Interhemispheric changes in alpha rhythm related to time perception

Each cerebral hemisphere processes environmental information in a different but complementary manner. Structures located in the left hemisphere are assumed to participate in symbolic-logic thinking. Time perception may be considered among such thinking processes. The present study evaluates bilateral occipito-central EEG activity in healthy, right-handed subjects which was produced while they performed a visuomotor monitoring task. The task consisted of two stages. The first stage involved the subject's learning a fixed time interval (10 sec) and the measurement of their reaction time. Subjects responded to an isolated light stimulus by pressing a button with the dominant hand. In the second stage, the subjects accuracy in estimating interval-length was evaluated. Two forms of EEG analysis were used, frequency and alpha ratio, each of which was measured both prior to and subsequent to the motor response. A reversal group was used to carry out a complementary test. Subjects responded in the first block of experiments with the non-dominant (left) hand and with the dominant hand in the second. Results showed that left hemisphere activity was continuous during the interval-learning stage and with optimal reaction times and remained continuous when estimation values approximated the real interval. In addition, in optimal reaction time and near to optimal time estimation responses, the left side showed lower frequency and alpha ratio than did the right. Finally a progressive enhancement in both parameters from the right hemisphere was related to deterioration in test performance. Results from the reversal group did not differ from those of the first group. As evaluated by gross measurements of the EEG, a predominant participation of the left hemisphere in time processing is concluded.