Efficacy of SMR-Beta Neurofeedback for Attentional Processes
David A. Kaiser and Siegfried Othmer
EEG Spectrum, Inc. Encino, CA
Four hundred and eight children and adolescents (age 6 to 16 years, mean 10.7) and 122 adults (17 to 67 years, mean 37.2) participated in this study. Females comprised less than one-quarter of the child and adolescents group and nearly one-half of the adults (92 and 58, respectively). Subjects were obtained in nine clinical settings affiliated with EEG Spectrum, Inc. and were selected based on the availability of pre- and post-training data for the TOVA. None of these subjects were on any stimulant or antidepressant medications during the test. Although a plurality of subjects suffered from ADHD, many also exhibited comorbid conditions of more severe behavioral disorders (ODD and Conduct Disorder), Tourette’s Syndrome, minor traumatic brain injury, epilepsy, anxiety disorders, and depression. The subjects also included some who were referred for ADHD but may not have met the classical diagnostic criteria for the condition. Adults varied on diagnosis with the majority exhibiting some form of ADD.
EEG biofeedback training was performed on Neurocybernetics 2-Channel EEG systems. All subjects were evaluated with the Test of Variables of Attention (TOVA) (Greenberg, 1987), a continuous performance task (CPT) that presents to a subject a geometric target or non-target. The use of a single non-target allows this test to be conceptualized as a Go/No-Go task, a form of test which is associated with frontal lobe function (e.g., Levin et al., 1991). Results from the TOVA include measures of omission errors (inattention), commission errors (impulsivity), response time (speed of information processing), and response time variability (consistency of response). Scores are presented in standard scores with every standard deviation presented as 15 points above or below the mean. This test was administered on a PC computer and used a single switch for response. This test consists of only two non-verbal stimuli which requires a subject to pay attention for 22.5 min without prolonged rest. Presentation probabilities for targets and non-targets are mixed between test halves in order to evaluate high-likelihood and low- likelihood response conditions (i.e., 20% targets first half of test, 80% targets second half), and thereby provide measures of impulsivity and inattention, respectively. Normative age-based data is available for each gender; for children, in single-year age groups, and for adults in 10-year age groups (Greenberg & Waldman, 1993).
The training protocol consisted of rewarding enhanced EEG amplitudes in the 12-18 Hz frequency regime, while simultaneously inhibiting excessive amplitudes in the low frequency (4-7 Hz) and high-frequency (22-30 Hz) regimes. Electrode placement always included one electrode site on the sensorimotor strip (at either C3 or C4 in the standard 10-20 system) and less commonly one electrode with either frontal or parietal placement. If training was done solely at C3 and C4, then the montage was referential to the proximate ear. If training involved frontal or parietal placement, the montage was bipolar with either C3-Fpz or C4-Pz. Left-side (C3) and right-side (C4) training involved rewarding activity in the 15-18 Hz and 12-15 Hz, respectively. Occasionally, these two protocols were used in succession during a single training session with the respective duration (e.g., 10 min SMR, 20 min Beta) of the two protocols titrated on the basis of changing symptomatology and TOVA results (Greenberg, 1987). Left-hemisphere training (e.g., C3) involved Beta reward only whereas right-hemisphere training involved SMR reward only.
Training consisted of 30 min of visual and auditory feedback on the instrument, within a 45-min contact hour. Visual feedback was provided by a variety of means which map the EEG amplitude in the reward and inhibit bands into the brightness, size, and/or velocity of objects on a computer monitor. Most commonly, information about the amplitude of signals in each of the bands was given independently. Alternatively, the subject was simply be notified that an inhibit threshold was exceeded by the withholding of the conventional reward. When all reward conditions were satisfied for a minimum of 0.5 s, an auditory beep and visual incentive (e.g., highway stripe, star in sky) was provided as reinforcement. The visual feedback signal was occasionally complemented with direct tactile and auditory feedback of EEG amplitude in the reward band.
Subjects were evaluated prior to training and after approximately 20 sessions. Those subjects who were further treated were retested after approximately 40 training sessions. Most subjects completed or discontinued training after 20 sessions (mean 24.1, range 18 to 61 sessions).
A Huynh-Feldt correction for degrees of freedom was applied to all interactions to counter potential nonsphericity of the four dependent measures. When an interaction of condition (treatment by dependent measures) was significant at the .01 level, planned comparison t-tests were used to evaluate differences for each dependent measure. The Bonferroni correction for multiple tests was consequently applied to planned comparisons.