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Biomedical subjects

M Hoke

Publications and source records attributed to M Hoke.

At least 19 recordsLinked to original sources
PubMed1998

Auditory afterimage: tonotopic representation in the auditory cortex.

The auditory afterimage is a sensation which occurs for several seconds after the exciting acoustic signal has been switched off, and which roughly corresponds to the inverse of the spectrum of the exciting signal. In contrast to the well-known visual afterimage, the physiological mechanism generating the auditory afterimage has been questionable so far. Neuromagnetic source imaging revealed that the source of cortical neural activity which coincides with the sensation of the afterimage is located in the auditory cortex and exhibits a tonotopic organization similar to that of the sustained response which occurs during continuous presentation of an acoustic stimulus. It is concluded that the neural processes leading to the generation of the two phenomena -sustained response and auditory afterimage - are similar.

Acoustic Stimulation↗
PubMed1998

Increased auditory cortical representation in musicians.

Acoustic stimuli are processed throughout the auditory projection pathway, including the neocortex, by neurons that are aggregated into 'tonotopic' maps according to their specific frequency tunings. Research on animals has shown that tonotopic representations are not statically fixed in the adult organism but can reorganize after damage to the cochlea or after training the intact subject to discriminate between auditory stimuli. Here we used functional magnetic source imaging (single dipole model) to measure cortical representations in highly skilled musicians. Dipole moments for piano tones, but not for pure tones of similar fundamental frequency (matched in loudness), were found to be enlarged by about 25% in musicians compared with control subjects who had never played an instrument. Enlargement was correlated with the age at which musicians began to practise and did not differ between musicians with absolute or relative pitch. These results, when interpreted with evidence for modified somatosensory representations of the fingering digits in skilled violinists, suggest that use-dependent functional reorganization extends across the sensory cortices to reflect the pattern of sensory input processed by the subject during development of musical skill.

Adult↗
PubMed1997

[Decrease in cardiovascular disease mortality in the Czech Republic from 1984 to 1993 and its possible causes].

BACKGROUND: The objective of the investigation was to evaluate the ten-year development of the cardiovascular mortality rate in two population groups in the age bracket from 25 to 64 years, i.e. in subjects living in six districts which participated in the international WHO project MONICA and in the population of the whole Czech Republic. METHODS AND RESULTS: Data on the mortality rate in 1984-1993 for the age group from 25-64 years were provided by the Institute of Health Information and Statistics, information on the prevalence of risk factors was obtained in three cross-sectional studies implemented in six districts as part of the MONICA project in 1985, 1988 and 1992. In the mortality rate per 100,000 population in the six districts the following changes were revealed (in parentheses the values for 1984 and 1993 are given): men - a statistically significant declining trend in the from all caused mortality (849.3-742.5; p < 0.001) and cardiovascular mortality (367.2-280.4; p < 0.001) and cerebrovascular mortality (69.7-44.8; p < 0.001). In the mortality from ischaemic heart disease (215.7-170.6; ns) a declining trend was not recorded. In women aged 25-64 years in the six districts there was a statistically significant decline of the mortality from all caused (359.5-322.1; p < 0.001), the cardiovascular mortality (115.6-100.6; p < 0.001) and cerebrovascular mortality (31.1-23.6; p < 0.001). The mortality from ischaemic heart disease did not change (49.2-48.8; ns). In the population of the Czech Republic in men the following were detected: a drop of the from all caused mortality (907.1-784.8; P < 0.001), the cardiovascular mortality (383.5-308.4; p < 0.001) and cerebrovascular mortality (76.5-55.3; p < 0.001). Also in women of the Czech Republic a decline of the mortality from all caused was recorded (390.1-328.5; p < 0.001), the cardiovascular mortality (135.3-103.8; p < 0.001), ischaemic heart disease (58.0-48.6; p < 0.001) and cerebrovascular mortality (43.5-27.4; p < 0.001). In 1990 an increased cardiovascular mortality was recorded in men different from the trend during 1984-1993, statistically significant in the Czech Republic (p < 0.05) and in the six districts (p < 0.05). The reasons of this trend are not clear. The role of health services in the mortality drop is not clear, although available data indicate their improvement. Favourable changes were found in risk factors: during the period from 1985-1992 the prevalence of hypercholesterolaemia declined significantly in men and women, the prevalence of hypertension in women and the prevalence of smoking in men declined in the six districts. From nationwide data ensues that after 1989 significant changes occurred in the diet of the Czech population. The meat consumption declined by 1993 by 13%, the milk and dairy product consumption by 26.8% the butter consumption by 43.6% the consumption of vegetable fats increased by 16%, of vegetables by 8%, tropical fruit by 43.2%. These changes probably had an impact on the cholesterol level and BMI of the Czech population. CONCLUSIONS: In the declining cardiovascular mortality trend during 1984-1993 the following may have participated: improved medical care, dietary changes, improvement of the risk profile and other, in particular socioeconomic factors. With regard to the close temporal association of the investigated changes it may be assumed that this development is at least partly associated with changes of the political and economic position in the Czech Republic after 1989.

