Central adaptations to repetitive grasping in healthy aging.

Augmented cortical activity during repetitive grasping mitigates repetition-related decrease in cortical efficiency in young adults. It is unclear if similar processes occur with healthy aging. We recorded movement-related cortical potentials (MRCP) during 150 repetitive handgrip contractions at 70% of maximal voluntary contraction (MVC) in healthy young (n = 10) and old (n = 10) adults. Repetitions were grouped into two Blocks (Block 1 and 2: repetitions 1-60 and 91-150, respectively) and analyzed separately to assess the effects of aging and block. EMG of the flexor digitorum superficialis and handgrip force were also recorded. No changes in EMG or MVC were observed across blocks for either group. Significant interactions (P < 0.05) were observed for MRCPs recorded from mesial (FCz, Cz, CPz) and motor (C1, C3, Cz) electrode sites, with younger adults demonstrating significant increases in MRCP amplitude. Focal MRCP activity in response to repetitive grasping resulted in minimal changes (i.e. Block 1 versus Block 2) in older adults. Central adaptive processes change across the lifespan, showing increasingly less focal activation in older adults during repetitive grasping. Our findings are consistent with previous paradigms demonstrating more diffuse cortical activation during motor tasks in older adults.

Resistance training induces supraspinal adaptations: evidence from movement-related cortical potentials.

Early effects of a resistance training program include neural adaptations at multiple levels of the neuraxis, but direct evidence of central changes is lacking. Plasticity exhibited by multiple supraspinal centers following training may alter slow negative electroencephalographic activity, referred to as movement-related cortical potentials (MRCP). The purpose of this study was to determine whether MRCPs are altered in response to resistance training. Eleven healthy participants (24.6 +/- 3.5 years) performed 3 weeks of explosive unilateral leg extensor resistance training. MRCP were assessed during 60 self-paced leg extensions against a constant nominal load before and after training. Resistance training was effective (P < 0.001) in increasing leg extensor peak force (+22%), rate of force production (+32%) as well as muscle activity (iEMG; +47%, P < 0.05). These changes were accompanied by several MRCP effects. Following training, MRCP amplitude was attenuated at several scalp sites overlying motor-related cortical areas (P < 0.05), and the onset of MRCP at the vertex was 28% (561 ms) earlier. In conclusion, the 3-week training protocol in the present study elicited significant strength gains which were accompanied by neural adaptations at the level of the cortex. We interpret our findings of attenuated cortical demand for submaximal voluntary movement as evidence for enhanced neural economy as a result of resistance training.

Substance use, trait measures, and subjective response to nicotine in never-smokers stratified on parental smoking history and sex.

INTRODUCTION: Male and female never-smokers stratified on parental history of smoking were tested for possible differences in susceptibility to the hedonic effects of nicotine. METHODS: We recruited nicotine-exposed never-smokers with two never-smoking biological parents (PH-) or two ever-smoking biological parents (PH+). After completing a baseline assessment battery focusing on conditions or behaviors associated with smoking, participants were tested for subjective and hedonic effects in response to administration of three different nicotine doses (0.0, 0.5, and 1.0 mg) via nasal spray. Physiological and biochemical reactivity also was monitored. RESULTS: PH+ were significantly more likely to report having experienced a "buzz" upon early smoking experimentation and to have histories of alcohol abuse and alcoholism; they also scored higher on disordered eating. In response to nicotine dosing, PH+ reported an increase in depressed mood, compared with a minimal response in PH-, in keeping with our expectation that nicotine would have more pronounced effects in PH+. Regardless of parental history, women reported experiencing greater anxiety in response to the highest nicotine dose, compared with men. DISCUSSION: Further exploration in larger samples, using more stringent selection criteria, a wider range of measures, and a less aversive dosing method, may provide a full test of the possible utility of the parental history model for illuminating biobehavioral mechanisms underlying response to nicotine. Also important would be broadening the scope of inquiry to include comparisons with ever-smokers to determine what protected PH+ from becoming smokers, despite the presence of factors that might be expected to decrease resilience and increase susceptibility.

Cardiorespiratory interactions: Noncontact assessment using laser Doppler vibrometry.

