$$
\mathrm {a} _ {1}, \mathrm {a} _ {2}
$$
$$
\left[ b _ {1}: \right.
$$
$$
b _ {1} - b _ {5}
$$
$$
b _ {2}:
$$
$$
b _ {5}
$$
D "Envelope" threshold curve for extrasystole elicitation and ventricullar fibrillation; stimulation, 1 sec or longer (injury threshold).
$ c_{1}, c_{2} $ Extra-cellular stimulation thresholds of single cells $ (c_{1} $ : Roberts and Smith, 1973; $ c_{2} $ : Ranck, 1975).
d Frequency dependence of stimulation thresholds for nerve/muscle systems (modified from Schaefer, 1940). This curve may be used as a lower "envelope" curve for excitation thresholds for single unidirectional pulses or pulse sequences.
$ I_{1} $ Threshold for modulation among different neurons (Chan and Nicholson, 1986).
$ I_{2} $ Modulation of neuronal excitability in rat hippocampal slices (Bawin et al., 1984).
C "Envelope" threshold value curve for stimulating effects (possibly hazardous).
h, i, j, B Calculated current densities for the threshold values of electrophosphenes (h: Adrian, 1977) magnetophosphenes (calculated current densities; $ i_{1} $ : Silny, 1981; $ i_{2} $ and $ i_{3} $ : Bernhardt, 1985) and variations of optically-generated reaction potentials (j: Silny, 1981). B shows the range over which biological effects are expected and observed.
A. Average value of naturally-flowing current density in the body tissue; the values of the current densities due to the electrical events in the brain or in the heart are usually much larger at a microscopic level. Below this current density, absence of detectable effects is assumed.
1 W/kg The current density range above which additional thermal effects have to be considered.
FIGURE F-3: THRESHOLD VALUES OF ELECTRIC CURRENT DENSITY FOR DIFFERENT BIOLOGICAL EFFECTS