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At least 199 records · Page 11Linked to original sources
PubMed2004

The physiological basis of transcranial motor cortex stimulation in conscious humans.

Transcranial stimulation of the human motor cortex can evoke several different kinds of descending activity depending on the type of stimulation, the intensity of stimulation and the area of the cortex being stimulated. Thus, transcranial magnetic stimulation preferentially activates different structures than transcranial electrical stimulation. In addition, the response to magnetic stimulation depends on the direction of the induced current in the brain, the waveform of the stimulating current, and the shape of the coil. Stimulation of the lower limb area of motor cortex recruits different elements than stimulation of the upper limb area. These differences occur because different structures in the motor cortex have a differential threshold to the different techniques of stimulation. We have had the opportunity to perform a series of direct recordings of the corticospinal volley evoked by the different techniques of transcranial stimulation from the epidural space of conscious patients with chronically implanted spinal electrodes. These recordings provide insights about the physiological basis of the excitatory and inhibitory phenomena produced by transcranial stimulation.

Efferent Pathways↗
PubMed2006

Rehabilitation plasticity: influence of hearing aid fitting on frequency discrimination performance near the hearing-loss cut-off.

Several studies have already demonstrated that patients with steeply sloping hearing loss of cochlear origin exhibit an improvement in frequency discrimination performance at or around the cut-off frequency. This enhancement cannot be explained in terms of peripheral mechanisms and should rather be interpreted in terms of central reorganization: i.e., injury-induced cortical plasticity. However, the reversibility and time course of such reorganization has not yet been described. The main goal of the present study was therefore to investigate the occurrence of rehabilitation plasticity associated with hearing-aid fitting in human subjects. Nine subjects with steeply sloping hearing loss and who were candidates for auditory rehabilitation were tested. Discrimination-limen-for-frequency (DLF) enhancement was investigated at the frequency with the best DLF (bDLF) for each individual subject before and during auditory rehabilitation (at 1 month, 3 months and 6 months). From 1 month on, frequency discrimination performance decreased significantly at the bDLF frequency, while remaining stable at other frequencies. This normalization may reflect a new central reorganization reversing the initial injury-induced changes in the cortical map. A correlation between subject's age and alteration in DLF at 1 month was also found, suggesting that plasticity operates faster in younger patients.

Adult↗
PubMed1989

Manual asymmetry in weight discrimination: hand preference or hemispheric specialization?

One-handed weight discrimination was investigated as a function of hand, hand preference and hemispheric specialization. Differential thresholds (DLs) were measured for the left and right hands and left- and right-handed male and female subjects. DLs were found to be lower for the hand contralateral to the ear that proved superior in a verbal dichotic listening task. These results establish the existence of a manual asymmetry for the discrimination of lifted weight with the advantage accruing for the hand contralateral to the non-language cerebral hemisphere.

Adult↗
PubMed1976

Studies on the physiology and biochemistry of mammalian epididymis: effect of flutamide, a nonsteroidal antiandrogen, on the epididymis of the rat.

The effect of flutamide (Sch 13521; 4'-nitro-3'-trifluoromethylisobutyranilide), a nonsteroidal antiandrogen, on male rat genital organs was studied. Administered at a dose of 25 mg/kg body weight daily for 30 days, flutamide caused a significant increase in the weight of the testis but had no effect on spermatogenesis and Leydig cell morphology. The secretory activity of the epididymis, as evidenced by the level of glycerylphosphoryl-choline and sialic acid, either remained unaffected or was stimulated. There was a significant decrease in seminal vesicle and ventral prostate weight and in the fructose content of the coagulating gland. The anti-androgen at the dose used did not affect the fertility of the rats. The significance of these findings is viewed in relation to the hypothesis of a differential threshold requirement of androgen for the epididymis and the accessory sex glands. The potentiality of antiandrogens as extragonadal antifertility agents in the male is discussed.

Anilides↗
PubMed1985

Heart-rate responses of infant rats and guinea pigs to stimulus onset and offset: tests of the generality of a bidirectional effect.

To test the generality, across modality and across species, of a bidirectional effect of photic stimulation in infant rats found in previous experiments, two experiments examined the effects on heart rate (HR) of onset and offset of auditory stimulation in rats and of photic stimulation in guinea pigs. Experiment 1 demonstrated a unidirectional, decelerative response in rats 17 and 21 days of age to the onset and offset of a 1-kHz tone, at both low (80 dB) and high (100 dB) intensity levels and at 14 days to the onset of the high-intensity tone. Experiment 2 demonstrated that infant guinea pigs, which unlike infant rats are precocial and not nocturnal, responded to the offset but not to the onset of light, and that this response was decelerative. These results indicated a lack of generality of the bidirectional HR effect, and were discussed in terms of the orienting/defensive reflex distinction.

