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Biomedical subjects

B Ross

Publications and source records attributed to B Ross.

At least 19 recordsLinked to original sources
PubMed2006

Magnetoencephalographic study of vibrotactile evoked transient and steady-state responses in human somatosensory cortex.

Somatosensory responses to vibrotactile stimulation applied to the index fingertip were recorded with whole-head MEG in eleven healthy young adult participants. Stimulus trains were produced by a pneumatically driven membrane oscillating at 22 Hz for a trial duration of 1 s, separated by interstimulus intervals (ISIs) of 0.5, 1.0, 3.0, and 7.0 s. Data analysis was performed in two frequency bands. Transient onset responses in the lower frequency band (<20 Hz) contained a clearly expressed P50 component. The higher frequency band (18-30 Hz) revealed a gamma-band response (GBR) within the first 200 ms followed by rhythmic activity at the stimulus frequency that continued throughout the stimulus duration, known as the steady-state response (SSR). Dipoles associated with the transient responses and SSRs were localized in two distinct regions within the primary somatosensory cortex (SI), with transient responses located on average 3 mm more medial and inferior than the SSRs. The transient and GBR peak amplitudes increased with ISI, whereas the SSR amplitude showed no ISI dependence. These results may reflect functionally and spatially distinct neural populations. Further investigations are required to assess the implications of these findings for probing the somatosensory system using other functional neuroimaging methods such as fMRI.

Adult↗
PubMed2006

Correlates of eye blinking as determined by synthetic aperture magnetometry.

OBJECTIVE: To evaluate the spatiotemporal characteristics of ocular and cerebral current sources during voluntary eyeblinking. METHODS: Whole-head magnetoencephalographic (MEG) recordings were acquired during voluntary blinking in eight healthy adults and analysed using synthetic aperture magnetometry (SAM). RESULTS: Fronto-temporal MEG sensors showed a large slow wave lasting approximately 400 ms and a small burst of activity with frequencies above 30 Hz at the initiation of the blink. Group maps of blink-related oscillatory activity at frequencies between 1-18 Hz and 32-64 Hz showed increased activity in and around the orbits during the 400 ms following blink onset. Increased oscillatory activity occurred in occipital regions 200 ms after blink onset at frequencies between 18 and 64 Hz. CONCLUSIONS: Blink-related MEG signals are recorded in the regions of the eyes and in the occipital cortex. The anterior activation is likely a combination of muscle contraction and eyelid currents. Occipital activation likely represents neural processes concerned with re-establishing the visual image after transient ocular occlusion. SIGNIFICANCE: The possibility of eyeblink-related fields should be considered when interpreting frontal and occipital source activities during SAM analyses.

Adult↗
PubMed2005

Dilated cardiomyopathy in two adult human immunodeficiency positive (HIV+) patients possibly related to highly active antiretroviral therapy (HAART).

Human immunodeficiency virus (HIV) and acute immunodeficiency syndrome are known to be associated with cardiac involvement. In this respect, a relation between HIV and dilated cardiomyopathy has been described. Additionally, highly active antiretroviral therapy (HAART) may independently contribute to cardiac impairment. We here report two cases of severely reduced left ventricular function detected in the context of a recent standardized screening of 132 HIV+ individuals of the German heart failure network. Both patients presented in a poor overall condition and progressive exercise-induced dyspnea accompanied by edema or angina pectoris, respectively. Subsequent examinations revealed left bundle-branch blockade, ventricular arrhythmia, elevated serum BNP-levels as well as pathologic transthoracic echocardiography, left ventricular angiography, electron beam tomography and cardiac magnetic resonance imaging without significant coronary stenoses or immunohistological signs of an ongoing or prior myocarditis. Clinical signs of progressive chronic heart failure developed slowly but constantly following initiation of the HAART regimen. Patients were treated by an implantation of a biventricular implantable cardioverter defibrillator beside conventional conservative standard therapy followed by a significant improvement of clinical symptoms. Antiviral medication could be maintained in both patients. Taking all data into account, the diagnosis of a HAART-associated dilated cardiomyopathy could be assessed. Even though the pathogenesis of secondary heart failure after HAART is still object of investigation a mitochondrial impairment by antiviral drugs is thought to contribute the development of dilated cardiomyopathy. However, due to the coexistence of an eminent HIV infection, a direct effect of the HI virus itself can not be completely excluded.

Antiretroviral Therapy, Highly Active↗
PubMed2005

Stimulus induced desynchronization of human auditory 40-Hz steady-state responses.

