A comparison of two methods for estimating 50% of the maximal motor evoked potential

OBJECTIVES: Two commonly-used methods for setting stimulus intensities in transcranial magnetic brain stimulation studies were compared to determine which best approximated a motor evoked potential (MEP) of 50% of the maximal MEP amplitude (SI50); a suprathreshold intensity relative to resting motor threshold (rMT) or adjusting the intensity to evoke an MEP amplitude of 1mV. METHODS: Corticomotor stimulus-response curves and rMT for the right first dorsal interosseous (FDI) muscle of 176 subjects (aged 10-74years) were retrospectively analysed. RESULTS: Regardless of subject age or sex, SI50 occurred at 127.5+/-11.3% rMT. Except in young children, MEPs of 1mV were significantly smaller than those evoked at SI50. CONCLUSIONS: In the inactive FDI muscle, a stimulus intensity of 127-128% rMT consistently gives the best approximation of SI50 in most subjects, except perhaps young children. SIGNIFICANCE: Setting TMS stimulus intensities relative to rMT provides a less variable inter-subject comparator, with respect to individual differences in corticomotor input-output characteristics, than adjusting the stimulator output to give an absolute MEP magnitude

Hydrological dynamics of the Panola Mountain Research Watershed, Georgia, USA. Ground Water.

Relations between stormflow characteristics and soil-moisture content, water table elevation in wells along several transects perpendicular to the stream, and precipitation were evaluated for the Panola Mountain Research Watershed, Georgia, from water years 1986 through 2001 to refine the conceptualization of streamflow generation, including the relations between ground water dynamics and streamflow. For 759 rainstorms during 16 water years, stormflow water yield correlates best with maximum soil-moisture content and with maximum water table elevation; the relations are linear above thresholds for the entire period and vary by season. For moderate to large rainstorms, relations among wetness parameters and stormflow water yield are better (less scatter) and more consistent when the watershed is seasonally wet than when the watershed is dry. During rainstorms, soil-moisture content (minimum or maximum) is highly correlated among soil depths and with water table elevations. The soil-moisture measurements were made at one site at the base of a hillslope, and the values at any depth are likely to vary spatially and with respect to timing, other landscape positions, and soil types. Stormflow water yield is linearly related to soil-moisture content at the deepest location (70 cm) above 37% volumetric moisture content, which occurs 20% of the time. Maximum water table elevation is linearly related to maximum soil-moisture content above a threshold, and the soil-moisture threshold increases with upslope position; the soil-moisture threshold for flow to occur at a trench hillslope site is 41%, which occurs <0.5% of the time. The general relations among streamflow, soil moisture, and water table response are attributed to variable source areas, particularly the ground water contribution from a riparian zone aquifer ≤5 m thick that expands as the watershed becomes wetter