Acoustic Stimulation↗
PubMed2000

Thermal damage threshold at 633 nm of tympanic membrane of pig.

Doppler vibrometers are used by many research groups to monitor the motion of the tympanic membrane (TM) and of middle ear ossicles for in vivo and in vitro studies. Power densities in these applications reach 80 W/cm(2). To determine the safe limit of exposure, a cw dye laser at a wavelength of 633 nm was used to investigate the threshold of thermal damage of TM of pigs under exposure times of 60 s. To determine the applied power density accurately, the spot size of the laser beam was monitored by an objective lens and a CCD camera. Twenty-six laser exposed samples of TM were stained by haematoxylin and eosin stain and the semi-thin sections were examined microscopically. In none of the sections was any laser induced damage observed with power densities below 7.1 kW/cm(2), whereas serious damage occurred showing coagulation, carbonisation and perforation in all cases with laser powers above 8.2 kW/cm(2). The threshold for damage and the conical shape of the damage zone is explained by photon propagation and absorption in the tissue especially by the increase of the scattering factor at higher tissue temperature. The thermal damage threshold of 8 kW/cm(2) is compared to the maximum permissible exposure given in laser safety standards for skin.

Absorption↗
PubMed1996

Postsynaptic levels of [Ca2+]i needed to trigger LTD and LTP.

Long-term potentiation (LTP) and long-term depression (LTD) in CA1 pyramidal neurons are both triggered by a postsynaptic rise in intracellular Ca2+ concentration ([Ca2+]i). We used photolysis of postsynaptic caged Ca2+ compounds to search for differential thresholds for activation of these processes. Long-lasting potentiation (LLP) resembling LTP, and long-lasting depression (LLD) resembling LTD, were evoked by [Ca2+]i elevations of comparable magnitude and duration in different cells. No distinctions in threshold for these processes were detectable. LLP was occluded by tetanically induced LTP and blocked by calmodulin inhibition, and LLD was occluded by electrically induced LTD and blocked by phosphatase inhibition.

Age Factors↗
PubMed2004

Mechanisms of disorders of the characteristics of fine movements in long-term hypokinesia.

The precision and electromyographic characteristics of single-joint voluntary movements of the human foot, of the programmed and tracking types, were studied, along with the characteristics of rhythmic activity of motor units before and during 120-day antiorthostatic hypokinesia. This latter was accompanied by significant decreases in the precision of the control system, evident as decreases in the number of discriminable force gradations, increases in the absolute and differential thresholds for movements of the programmed type, and sharp increases in the variability of integrated EMG traces from the working muscles during tracking movements. The direction and dynamics of changes in the activity of motor units at different stages of antiorthostatic hypokinesia were different: during the first 14-30 days (stage I), there was a sharp increase in the variability of interspike intervals and an increase in the extent of synchronization of motor unit activity; from day 30 onwards (stage II), there was a reproducible decrease in the duration of interspike intervals, along with disappearance of the synchronization of motor units, while the high level of variability of spike activity persisted. The results obtained here suggest that impairments of precision during stages I and II of antiorthostatic hypokinesia are different in nature and are associated with reflex responses to support unloading at stage I and with atrophic processes in muscles in stage II.

Electromyography↗
PubMed1984

Factors influencing the masking level difference in cochlear hearing-impaired and normal-hearing listeners.

The masking level difference (MLD) at 500 Hz was examined in wide-band (960 Hz) and narrow-band (50 Hz) noise for normal-hearing subjects and subjects with symmetrical mild-to-moderate cochlear hearing loss. Monaural tasks of intensity discrimination, temporal resolution, and frequency resolution were performed in order to examine relationships between monaural dysfunction and MLD performance. Interaural time discrimination for a 500-Hz pure tone also was examined. The performance of the hearing-impaired subjects was poorer than that of the normal-hearing subjects for MLD, interaural delta t, and most monaural tasks. However, no significant relationships were found between monaural and MLD performance when effects of threshold were taken into account. MLDs were more reduced in wide-band noise than in narrow-band noise for the hearing-impaired subjects (when contrasted with normal-hearing subjects). MLD performance was correlated with interaural time discrimination, and it is suggested that one reason for poor MLD performance with hearing impairment may be poor temporal coding of stimulus-fine structure.