The hypothesis that gamma-band oscillations are related to the representation of an environmental scene in the cerebral cortex after binding of corresponding perceptual elements is currently under discussion. One question is how the sensory system reacts to a fast change in the scene if perceptual elements are rigidly bound together. A reset of the gamma-band oscillation forced by a change in sensory input may dissolve the binding, which then would be re-established for the new sensation. We studied the reset of gamma-band oscillations on the 40-Hz auditory steady-state responses (ASSR) by means of whole-head magnetoencephalography (MEG). The rhythm of 40-Hz AM of a 500-Hz tone evoked the ASSR, and a short noise burst served as a concurrent stimulus. Possible direct interactions of the auditory stimuli were excluded by presenting the noise impulse in a different frequency channel (2,000-3,000 Hz) to the contralateral ear. The concurrent stimulus induced a considerable decrement in the amplitude of ASSR, which was localized in primary auditory cortices. This decrement lasted 250 ms and was significantly longer than the duration of the transient gamma-band response evoked by the noise burst. Thus it could not be explained by any linear superimposition of the responses. The time courses of ASSR amplitude and phase during recovery from the decrement resembled those after stimulus onset, indicating that a new ASSR was built up after the resetting stimulus. The results are discussed as reset of oscillations in human thalamocortical networks.

Acoustic Stimulation↗
PubMed2005

Dynamics of auditory plasticity after cochlear implantation: a longitudinal study.

Human representational cortex may fundamentally alter its organization and (re)gain the capacity for auditory processing even when it is deprived of its input for more than two decades. Stimulus-evoked brain activity was recorded in post-lingual deaf patients after implantation of a cochlear prosthesis, which partly restored their hearing. During a 2 year follow-up study this activity revealed almost normal component configuration and was localized in the auditory cortex, demonstrating adequacy of the cochlear implant stimulation. Evoked brain activity increased over several months after the cochlear implant was turned on. This is taken as a measure of the temporal dynamics of plasticity of the human auditory system after implantation of cochlear prosthesis.

Acoustic Stimulation↗
PubMed2005

Right hemispheric laterality of human 40 Hz auditory steady-state responses.

Hemispheric asymmetries during auditory sensory processing were examined using whole-head magnetoencephalographic recordings of auditory evoked responses to monaurally and binaurally presented amplitude-modulated sounds. Laterality indices were calculated for the transient onset responses (P1m and N1m), the transient gamma-band response, the sustained field (SF) and the 40 Hz auditory steady-state response (ASSR). All response components showed laterality toward the hemisphere contralateral to the stimulated ear. In addition, the SF and ASSR showed right hemispheric (RH) dominance. Thus, laterality of sustained response components (SF and ASSR) was distinct from that of transient responses. ASSR and SF are sensitive to stimulus periodicity. Consequently, ASSR and SF likely reflect periodic stimulus attributes and might be relevant for pitch processing based on temporal stimulus regularities. In summary, the results of the present studies demonstrate that asymmetric organization in the cerebral auditory cortex is already established on the level of sensory processing.

Acoustic Stimulation↗
PubMed2005

Efficiency and efficacy of multi-channel gastric electrical stimulation.

Gastric electrical stimulation (GES) using single channel has been under investigation for its therapeutic potential for gastroparesis. The aim of this study was to study the efficacy and efficiency of multi-channel GES in accelerating gastric emptying in dogs. The study was performed in eight dogs, and gastric emptying of liquid was assessed in three randomized sessions of control, one-channel GES and four-channel GES. It was found that (i) GES of both one-channel and four-channel was able to completely entrain the slow waves in the entire stomach. However, the stimulation energy required by four-channel GES was only 1% of that required by one-channel GES. (ii) Four-channel, but not one-channel, GES significantly and substantially accelerated gastric emptying. An increase of 121.0 and 93.9% was noted with four-channel GES at 30 and 60 min after the meal, respectively. It was concluded that four-channel GES is substantially more efficient and effective than conventional single-channel GES in improving gastric emptying. It is worthy to explore its therapeutic potential for gastroparesis in clinical settings.

Animals↗
PubMed2004

The effect of attention on the auditory steady-state response.

40-Hz auditory steady state responses to amplitude modulated tones were recorded with magnetoencephalography to investigate the effect of focused attention. A modulation discrimination task and a destructive visual task established the attended and the non-attended experimental conditions. A strong contrast between these conditions was demonstrated by largely enhanced sustained responses under the attention condition. A significant attentional effect on the ASSR amplitude was observed mostly in the left hemisphere between 200 to 500 ms after stimulus onset. In contrast, transient gamma-band and N1 responses were not affected by the different states of attention.

Acoustic Stimulation↗
PubMed2004

Stimulus induced reset of 40-Hz auditory steady-state responses.