Adult↗
PubMed1997

Magnetic brain imaging of extinction processes in human classical conditioning.

By recording neuromagnetic events during aversive classical conditioning, we examined the extinction of a previously described conditioned response. Averaging over non-reinforced exposures to the conditioned stimulus revealed magnetic activity in the secondary somatosensory and insular cortices, appearing between 110 and 140 ms after the omitted unconditioned electric shock. We suggest this activity to be elicited by the discrepancy between shock expectancy and perceptual processes associated with the omission of the unconditioned stimulus, reflecting one of several brain processes in extinction.

Adult↗
PubMed1997

Mismatch field to tone pairs: neuromagnetic evidence for temporal integration at the sensory level.

The mismatch field (MMF) to minor pitch changes in two experimental conditions was studied. Standard tones of 1000 Hz and deviant tones of 1050 Hz both of 50 ms duration were delivered in single tone condition. Paired tones of the same duration were used in the paired tone condition. The standard tone pair consisted of two 1000 Hz tones, whereas the deviant tone pair was composed of a 1000 Hz tone in the first position and a 1050 Hz tone in the second position with a silent interval of 15 ms between the two. Standards of 90% and deviants of 10% probability were presented in random order and with a randomized interstimulus interval between 600 and 900 ms. The source analysis showed a more lateral location for the MMF obtained in the paired tone condition (MMF.P) compared to the MMF elicited by the single deviants (MMF.S). The source location of both the MMF.P and MMF.S turned out to be significantly anterior relative to the sources of the M100. The increased stimulus repetition in the paired tone condition (two times more stimuli than in the single tone condition) lead to a strong suppression of the field amplitude and of the dipole moment of the M100, while this effect could not be seen for the MMF. The data demonstrate a fundamental difference between the processes reflected by the M100 and the MMF: while the M100 represents the processing of every individual tone, the MMF reflects the change detection of the paired stimuli as unitary events, forming a perceptual group. The different sources of the MMF.P and MMF.S also support an integrated processing of the paired stimuli.

Acoustic Stimulation↗
PubMed1997

Possibilities and limitations of magnetic source imaging of methohexital-induced epileptiform patterns in temporal lobe epilepsy patients.

The usefulness of MEG-based techniques in lateralizing and localizing the epileptogenic area was investigated in the present study. Spontaneous and methohexital-induced spikes were studied in a group of 15 patients with temporomesial epilepsy using a 37-channel neuromagnetometer. The accuracy of the magnetic source imaging was compared to the results of electrocorticographic (ECoG) recordings. Differences of drug-induced spike densities in the MEG recordings between both sides confirmed a similar lateralizing power of the MEG and ECoG recordings. Source location analyses based on a moving dipole model resp. a rotating dipole model were performed using a spherical head model. After subdivision of the volume of each patient's head, 8 cm3 cubicles containing at least 3 source locations were projected onto the individual MRI scan and resulted in source locations within or close to the presurgically defined primary epileptogenic area only in 3 of the 15 patients. Spike induction by methohexital has the advantage of shortening the recording period as compared to recordings of interictal epileptiform discharges. However, the correlation analyses of spike densities from MEG and ECoG recordings and the source location analyses from MEG recordings indicate that spike generated in deep temporomesial structures may escape the MEG registration.

Adolescent↗
PubMed1997

Methohexital-induced changes in spectral power of neuromagnetic signals: beta augmentation is smaller over the hemisphere containing the epileptogenic focus.

