Search Results

You are looking at 1 - 10 of 50 items for :

  • "evoked potentials" x
  • Refine by Access: All Content x
Clear All
Restricted access

Susumu Yahagi, Zhen Ni, Makoto Takahashi, Yusaku Takeda, Toshio Tsuji, and Tatsuya Kasai

Using transcranial magnetic stimulation (TMS), differences in the excitability changes of motor evoked potentials (MEPs) between isometric (force task) and isotonic (movement task) muscle contractions in a distal (first dorsal interosseous; FDI) and a proximal (middle deltoid; MD) muscle were studied. In the FDI muscle, the active threshold of MEP recruitment was significantly lower in the isotonic than that in the isometric muscle contraction in spite of identical background EMG activity levels. Additionally, the dependence of the MEP amplitude on background EMG activity was significantly greater in the isotonic than in the isometric muscle contraction at low EMG activity levels, but the difference disappeared beyond middle EMG activity levels. In the MD muscle, the dependence of the MEP amplitude on background EMG activity was significantly greater in the isotonic than in the isometric muscle contraction, and further this dependence was kept at all muscle contraction levels. These results indicate that the dependence of the MEP amplitude on background EMG activity is modulated not only by the different muscle contraction modes (isotonic and isometric), but also by muscle properties (distal and proximal). Thus, the present findings suggest that the task-specific extra excitation in the proximal muscle is definitely produced corresponding to task differences (task-dependent subliminal fringe), which might be explained by the predominant frequency principle if applied to the proximal muscle. On the other hand, the lack of task-dependent extra excitation in the distal muscle is explained by the predominant recruitment principle for force grading in small hand muscles.

Restricted access

Bradley D. Hatfield, Thomas W. Spalding, Ross J. Apparies, Amy J. Haufler, and D. Laine Santa Maria

Latencies and peak-to-peak amplitudes of pattern-reversal evoked-potential (PREP) components of active and inactive community-dwelling healthy 61- to 77-year-olds were compared with those of active and inactive 18- to 31-year-olds to determine whether long-term physical activity involvement was associated with attenuation of age-related changes in sensory processes. Binocular PREPs were derived for each of 2 check sizes (22 × 15 ft and 41 × 30 ft of visual angle) to provide increasing challenge of spatial resolution. Analyses of the latencies revealed significant effects for age, gender, and check size such that latencies were longer for older than for young participants, men than for women, and small than for larger check sizes. Amplitudes were larger in older adults for the P100-N150 peak-to-peak difference, but physical activity history was not associated with reduction of the observed age-related increases in component latencies and amplitude. As such, physical activity does not appear to attenuate age-related decline in visual sensory processing.

Restricted access

Takashi Kato, Yusaku Takeda, Toshio Tsuji, and Tatsuya Kasai

The present study investigated the relative contribution of the cortical and spinal mechanisms for post-exercise excitability changes in human motoneurons. Seven healthy right-handed adults with no known neuromuscular disabilities performed an isometric voluntary wrist flexion at submaximum continuous exertion. After the subjects continued muscle contraction until volitional fatigue, the H-reflexes induced by an electric stimulation and motor evoked potentials (MEPs) induced by a transcranial magnetic stimulation (TMS) from a flexor carpi radialis (FCR) muscle were recorded 7 times every 20 s. The H-reflex was used to assess excitability changes at the spinal level, and the MEP was used to study excitability changes at the cortical level. H-reflexes showed a depression (30% of control value) soon after the cessation of wrist flexion and recovered with time thereafter. On the other hand, an early (short latency) MEP showed facilitation immediately after the cessation of wrist flexion (50% of control value) and thereafter decreased. A possible mechanism for the contradictory results of the 2 tests, in spite of focusing on the same motoneuron pool, might be the different test potential sizes between them. In addition, a late (long latency) MEP response appeared with increasing exercise. With regard to the occurrence of late MEP response, a central mechanism may be proposed to explain the origin—that is, neural pathways with a high threshold that do not participate under normal circumstances might respond to an emergency level of muscle exercise, probably reflecting central effects of fatigue.

Restricted access

Robert E. Dustman, Rita Emmerson, and Donald Shearer

Findings from three research paradigms that employed aerobic exercise as an independent variable were used to test the hypothesis that aerobic exercise improves cognitive-neuropsychological functioning. The research paradigms were animal intervention studies, cross-sectional human studies, and human intervention studies. Results from studies of animals, usually rodents, provide consistent evidence that aerobic fitness is associated with improved neurobiological and behavioral functioning. Cross-sectional studies with humans indicate a strong positive association between physical activity level and cognitive-neuropsychological performance. However, results from these studies must be interpreted cautiously, as individuals who elect to exercise or not exercise may differ on other variables that could influence cognitive-neuropsychological performance. To date, human intervention studies have not consistently demonstrated cognitive-neuropsychological improvements following exercise training. To satisfactorily test the exercise/cognition hypothesis with humans, carefully controlled intervention studies that last longer than those previously employed are needed.

Restricted access

Thorben Hülsdünker, Martin Ostermann, and Andreas Mierau

, & Mierau, 2017a ) and table tennis ( Hülsdünker, Ostermann, & Mierau, 2019b ) players. Specifically, previous experiments identified the N2 and N2-r visual evoked potentials (VEPs) in the motion-sensitive mid-temporal (MT) visual area. The N2 is a stimulus-locked VEP occurring around 170 ms following

Restricted access

Nicholas D. Gilson, Caitlin Hall, Angela Renton, Norman Ng, and William von Hippel

color were always present, but were not behaviorally relevant (neutral objects). These sets of moving objects each flickered at unique frequencies (8, 10, and 12 Hz), producing steady-state visually evoked potential (SSVEP; microvolt) indicative of relative attentional resource allocation toward objects

Open access

Laura Duval, Lei Zhang, Anne-Sophie Lauzé, Yu Q. Zhu, Dorothy Barthélemy, Numa Dancause, Mindy F. Levin, and Anatol G. Feldman

position. In addition, by varying object texture, we investigated whether referent control relies on cutaneous inputs to α-MNs. By assuming that iCS influences are modulated similarly in bimanual tasks, we assessed iCS influences by analyzing ipsilateral motor evoked potentials (iMEPs) elicited in wrist

Restricted access

Stephen P. Bailey, Julie Hibbard, Darrin La Forge, Madison Mitchell, Bart Roelands, G. Keith Harris, and Stephen Folger

improvement in performance is unclear; however, it is believed that the CHO MR enhances the excitability of the motor cortex via oral CHO receptors. Gant et al 3 provided supportive evidence for this premise when they found that the motor-evoked potential (MEP) response to transcranial magnetic stimulation

Restricted access

Julie P. Burland, Adam S. Lepley, Marc Cormier, Lindsay J. DiStefano, and Lindsey K. Lepley

corticospinal excitability by determining the active motor thresholds (AMTs) and amplitude of motor evoked potentials (MEPs) elicited at 120% of AMT. Two 10-mm electromyographic electrodes were positioned in the same manner as during spinal-reflex excitability testing. Debridement and cleaning of the collection

Restricted access

Thorben Hülsdünker, Clara Rentz, Diemo Ruhnow, Hannes Käsbauer, Heiko K. Strüder, and Andreas Mierau

their faster processing of visual information, as reflected by an earlier N2 visual evoked potential in the midtemporal motion sensitive area (area MT) of the visual cortex. 4 Importantly, visual processes not only differentiated athletes from nonathletes but further determined visuomotor performance