EEG and Intelligence
M. Doppelmayr, PhD and W. Klimesch, PhD
University of Salzburg, Department of Physiological Psychology, AUSTRIA michael.doppelmayr@sbg.ac.at

Introduction

Since the pioneering work of Hans Berger, there have been many attempts to find electrophysiological correlates of intelligence by using a variety of different measures which in most cases were based on event-related potentials (ERPs).Method.We report findings from a different approach which is based on the analysis of small frequency bands that are dynamically adjusted to individual alpha frequency and bandwidths (Doppelmayr, Klimesch, Pachinger, & Ripper, 1998). Previous work indicates that increasing demands on working memory are associated with an event-related increase in theta band power whereas increasing demands on semantic (long-term) memory are reflected by a selective decrease in upper alpha band power (Klimesch 1997; 1999).Findings.Based on a similar methodological approach Neubauer, Freudenthaler and Pfurtscheller (1995) and Neubauer, Sange, and Pfurtscheller (1999) have obtained interesting results with respect to intelligence. As an example, they have found that the extent of decrease in upper alpha power (event-related desynchronization or ERD) is negatively associated with intelligence: More intelligent subjects exhibit a smaller ERD than less intelligent subject. This finding was interpreted on the basis of the 'neural efficiency' hypothesis.In a recent study from our laboratory (Doppelmayr, Klimesch, Stadler, Pollhuber & Heine, 2002) we have found different effects for the lower and upper alpha band in a resting situation with respect to the performance of tasks with high demands either on attentional or long-term memory processes. Whereas intelligence tasks with high attentional demands (such as the LGT-3) selectively affected the lower alpha band, those with high demands on long-term memory (such as the IST-70) primarily affect the upper alpha band. These findings could be replicated and extended by analyzing the EEG while subjects were performing a combination of the Ravens Standard and Progressive Matrices. Analyzing task performance according to an additional intelligence test (CFT-3) and the amount of band power changes for individually adjusted frequency bands and bandwidths revealed several significant results for different time segments, frequency bands and topographical positions.

Discussion

The findings of the different studies show several significant differences in band power changes between higher and less intelligent subjects, mainly in the alpha bands. While the results underline the different functional meaning of specific frequency bands as reported by Klimesch (1999) not all of the findings of Neubauer et al. (1999) could be replicated. The results will be discussed in detail with respect to the neural efficiency hypothesis.

References.
Doppelmayr, M., Klimesch, W., Pachinger, Th., & Ripper, B. (1998). Individual differences in brain dynamics: Important implications for the calculation of event-related band power measures. Biological Cybernetics, 79, 49-57.
Doppelmayr M., Klimesch W., Stadler W., Pöllhuber D, & Heine C. (2002). Alpha power and intelligence. Intelligence, 30, 289-302.
Klimesch, W. (1997). EEG-alpha rhythms and memory processes. International Journal of Psychophysiology, 26, 319-340.
Klimesch, W. (1999). EEG alpha and theta oscillations reflect cognitive and memory performance: A review and analysis. Brain Research Reviews, 29, 169-195.
Neubauer, A. Freudenthaler, H., & Pfurtscheller, G. (1995). Intelligence and spatiotemporal patterns of event-related desynchronization (ERD). Intelligence, 20, 249-266.
Neubauer, A., Sange, G. & Pfurtscheller, G. (1999). Psychometric intelligence and event-related desynchronization during performance of a letter matching task. In G. Pfurtscheller & F. H. Lopes da Silva (Eds.) Event-Related Desynchronization (ERD) - and related oscillatory EEG-phenomena of the awake brain, Handbook of EEG and Clinical Neurophysiology, Revised Series, Vol. 6 (pp. 219-231). Amsterdam: Elsevier.