positive and negative feedback on reaction time in brain-damaged patients.

Little is known about the impact of feedback on the reaction times (RTs) of brain-damaged (BD) patients. The authors therefore investigated the effect of positive and negative feedback on these patients, using a 4-choice RT task. Participants were 107 BD patients with different etiologies and 50 orthopedic (OG) control patients. Patients were assigned to 3 groups in which performance-independent negative, positive, and no feedback were given. Statistical analysis showed that negative feedback led to significantly shorter RTs in BD patients. Even BD patients with high depression scores were affected by negative feedback. In contrast, negative feedback had no impact on the RTs of the OG controls, and positive feedback had no influence on the RTs of any group. These results raise some interesting questions about motivational processes in BD patients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of breast size on late radiation effects and association with radiotherapy dose inhomogeneity

A prospective assessment of late changes in breast appearance in 559 patients after tumour excision and radiotherapy for early breast cancer noted a strong association with breast size. Only 3/48 (6%) patients with small breasts developed moderate or severe late changes compared with 94/423 (22%) with medium sized breasts and 34/88 (39%) patients with large breasts (p < 0.001). One possibility is that greater radiation changes are related to greater dose inhomogeneity in women with large breasts. To explore this hypothesis, radiation dose distributions were assessed in a separate group of 37 women in whom three-level transverse computer tomographic images of the breast in the treatment position were available. A significant correlation was found between breast size and dose inhomogeneity which may account for the marked changes in breast appearance reported in women with large breasts.     

The effects of postradiation treatment with tamoxifen on local control and cosmetic outcome in the conservatively treated breast

BACKGROUND: The aim of this study was to evaluate the impact on disease recurrence and cosmetic outcome of tamoxifen treatment initiated after breast-conserving therapy (BCT). METHODS: Between 1982 and 1994, 498 women (509 breasts) were treated with BCT in accordance with a highly standardized institutional protocol. Adjuvant tamoxifen was administered to 130 patients (134 breasts), beginning 1-6 weeks after irradiation. The median ages and duration of follow-up for groups who received tamoxifen (TAM+) and no tamoxifen (TAM-) were 62.5 years/56 months and 53 years/60 months, respectively. The members of the TAM+ group were significantly older (P = 0.0001) and had increased incidences of positive axillary lymph nodes or undissected axilla (P = 0.001). There was a significant (P = 0.001) difference between the TAM+ and TAM- groups in the distribution of histopathologic subtypes; this reflected an increased proportion of associated ductal carcinoma in situ in the TAM- group. More extensive regional lymphatic irradiation was administered to the TAM+ group. Chemotherapy was administered to 15% of TAM+ and 28% (P = 0.003) of TAM- patients. There were no significant differences between the groups with respect to tumor size, reexcision, total excised tissue volume, final margin status, total radiation dose, or use of interstitial implant boost. RESULTS: There was no significant difference between the TAM+ and TAM- groups in the overall distribution of cosmetic scores (P = 0.18). The 5-, 7-, and 10-year actuarial local failure rates for TAM+ versus TAM- patients were 0% versus 3.1%, 1.9% versus 5.4%, and 1.9% versus 8.4%, respectively. Multivariate regression analyses of potentially confounding variables revealed no significant associations between tamoxifen and either cosmetic outcome or local failure. CONCLUSIONS: Radiotherapy followed by tamoxifen has no adverse interactive effect on cosmesis, and tamoxifen is associated with a trend toward enhanced 5-year local control probability.     

The effect of divided attention on probe reaction time in multiple-task performance.

Examined information processing demands in 5 experiments in which a total of 72 candidates who were being processed for aircrew selection and pilot training performed a serial addition, pursuit tracking, or probe reaction time (PRT) task separately and in dual- and triple-task combinations. The experiments manipulated the assigned priority and the capacity requirements of the serial addition and tracking tasks. PRT is usually assumed to reflect spare processing capacity in dual-task studies and to increase with greater processing demands. Since PRT did not increase between dual- and triple-task conditions, results of the present studies suggest that PRT could be measuring spare capacity, which remained relatively constant as processing demands increased. Analogous data were reported by C. D. Wickens (see record 1976-09005-001) for a triple-task situation. These observations would not have been predicted by available models of divided-attention performance. (French summary) (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of aging on reaction time in a signal detection task.

The effects of aging on response time are examined in 2 simple signal detection tasks with young and older subjects (age 60 years and older). Older subjects were generally slower than young subjects, and standard Brinley plot analyses of response times showed typical results: slopes greater than 1 and (mostly) negative intercepts. R. Ratcliff, D. Spieler, and G. McKoon (2000) showed that the slopes of Brinley plots measure the relative standard deviations of the distributions of response times for older versus young subjects. Applying R. Ratcliffs (1978) diffusion model to fit the response times, their distributions, and response accuracy, it was found that the larger spread in older subjects' response times and their slowness relative to young subjects comes from a 50-ms slowing of the nondecision components of response time and more from conservative settings of response criteria. (PsycINFO Database Record (c) 2010 APA, all rights reserved)