Is There a Cerebral Dominance for Consciousness?

IS THERE A CEREBRAL DOMINANCE FOR CONSCIOUSNESS? E. A. SERAFETINIDES* Introduction When the articles on cerebral dominance for speech and consciousness first appeared in 1964-1965 [1-3], there were few, if any, precedents for such a sweeping claim in the history of cerebral localization of mental functions. Indeed, even the term localization was, and still is, anathema to many, in this respect. However, that is not the object of this review. Suffice it to say that a pattern can be discerned in the history of neurosciences, whereby one can plot instances of "localizational" claims, followed by ridicule, followed by incorporation—albeit in a modified form—of the original claims. Furthermore, despite the opprobrium that the term localization provokes in many neuroscientists, neuroscience itself would not be what it is today without its inevitable localizational foundations. Perhaps it is the name itself which offends, as it is redolent of that old chestnut, the Cartesian dualism of mind and body, and the undying feud that dualism has sparked during the last few centuries. Intracarotid Studies Terzian [4] was among the first investigators to report on effects of consciousness by using the intracarotid sodium amytal injection technique . After observing the results of this method as applied on epileptic The author acknowledges the support of the Medical Research Service of the Department of Veterans Affairs. *Associate Chief of Staff, Research and Development, VA Medical Center, West Los Angeles (691/B151), (Brentwood Division), Wilshire and Sawtelle Boulevards, Los Angeles, California 90073, and professor, Department of Psychiatry and the Brain Research Institute, UCLA Medical Center.© 1993 by The University of Chicago. All rights reserved. 003 1 -5982/93/3603-0808$0 1 .00 420 E. A. Serafetinides · Cerebral Dominancefor Consciousness? patients to determine the cerebral hemisphere dominant for speech, he commented as follows: The aspect to which I would particularly like to draw attention, and that seems to me to put clearly into evidence the peculiar function of the dominant hemisphere , is that of the absolute and immediate arrest of any communication, both verbal and non verbal, in the first 30-60 seconds after the injection of the drug into the carotid artery of the dominant side: in the meantime the subject whose mechanisms of propositional function are abruptly, acutely and suddenly disorganized , shows an absolute and total loss of contact with the surrounding world, that is to say a complete loss of consciousness. As, however, observations on consciousness by other intracarotid studies investigators were either missing or dealt with in an undifferentiated way, Serafetinides, et al. [1—3], published a series of reports on intracarotid sodium amytal studies from the point of view of cerebral dominance for consciousness per se. First, the method was modified to allow for a more controlled procedure . Thus, instead of injecting the common carotid, the internal one was chosen for greater accuracy of lateralization; furthermore, instead of injecting the drug in one rapid bolus of 10 percent 200mg. solution, as originally practiced, the injection was given at the rate of 1 ml (of a 5 percent sodium amytal solution) every 5 seconds, which was stopped as soon as contralateral hemiparesis developed [I]. All tests were angiographically and electroencephalographically monitored. This modification avoided accidental contralateral filling (confirmed angiographically and electroencephalographically), thus enhancing confidence in the validity of the lateralization findings. The lateralization findings were further refined by the fact that the modified method made it possible for the subjects to be tested on both sides successively in the same session, and for the findings to be assessed quantitatively. (For more details on the method, the subjects, and the results, as well as discussion of previous intracarotid studies, see Serafetinides, et al. [1-3].) The authors concluded as follows: "Confusion" or loss of consciousness has been reported fairly consistently after the injection on either side with the rapid injection method of Wada. It has been suggested that this is due to crossing of the drug to the other side or to involvement of brain-stem centres . . . Either of these would appear to be likely with forceful injections though not with gradual ones. The impairment or loss of consciousness present after the gradual injection does not occur uniformly or irrespective of side...