Adult↗
PubMed1991

[Automatic perimetry of the central visual field in diseases of the macula].

We developed a program for testing the central 12 degrees of the visual field with a spatial resolution of 1.6 degrees that was easy to operate. The program was designed for the Octopus computer-perimeter and created by means of the SARGON-utility. Our way of examining differed slightly from the standard Octopus procedure. We tested 16 normal eyes and 13 eyes of patients with various diseases of the central retina. Our normal values of differential threshold sensitivities were about 1.8 dB below the normal values of the Octopus system. Sensitivity and specificity of the program were nearly identical irrespective of using our normal values or the Octopus normal values for the calculation of the above mentioned parameters. Sensitivity was 84.6%, specificity 87.5%. The ability of the program to correctly localize retinal defects was shown. The program was designed for follow-up of patients having undergone paramacular lasercoagulation.

Adult↗
PubMed1997

Viscosity discrimination: a comparison of an adaptive two-alternative forced-choice and an adjustment procedure.

Differential thresholds for viscosity were measured in ten subjects with the use of an adaptive two-alternative forced-choice procedure. An electromagnetic linear motor was connected to each wrist and the viscosity of the motors was under computer servo control. For each block of 50 trials the viscosity of one motor was fixed at a reference value which ranged from 4 to 512 N s m-1, and the viscosity of the other motor varied according to the subject's responses. On each trial subjects were required to indicate which motor had the greater viscosity and were given feedback of the correct response. By this procedure the Weber fraction for viscosity was calculated to be 19%, which is lower than the Weber fraction of 34% estimated by using the method of adjustment. The criterion used for determining the threshold differs in the two procedures (71% and 84% correct, respectively), and the results from the two studies were found to be consistent. They suggest that the Weber fraction for viscosity remains remarkably stable despite differences in the methods of measurement.

Adult↗
PubMed2003

Effects of isoflurane on the auditory brainstem responses and middle latency responses of rats.

OBJECTIVE: To evaluate the effects of a volatile anesthetic, isoflurane, on auditory brainstem responses (ABRs) and middle latency responses (MLRs) recorded in rats. MATERIAL AND METHODS: ABRs and MLRs evoked by click stimuli were simultaneously recorded in eight rats in the awake condition and during anesthesia with isoflurane at clinically relevant concentrations. RESULTS: Vertex-recorded ABRs showed a significant increase in the latency of waves I-IV during anesthesia and the latency changes appeared to be significantly related to the isoflurane concentration. The I-IV interval also appeared to be significantly increased in comparison to the awake condition, while minor changes in ABR amplitudes were induced by isoflurane. MLRs, which were recorded by means of epidural electrodes implanted over the auditory cortex, appeared to be attenuated in amplitude and increased in latency during anesthesia. Only latency changes appeared to be significantly related to the isoflurane concentration. Moreover, "bursts" of high amplitude MLRs were observed during anesthesia at each concentration. CONCLUSION: The present findings indicate that both ABR and MLR latencies are increased by isoflurane in a concentration-dependent manner, whilst the anesthetic-induced attenuation in amplitude does not appear to be related to the isoflurane concentration.

Animals↗
PubMed2005

Neural response correlates of detection of monaurally and binaurally created pitches in humans.

Recent magnetoencephalography (MEG) and functional magnetic resonance imaging studies of human auditory cortex are pointing to brain areas on lateral Heschl's gyrus as the 'pitch-processing center'. Here we describe results of a combined MEG-psychophysical study designed to investigate the timing of the formation of the percept of pitch and the generality of the hypothesized 'pitch-center'. We compared the cortical and behavioral responses to Huggins pitch (HP), a stimulus requiring binaural processing to elicit a pitch percept, with responses to tones embedded in noise (TN)-perceptually similar but physically very different signals. The stimuli were crafted to separate the electrophysiological responses to onset of the pitch percept from the onset of the initial stimulus. Our results demonstrate that responses to monaural pitch stimuli are affected by cross-correlational processes in the binaural pathway. Additionally, we show that MEG illuminates processes not simply observable in behavior. Crucially, the MEG data show that, although physically disparate, both HP and TN are mapped onto similar representations by 150 ms post-onset, and provide critical new evidence that the 'pitch onset response' reflects central pitch mechanisms, in agreement with models postulating a single, central pitch extractor.