Auditory steady-state responses (ASSR) were evoked with 40-Hz amplitude modulated 500-Hz tones. An additional impulse-like noise stimulus (2,000 +/- 500 Hz) with spectrum clearly distinct from the one of the AM sound, induced pronounced perturbations in the ASSR. The effect of the interfering noise was interpreted as (1) reset of the ASSR because of a sudden loss in phase coherence, (2) a decrease in signal power immediately after presentation of the noise impulse, and (3) a modulation of ASSR amplitude and phase resembling the time course of the ASSR onset. The time-course of the ASSR onset was interpreted as reflecting temporal integration over several 100 ms. The reset of the ASSR was discussed as a powerful mechanism, which allows for fast reaction to a short stimulus change that overcomes the disadvantage of the ASSR's long integration time constant.

Acoustic Stimulation↗
PubMed2004

Cortical oscillations modulated by congruent and incongruent audiovisual stimuli.

Congruent or incongruent grapheme-phoneme stimuli are easily perceived as one or two linguistic objects. The main objective of this study was to investigate the changes in cortical oscillations that reflect the processing of congruent and incongruent audiovisual stimuli. Graphemes were Japanese Hiragana characters for four different vowels (/a/, /o/, /u/, and /i/). They were presented simultaneously with their corresponding phonemes (congruent) or non-corresponding phonemes (incongruent) to native-speaking Japanese participants. Participants' reaction times to the congruent audiovisual stimuli were significantly faster by 57 ms as compared to reaction times to incongruent stimuli. We recorded the brain responses for each condition using a whole-head magnetoencephalograph (MEG). A novel approach to analysing MEG data, called synthetic aperture magnetometry (SAM), was used to identify event-related changes in cortical oscillations involved in audiovisual processing. The SAM contrast between congruent and incongruent responses revealed greater event-related desynchonization (8-16 Hz) bilaterally in the occipital lobes and greater event-related synchronization (4-8 Hz) in the left transverse temporal gyrus. Results from this study further support the concept of interactions between the auditory and visual sensory cortices in multi-sensory processing of audiovisual objects.

Acoustic Stimulation↗
PubMed2004

Auditory cortex responses to the transition from monophonic to pseudo-stereo sound.

Human cortical responses to the change in spaciousness of sound were recorded with the method of magnetoencephalography (MEG). The phases of dichotically presented 500-Hz tones were shifted so that the sound was perceived as originating either from a point-like source centered in the head or from separated sources in space. The phase shift was embedded in 40-Hz amplitude modulation. Thus, the phase shift could not be detected from a monaural signal. The transition between 'mono' and 'pseudo-stereo' quality of the sound elicited a P1-N1-P2 response similar to the onset response as well as a decrement in the steady-state response. The responses were discussed as reflecting binaural processing in the central auditory system.

Acoustic Stimulation↗
PubMed2004

Cardiovascular risk factors and probability for cardiovascular events in HIV-infected patients. Part II: gender differences.

OBJECTIVE: Due to the side effects of antiretroviral therapy and long term survival there is an increasing concern of an elevated rate of cardiovascular diseases in HIV-infected patients. The present study analysed the cardiovascular risk profile and the probability of cardiovascular events in HIV-infected patients, due to differences of gender. METHODS: Cardiovascular risk factors of 309 HIV-infected adults, including 240 males were analysed. Overall 10-years probability for cardiovascular events was evaluated by the Framingham algorithm. RESULTS: Gender differences were detected in cardiovascular risk factors such as lipid values, blood pressure and the rate of smoking. Tobacco use was much more common in HIV-infected males compared with HIV-infected females (67.5% vs. 49.3%; p<0.001). Although no significant difference was noticed in total cholesterol (5.49 +/- 0.09 vs. 5.53 +/- 0.19 mmol/L, p = 0.84), the HDL-cholesterol concentration was significantly lower (1.09 +/- 0.03 vs. 1.36 +/- 0.06 mmol/L, p < 0.001) and the triglyceride concentration higher (3.01 +/- 0.21 vs. 2.06 +/- 0.26 mmol/L, p = 0.02) in HIV-infected males compared to HIV-infected females. Additionally, systolic blood pressure was higher in HIV-infected males compared with HIV-infected females (123.1 +/- 1.1 vs. 115.4 +/- 2.1 mmHg, p < 0.01). No significant differences were detected in HbA1c concentrations between both groups (5.15 +/- 0.07 vs. 5.31 +/- 0.11, p = 0.26). The overall 10-years probability for cardiovascular events was 8.7% (median) in HIV-infected males and 1.7% in HIV-infected females (p < 0.0001). CONCLUSIONS: In the present study, we observed gender differences in the cardiovascular risk profile of HIV-infected individuals. The risk of premature atherosclerosis and associated cardiovascular events was significantly higher in HIV-infected males.

Adult↗
PubMed2004

N1m recovery from decline after exposure to noise with strong spectral contrasts.

