Reliability of transcallosal inhibition in healthy adults

Transcallosal inhibition (TCI), assessed using transcranial magnetic stimulation, can provide insight into the neurophysiology of aging and of neurological disorders such as stroke. However, the reliability of TCI using the ipsilateral silent period (iSP) has not been formally assessed, despite its use in longitudinal studies. This study aimed to determine the reliability of iSP onset latency, duration and depth in healthy young and older adults. A sample of 18 younger (mean age 27.7 years, range: 19–42) and 13 older healthy adults (mean age 68.1 years, range: 58–79) attended four sessions whereby the iSP was measured from the first dorsal interosseous (FDI) muscle of each hand. 20 single pulse stimuli were delivered to each primary motor cortex at 80% maximum stimulator output while the participant maintained an isometric contraction of the ipsilateral FDI. The average onset latency, duration of the iSP, and depth of inhibition relative to baseline electromyography activity was calculated for each hand in each session. Intraclass correlation coefficients (ICCs) were calculated for all four sessions, or the first two sessions only. For iSP onset latency the reliability ranged from poor to good. For iSP duration there was moderate to good reliability (ICC > 0.6). Depth of inhibition demonstrated variation in reproducibility depending on which hand was assessed and whether two or four sessions were compared. Bland and Altman analyses showed wide limits of agreement between the first two sessions, particularly for iSP depth. However, there was no systematic pattern to the variability. These results indicate that although iSP duration is reliable in healthy adults, changes in longitudinal studies should be interpreted with caution, particularly for iSP depth. Future studies are needed to determine reliability in clinical populations

P244 The effect of transcranial direct current stimulation on motor sequence learning and upper limb function after stroke

OBJECTIVE: To assess the impact of electrode arrangement on the efficacy of tDCS in stroke survivors and determine whether changes in transcallosal inhibition (TCI) underlie improvements. METHODS: 24 stroke survivors (3-124months post-stroke) with upper limb impairment participated. They received blinded tDCS during a motor sequence learning task, requiring the paretic arm to direct a cursor to illuminating targets on a monitor. Four tDCS conditions were studied (crossover); anodal to ipsilesional M1, cathodal to contralesional M1, bihemispheric, sham. The Jebsen Taylor hand function test (JTT) was assessed pre- and post-stimulation and TCI assessed as the ipsilateral silent period (iSP) duration using transcranial magnetic stimulation. RESULTS: The time to react to target illumination reduced with learning of the movement sequence, irrespective of tDCS condition (p>0.1). JTT performance improved after unilateral tDCS (anodal or cathodal) compared with sham (p0.1). There was no effect of tDCS on change in iSP duration (p>0.1). CONCLUSIONS: Unilateral tDCS is effective for improving JTT performance, but not motor sequence learning. SIGNIFICANCE: This has implications for the design of future clinical trials

The human force: velocity relationship; activity in the knee flexor and extensor muscles before and after eccentric practice

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Quadriceps function, proprioceptive acuity and functional performance in healthy young, middle-aged and elderly subjects

BACKGROUND: Muscle functions to generate force-producing movement and also has a role in proprioception. If ageing compromises these sensorimotor functions of muscle, the ability of older subjects to detect and correct postural sway may be impeded, resulting in impairment of functional performance. METHOD: To see if age-related changes occurred and, if so, what their effects might be. Quadriceps strength, proprioception, postural stability and functional performance were assessed in young (n = 20, mean age 23 years), middle-aged (n = 10, mean age 56 years) and elderly (n = 15, mean age 72 years) subjects. RESULTS: With increasing age there were decreases in quadriceps strength (r = -0.511; P < 0.001), acuity of joint position sense (r = -0.603; P < 0.001) and postural stability (ANOVA < 0.002) during stance conditions which placed a greater reliance on muscle proprioceptors. These changes may decrease postural stability confidence, resulting in impaired performance of common activities of daily living (r = 0.635; P < 0.001). CONCLUSIONS: The age-related deterioration in sensorimotor function of muscle may contribute to the increased fear and frequency of falls in elderly subjects, thereby decreasing independence