Alpha waves--artifacts?

Abstract

Kennedy has argued that alpha rhythm recordings are artifacts caused by the mechanical pulsation (choroid plexus pump) of a gel (the living brain) with different electrical potentials. This paper has been republished in a recent collection by Evans and Robertson. Kennedy's hypothesis seemed insufficiently supported, and contradicted the consensus concerning the origin of alpha waves which existed at the time. Significant recent research is examined which provides strong, if not conclusive, evidence that alpha waves represent a basic cellular process probably related to excitability. It is suggested that Kennedy's phenomenon be explored further to clarify any effect it may have on standard EEC recordings. A few years ago, Kennedy (1959) presented a rather surprising article suggesting that the externally recorded cortical alpha rhythm could possibly be—in fact probably was—a recording artifact. This was in direct contradiction to the trend of theorizing about the nature of alpha waves. Kennedy's paper did not cause any great uproar nor did it change the direction of research or writing on the EEC. Recently, however, this same paper has made a reappearance in a book of collected readings (Evans & Robertson, 1966). This renewed presentation compels comment. In essence, Kennedy suggested that the alpha rhythm does not represent a basic process at the cellular level, but is merely an artifact due to the gross physical properties of materials from which the recordings are made. He suggested that the alpha rhythm may be due to three sets of conditions normally found in the brain: (a) an electrically charged state, presumed to arise through chemical oxidation reduction reactions; (6) a gel mass with a co-efficient of elasticity approximated by commercial gelatin; and (c) a periodic mechanical pulse, to set the gel into oscillation at its resonant frequency. It is proposed that the interaction of these conditions in the skull may produce the oscillating potentials recorded from normal humans by standard electroencephalographic equipment [Kennedy, 1959, p. 352], In order to demonstrate this mechanism, Kennedy used a mass of commercial gelatin under conditions roughly similar to the human brain. He mechanically pulsed this mass to simulate the arterial pulsing of the brain so that it resonated at its particular frequency. He demonstrated that this resonance is capable of producing rhythmic potential changes which roughly resemble the alpha wave of the cortical EEC. As further support, he established an alpha rhythm in a subject in whom it was not previously evident by restoring his intracranial pressure to normal through use of a head plate to cover a small cranial wound. These demonstrations are ingenious and they should certainly dictate caution in any interpretations of such recordings. They do not, however, seem to disprove the more orthodox hypotheses.