P300, stimulus intensity,and modality

Auditory and visual stimulus intensity levels were manipulated systematically in separate conditions to assess the influence of these variables on the P300 event-related brain potential (ERP). Increases in stimulus intensity produced increases in P300 amplitude and decreases in peak latency for both modalities, although the latency effects were stronger for visual stimulation. Similar, somewhat weaker stimulus intensity effects also were observed for the N100, P200, and N200 components. The findings suggest that stimulus intensity contributes to both P300 amplitude and latency measures in important ways and are discussed in relation to the use of ERPs in applied contexts.     

Features of Auditory P300 in Relatives of Schizophrenic Patients

The subjects were parents, siblings, and children of schizophrenic patients. Auditory evoked potentials (EPs) (P300) were recorded in the standard oddball paradigm with a probability of the target stimuli presentation of 0.2 and sound (tone) intensity of 60 dB. A comparison of these data with the results of the examination of reference groups (normal subjects free of a family history of mental pathology) showed significantly longer latent periods of N1, N2, and P3 in EPs to target stimuli in siblings and children of schizophrenic patients, as well as significantly decreased amplitudes of N1 and P2 in EPs to nontarget (standard) stimuli and longer latent periods of N2 in EPs to target stimuli in the parents of schizophrenic patients.     

Prediction of Auditory and Visual P300 Brain-Computer Interface Aptitude

Objective

Brain-computer interfaces (BCIs) provide a non-muscular communication channel for patients with late-stage motoneuron disease (e.g., amyotrophic lateral sclerosis (ALS)) or otherwise motor impaired people and are also used for motor rehabilitation in chronic stroke. Differences in the ability to use a BCI vary from person to person and from session to session. A reliable predictor of aptitude would allow for the selection of suitable BCI paradigms. For this reason, we investigated whether P300 BCI aptitude could be predicted from a short experiment with a standard auditory oddball.

Methods

Forty healthy participants performed an electroencephalography (EEG) based visual and auditory P300-BCI spelling task in a single session. In addition, prior to each session an auditory oddball was presented. Features extracted from the auditory oddball were analyzed with respect to predictive power for BCI aptitude.

Results

Correlation between auditory oddball response and P300 BCI accuracy revealed a strong relationship between accuracy and N2 amplitude and the amplitude of a late ERP component between 400 and 600 ms. Interestingly, the P3 amplitude of the auditory oddball response was not correlated with accuracy.

Conclusions

Event-related potentials recorded during a standard auditory oddball session moderately predict aptitude in an audiory and highly in a visual P300 BCI. The predictor will allow for faster paradigm selection.

Significance

Our method will reduce strain on patients because unsuccessful training may be avoided, provided the results can be generalized to the patient population.     

Auditory selective attention in middle-aged and elderly subjects: an event-related brain potential study

Reaction times (RTs) and event-related brain potentials (ERPs) were recorded in middle-aged (MA) and elderly (ELD) subjects performing an auditory selective attention task. Subjets attended to tone bursts of a specified pitch and ear of delivery and responded to occasional longer duration target tones (75 vs. 25 msec). Infrequent novel stimuli (computer synthesized sounds and digitized environmental noises) were also included in the stimulus sequence.No significant age-related differences were found in the speed or accuracy of target detection. However, in both groups, RTs were delayed (by more than 300 msec) to targets that followed novel sounds. The prolongation was greater following novel sounds in the attended ear, particularly in the ELD group.The effects of selective attention on ERPs to standard tones were isolated as negative difference waves (Nds) by subtracting ERPs to non-attended stimuli from ERPs to the same signals when attended. Nds had similar amplitudes, latencies of onset (60 msec), and distributions in ELD and MA groups. In both groups, Nd waves were more prominent following right ear stimulation, reflecting possible hemispheric asymmetries of generators in posterior temporal regions.The mismatch negativity (MMN) was isolated by subtracting ERPs to standard tones from ERPs to deviant stimuli. MMN amplitudes were reduced in the ELD group. There was also a significant change in MMN distribution with age: the MMN was larger over the right hemisphere for MA subjects but larger over the left for ELD subjects. Elderly subjects showed a trend toward smaller P3 amplitudes and delayed P3 latencies, but group differences did not reach statistical significance. ERPs to novel sounds were characterized by centrally distributed N2 and P3a components. Although the novel P3a was enhanced with attention, no novel Nd waves could be isolated. This suggests that novel sounds fell outside the focus of attention.     

