136 stimuli elicit an oscillatory response at about 40 Hz. Continu- ous stimulation by 40 Hz clicks elicits a sinusoidal response, which is larger in amplitude than that to 20 or 50 Hz stimula- tion. The relation between these responses is not clear. The magnetic and electric 40-Hz steady-state responses can be modeled by linear summation of responses to 10 Hz stimuli. Magnetic source localization shows that the generator areas of the responses to transient and steady-state 40-Hz stimuli lie close to each other in the supratemporal auditory cortex. In intracortical recordings of cats, responses to 40-Hz click trains, measured from the cortical surface, show morphologi- cal resemblance to those measured with MEG in humans. The intracortical distribution of the response is similar to that seen in responses to single clicks. With continuous 40-Hz stimulation, however, the intracortical distribution of the re- sponse is conspicuously different from that to single clicks or click trains. The response in upper layers of the cortex to continuous 40-Hz stimulation is also drastically dampened in slow-wave sleep, in line with reports of human electrice 40-Hz steady-state responses, whereas responses to 40-Hz click trains are clearly less affected. Pentobarbital anesthesia, however, affects both the 40 Hz response to click trains and continuous 40-Hz clicks in quite similar manner. Taken together, the results suggest that, whereas the 40-Hz responses to click trains and continuous clicks are related, intracortical re- sponses to continuous clicks cannot be explained by simple linear summation of transient responses. GAMMA-BAND EVENT-RELATED BRAIN DYNAMICS: HISTORIC PERSPECTIVE Scott Makeig Naval Health Research Center, San Diego, CA, USA Since the discovery of the human EEG in the 1930s by Berger, LEG oscillations in the gamma range (30 90 Hz), have been proposed to represent a physiological substrate for cognition. In his address to the first meeting of the EEG Society in 1947, Adrian chose one slide to exemplify the mystery and promise of the EEG. It showed near 40-Hz bursts of electrical oscillations evoked or induced in a rabbit's brain when it sniffed a new odor, a phenomenon now studied extensively by Walter Freeman and others. In 1980, a student of Robert Galambos, Peter Talmachoff, rediscovered the ten- dency of the auditory steady-state response (SSR) to have an amplitude maximum at stimulus rates near 40 per s. Galam- bos and I then noted that gamma-band SSRs also exist for the human visual and somatosensory modalities, while Erol Basar and others had identified evoked rhythmicities in the same range in a variety of animal brain locations. In succeeding years we, Terry Picton, John Rohrbaugh and others explored the parameters of the auditory SSR, and also its spontaneous dynamics, relation to sleep, and response to perturbation. Later, I found, and Christo Pantev has confirmed, that the auditory Middle Latency Response is, in many subjects, only the beginning of a longer auditory-evoked gamma band re- sponse (GBR) which is the timedomain precursor of the SSR. At the same time, Gray and Singer discovered visual GBRs in cat visual cortex. It is now proposed that phase-coherent oscillations at gamma band and other frequencies may coa- lesce transient cooperative neuronal assemblies mediating ob- ject recognition and supporting higher-order cognition and motor control processes. It appears averaged scalp responses may capture only a phase-coherent residue of gamma-band brain response dynamics, which may be seen more fully in spectral transforms of single or selectively averaged epochs. PSYCHOPHYSIOLOGICAL DEVELOPMENT OF LEARNING ABILITIES AND PURPOSEFUL BEHAV- IOR Constantine A. Mangina Montreal Research and Treatment Center for Learning Abili- ties and Disabilities, Montreal, Quebec, Canada This paper aims to discuss the link between the development of learning abilities and purposeful behavior based on the following research data: (1), degrees of 'analytical-specific perceptual skills' and learning potential as measured by the Mangina Test; (2), the identification and standardization of bilateral electrodermal parameters of learning abilities and disabilities; (3), effects of psychophysiological treatment (Mangina Treatment Method) for learning disabilities. Evi- dence for the effectiveness of this treatment method was found based on different experimental conditions. ANOVA and Multiple Comparison Tests indicate that beneficial ef- fects were only obtained by the administration of the full treatment method and were significant at all three time inter- vals investigated (P < 0.001). The evidence supports that the treatment method has induced a 'synergistic simultaneity' which is required by the brain both in terms of its bilaterally 'optimal' physiological state and the appropriate quality of incoming stimulation in order to produce a beneficial neural integration. Our research evidence leads to the conclusion that new treatment possibilities are now available for the neurocogni- tive development and purposeful behavior in children, adoles- cents and youth with learning disorders. THE ROLE OF VARIABILITY IN THE DEVELOPMENT OF SKILLED ACTION E. de J. Manoel and K.J. Connolly Department of Psychology, University of Sheffield, Sheffield, UK Skilled motor actions are creative because the pattern of an individual's interaction with the environment is changing con- tinuously. Consequently, the distinction between movements and action is important; actions are defined by their goal (picking up an object, cutting with a knife and so forth) and