The influence of low-level, event-related dc-currents during time estimation in humans

Two experiments were designed to investigate further the influence of low-level transcephalic DC currents on human reaction time and time perception. Thirty-two subjects participated in the experiments, with the second one a replication of the first. During a first trial series, subjects responded to the offset of a 6 second tone. Simultaneous to tone presentation a current was applied between vertex and collar bone electrodes. Current polarity varied randomly across trials. During a second trial series, subjects interrupted tone and current when they estimated a time interval of same length as the previously experienced had elapsed. In both studies subjects interrupted the tone/current after a shorter interval when the negative pole was applied as compared to vertex-positive trials. Results suggest that a vertex-negative external current suppresses an internally required state, whereas an external positive current supports internal SP-generation. The brain may tend to terminate the former state earlier than the latter.