Sit-to-stand motor strategies investigated in able-bodied young and elderly subjects

For the execution of a certain motor task, a motor strategy is chosen by each individual among those that are consistent with the structural and functional constraints of his/her locomotor system, and that tends to maximise the effectiveness of the motor act. The identification of this strategy allows for the assessment of the individual's functional status. This study aimed at identifying the motor strategies adopted for the execution of the sit-to-stand motor task, at different speeds and initial postures, in a sample of 35 community-dwelling elders and in a sample of 16 young able-bodied individuals. This was done using a method, least perceivable to the test subject and "economical" for the experimenter, which entailed the recording of external forces only. A musculo-skeletal system model, based on a telescopic inverted-pendulum (TIP) moved by a linear and two rotational muscle-equivalent actuators, was then used. Parameters describing the kinematics and dynamics of these actuators were extracted and submitted to statistical analysis. Different motor strategies were identified in the two age groups, as well as associated with both a different initial posture (ankle dorsiflexion angle) and speed of execution of the motor task. In particular, the elder group, as compared with the young group, prior to seat-off tended to flex the trunk more, thus bringing the CM closer to the base of support, and at a higher velocity, thus gaining a higher momentum. After seat-off, elders rotated the body forward and, only after having brought their CM over the base of support, effectively started elevation. Both global muscular effort and coordination effort associated with the achievement of balance and raising were lower. However, maximal speed was also lower. The above results indicated that the elders could count on a lower functional reserve than the young individuals and, from the methodological viewpoint, that the TIP approach is a good candidate for subject-specific functional evaluation in a clinical context.     

Haemodynamic response to exercise in healthy young and elderly subjects

Whereas with advancing age, peak heart rate (HR) and cardiac index (CI) are clearly reduced, peak stroke index (SI) may decrease, remain constant or even increase. The aim of this study was to describe the patterns of HR, SI, CI, arteriovenous difference in oxygen concentration (C _a-vO₂), mean arterial pressure (MAP), systemic vascular resistance index (SVRI), stroke work index (SWI) and mean systolic ejection rate index (MSERI) in two age groups (A: 20–30 years, n = 20; B: 50–60 years n = 20. After determination of pulmonary function, an incremental bicycle exercise test was performed, with standard gas-exchange measurements and SI assessment using electrical impedance cardiography. The following age-related changes were found: similar submaximal HR response to exercise in both groups and a higher peak HR in A than in B[185 (SD 9) vs 167 (SD 14) beats · min⁻¹, P < 0.0005]; increase in SI with exercise up to 60–90 W and subsequent stabilization in both groups. As SI decreased towards the end of exercise in B, a higher peak SI was found in A [57.5 (SD 14.0) vs 43.6 (SD 7.7) ml · m⁻², P < 0.0005]; similar submaximal CI response to exercise, higher peak CI in A [10.6 (SD 2.5) vs 7.2 (SD 1.3) l · min⁻¹ · m⁻², P < 0.0005]; no differences in C _a-vO₂ during exercise; higher MAP at all levels of exercise in B; higher SVRI at all levels of exercise in B; lower SWI in B after recovery; higher MSERI at all levels of exercise in A. The decrease in SI with advancing age would seem to be related to a decrease in myocardial contractility, which can no longer be compensated for by an increase in preload (as during submaximal exercise). Increases in systemic blood pressure may also compromise ventricular function but would seem to be of minor importance. Accepted: 24 September 1996     

Mild dehydration and atrial natriuretic peptide in young and elderly subjects.

The influence of mild dehydration on plasma levels of atrial natriuretic peptide (ANP) was studied in both young (aged 18 to 25 years) and elderly (aged 72 to 86 years) subjects. We expected that dehydration would lower ANP concentrations due to the ensuing volume contraction. A different response of the ANP hormonal system in the elderly might help to explain the observation that elderly subjects are more predisposed to dehydration as compared to young subjects. Dehydration was induced by restriction of fluid intake to 25% of normal for one day. During the study, urinary osmolality increased while osmolar clearance and body weight decreased. Basal ANP concentrations were higher in the elderly subjects. However, these levels did not change during the dehydration study neither in the young nor in the elderly subjects. This may be explained by the activation of counter-regulatory systems preventing a decrease in central blood volume and hence a decrease in ANP concentration.     