Previous research has suggested that methohexital, a short-term barbiturate, alters activity in the primary epileptogenic area. It can be assumed that drug-induced activation of the epileptogenic focus provides a rapid and safe method to obtain a sufficient amount of information relevant for the lateralization and localisation of the primary epileptogenic area. This study shows that methohexital changes spectral power in the beta band derived from magnetoencephalographic (MEG) signals over the hemisphere ipsilateral to the primary epileptogenic area. This effect was demonstrated for 10/13 of the investigated patients suffering from unilateral temporal lobe epilepsy (TLE). The side and location of the primary epileptogenic area of these patients (5 left TLE, 8 right TEL) was determined invasively during presurgical evaluation. During a 1-2 minute interval after intravenous bolus injection of 100 mg methohexital a clear lateralization effect in the beta band was observed, which differed marginally between fronto-central, fronto-temporal and temporo-parietal brain regions. In addition, bilateral spectral power changes were obtained in the theta, alpha and gamma bands that differed between brain regions. Analyses of simultaneously recorded scalp electroencephalographic (EEG) data revealed effects consistent with those of the MEG analysis. The reduced enhancement of beta band spectral power of MEG recordings provides a potential application for the non-invasive lateralization of the primary epileptogenic area.

Adult↗
PubMed1996

[Is the recent decrease in cholesterolemia in the Czech Republic convincing evidence?].

BACKGROUND: The objective of the study was to evaluate the 8-year trend of serum cholesterol levels in six districts of the Czech Republic, to assess whether the reduction of mean values of total cholesterol recorded during the period between 1985 and 1992 was convincing and to discuss possible causes and consequences of this development. METHODS AND RESULTS: Three cross-sectional surveys of risk factors were implemented in independent random 1% samples of the population aged 25-64 years. In 1985 1256 men (respondence rate 81.5%) and 1317 women (85%) were examined, In 1988 1357 men (85.2%) and 1412 women (88.4%), in 1992 1142 men (73.2%) and 1211 women (76.7%). A detailed check of the deviations in estimations during different time intervals from reference values provided evidence that the analytical method did not have an impact on the revealed changes. In men the mean total cholesterol level was 6.21 (95% confidence limit 6.14-6.28 mmol/l in 1985; 6.29 (6.23-6.35) mmol/l in 1988; 5.99 (5.91-6.06) mmol/l in 1992. In women the mean value of the total cholesterol level was 6.19 (6.12-6.25) mmol/l in 1985; 6.23 (6.17-6.30) mmol/l in 1988; 5.95 (5.88-6.02) mmol/l in 1992. According to variance analysis (ANOVA) the serum cholesterol in 1992 was lower by 0.22 mmol/l (p < 0.0001) than in 1985 and by 0.28 mmol/l (p < 0.0001) lower than in 1988. The drop of cholesterol between 1988-1992 may have been caused by dietary changes recorded in the population. According to nationwide data after 1990 there was a marked drop of the consumption of meat and meat products, milk and dairy products and animal fats, while the consumption of vegetable fats increased. Despite these dietary improvements, in six districts in 1992 fats accounted for 37% of the energy intake, the P/S ratio was only 0.41 in men and 0.46 in women. In these districts in 1992 and 1993 a decline of the standardized mortality rate from IHD in men was recorded. CONCLUSIONS: During an eight-year period the mean serum cholesterol level of men and women decreased significantly in six districts of the Czech Republic. This change was probably associated with a restricted intake of foods which have an impact on the serum cholesterol level.

Adult↗
PubMed1996

Magnetic imaging in human classical conditioning.

Magnetoencephalography (MEG) was recorded during aversive classical conditioning in an attempt to elucidate the temporal coding of primary somatosensory cortex (SI) activation previously found with positron emission tomography. Four healthy volunteers participated in the experiment. The reinforced conditioned stimulus was displayed on a screen for 2 s, and as it disappeared an unconditioned electric shock to the right middle finger followed. A control stimulus, not paired with a shock was also presented. With MEG, we observed a conditioned magnetic response located in the SI. The conditioned response predated the shock presentation and is interpreted as evidence for functional control of nociception mediated by corticothalamic projections.

