The EEG Consistency Index as a Psycho-Physiological Marker of ADHD and Methylphenidate Response: Replication of Results


  • Jennifer Kim Penberthy
  • Daniel Cox
  • Raina Robeva
  • Boris Kovatchev
  • R. Lawrence Merkel



The current study replicates the design and findings of earlier studies examining an EEG measure called the Consistency Index (CI) as a physiological measure of ADHD (Cox et al., 1998; Cox, Merkel, Kovatchev, & Seward, 2000; Kovatchev et al., 2001) and medication response (Merkel et al., 2000). Six males diagnosed with ADHD between the ages of 16 and 19 were examined in this study. The average CI for participants while off of medication was 26%, indicative of ADHD (CI < 40% strong likelihood of ADHD). These CI readings changed significantly when the participants were on therapeutic dosages of methylphenidate. Five of six participants demonstrated a CI > 50%, which is similar to the CI of an individual with no ADHD (Cox et al., 1998, 2000; Kovatchev et al., 2001). Overall, the average CI when on an effective dose of methylphenidate was 57% (CI > 50% strong likelihood of no ADHD). These changes in overall CI were statistically significant (p < 0.05) and demonstrate exciting possibilities for the utility of the CI as a physiological marker of ADHD.