The possible meaning of the upper and lower alpha frequency ranges for cognitive and creative tasks
Introduction
It has often been claimed that the subdivision of the EEG into different frequency bands, which goes back to Hans Berger and has its origin in the clinical EEG, is justified also from a functional point of view. However, its alleged uniformity has often been questioned, particularly with regard to the alpha band. Although the problem of its individuality was studied by several authors by means of factor analysis (Herrmann et al., 1980) no unanimous answer to this question has been found so far. Based on structure–analytic reflections several authors recommended a subdivision of the alpha into at least two bands. Since, moreover, several psychological studies also support the idea of a functionally different meaning of higher and lower-frequency alphas (Klimesch et al., 1993), we wanted to know whether differences within the alpha range might also show up in cognition studies with ERP in the on-going EEG. For this purpose two spectral parameters, amplitude and coherence, were used as indices. Klimesch (1996)found that the upper alpha band reflects the retrieving of semantic long-term memory information by determining an `individual alpha peak frequency' for each subject separately. Our study, based on broad frequency bands, therefore, had a priori lower chance to help solving this problem, all the less as our studies were performed mainly on groups and not on individuals. In spite of these drawbacks, our amplitude and coherence studies on cognitive processes brought further evidence that splitting the alpha may allow more insight into the possible functional meaning of the alpha rhythms.
With this aim in mind the ongoing EEG was studied in several sets of experiments. One of them concerned the visual world with contemplating and memorizing pictures, mentally creating images and silently reading, another the world of sounds while listening to and composing music. The third set of experiments concerned eventual correlations between the skill in performing mental tasks and the amount of coherence changes. We called the two frequency bands to be studied alpha 1 and 2; they were arbitrarily defined between 7.5 and 9, and between 9.5 and 12.5 Hz, respectively.
Section snippets
Method
The method used in this study has been developed by us several years ago (Rappelsberger and Petsche, 1988). It compares the values of amplitude and coherence during a mental process with those during the averaged EEG at rest. Since this method is based on EEG epochs of at least 1 min duration, the results represent average values of the changes of these parameters by a mental process. The EEG is recorded from the usual 19 electrodes of the 10/20 system with respect to averaged recordings from
Visual tasks
The first series to be reported concerns visual tasks. The following results are from an experiment on 38 females in which four different visual tasks had to be performed: (1) to contemplate a slide of a painting projected onto the wall; (2) to silently read a text, for distraction; (3) to memorize the painting shown just before; and (4) to mentally create a picture of one's own choice. Each task was performed for 2 min and was repeated with four paintings of different periods of the history of
Discussion
Previous papers on the significance of the alpha relate almost exclusively on amplitude. Apart from the initial idea that alpha is related to attention, Wertheim (1981)was among the first to claim that alpha depends on oculomotor functioning rather than on the quality of perception; this means that alpha blocking would be due to visual activity involving retinal feedback (Shaw, 1992). If this hypothesis were correct, differences in the degree of alpha blocking should be expected between the
Acknowledgements
This work was supported by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung, Project S 49-02.
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2021, Developmental Cognitive NeuroscienceCitation Excerpt :This perspective follows from the hypothesis that activity in those bands has, to some extent, the same functional role from the earliest stages of human life (i.e., the fixed bands hypothesis (Red’ka and Mayorov, 2014)). Evidence shows that the alpha1 and alpha2 bands are linked to different perceptual-cognitive functions (Petsche et al., 1997). Alpha2 is associated with memory and semantics (Doppelmayr et al., 2002; Klimesch, 1997; Klimesch et al., 1994), while alpha1 is more related to attention, expectation and encoding (Doppelmayr et al., 2002; Klimesch, 1997; Klimesch et al., 1993).