Adult↗
PubMed1993

Effects of continuous treatment with low dose mifepristone throughout one menstrual cycle.

The effects of continuous low dose mifepristone (RU 486) 10, 5 or 1 mg/day on the menstrual cycle were assessed in groups of five volunteers, who were treated for 30 days from the beginning of the cycle. Hormonal determinations in blood and urine samples, ovarian ultrasonography and an endometrial biopsy taken on day 22-29 of treatment were used to monitor the cycle. Pre- and post-treatment cycles presented a normal profile. During treatment, concentrations of RU 486 in plasma ranged from 65 nmol/l with 1 mg/day to 1000 nmol/l with 10 mg/day. With 10 or 5 mg/day, all treated cycles were prolonged as a result of arrested or slower follicular growth during treatment. Gonadotrophins, sex steroids and their urinary metabolites remained at early follicular phase levels throughout treatment, whereas androstenedione, prolactin and cortisol were unaffected. Follicular maturation resumed after discontinuation of treatment and several days later a luteinizing hormone surge followed by a luteal phase was observed in all cases. Ovulation was suppressed during treatment only in one of the five cycles treated with 1 mg/day. Endometrial maturation was disturbed by all doses. These data demonstrate a differential threshold of the follicle and the endometrium to mifepristone. This finding has potential application in the contraceptive field.

Adult↗
PubMed2006

CD4 percentages and total lymphocyte counts as early surrogate markers for pediatric HIV-1 infection in resource-limited settings.

The early diagnosis of pediatric HIV-1 infection is a critical issue in resource-limited settings to prioritize eligibility for antiretroviral therapy among HIV-1-infected children. A case-control study was performed within the ANRS 1201/1202 Ditrame Plus cohort (Abidjan, Côte d'Ivoire) to assess the usefulness of CD4+ T-cell percentage (CD4%) and total lymphocyte count (TLC) measured early in life in African children born to HIV-1-infected mothers. Using plasma HIV-1 RNA testing at 4 weeks of life as gold standard, CD4% and TLC were determined at month 3 and 6 in all 33 children HIV-1-infected in utero or intrapartum/early postpartum (cases) born to mothers receiving peripartum antiretroviral prophylaxis. Controls were 66 HIV-1-uninfected children from the same cohort. At month 3, the median CD4% was significantly lower in HIV-1-infected children (17.7%, 95% percentiles, 7.1-27.4) than in uninfected controls (34.8%, 18.5-45.3) (P < 0.001). A comparable difference was also observed at month 6. At the same time points, no significant difference was measurable for TLCs. The best threshold differentiating HIV-infected and uninfected children at month 3 was 25% CD4+. Compared to HIV-1 RNA results, sensitivity of this marker was 87.1% (95% confidence interval, 70.2-96.4) at month 3 and 88.9% (70.8-97.6) at month 6. Specificity was 78.3% (63.6-89.0) and 88.3% (77.4-95.2), respectively. Early CD4% measurement allows one to classify adequately the vast majority of exposed children according to their HIV status. CD4% should be further evaluated under field conditions for the diagnosis of pediatric HIV-1 infection and the monitoring of pediatric antiretroviral therapy.

CD4 Lymphocyte Count↗
PubMed2006

Immunohistochemical detection of P-glycoprotein (clone C494) in canine mammary gland tumours.

Elevated levels of P-glycoprotein have been reported in multidrug-resistant tumours in both humans and dogs. In the present study, we investigated the expression of P-glycoprotein in 57 canine mammary gland tumours, 10 mammary gland hyperplasia and seven normal mammary glands by immunohistochemistry. Tissue sections were incubated with an anti-Pgp monoclonal antibody and visualized with En Vision-DAB polymer. Normal and hyperplastic mammary tissues were negative or showed slight cytoplasmic immunoreactivity. Neoplastic cells in benign mammary tumours showed diffuse cytoplasmic staining, in contrast to malignant tumours that showed mainly a membranous staining pattern for Pgp (C494). We observed statistically significant differences among all the different groups of tissues analysed except for benign tumours versus hyperplasia (P = 0.221). Receiver-operating characteristic analysis showed that the best cut-off point to differentiate the threshold to differentiate negative from positive tissue samples was 18.40% of immunostained cells. These results provide a first indication that routine evaluation of Pgp expression in canine mammary gland tumours, taking into consideration a cut-off point for positivity, may be useful for selecting cases for chemotherapy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