Ventilatory and arousal patterns during sleep in normal young and elderly subjects

Since elderly subjects have lower chemosensitivity, we postulated that ventilation might be more state dependent in the elderly. To address this we investigated the changes in ventilation, measured by respiratory inductive plethysmography, with sleep in 12 healthy young (19-29 yr) and 13 elderly (greater than 65 yr) subjects. Ventilation was measured in representative periods in each sleep state. These data showed that there is no difference between the elderly and the young either in mean ventilation or in the variability of ventilation awake or in the different states of sleep. In both groups ventilation was variable in stage 1-2 sleep and least variable in stage 3-4 sleep. The variability in stage 1-2 sleep was due to periodic breathing (cycle time approximately 45 s) in both age groups. Although within a sleep state no differences were observed, over the night of study the elderly behaved differently from the young. Apneas occurred more frequently in the elderly, and 5 of 13 elderly met the criteria for sleep apnea syndrome compared with 1 of 12 young subjects. Apneas tended to occur predominantly in stage 1-2 sleep and seem to be an exaggeration of the periodicity that is typical of this state. Four of the elderly with apnea remained in this stage of sleep throughout the night of study. The apneic episodes usually terminated with an electroencephalogram arousal that occurred prior to or simultaneously with the onset of ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of pain,intensity and P300 components in the pain evoked potential

This study examined the relationships among 3 components of the somatosensory evoked potential (SEP) to painful stimuli. Painful stimuli were produced using intracutaneous electrical stimulation of a fingertip and two levels of non-painful stimuli were produced by superficial electrical stimulation of a neighboring fingertip. SEPs were recorded from Cz-A1 and Pz-A1, and difference waves were computed for 3 components: (1) a pain component (the difference between SEPs to painful vs. strong but non-painful stimuli); (2) an intensity component that is not related to pain (the difference between SEPs to strong non-painful vs. mild non-painful stimuli); and (3) a P300 component (the difference between SEPs to the same stimuli under Target instructions vs. Standard instructions).The positive peaks in the 3 types of difference waves differed in both latency and topography, although with latency and topography overlap. The intensity component had an earlier positive peak than the pain component, and the pain component had an earlier positive peak than the P300 component. The pain and intensity components were larger at Cz than Pz, whereas the P300 component was larger at Pz than Cz. Under certain conditions, the pain evoked SEP consists of a weighted combination of the 3 components, complicating interpretation of the positive peaks in the recorded wave forms.     

Dispersion of helical axes during shoulder movements in young and elderly subjects

The shoulder complex (SC) consists of joints with little congruence and its active and passive structures ensure its stability. Stability of the SC rotation centre during upper arm movements can be estimated through the analysis of Helical Axes (HAs) dispersion.The aim of this study was to describe shoulder HAs dispersion during upper limb movements performed with dominant and non-dominant arms by young and elderly subjects. Forty subjects participated in the study (20 young: age 24.8 ± 2.8 years and 20 elderly: age 71.7 ± 6.3 years). Subjects were asked to perform four cycles of 15 rotations, flexions, elevations and abductions with one arm at a time at constant speed. Reflective markers were placed on participants’ arms and trunk in order to detect movements and the HAs dispersion with an optoelectronic system. Mean Distance (MD) from the HAs barycenter and Mean Angle (MA) were used as HAs dispersion indexes. Young subjects showed significant lower MD compared to the elderly during all motion ranges of rotation, flexion and elevation (p < 0.001). Moreover, the MD was lower in the dominant arm compared to the contralateral for rotation (p = 0.049) and flexion (p = 0.019). The results may be due to joint degeneration described in elderly subjects and differences in neuromuscular control of SC stability.     

Peripheral effects of endurance training in young and old subjects

The effects of 12 wk of endurance training at 70% peak O2 consumption (VO2) were studied in 10 elderly (65.1 +/- 2.9 yr) and 10 young (23.6 +/- 1.8 yr) healthy men and women. Training had no effect on weight or body composition in either group. The elderly had more adipose tissue and less muscle mass than the young. Initial peak VO2 was lower in the elderly, but the absolute increase of 5.5-6.0 ml.kg-1.min-1 after training was similar for both groups. Muscle biopsies taken at rest showed that, before training, muscle glycogen stores were 61% higher in the young. Before training, glycogen utilization per joule during submaximal exercise was higher in the elderly. Glycogen stores and muscle O2 consumption increased significantly in response to training in the elderly only. After training, the proportion of energy derived from whole body carbohydrate oxidation during submaximal exercise declined in the young only. The absolute changes that training produced in peak VO2 were similar in both age groups, but the 128% increase in muscle oxidative capacity was greater in the elderly, suggesting that peripheral factors play an important role in the response of the elderly to endurance exercise.     

