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Afferent responses in single-fibre and multi-fibre preparations of the n. infraorbitalis leading from mechanosensitive receptors of the cat's vibrissae were investigated by application of different isotonic solutions of ionised calcium, sodium, potassium and magnesium. Under quasi-stationary as well as under time-variable conditions the doseresponse studies of calcium and potassium revealed a non-linear, depressive action on synchronised impulse patterns as far as the spike rate and the spike phase was concerned. In coincidence with the inhibition of neural activity the impulses were shifted to a higher phase angle and a considerable instability of the trigger time point was observed. Contrarily, sodium had an activating effect on the discharge combined with higher spike rates, lower phase angles and a stabilising influence on the synchronisation of afferent impulse patterns. After injection of magnesium no significant modification was found. [ABSTRACT FROM AUTHOR]