Comb-filtered noise (CFN, derived from white noise by suppressing regularly spaced frequency regions) was presented for 3 s followed by two types of test stimuli. One test stimulus (SB) was comprised of spectra centered in the stop-band regions of the CFN and the other test stimulus (PB) of spectra centered in the band pass regions of the CFN. Magnetoencephalographically recorded N1m responses evoked by SB stimuli were decreased relative to the N1m response evoked by PB stimuli. This effect was maximal when the interval between the CFN and test stimuli was short (0.5 s) but was detected at intervals up to 2 s. The results suggest lateral inhibition in the auditory cortex and point to a decay of inhibition lasting on the order of seconds.

Acoustic Stimulation↗
PubMed2004

Lateral inhibition and habituation of the human auditory cortex.

The goal of this study was to compare the lateral inhibition and the habituation in the human auditory cortex, two important physiological effects during auditory processing that can be reliably measured by means of magnetoencephalography when recording auditory evoked fields. Applying 40-Hz amplitude-modulated stimuli allowed us to record simultaneously the slow transient evoked and the steady-state fields and thus to characterize the lateral inhibition and the habituation effect in primary and non-primary auditory cortical structures. The main finding of the study is that the lateral inhibition effect of non-primary auditory areas as measured on the major component of the slow transient auditory evoked field (N1) is significantly stronger than the corresponding habituation effect. By contrast, this effect was not observed for the 40-Hz steady-state fields, characterizing the activation of the primary auditory cortex in humans. The results might be interpreted as (i) evidence that the inhibition mediated by lateral connections is stronger than the habituation of excitatory neurons in the non-primary auditory cortex and (ii) the processing hierarchy in the human auditory cortex is demonstrated by the different behaviour of lateral inhibition and habituation in primary and non-primary auditory cortical structures.

Acoustic Stimulation↗
PubMed2003

Cardiovascular risk factors and probability for cardiovascular events in HIV-infected patients: part I. Differences due to the acquisition of HIV-infection.

OBJECTIVE: Due to side effects, such as hyperlipidaemia and insulin resistance, there is an increasing concern that antiretroviral drugs lead to an epidemic of cardiovascular diseases in HIV-infected patients. The present study characterizes the cardiovascular risk profile of HIV-infected individuals, due to the acquisition of HIV-infection. METHODS: Cardiovascular risk factors of 309 HIV-infected adults (HIV-acquisition: 59.2% by homosexual contact (group 1), 28.5% by heterosexual contact (group 2), 9.1% by intravenous drug abuse (group 3) and 3.2% by blood transfusion (group 4)) were analysed. Overall 10-years probability for cardiovascular events was analysed by the Framingham algorithm. RESULTS: Tobacco use was more common in group 1 subjects compared with group 2 subjects (67% vs. 52%; p<0.05). Additionally, group 1 subjects exhibited elevated total cholesterol (5.6 +/- 0.1 mmol/L vs. 4.8 +/- 0.3), LDL-cholesterol (3.6 +/- 0.1 mmol/L vs. 2.8 +/- 0.2) and triglyceride concentrations (3.2 +/- 0.3 mmol/L vs. 1.7 +/- 0.2) compared with group 3 (all p<0.05). No significant differences between the groups were detected in glucose metabolism. The overall 10-years probability for cardiovascular events was significantly higher in group 1 compared with group 2 and group 3 (12.2 +/- 0.8% vs. 6.6 +/- 0.9% and 7.9 +/- 1.6%, p<0.05). CONCLUSIONS: The cardiovascular risk profile differs between subgroups of HIV-infected individuals, leading to significant higher probability of cardiovascular events in group 1 subjects. The risk of premature atherosclerosis by HIV-infected individuals and therapeutic options remains to be established.

Adult↗
PubMed2003

Use of an augmented reality display of patient monitoring data to enhance anesthesiologists' response to abnormal clinical events.

One obstacle to safety in the operating room is anesthesiologist distraction having to shift attention back and forth from the patient to a vital sign monitor while performing either routine or emergency procedures. The purpose of this study was to measure the decrease in anesthesiologist distraction made possible by using a head-worn, see-through personal display (HWD) using retinal scanning technology. With the head-up display, they were able to focus their attention exclusively on the patient and the task at hand. The Nomad reduced the number of times the anesthesiologist had to shift their attention by a more than a third (17 times versus 58 times). This allowed them to spend more time focused on the patient.

Anesthesiology↗
PubMed2002

Acoustically and electrically evoked responses of the human cortex before and after cochlear implantation.

Multi-channel auditory evoked potentials (AEP) were recorded before and after cochlear implantation (CI) from a patient suffering from severe high frequency hearing loss with residual, but highly fluctuating hearing around 250 Hz. Immediately after CI activation early components of the N1 were present. Later N1 components developed during the use of CI. The unique result of this single case study is the concordance of the cortical AEP pattern obtained by native and artificial peripheral stimulation, which can be regarded as an indicator for the adequate function of the CI.

Acoustic Stimulation↗