Effect of concentration on taste-taste interactions in foods for elderly and young subjects

An increase in concentration of one of the tastants in a 'real food' might affect not only the perception of the taste quality of that manipulated tastant but also the other perceivable taste qualities. The influence of concentration increase of sodium or potassium chloride in tomato soup, sucrose or aspartame in iced tea, acetic or citric acid in mayonnaise, caffeine or quinine HCl in chocolate drink, monosodium glutamate (MSG) or inosine 5'-monophosphate (IMP) in broth on the other perceivable taste qualities in these foods was studied in 21 young subjects (19-33 years) and 21 older subjects (60-75 years). The results showed that for each of these tastants, except for the two acids, increasing the concentration provoked significant positive or negative interaction effects on the perception of one or more other taste qualities of the product. Especially in the young, olfaction plays a larger role in the assessment of taste intensity than has been hitherto assumed. The elderly are less able to discriminate between the taste qualities in a product, whereas the young are more able to do so.     

3D gait assessment in young and elderly subjects using foot-worn inertial sensors

This study describes the validation of a new wearable system for assessment of 3D spatial parameters of gait. The new method is based on the detection of temporal parameters, coupled to optimized fusion and de-drifted integration of inertial signals. Composed of two wirelesses inertial modules attached on feet, the system provides stride length, stride velocity, foot clearance, and turning angle parameters at each gait cycle, based on the computation of 3D foot kinematics. Accuracy and precision of the proposed system were compared to an optical motion capture system as reference. Its repeatability across measurements (test-retest reliability) was also evaluated. Measurements were performed in 10 young (mean age 26.1±2.8 years) and 10 elderly volunteers (mean age 71.6±4.6 years) who were asked to perform U-shaped and 8-shaped walking trials, and then a 6-min walking test (6 MWT). A total of 974 gait cycles were used to compare gait parameters with the reference system. Mean accuracy±precision was 1.5±6.8 cm for stride length, 1.4±5.6 cm/s for stride velocity, 1.9±2.0 cm for foot clearance, and 1.6±6.1° for turning angle. Difference in gait performance was observed between young and elderly volunteers during the 6 MWT particularly in foot clearance. The proposed method allows to analyze various aspects of gait, including turns, gait initiation and termination, or inter-cycle variability. The system is lightweight, easy to wear and use, and suitable for clinical application requiring objective evaluation of gait outside of the lab environment.     

Thresholds for sodium salts in young and elderly human subjects: correlation with molar conductivity of anion

Taste detection thresholds in humans for eight out of ten sodiumsalts studied arc linearly correlated with molar conductivityvalues at infinite dilution of their anions. Thus, detectionthresholds for these salts appear to be determineted by thecharge mobihty of the anion. Age-related losses in detectionthreshold are greatest for salts with anions having the greatestmolar conductivity.     

Diversity-disturbance relationships: frequency and intensity interact

An influential ecological theory, the intermediate disturbance hypothesis (IDH), predicts that intermediate levels of disturbance will maximize species diversity. Empirical studies, however, have described a wide variety of diversity-disturbance relationships (DDRs). Using experimental populations of microbes, we show that the form of the DDR depends on an interaction between disturbance frequency and intensity. We find that diversity shows a monotonically increasing, unimodal or flat relationship with disturbance, depending on the values of the disturbance aspects considered. These results confirm recent theoretical predictions, and potentially reconcile the conflicting body of empirical evidence on DDRs.     

Evoked cortical activity to sounds of differing signal meaning in young and elderly subjects

In elderly people, in comparison with the young ones, the latency of wave P300 is increased in response to all applied acoustic signals, the amplitude of P300 is lower only in response to significant stimuli. No age changes of the wave N150 parameters are noticed. P300 (or N150) wave amplitude depends on signal significance of the sound; it is the lowest in response to significant stimuli and the highest to the ignored ones. Possible reasons of this paradoxical phenomenon are discussed. Preferential participation of different stages of cortical information processing is determined by the difficulty of perceptive task solution. Cortical electrical reaction to separate stimuli is significantly determined by the context of the information perceived in the given period, creating psychological state of the personality.     

Comparison of contact pressures measured at the sacrum of young and elderly subjects

Contact (interface) pressure measurements were made between the sacrum of groups of young and elderly subjects lying upon two special mattresses used to prevent pressure sores. One mattress was an alternating air pressure mattress, the other a foam mattress. Contact pressures were measured using a hydraulic sensor taped directly to the skin over the sacrum. All mean pressures and ‘pressure impulses’ (total applied pressure per standard time period) appeared higher when measured among the elderly subjects. Compared with the pressures measured from young subjects, the maximum contact pressures were significantly higher (p < 0.05) on both mattresses, with the pressure impulse higher while lying upon the foam mattress (p < 0.05).