The application of a noncontact physiological recording technique, based on the method of laser Doppler vibrometry (LDV), is described. The effectiveness of the LDV method as a physiological recording modality lies in the ability to detect very small movements of the skin, associated with internal mechanophysiological activities. The method is validated for a range of cardiovascular variables, extracted from the contour of the carotid pulse waveform as a function of phase of the respiration cycle. Data were obtained from 32 young healthy participants, while resting and breathing spontaneously. Individual beats were assigned to four segments, corresponding with inspiration and expiration peaks and transitional periods. Measures relating to cardiac and vascular dynamics are shown to agree with the pattern of effects seen in the substantial body of literature based on human and animal experiments, and with selected signals recorded simultaneously with conventional sensors. These effects include changes in heart rate, systolic time intervals, and stroke volume. There was also some evidence for vascular adjustments over the respiration cycle. The effectiveness of custom algorithmic approaches for extracting the key signal features was confirmed. The advantages of the LDV method are discussed in terms of the metrological properties and utility in psychophysiological research. Although used here within a suite of conventional sensors and electrodes, the LDV method can be used on a stand-alone, noncontact basis, with no requirement for skin preparation, and can be used in harsh environments including the MR scanner.

Effects of lifetime ethanol consumption on postural control: a computerized dynamic posturography study.

The relationship between lifetime alcohol consumption and postural control was investigated in 35 subjects with no clinically-detectable neurologic abnormalities, using computerized dynamic posturography (CDP) procedures. The estimated total number of lifetime alcoholic drinks was positively correlated with anteroposterior sway spectral power within the 2-4 Hz and 4-6 Hz frequency bands, in three Sensory Organization Test (SOT) conditions: eyes closed with stable support surface (SOT 2), eyes open with sway-referenced support (SOT 4), and eyes closed with sway-referenced support (SOT 5). All correlations remained significant after controlling for subject age, and were increased after excluding nine drug-abusing subjects. In contrast to the strong findings for frequency-based measures, no correlation was observed using conventional amplitude-based sway measures. These results suggest that 1) alcohol consumption compromises postural control in an exposure-dependent manner, and 2) sway frequency analysis reveals pathological processes not manifested in conventional CDP measures of sway amplitude.

Laser Doppler vibrometry measurement of the mechanical myogram.

Contracting muscles show complex dimensional changes that include lateral expansion. Because this expansion process is intrinsically vibrational, driven by repetitive actions of multiple motor units, it can be sensed and quantified using the method of Laser Doppler Vibrometry (LDV). LDV has a number of advantages over more traditional mechanical methods based on microphones and accelerometers. The LDV mechanical myogram from a small hand muscle (the first dorsal interosseous) was studied under conditions of elastic loading applied to the tip of the abducted index finger. The LDV signal was shown to be related systematically to the level of force production, and to compare favorably with conventional methods for sensing the mechanical and electrical aspects of muscle contraction.

Hidden state models for noncontact measurements of the carotid pulse using a laser Doppler vibrometer.

The method of laser Doppler vibrometry (LDV) is used to sense movements of the skin overlying the carotid artery. When pointed at the skin overlying the carotid artery, the mechanical movements of the skin disclose physiological activity relating to the blood pressure pulse over the cardiac cycle. In this paper, signal modeling is addressed, with close attention to the underlying physiology. Segments of the LDV signal corresponding to single heartbeats, called LDV pulses, are extracted. Hidden Markov models (HMMs) are used to capture the dynamics of the LDV pulses from beat to beat based on pulse morphology; under resting conditions these dynamics are primarily due to respiration-related effects. LDV pulses are classified according to state, by computing the optimal state path through the data using trained HMMs. HMM state dynamics are examined within the context of respiratory effort using strain gauges placed around the abdomen. This study presented here provides a graphical model approach to modeling the dependence of the LDV pulse on latent states.

Hidden state dynamics in laser Doppler vibrometery measurements of the carotid pulse under resting conditions.

A laser Doppler vibrometer (LDV) is used to sense movements of the skin overlying the carotid artery. Fluctuations in carotid artery diameter due to variations in the underlying blood pressure are sensed at the surface of the skin. Portions of the LDV signal corresponding to single heartbeats, called the LDV pulses, are extracted. This paper introduces the use of hidden Markov models (HMMs) to model the dynamics of the LDV pulse from beat to beat based on pulse morphology, which under resting conditions are primarily due to breathing effects. LDV pulses are classified according to state, by computing the optimal state path through the data using trained HMMs. HMM state dynamics are compared to simultaneous recordings of strain gauges placed on the abdomen. The work presented here provides a robust statistical approach to modeling the dependence of the LDV pulse on latent states.