Conditioning, Classical↗
PubMed1994

[Changes in the cardiovascular risk profile of the population of the Czech Republic--MONICA 1992].

BACKGROUND: The cardiovascular risk profile of the population in the Czech Republic is unfavourable, the mortality of the population from cardiovascular diseases is among the highest in the world. The objective of the present work was to compare the prevalence of the most serious risk factors in 1988 and 1992 and to find out whether the change of the political and economic system in 1989 had an impact on the risk profile of the population. Within the framework of the international WHO project MONICA independent 1% random population samples, age bracket 25-64 years, were examined in six districts of the Czech Republic. METHODS AND RESULTS: In 1988 1,357 men (response rate 85.5%) and 1,412 women (88.4%) were examined; in 1992 1,139 men (71.2%) and 1,214 women (75.0%) attended the examination. The prevalence of smokers (regular consumption of more than 1 cigarette per day) did not differ significantly in men: 41.8% in 1988, 40.3% in 1992 nor in women: 25.3%-24.1%. Also the prevalence of elevated blood pressure levels (BPs > 21.3 and/or BPd > 12.7 kPa) did not reveal a significant difference neither in men: 19.1%-20.4% nor in women 14.0%-15.0%. The prevalence of hypercholesterolaemia (total cholesterol > 6.5 mmol/l) was in 1992 significantly lower than in 1988--in men by 9% (39.6%-30.6%, p < 0.001) and in women by 6.3% (36.3%-30.0%, p < 0.001). Also in the prevalence of obesity (BMI men > 30, women > 29) a significant drop was recorded in men by 5.2% (23.8%-18.6%, p < 0.01) in women by 5.1% (33.3%-28.2%, p < 0.01). CONCLUSIONS: The probable reason for this partial improvement of the risk profile in 1992, as compared with data in 1988, are dietary changes which may be the result of the introduced market economy and global transformation of society after the political change in 1989.

Adult↗
PubMed1994

The auditory evoked sustained field: origin and frequency dependence.

A sound lasting for several seconds is known to elicit a baseline shift in electrical and magnetic records. We have studied the dependence of the magnetic field distribution of this "per-stimulatory" sustained field (SF) on tone frequency. Tone bursts of 2 sec duration and 60 dB nHL intensity were presented to 11 subjects at varying interstimulus intervals between 5 and 7 sec. The carrier frequencies of 250, 1000 and 4000 Hz varied randomly from trial to trial. The field distributions obtained are consistent with the view that the auditory evoked sustained field activity originates in the supratemporal cortex. Differences in the locations of equivalent current dipoles of the SF from those of the M100 wave of the slow auditory evoked field are consistent across subjects. The SF source locations corresponding to stimulus frequencies over an extended frequency range are arranged in a tonotopic manner and support the idea that the sources of the M100 and the SF are current dipole sheets located on the superior surface of the primary auditory cortex.

Acoustic Stimulation↗
PubMed1994

The magnetic counterpart of the contingent negative variation.

The magnetic counterpart of the CNV, the contingent magnetic variation (CMV), was investigated in an Go/No Go design: subjects moved their index finger to the offset of a 4 sec tone of a certain frequency in the Go condition and were asked not to move during presentation of a 4 sec tone of different frequency in the No Go condition. During the preparatory interval, both the CMV and the electrical wave form followed a similar time course and both produced an equally pronounced statistical difference between conditions (Go and No Go). Compared to the variability in the auditory evoked fields, the CMV showed considerably more variance in the field distribution across subjects. The polarity reversal across the temporal surface of the head and the pronounced amplitudes over inferior temporal areas led us to conclude that a significant temporal activity contributes to both the late and the early CMV. However, neither for the early nor for the late CMV component did a single equivalent dipole prove to be a satisfying model. The data are consistent with the suggestion that the earlier as well as the later aspects of the CMV are fed through distributed sources in motoric, sensory and association areas, a distribution with considerable intersubject variability.

Acoustic Stimulation↗
PubMed1993

Development of the cardiovascular risk in the population of the Czech Republic.

Population surveys of the major cardiovascular risk factors were conducted in six districts of the Czech Republic in 1988 and 1992 as part of the WHO MONICA Project. One-percent independent random samples of the population aged 25-64 years were examined and investigated; in 1988, the survey included 1357 men and 1412 women (response rates of 85.5% and 88.4%, respectively); 1139 men and 1214 women with the response rate 71.2% and 75.0%, respectively, were enrolled in 1992. Over the four years, the mean levels of diastolic blood pressure rose from 83.8 mmHg to 85.5 mmHg (p < 0.001) in men; the rise in women from 80.7 mmHg to 81.6 mmHg was non-significant. Systolic blood pressure between the two surveys did not differ significantly. Mean total cholesterol levels declined from 6.24 mmol/l to 5.91 mmol/l (p < 0.001) in men and from 6.16 mmol/l to 5.87 mmol/l (p < 0.001) in women. Mean BMI decreased from 27.5 to 26.9 (p < 0.001) in men and from 27.4 to 26.5 (p < 0.001) in women. The authors assume that the significant decreases in cholesterolaemia and BMI may be caused by changes in the dietary pattern resulting from the market economy principles setting in after the 1989 revolution, and by an increased attention of the population to their health in the new socioeconomic conditions. If the trend continues, one might expect a decrease in mortality from IHD. On the other hand, the rise in diastolic blood pressure may be due to deteriorated control of hypertension.

Adult↗
PubMed1992

Inhibition of growth factor binding, Ca2+ signaling and cell growth by polysulfonated azo dyes related to the antitumor agent suramin.

The ability of the polysulfonated antitumor drug suramin and six related polysulfonated azo dyes to inhibit the cell growth, platelet-derived growth factor (PDGF)-receptor binding, and intracellular Ca2+ signaling of Swiss 3T3 fibroblasts was studied. Some of the azo dyes were more potent inhibitors of PDGF binding than was suramin. The concentration giving 50% inhibition (IC50) of PDGF binding was 0.5 microM for the most potent azo dye as compared with 10 microM for suramin. The azo dyes were generally more potent inhibitors of nonmitochondrial Ca2+ uptake and of inositol(1,4,5)trisphosphate-mediated Ca2+ release in permeabilized Swiss 3T3 cells than was suramin, and they were more potent inhibitors of PDGF-induced Ca2+ signaling in intact Swiss 3T3 cells. The azo dyes were only as effective as or less effective than suramin in inhibiting the growth of Swiss 3T3 cells, with IC50 values of between 74 and 361 microM being noted for the dyes as compared with 70 microM for suramin. The difference between the growth-inhibitory activity of the azo dyes and that of suramin could not be explained by metabolism of the compounds, which was not detectable in either Swiss 3T3 cells or human liver slice preparations. The results suggest that suramin and some of the azo dyes have actions on cell growth in addition to inhibition of growth factor binding and of Ca2+ signaling.

3T3 Cells↗
PubMed1992

Inhibition of growth factor binding and intracellular Ca2+ signalling by dextran sulfates of different sizes and degrees of sulfation.

The ability of dextran sulfates of varying molecular sizes (5-500 kDa) and degrees of sulfate substitution (0.3-1.9) to inhibit the binding of platelet-derived growth factor (PDGF) to intact Swiss 3T3 fibroblasts and to inhibit inositol(1,4,5)trisphosphate-dependent release of Ca2+ in permeabilized Swiss 3T3 cells was examined in the present study. Significant correlations were found between increased molecular size of the dextran sulfates and inhibition of both PDGF binding (r = 0.77) and Ca2+ release (r = 0.72). The degree of sulfate substitution did not correlate with inhibition of either activity.

3T3 Cells↗
PubMed1991

Human auditory evoked gamma-band magnetic fields.

We have discovered a ca. 40-Hz transient magnetic oscillatory response, evoked in the human brain by the onset of auditory stimuli, consisting of four or more cycles locked in phase to stimulus onset in approximately the 20- to 130-ms poststimulus interval. The response originates in the supratemporal auditory cortex, some millimeters deeper and anterior to the source of the larger-amplitude slow-wave M100 component of the evoked magnetic field and moves in a posterior arcing trajectory 1 cm or more in length. The oscillatory cortical activation elicited by auditory stimuli may be similar to the gamma-band cortical oscillations elicited by olfactory and visual stimuli and may represent an essential component of auditory perceptual processing.

Acoustic Stimulation↗